Arxivsorter uses the network of co-authorship to estimate a proximity between people.
It then ranks a list of publications using a friends-of-friends algorithm.

It is not a filter and therefore does not lose any information.

J.P. Magué & B. Ménard

[1]
Title: Does SEGUE/SDSS indicate a dual Galactic halo?
Comments: 13 pages, 10 figures accepted for publication in ApJ
Subjects: Galaxy Astrophysics (astro-ph.GA)

We re-examine recent claims of observational evidence for a dual Galactic halo in SEGUE/SDSS data, and trace them back to improper error treatment and neglect of selection effects. In particular, the detection of a vertical abundance gradient in the halo can be explained as a metallicity bias in distance. A similar bias, and the impact of disk contamination, affect the sample of blue horizontal branch stars. These examples highlight why non-volume complete samples require forward-modelling from theoretical models or extensive bias-corrections. We also show how observational uncertainties produce the specific non-Gaussianity in the observed azimuthal velocity distribution of halo stars, which can be erroneously identified as two Gaussian components. A single kinematic component yields an excellent fit to the observed data, when we model the measurement process including distance uncertainties. Furthermore, we show that sample differences in proper motion space are the direct consequence of kinematic cuts, and are enhanced when distance estimates are less accurate. Thus, their presence is neither a proof for a separate population, nor a measure of reliability for the applied distances. We conclude that currently there is no evidence from SEGUE/SDSS that would favour a dual Galactic halo over a single halo full of substructure.

[2]
Title: The Black Hole Meissner Effect and Blandford-Znajek Jets
Authors: Robert F. Penna
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

Spinning black holes tend to expel magnetic fields. In this way they are similar to superconductors. It has been a persistent concern that this black hole "Meissner effect" could quench jet power at high spins. We show that split monopole fields are not expelled by the Meissner effect and may continue to power jets up to the extremal limit. This provides a natural way for the rapidly rotating black holes in Cyg X-1 and GRS 1915+105 to power jets. We consider two earlier proposals for evading the Meissner effect: the claim that hoop stresses in a conductive magnetosphere can drag fields onto the horizon despite the Meissner effect and the claim that spin-powered jets can exist even if field lines do not thread the horizon. We show that both of these proposals are impossible. Finally, we note that in our general relativistic magnetohydrodynamic simulations of black hole jets, there is no evidence that jets are quenched by the Meissner effect. The simulated jets develop a large split monopole component spontaneously which supports our proposal for how the Meissner effect is evaded and jets from rapidly rotating black holes are powered in nature.

[3]
Title: Multi-Wavelength Coverage of State Transitions in the New Black Hole X-Ray Binary Swift J1910.2-0546
Comments: 8 pages, 5 figures, 1 table. To be published in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Understanding how black holes accrete and supply feedback to their environment is one of the outstanding challenges of modern astrophysics. Swift J1910.2-0546 is a candidate black hole low-mass X-ray binary that was discovered in 2012 when it entered an accretion outburst. To investigate the binary configuration and the accretion morphology we monitored the evolution of the outburst for ~3 months at X-ray, UV, optical (B,V,R,I), and near-infrared (J,H,K) wavelengths using Swift and SMARTS. The source evolved from a hard to a soft X-ray spectral state with a relatively cold accretion disk that peaked at ~0.5 keV. A Chandra/HETG spectrum obtained during this soft state did not reveal signatures of an ionized disk wind. Both the low disk temperature and the absence of a detectable wind could indicate that the system is viewed at relatively low inclination. The multi-wavelength light curves revealed two notable features that appear to be related to X-ray state changes. Firstly, a prominent flux decrease was observed in all wavebands ~1-2 weeks before the source entered the soft state. This dip occurred in (0.6-10 keV) X-rays ~6 days later than at longer wavelengths, which could possibly reflect the viscous time scale of the disk. Secondly, about two weeks after the source transitioned back into the hard state, the UV emission significantly increased while the X-rays steadily decayed. We discuss how these observations may reflect changes in the accretion flow morphology, perhaps related to the quenching/launch of a jet or the collapse/recovery of a hot flow.

[4]
Title: On the use of semi-numerical simulations in predicting the 21-cm signal from the epoch of reionization
Authors: Suman Majumdar (Stockholm U), Garrelt Mellema (Stockholm U), Kanan K. Datta (NCRA-TIFR), Hannes Jensen (Stockholm U), T. Roy Choudhury (NCRA-TIFR), Somnath Bharadwaj (IIT Kharagpur), Martina M. Friedrich (CCA UNAM)
Comments: 18 pages, 13 figures, 1 table. Submitted to MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We perform a detailed comparison of three different simulations of the neutral hydrogen distribution during the epoch of reionization (EoR). Our benchmark is a radiative transfer simulation (C2RAY). Such simulations can produce realistic results, but are computationally expensive. We compare it with two different semi-numerical techniques: one using the same halos as C2RAY as its sources (Sem-Num), and one using a conditional Press-Schechter scheme (CPS+GS). These are more computationally efficient than C2RAY, but use more simplistic physics. We evaluate them in terms of how well they can reproduce the history and morphology of EoR. We find that Sem-Num can produce an ionization history and morphology that is very close to C2RAY. Considering the effects of redshift space distortions due to peculiar velocities, we also study a number of statistics such as: the variance, spherically averaged power spectrum and various angular multipole moments of the power spectrum of the 21-cm signal from EoR,that will be observable by upcoming radio telescopes. We find that both semi-numerical models perform quite well in predicting these observables at length scales relevant for the present and future experiments. We also observe that predictions from Sem-Num are slightly better (by $\sim 10\%$) than CPS+GS for most of the observables. However, the predictions for the reionization history and the morphology of the ionization maps are significantly better (by $\sim 25-50\%$) in Sem-Num than CPS+GS. As the predictions for the 21-cm signal together with the reionization history would be required for parametrization of EoR from the observations, it would be better to use a semi-numerical simulation which can predict both with an acceptable accuracy. Our analysis shows that among the two semi-numerical simulations Sem-Num satisfies this criteria very well as it uses a source model very similar to C2RAY.

[5]
Title: Metal-line absorption around $z\approx$2.4 star-forming galaxies in the Keck Baryonic Structure Survey
Authors: Monica L. Turner (1), Joop Schaye (1), Charles C. Steidel (2), Gwen C. Rudie (3), Allison L. Strom (2) ((1) Leiden Observatory, Leiden University, (2) California Institute of Technology, (3) Carnegie Observatories)
Comments: Submitted to MNRAS, 21 pages, 12 figures (not including appendices)
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

(Abridged) We study metal absorption by the circumgalactic medium of 843 $z\approx$2.4 star-forming galaxies taken from the Keck Baryonic Structure Survey. The galaxies examined in this work lie in the fields of 15 background QSOs, which all have high-quality Keck/HIRES spectra, with galaxy impact parameters ranging from 35 kpc to 2 Mpc. Using the pixel optical depth technique, we present the first galaxy-centred 2-D maps of the median absorption by OVI, NV, CIV, CIII, and SIV, as well as updated results for HI. At small galactocentric radii the absorption is strongly enhanced. The enhancement extends out to at least 180 kpc for OVI, CIII and SiIV (and 2 Mpc for HI and CIV) in the transverse direction, and $\pm$240 km/s along the line of sight (which would correspond to ~1 Mpc in the case of pure Hubble flow). After normalising the median absorption profiles to account for variations in line strengths and detection limits, we find no evidence for differences in the spatial distribution between HI and metals. We also present measurements of the scatter in the optical depths, covering factors, and equivalent widths as a function of projected galaxy distance. The current sample contains 318 galaxies whose redshifts have been measured from nebular emission lines using MOSFIRE, and have uncertainties of only ~18 km/s, compared to ~150 km/s for the previous determinations using rest-frame UV spectra. Limiting the sample to galaxies with nebular emission line redshifts does not decrease the extent of the enhancement along the line of sight compared to that in the transverse direction. This rules out redshift errors as the source of the observed redshift-space anisotropy and thus implies that we have detected the signature of gas peculiar velocities from infall, outflows, or virial motions for HI, OVI, CIV, CIII, and SiIV.

[6]
Title: The COS-Halos Survey: Physical Conditions and Baryonic Mass in the Low-Redshift Circumgalactic Medium
Comments: 19 pages, 12 Figures, and a 37-page Appendix with 36 additional figures. Submitted to ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We analyze the physical conditions of the cool (T ~ 10^4 K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density measurements taken along 38 quasar sightlines passing within 160 kpc of L ~ L* galaxies at z~0.2. These data are well described by simple photoionization models, with the gas highly ionized (n_HII/n_H > 99%) by the extragalactic ultraviolet background (EUVB). Scaling by estimates for the virial radius, R_vir, we show that the ionization state (tracked by the dimensionless ionization parameter, U) increases with distance from the host galaxy. This correlation has a power-law form of U = (0.006 +/- 0.003)(R/R_vir)^(0.8 +/- 0.3), with significant scatter. The ionization parameters imply a decreasing volume density profile n_ H = 10^(-4.2 +/- 0.25) (R/R_vir)^(-0.8 +/-0.3). Our derived gas volume densities are several orders of magnitude lower than predictions from standard two-phase models with a cool medium in pressure equilibrium with a hot, diffuse medium. Applying the ionization corrections to the HI column densities, we estimate a lower limit to the cool gas mass M_ CGMcool > 6.5 x 10^10 M_sun for the volume within R < R_vir. Allowing for an additional warm, OVI-traced phase, the CGM accounts for *at least* half of the baryons purported to be missing from galaxy dark matter halos.

[7]
Title: Resonantly-Produced 7 keV Sterile Neutrino Dark Matter Models and the Properties of Milky Way Satellites
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

Sterile neutrinos produced through a resonant Shi-Fuller mechanism are arguably the simplest model for a dark matter interpretation origin of the recent unidentified X-ray line seen toward a number of objects harboring dark matter. Here, I calculate the exact parameters required in this mechanism to produce the signal. The suppression of small scale structure predicted by these models is consistent with Local Group and high-$z$ galaxy count constraints. Very significantly, the parameters necessary in these models to produce the full dark matter density fulfill previously determined requirements to successfully match the Milky Way Galaxy's total satellite abundance, the satellites' radial distribution and their mass density profile, or "too big to fail problem." I also discuss how further precision determinations of the detailed properties of the candidate sterile neutrino dark matter can probe the nature of the quark-hadron transition, which takes place during the dark matter production.

[8]
Title: Jet collimation in the ejecta of double neutron star merger: new canonical picture of short gamma-ray bursts
Comments: 6 pages, 3 figures, accepted for publication in the Astrophysical Journal Letters
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The observations of jet breaks in the afterglows of short gamma-ray bursts (SGRBs) indicate that the jet has a small opening angle of < 10{\deg}. The collimation mechanism of the jet is a longstanding theoretical problem. We numerically analyze the jet propagation in the material ejected by double neutron star merger, and demonstrate that if the ejecta mass is > 10^{-2} M_{sun}, the jet is well confined by the cocoon and emerges from the ejecta with the required collimation angle. Our results also suggest that there are some populations of choked (failed) SGRBs or low-luminous new types of event. By constructing a model for SGRB 130603B, which is associated with the first kilonova/macronova can- didate, we infer that the equation-of-state of neutron stars would be soft enough to provide sufficient ejecta to collimate the jet, if this event was associated with a double neutron star merger.

[9]
Comments: 27 pages, 16 figures, 6 tables, accepted to MNRAS, full Appendix A at this http URL
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We investigate C IV broad absorption line (BAL) variability within a sample of 46 radio-loud quasars (RLQs), selected from SDSS/FIRST data to include both core-dominated (39) and lobe-dominated (7) objects. The sample consists primarily of high-ionization BAL quasars, and a substantial fraction have large BAL velocities or equivalent widths; their radio luminosities and radio-loudness values span ~2.5 orders of magnitude. We have obtained 34 new Hobby-Eberly Telescope (HET) spectra of 28 BAL RLQs to compare to earlier SDSS data, and we also incorporate archival coverage (primarily dual-epoch SDSS) for a total set of 78 pairs of equivalent width measurements for 46 BAL RLQs, probing rest-frame timescales of ~80-6000 d (median 500 d). In general, only modest changes in the depths of segments of absorption troughs are observed, akin to those seen in prior studies of BAL RQQs. Also similar to previous findings for RQQs, the RLQs studied here are more likely to display BAL variability on longer rest-frame timescales. However, typical values of |Delta_EW| and |Delta_EW|/<EW> are about 40+/-20% lower for BAL RLQs when compared with those of a timescale-matched sample of BAL RQQs. Optical continuum variability is of similar amplitude in BAL RLQs and BAL RQQs; for both RLQs and RQQs, continuum variability tends to be stronger on longer timescales. BAL variability in RLQs does not obviously depend upon their radio luminosities or radio-loudness values, but we do find tentative evidence for greater fractional BAL variability within lobe-dominated RLQs. Enhanced BAL variability within more edge-on (lobe-dominated) RLQs supports some geometrical dependence to the outflow structure.

[10]
Title: A Near-Infrared Survey of the Inner Galactic Plane for Wolf-Rayet Stars III. New Methods: Most Distant Known Galactic WR Stars
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

A new method of image subtraction is applied to images from a J, K, and narrow-band imaging survey of 300 square degrees of the plane of the Galaxy, searching for new Wolf-Rayet stars. Our survey spans 150 degrees in Galactic longitude and reaches 1 degree above and below the Galactic plane. The survey has a useful limiting magnitude of K $=15$ over most of the observed Galactic plane, and K $=14$ (due to severe crowding) within a few degrees of the Galactic center. The new image subtraction methods (better than aperture or even point-spread-function photometry in very crowded fields) detected several thousand emission-line candidates. In June and July 2011 and 2012, we spectroscopically followed up on 333 candidates with MDM-TIFKAM and IRTF-SPEX, discovering 90 new emission-line sources. These include 55 new Wolf-Rayet stars, comprising the most distant known Galactic WR stars, more than doubling the number on the far side of the Milky Way. We also demonstrate our survey's ability to detect very distant PNe and other NIR emission objects.

[11]
Title: G0.253+0.016: A centrally condensed, high-mass protocluster
Comments: 57 pages. 29 figures. Accepted ApJ
Subjects: Galaxy Astrophysics (astro-ph.GA)

Despite their importance as stellar nurseries and the building blocks of galaxies, very little is known about the formation of the highest mass clusters. The dense clump G0.253+0.016 represents an example of a clump that may form an Arches-like, high-mass cluster. Here we present molecular line maps toward G0.253+0.016 taken as part of the MALT90 molecular line survey, complemented with APEX observations. Combined, these data reveal the global physical properties and kinematics of G0.253+0.016. Recent Herschel data show that while the dust temperature is low (~19 K) toward its centre, the dust temperature on the exterior is higher (~27 K) due to external heating. Our new molecular line data reveal that, overall, the morphology of dense gas detected toward G0.253+0.016 matches very well its IR extinction and dust continuum emission. An anti-correlation between the dust and gas column densities toward its centre indicates that the clump is centrally condensed with a cold, dense interior in which the molecular gas is chemically depleted. The velocity field shows a strong gradient along the clump's major axis, with the blue-shifted side at higher Galactic longitude. The optically thick gas tracers are systematically red-shifted with respect to the optically thin and hot gas tracers, indicating radial motions. The gas kinematics and line ratios support the recently proposed scenario in which G0.253+0.016 results from a tidal compression during a recent pericentre passage near SgrA*. Because G0.253+0.016 represents an excellent example of a clump that may form a high-mass cluster, its detailed study should reveal a wealth of knowledge about the early stages of cluster formation.

[12]
Title: Optically thick HI dominant in the local interstellar medium; an alternative interpretation to "dark gas"
Comments: 41 pages, 17 figures, 3 tables, Submitted to ApJ
Subjects: Galaxy Astrophysics (astro-ph.GA)

Dark gas in the interstellar medium (ISM) is believed to be not detectable either in CO or HI radio emission, but it is detected in the other means including gamma-rays, dust emission and extinction. In these analyses, the 21-cm HI emission is usually assumed to be completely optically thin. We have reanalyzed the HI emission from the whole sky at |b|>15 degrees by considering temperature stratification in the ISM inferred from the Planck/IRAS analysis of the dust properties. The results indicate that the HI emission is saturated with an optical depth ranging from 0.5 to 5 for 80 % of the local HI gas. This optically thick HI is characterized by spin temperature in the range 15 K - 70 K, significantly lower than previously postulated in the literature, whereas such low temperature is consistent with emission/absorption measurements of HI toward radio continuum sources. The distribution and the column density of the HI are consistent with those of the dark gas suggested by gamma-rays, and we infer that the dark gas in the Galaxy is dominated by optically thick cold HI gas. This result implies that the average density of HI is two times higher than that derived on the optically-thin assumption in the local interstellar space.

[13]
Title: Satellite Alignment: I. Distribution of Substructures and Their Dependence On Assembly History From N-Body Simulations
Comments: 12 pages, 11 figures, accepted by ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Observations have shown that the spatial distribution of satellite galaxies is not random, but aligned with the major axes of central galaxies. This alignment is dependent on galaxy properties, such that red satellites are more strongly aligned than blue satellites. Theoretical work done to interpret this phenomena has found that it is due to the non-spherical nature of dark matter halos. However, most studies over-predict the alignment signal under the assumption that the central galaxy shape follows the shape of the host halo. It is also not clear whether the color dependence of alignment is due to an assembly bias or an evolution effect. In this paper we study these problems using a cosmological N-body simulation. Subhalos are used to trace the positions of satellite galaxies. It is found that the shape of dark matter halos are mis-aligned at different radii. If the central galaxy shares the same shape as the inner host halo, then the alignment effect is weaker and agrees with observational data. However, it predicts almost no dependence of alignment on the color of satellite galaxies, though the late accreted subhalos show stronger alignment with the outer layer of the host halo than their early accreted counterparts. We find that this is due to the limitation of pure N-body simulations that satellites galaxies without associated subhalos ('orphan galaxies') are not resolved. These orphan (mostly red) satellites often reside in the inner region of host halos and should follow the shape of the host halo in the inner region.

[14]
Title: The corona of HD 189733 and its X-ray activity
Comments: Preprint format, 28 Pages, 10 Figures, accepted for publication on ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Abridged. Here we report on the X-ray activity of the primary star, HD189733 A, using a new XMM-Newton observation and a comparison with the previous X-ray observations. The spectrum in the quiescent intervals is described by two temperatures at 0.2 keV and 0.7 keV, while during the flares a third component at 0.9 keV is detected. We obtain estimates of the electron density in the range $n_e = 1.6 - 13 \times 10^{10}$ cm$^{-3}$ and thus the corona of HD189733 A appears denser than the solar one. {For the third time, we observe a large flare that occurred just after the eclipse of the planet. Together with the flares observed in 2009 and 2011, the events are restricted to a small planetary phase range of $\phi = 0.55-0.65$. Although we do not find conclusive evidence of a significant excess of flares after the secondary transits, we suggest that the planet might trigger such flares when it passes close to locally high magnetic field of the underlying star at particular combinations of stellar rotational phases and orbital planetary phases. For the most recent flares, a wavelet analysis of the light curve suggests a loop of length of four stellar radii at the location of the bright flare, and a local magnetic field of order of 40-100 G, in agreement with the global field measured in other studies. The loop size suggests an interaction of magnetic nature between planet and star, separated by only $\sim8 R_*$. We also detect the stellar companion (HD 189733 B, $\sim12"$ from the primary star) in this XMM observation. Its very low X-ray luminosity ($L_X = 3.4\times 10^{26}$ erg s$^{-1}$) confirms the old age of this star and of the binary system. The high activity of the primary star is best explained by a transfer of angular momentum from the planet to the star.

[15]
Title: Reevaluating of the feasibility of ground-based earth-mass microlensing planet detections
Comments: 4 pages, 3 figures, ApJ accepted
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

One important strength of the microlensing method in detecting extrasolar planets is its high sensitivity to low-mass planets. However, it is often believed that microlensing detections of Earth-mass planets from ground-based observation would be difficult due to the limit set by finite-source effects. This view comes from the previous estimation of the planet detection probability based on the fractional deviation of planetary signals, but proper probability estimation requires to additionally consider the source brightness, which is directly related to the photometric precision. In this paper, we reevaluate the feasibility of low-mass planet detections considering photometric precision for different populations of source stars. From this, it is found that contribution of the improved photometric precision to the planetary signal of a giant-source event is big enough to compensate the decrease of the magnification excess caused by finite-source effects. As a result, we find that giant-source events are suitable targets for Earth-mass planet detections with significantly higher detection probability than events involved with source stars of smaller radii and predict that Earth-mass planets would be detected by prospective high-cadence surveys.

[16]
Title: The nature of supernovae 2010O and 2010P in Arp 299 - II. Radio emission
Comments: 14 pages, 8 tables and 7 figures. Accepted for publication in MNRAS
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We report radio observations of two stripped-envelope supernovae (SNe), 2010O and 2010P, which exploded within a few days of each other in the luminous infrared galaxy Arp 299. Whilst SN 2010O remains undetected at radio frequencies, SN 2010P was detected (with an astrometric accuracy better than 1 milli arcsec in position) in its optically thin phase in epochs ranging from ~1 to ~3yr after its explosion date, indicating a very slow radio evolution and a strong interaction of the SN ejecta with the circumstellar medium. Our late-time radio observations toward SN 2010P probe the dense circumstellar envelope of this SN, and imply a mass-loss rate (Msun/yr) to wind velocity (in units of 10 km/s) ratio of (3.0-5.1)E-05, with a 5 GHz peak luminosity of ~1.2E+27 erg/s/Hz on day ~464 after explosion. This is consistent with a Type IIb classification for SN 2010P, making it the most distant and most slowly evolving Type IIb radio SN detected to date.

[17]
Title: RingFinder: automated detection of galaxy-scale gravitational lenses in ground-based multi-filter imaging data
Comments: 32 pages (aastex 2col format), 6 figs, ApJ Accepted
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present RingFinder, a tool for finding galaxy-scale strong gravitational lenses in multiband imaging data. By construction, the method is sensitive to configurations involving a massive foreground early-type galaxy and a faint, background, blue source. RingFinder detects the presence of blue residuals embedded in an otherwise smooth red light distribution by difference imaging in two bands. The method is automated for efficient application to current and future surveys, having originally been designed for the 150-deg2 Canada France Hawaii Telescope Legacy Survey (CFHTLS). We describe each of the steps of RingFinder. We then carry out extensive simulations to assess completeness and purity. For sources with magnification mu>4, RingFinder reaches 42% (resp. 25%) completeness and 29% (resp. 86%) purity before (resp. after) visual inspection. The completeness of RingFinder is substantially improved in the particular range of Einstein radii 0.8 < REin < 2. and lensed images brighter than g = 22.5, where it can be as high as 70%. RingFinder does not introduce any significant bias in the source or deflector population. We conclude by presenting the final catalog of RingFinder CFHTLS galaxy-scale strong lens candidates. Additional information obtained with Hubble Space Telescope and Keck Adaptive Optics high resolution imaging, and with Keck and Very Large Telescope spectroscopy, is used to assess the validity of our classification, and measure the redshift of the foreground and the background objects. From an initial sample of 640,000 early type galaxies, RingFinder returns 2500 candidates, which we further reduce by visual inspection to 330 candidates. We confirm 33 new gravitational lenses from the main sample of candidates, plus an additional 16 systems taken from earlier versions of RingFinder. First applications are presented in the SL2S galaxy-scale Lens Sample paper series.

[18]
Title: Short-period pulsar oscillations following a glitch
Comments: 38 Pages, 8 Figures, submitted to the Astrophysical Jounral
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

Following a glitch, the crust and magnetized plasma in the outer core of a neutron star are believed to rapidly establish a state of co-rotation within a few seconds by process analogous to classical Ekman pumping. However, in ideal magnetohydrodynamics, a final state of co-rotation is inconsistent with conservation of energy of the system. We demonstrate that, after the Ekman-like spin up is completed, magneto-inertial waves continue to propagate throughout the star, exciting torsional oscillations in the crust and plasma. The crust oscillation is irregular and quasi-periodic, with a dominant frequency of the order of seconds. Crust oscillations commence after an Alfv\'en crossing time, approximately half a minute at the magnetic pole, and are subsequently damped by the electron viscosity over approximately an hour. Because of their short periods, it is unlikely that the oscillations correspond to any observed phenomena in radio timing data.

[19]
Title: The Stagger-grid: A grid of 3D stellar atmosphere models - III. The relation to mixing length convection theory
Comments: 15 pages, 20 figures, 2 tables, submitted to A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We investigate the relation between 1D atmosphere models that rely on the mixing length theory and models based on full 3D radiative hydrodynamic (RHD) calculations to describe convection in the envelopes of late-type stars. The adiabatic entropy value of the deep convection zone, s_bot, and the entropy jump, {\Delta}s, determined from the 3D RHD models, are matched with the mixing length parameter, {\alpha}_MLT, from 1D hydrostatic atmosphere models with identical microphysics (opacities and equation-of-state). We also derive the mass mixing length, {\alpha}_m, and the vertical correlation length of the vertical velocity, C[v_z,v_z], directly from the 3D hydrodynamical simulations of stellar subsurface convection. The calibrated mixing length parameter for the Sun is {\alpha}_MLT (s_bot) = 1.98. For different stellar parameters, {\alpha}_MLT varies systematically in the range of 1.7 - 2.4. In particular, {\alpha}_MLT decreases towards higher effective temperature, lower surface gravity and higher metallicity. We find equivalent results for {\alpha}_MLT ({\Delta}s). Also, we find a tight correlation between the mixing length parameter and the inverse entropy jump. We derive an analytical expression from the hydrodynamic mean field equations that motivates the relation to the mass mixing length, {\alpha}_m, and find that it exhibits qualitatively a similar variation with stellar parameter (between 1.6 and 2.4) with a solar value of {\alpha}_m = 1.83. The vertical correlation length scaled with the pressure scale height yields for the Sun 1.71, but displays only a small systematic variation with stellar parameters, the correlation length slightly increasing with Teff. We derive mixing length parameters for various stellar parameters that can be used to replace a constant value. Within any convective envelope, {\alpha}_m and related quantities vary a lot.

[20]
Title: A PCA-based automated finder for galaxy-scale strong lenses
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present an algorithm using Principal Component Analysis (PCA) to subtract galaxies from imaging data, and also two algorithms to find strong, galaxy-scale gravitational lenses in the resulting residual image. The combined method is optimized to find full or partial Einstein rings. Starting from a pre-selection of potential massive galaxies, we first perform a PCA to build a set of basis vectors. The galaxy images are reconstructed using the PCA basis and subtracted from the data. We then filter the residual image with two different methods. The first uses a curvelet (curved wavelets) filter of the residual images to enhance any curved/ring feature. The resulting image is transformed in polar coordinates, centered on the lens galaxy center. In these coordinates, a ring is turned into a line, allowing us to detect very faint rings by taking advantage of the integrated signal-to-noise in the ring (a line in polar coordinates). The second way of analysing the PCA-subtracted images identifies structures in the residual images and assesses whether they are lensed images according to their orientation, multiplicity and elongation. We apply the two methods to a sample of simulated Einstein rings, as they would be observed with the ESA Euclid satellite in the VIS band. The polar coordinates transform allows us to reach a completeness of 90% and a purity of 86%, as soon as the signal-to-noise integrated in the ring is higher than 30, and almost independent of the size of the Einstein ring. Finally, we show with real data that our PCA-based galaxy subtraction scheme performs better than traditional subtraction based on model fitting to the data. Our algorithm can be developed and improved further using machine learning and dictionary learning methods, which would extend the capabilities of the method to more complex and diverse galaxy shapes.

[21]
Title: Star formation rates in nearby Markarian galaxies
Journal-ref: Astrophysics, 2014, Vol. 57, 1
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

The star formation rates for the 230 nearest Markarian galaxies with radial velocities V_LG<3500 km/s have been determined from their far ultraviolet fluxes obtained with the GALEX satellite. We briefly discuss the observed relationship between the star formation rate and other integral parameters of these galaxies: stellar mass, hydrogen mass, morphological type, and activity index. On the average, the Markarian galaxies have reserves of gas that are a factor of two smaller than those of galaxies in the field of the same stellar mass and type. Despite their elevated activity, the specific rate of star formation in the Markarian galaxies, SFR/M_*, does not exceed a limit of ~dex(-9.4) [yr^-1].

[22]
Title: Revealing the nature of the ULX and X-ray population of the spiral galaxy NGC 4088
Comments: 15 pages, 6 fig., accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

We present the first \textit{Chandra} and \textit{Swift} X-ray study of the spiral galaxy NGC\,4088 and its ultraluminous X-ray source (ULX N4088--X1). We also report very long baseline interferometry (VLBI) observations at 1.6 and 5 GHz performed quasi-simultaneously with the \textit{Swift} and \textit{Chandra} observations, respectively. Fifteen X-ray sources are detected by \textit{Chandra} within the D25 ellipse of NGC\,4088, from which we derive the X-ray luminosity function (XLF) of this galaxy. We find the XLF is very similar to those of star-forming galaxies and estimate a star-formation rate of 4.5 $M_{\odot}$ yr$^{-1}$. The \textit{Chandra} detection of the ULX yields its most accurate X-ray position, which is spatially coincident with compact radio emission at 1.6 GHz. The ULX \textit{Chandra} X-ray luminosity, $L_\mathrm{0.2-10.0 keV} = 3.4\ \times$ 10$^{39}$ erg s$^{-1}$, indicates that N4088--X1 could be located at the high-luminosity end of the high-mass X-ray binary (HMXB) population of NGC\,4088. The estimates of the black hole mass and ratio of radio to X-ray luminosity of N4088--X1 rule out a supermassive black hole nature. The \textit{Swift} X-ray spectrum of N4088--X1 is best described by a thermal Comptonization model and presents a statistically significant high-energy cut-off. We conclude that N4088--X1 is most likely a stellar remnant black hole in a HMXB, probably fed by Roche lobe overflow, residing in a super-Eddington ultraluminous state. The 1.6 GHz VLBI source is consistent with radio emission from possible ballistic jet ejections in this state.

[23]
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics - Phenomenology (hep-ph)

Some severe constraints on asymmetric dark matter are based on the scenario that certain types of WIMPs can form mini-black holes inside neutron stars that can lead to their destruction. A crucial element for the realization of this scenario is that the black hole grows after its formation (and eventually destroys the star) instead of evaporating. The fate of the black hole is dictated by the two opposite mechanics i.e. accretion of nuclear matter from the center of the star and Hawking radiation that tends to decrease the mass of the black hole. We study how the assumptions for the accretion rate can in fact affect the critical mass beyond which a black hole always grows. We also study to what extent degenerate nuclear matter can impede Hawking radiation due to the fact that emitted particles can be Pauli blocked at the core of the star.

[24]
Title: Analysis of single pulse radio flux measurements of PSR B1133+16 at 4.85 and 8.35 GHz
Comments: 10 pages, 7 figures, Accepted for publication by the MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

We show the results of microsecond resolution radio data analysis focused on flux measurements of single pulses of PSR~B1133+16. The data were recorded at 4.85 GHz and 8.35 GHz with 0.5 GHz and 1.1 GHz bandwidth, respectively, using Radio Telescope Effelsberg (MPIfR). The most important conclusion of the analysis is, that the strongest single pulse emission at 4.85 GHz and 8.35 GHz contributes almost exclusively to the trailing part of the leading component of the pulsar mean profile, whereas studies at lower frequencies report that the contribution is spread almost uniformly covering all phases of the pulsar mean profile. We also estimate the radio emission heights to be around 1%--2% of the light cylinder radius which is in agreement with previous studies. Additionally these observations allowed us to add two more measurements of the flux density to the PSR B1133+16 broadband radio spectrum covering frequencies from 16.7 MHz up to 32 GHz. We fit two different models to the spectrum: the broken power law and the spectrum based on flicker noise model, which represents the spectrum in a simpler but similarly accurate way.

[25]
Title: A comparison of CMB Angular Power Spectrum Estimators at Large Scales: the TT case
Comments: 9 pages, 7 figures. Accepted for publication in MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

In the context of cosmic microwave background (CMB) data analysis, we compare the efficiency at large scale of two angular power spectrum algorithms, implementing, respectively, the quadratic maximum likelihood (QML) estimator and the pseudo spectrum (pseudo-Cl) estimator. By exploiting 1000 realistic Monte Carlo (MC) simulations, we find that the QML approach is markedly superior in the range l=[2-100]. At the largest angular scales, e.g. l < 10, the variance of the QML is almost 1/3 (1/2) that of the pseudo-Cl, when we consider the WMAP kq85 (kq85 enlarged by 8 degrees) mask, making the pseudo spectrum estimator a very poor option. Even at multipoles l=[20-60], where pseudo-Cl methods are traditionally used to feed the CMB likelihood algorithms, we find an efficiency loss of about 20%, when we considered the WMAP kq85 mask, and of about 15% for the kq85 mask enlarged by 8 degrees. This should be taken into account when claiming accurate results based on pseudo-Cl methods. Some examples concerning typical large scale estimators are provided.

[26]
Title: Cosmology with Ricci-type dark energy
Comments: 6 pages, 3 figures, submitted to the Proceedings of the CosmoSurII conference, Valpara\'iso, Chile, 27 - 31 May 2013
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

We consider the dynamics of a cosmological substratum of pressureless matter and holographic dark energy with a cutoff length proportional to the Ricci scale. Stability requirements for the matter perturbations are shown to single out a model with a fixed relation between the present matter fraction $\Omega_{m0}$ and the present value $\omega_{0}$ of the equation-of-state parameter of the dark energy. This model has the same number of free parameters as the $\Lambda$CDM model but it has no $\Lambda$CDM limit. We discuss the consistency between background observations and the mentioned stability-guaranteeing parameter combination.

[27]
Title: Calibration of the Herschel SPIRE Fourier Transform Spectrometer
Comments: 20 pages, 18 figures, accepted for publication in MNRAS
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

The Herschel SPIRE instrument consists of an imaging photometric camera and an imaging Fourier Transform Spectrometer (FTS), both operating over a frequency range of 450-1550 GHz. In this paper, we briefly review the FTS design, operation, and data reduction, and describe in detail the approach taken to relative calibration (removal of instrument signatures) and absolute calibration against standard astronomical sources. The calibration scheme assumes a spatially extended source and uses the Herschel telescope as primary calibrator. Conversion from extended to point-source calibration is carried out using observations of the planet Uranus. The model of the telescope emission is shown to be accurate to within 6% and repeatable to better than 0.06% and, by comparison with models of Mars and Neptune, the Uranus model is shown to be accurate to within 3%. Multiple observations of a number of point-like sources show that the repeatability of the calibration is better than 1%, if the effects of the satellite absolute pointing error (APE) are corrected. The satellite APE leads to a decrement in the derived flux, which can be up to ~10% (1 sigma) at the high-frequency end of the SPIRE range in the first part of the mission, and ~4% after Herschel operational day 1011. The lower frequency range of the SPIRE band is unaffected by this pointing error due to the larger beam size. Overall, for well-pointed, point-like sources, the absolute flux calibration is better than 6%, and for extended sources where mapping is required it is better than 7%.

[28]
Title: Spatial and Kinematic Distributions of Transition Populations in Intermediate Redshift Galaxy Clusters
Comments: 39 pages, 14 figures. Accepted for publication in ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We analyze the spatial and velocity distributions of confirmed members in five massive clusters of galaxies at intermediate redshift (0.5 < z < 0.9) to investigate the physical processes driving galaxy evolution. Based on spectral classifications derived from broad- and narrow-band photometry, we define four distinct galaxy populations representing different evolutionary stages: red sequence (RS) galaxies, blue cloud (BC) galaxies, green valley (GV) galaxies, and luminous compact blue galaxies (LCBGs). For each galaxy class, we derive the projected spatial and velocity distribution and characterize the degree of subclustering. We find that RS, BC, and GV galaxies in these clusters have similar velocity distributions, but that BC and GV galaxies tend to avoid the core of the two z~0.55 clusters. GV galaxies exhibit subclustering properties similar to RS galaxies, but their radial velocity distribution is significantly platykurtic compared to the RS galaxies. The absence of GV galaxies in the cluster cores may explain their somewhat prolonged star-formation history. The LCBGs appear to have recently fallen into the cluster based on their larger velocity dispersion, absence from the cores of the clusters, and different radial velocity distribution than the RS galaxies. Both LCBG and BC galaxies show a high degree of subclustering on the smallest scales, leading us to conclude that star formation is likely triggered by galaxy-galaxy interactions during infall into the cluster.

[29]
Title: A new method for an objective, $χ^2$-based spectroscopic analysis of early-type stars
Comments: 32 pages, 4 figures, Astronomy and Astrophysics, accepted
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

A precise quantitative spectral analysis - encompassing atmospheric parameter and chemical elemental abundance determination - is time consuming due to its iterative nature and the multi-parameter space to be explored, especially when done "by eye". A robust automated fitting technique that is as trustworthy as traditional methods would allow for large samples of stars to be analyzed in a consistent manner in reasonable time. We present a semi-automated quantitative spectral analysis technique for early-type stars based on the concept of $\chi^2$ minimization. The method's main features are: far less subjective than typical "by eye" methods, correction for inaccurate continuum normalization, consideration of the whole useful spectral range, simultaneous sampling of the entire multi-parameter space (effective temperature, surface gravity, microturbulence, macroturbulence, projected rotational velocity, radial velocity, elemental abundances) to find the global best solution, applicable also to composite spectra. The method is fast, robust and reliable as seen from formal tests and from a comparison with previous analyses. Consistent quantitative spectral analyses of large samples of early-type stars can be performed quickly with very high accuracy.

[30]
Title: Epicyclic frequencies for rotating strange quark stars: the importance of stellar oblateness
Comments: 9 pages, 8 figures, submitted to Physical Review D
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc)

Kilohertz QPOs can be used as a probe of the inner regions of accretion disks in compact stars and hence also of the properties of the central object. Most models of kHz QPOs involve epicyclic frequencies to explain their origin. We compute the epicyclic frequencies of nearly circular orbits around rotating strange quark stars. The MIT bag model is used to model the equation of state of quark matter and the uniformly rotating stellar configurations are computed in full general relativity. The vertical epicyclic frequency and the related nodal precession rate of inclined orbits are very sensitive to the oblateness of the rotating star. For slowly rotating stellar models of moderate and high mass strange stars, the sense of the nodal precession changes at a certain rotation rate. At lower stellar rotation rates the orbital nodal precession is prograde, as it is in the Kerr metric, while at higher rotation rates the precession is retrograde, as it is for Maclaurin spheroids. Thus, qualitatively, the orbits around rapidly rotating strange quark stars are affected more strongly by the effects of stellar oblateness than by the effects of general relativity. We show that epicyclic and orbital frequencies calculated numerically for small mass strange stars are in very good agreement with analytical formulae for Maclaurin spheroids.

[31]
Title: Transient spirals as superposed instabilities
Authors: J. A. Sellwood (Rutgers University), R. G. Carlberg (University of Toronto)
Comments: Accepted to appear in ApJ, 13 pages, 11 figures. A version with full resolution figures is available at this http URL
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We present evidence that recurrent spiral activity, long manifested in simulations of disk galaxies, results from the super-position of a few transient spiral modes. Each mode lasts between five and ten rotations at its corotation radius where its amplitude is greatest. The scattering of stars as each wave decays takes place over narrow ranges of angular momentum, causing abrupt changes to the impedance of the disk to subsequent traveling waves. Partial reflections of waves at these newly created features, allows new standing-wave instabilities to appear that saturate and decay in their turn, scattering particles at new locations, creating a recurring cycle. The spiral activity causes the general level of random motion to rise, gradually decreasing the ability of the disk to support further activity unless the disk contains a dissipative gas component from which stars form on near-circular orbits. We also show that this interpretation is consistent with the behavior reported in other recent simulations with low mass-disks.

[32]
Title: Type II-Plateau supernovae as metallicity probes of the Universe
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We explore a method for metallicity determinations based on quantitative spectroscopy of type II-Plateau (II-P) supernovae (SNe). For consistency, we first evolve a set of 15Msun main sequence stars at 0.1, 0.4, 1, and 2 x the solar metallicity. At the onset of core collapse, we trigger a piston-driven explosion and model the resulting ejecta and radiation. Our theoretical models of such red-supergiant-star explosions at different metallicity show that synthetic spectra of SNe II-P possess optical signatures during the recombination phase that are sensitive to metallicity variations. This sensitivity can be quantified and the metallicity inferred from the strength of metal-line absorptions. Furthermore, these signatures are not limited to O, but also include Na, Ca, Sc, Ti, or Fe. When compared to a sample of SNe II-P from the Carnegie SN Project and previous SN followup programs, we find that most events lie at a metallicity between 0.4 and 2 x solar, with a marked scarcity of SN II-P events at SMC metallicity. This most likely reflects the paucity of low metallicity star forming regions in the local Universe.
SNe II-P have high plateau luminosities that make them observable spectroscopically at large distances. Because they exhibit signatures of diverse metal species, in the future they may offer a means to constrain the evolution of the composition (e.g., the O/Fe ratio) in the Universe out to a redshift of one and beyond.

[33]
Title: The triggering mechanism and properties of ionized outflows in the nearest obscured quasars
Comments: 20 pages, 12 figures, 6 tables. Accepted for publication in MNRAS
Subjects: Galaxy Astrophysics (astro-ph.GA)

We have identified ionized outflows in the narrow line region of all but one SDSS type 2 quasars (QSO2) at z<~0.1 (20/21, detection rate 95%), implying that this is a ubiquitous phenomenon in this object class also at the lowest z. The outflowing gas has high densities (n_e>1000 cm-3) and covers a region the size of a few kpc. This implies ionized outflow masses M~(0.3-2.4)x1e6 Msun and mass outflow rates M(dot)<few Msun yr-1.
The triggering mechanism of the outflows is related to the nuclear activity. The QSO2 can be classified in two groups according to the behavior and properties of the outflowing gas. QSO2 in Group 1 (5/20 objects) show the most extreme turbulence, they have on average higher radio luminosities and higher excess of radio emission. QSO2 in Group 2 (15/20 objects) show less extreme turbulence, they have lower radio luminosities and, on average, lower or no radio excess.
We propose that two competing outflow mechanisms are at work: radio jets and accretion disk winds. Radio jet induced outflows are dominant in Group 1, while disk winds dominate in Group 2. We find that the radio jet mode is capable of producing more extreme outflows. To test this interpretation we predict that: 1) high resolution VLBA imaging will reveal the presence of jets in Group 1 QSO2; 2) the morphology of their extended ionized nebulae must be more highly collimated and kinematically perturbed.

[34]
Title: Highest energy particle physics with the Pierre Auger Observatory
Comments: Proceedings of the XXXIII international symposium on Physics in Collision held in Beijing, China from 03 - 07 September 2013. To appear in International Journal of Modern Physics: Conference Series. 4 pages
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Astroparticles offer a new path for research in the field of particle physics, allowing investigations at energies above those accesible with accelerators. Ultra-high energy cosmic rays can be studied via the observation of the showers they generate in the atmosphere. The Pierre Auger Observatory is a hybrid detector for ultra-high energy cosmic rays, combining two complementary measurement techniques used by previous experiments, to get the best possible measurements of these air showers. Shower observations enable one to not only estimate the energy, direction and most probable mass of the primary cosmic particles but also to obtain some information about the properties of their hadronic interactions. Results that are most relevant in the context of determining hadronic interaction characteristics at ultra-high energies will be presented.

[35]
Title: Primordial Magnetic Helicity from Stochastic Electric Currents
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

We study the possibility that primordial magnetic fields generated in the transition between inflation and reheating posses magnetic helicity, $H_M$. The fields are induced by stochastic currents of scalar charged particles created during the mentioned transition. We estimate the rms value of the induced magnetic helicity by computing different four-point SQED Feynman diagrams. For any considered volume, the magnetic flux across its boundaries is in principle non null, which means that the magnetic helicity in those regions is gauge dependent. We use the prescription given by Berger and Field and interpret our result as the difference between two magnetic configurations that coincide in the exterior volume. In this case the magnetic helicity gives only the number of magnetic links inside the considered volume. We calculate a concrete value of $H_M$ for large scales and analyze the distribution of magnetic defects as a function of the scale. Those defects correspond to regular as well as random fields in the considered volume. We find that the fractal dimension of the distribution of topological defects is $D = 1/2$. We also study if the regular fields induced on large scales are helical, finding that they are and that the associated number of magnetic defects is independent of the scale. In this case the fractal dimension is $D=0$. We finally estimate the intensity of fields induced at the horizon scale of reheating, and evolve them until the decoupling of matter and radiation under the hypothesis of inverse cascade of magnetic helicity. The resulting intensity is high enough and the coherence length long enough to have an impact on the subsequent process of structure formation.

[36]
Title: Time delays between Fermi LAT and GBM light curves of GRBs
Comments: 9 pages, 3 figures, accepted for publication in Astronomy & Astrophysics
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Most Gamma-Ray Bursts (GRBs) detected by the Fermi Gamma-ray Space Telescope exhibit a delay of up to about 10 seconds between the trigger time of the hard X-ray signal as measured by the Fermi GBM and the onset of the MeV-GeV counterpart detected by the LAT. This delay may hint at important physics, whether it is due to the intrinsic variability of the inner engine or it is related to quantum dispersion effects in the velocity of light propagation from the sources to the observer. It is critical to have a proper assessment of how these time delays affect the overall properties of the light curves. We cross-correlated the 5 brightest GRBs of the 1st Fermi LAT Catalog by means of the continuous correlation function (CCF) and of the Discrete Correlation Function (DCF). A maximum in the DCF suggests the presence of a time lag between the curves, whose value and uncertainty are estimated through a Gaussian fitting of the DCF profile and light curve simulation via a Monte Carlo approach. The cross-correlation of the observed LAT and GBM light curves yields time lags that are mostly similar to those reported in the literature, but they are formally consistent with zero. The cross-correlation of the simulated light curves yields smaller errors on the time lags and more than one time lag for GRBs 090902B and 090926A; for all 5 GRBs, the time lags are significantly different from zero and consistent with those reported in the literature, when only the secondary maxima are considered for those two GRBs. The DCF method evidences the presence of time lags between the LAT and GBM light curves and underlines their complexity. While this suggests that the delays should be ascribed to intrinsic physical mechanisms, more sensitivity and larger statistics are needed to assess whether time lags are universally present in the early GRB emission and which dynamical time scales they trace.

[37]
Title: Widespread Rotationally-Hot Hydronium Ion in the Galactic Interstellar Medium
Comments: Accepted for publication in The Astrophysical Journal, 10 pages, 4 figures, 3 tables
Subjects: Galaxy Astrophysics (astro-ph.GA)

We present new observations of the (6,6) and (9,9) inversion transitions of the hydronium ion toward Sagittarius B2(N) and W31C. Sensitive observations toward Sagittarius B2(N) show that the high, ~ 500 K, rotational temperatures characterizing the population of the highly-excited metastable H3O+ rotational levels are present over a wide range of velocities corresponding to the Sagittarius B2 envelope, as well as the foreground gas clouds between the Sun and the source. Observations of the same lines toward W31C, a line of sight that does not intersect the Central Molecular Zone, but instead traces quiescent gas in the Galactic disk, also imply a high rotational temperature of ~ 380 K, well in excess of the kinetic temperature of the diffuse Galactic interstellar medium. While it is plausible that some fraction of the molecular gas may be heated to such high temperatures in the active environment of the Galactic center, characterized by high X-ray and cosmic ray fluxes, shocks and high degree of turbulence, this is unlikely in the largely quiescent environment of the Galactic disk clouds. We suggest instead that the highly-excited states of the hydronium ion are populated mainly by exoergic chemical formation processes and temperature describing the rotational level population does not represent the physical temperature of the medium. The same arguments may be applicable to other symmetric top rotors, such as ammonia. This offers a simple explanation to the long-standing puzzle of the presence of a pervasive, hot molecular gas component in the central region of the Milky Way. Moreover, our observations suggest that this is a universal process, not limited to the active environments associated with galactic nuclei.

[38]
Title: Decaying Dark Atom constituents and cosmic positron excess
Comments: 20 pages, 4 figures, submitted to Advances in High Energy Physics
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

We present a scenario where dark matter is in the form of dark atoms that can accomodate the experimentally observed excess of positrons in PAMELA and AMS-02 while being compatible with the constraints imposed on the gamma-ray flux from Fermi/LAT. This scenario assumes that the dominant component of dark matter is in the form of a bound state between a helium nucleus and a $-2$ particle and a small component is in the form of a WIMP-like dark atom compatible with direct searches in underground detectors. One of the constituents of this WIMP-like state is a $+2$ metastable particle with a mass of 1 TeV or slightly below that by decaying to $e^+e^+$, $\mu^+ \mu^+$ and $\tau^+ \tau^+$ produces the observed positron excess. These decays can naturally take place via GUT interactions. If it exists, such a metastable particle can be found in the next run of LHC. The model predicts also the ratio of leptons over baryons in the Universe to be close to -3.

[39]
Title: Material models of dark energy
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

We review and develop a new class of "dark energy" models, in which the relativistic theory of solids is used to construct material models of dark energy. These are models which include the effects of a continuous medium with well defined physical properties at the level of linearized perturbations. The formalism is constructed for a medium with arbitrary symmetry, and then specialised to isotropic media (which will be the case of interest for the majority of cosmological applications). We develop the theory of relativistic isotropic viscoelastic media whilst keeping in mind that we ultimately want to observationally constrain the allowed properties of the material model. We do this by obtaining the viscoelastic equations of state for perturbations (the entropy and anisotropic stress), as well as identifying the consistent corner of the theory which has constant equation of state parameter $\dot{w}=0$. We also connect to the non-relativistic theory of solids, by identifying the two quadratic invariants that are needed to construct the energy-momentum tensor, namely the Rayleigh dissipation function and Lagrangian for perturbations. Finally, we develop the notion that the viscoelastic behavior of the medium can be thought of as a non-minimally coupled massive gravity theory. This also provides a tool-kit for constructing consistent generalizations of coupled dark energy theories.

[40]
Title: Magnetorotational Core-Collapse Supernovae in Three Dimensions
Comments: 6 pages, 4 figures. Submitted to ApJL. Additional material and animations available at this http URL
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present results of new three-dimensional (3D) general-relativistic magnetohydrodynamic simulations of rapidly rotating strongly magnetized core collapse. These simulations are the first of their kind and include a microphysical finite-temperature equation of state and a leakage scheme that captures the overall energetics and lepton number exchange due to postbounce neutrino emission. Our results show that the 3D dynamics of magnetorotational core-collapse supernovae are fundamentally different from what was anticipated on the basis of previous simulations in axisymmetry (2D). A strong bipolar jet that develops in a simulation constrained to 2D is crippled by a spiral instability and fizzles in full 3D. While multiple (magneto-)hydrodynamic instabilities may be present, our analysis suggests that the jet is disrupted by an m=1 kink instability of the ultra-strong toroidal field near the rotation axis. Instead of an axially symmetric jet, a completely new, previously unreported flow structure develops. Highly magnetized spiral plasma funnels expelled from the core push out the shock in polar regions, creating wide secularly expanding lobes. We observe no runaway explosion by the end of the full 3D simulation at 185 ms after bounce. At this time, the lobes have reached maximum radii of 900 km.

[41]
Title: Disintegrating Asteroid P/2013 R3
Comments: 16 pages, 3 figures; accepted by ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Splitting of the nuclei of comets into multiple components has been frequently observed but, to date, no main-belt asteroid has been observed to break-up. Using the Hubble Space Telescope, we find that main-belt asteroid P/2013 R3 consists of 10 or more distinct components, the largest up to 200 m in radius (assumed geometric albedo of 0.05) each of which produces a coma and comet-like dust tail. A diffuse debris cloud with total mass roughly 2x10^8 kg further envelopes the entire system. The velocity dispersion among the components is about V = 0.2 to 0.5 m/s, is comparable to the gravitational escape speeds of the largest members, while their extrapolated plane-of-sky motions suggest break-up between February and September 2013. The broadband optical colors are those of a C-type asteroid. We find no spectral evidence for gaseous emission, placing model-dependent upper limits to the water production rate near 1 kg/s. Breakup may be due to a rotationally induced structural failure of the precursor body.

[42]
Title: The Supernova Remnant W44: confirmations and challenges for cosmic-ray acceleration
Comments: 13 pages, 11 figures, accepted by A&A
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The middle-aged supernova remnant (SNR) W44 has recently attracted attention because of its relevance regarding the origin of Galactic cosmic-rays. The gamma-ray missions AGILE and Fermi have established, for the first time for a SNR, the spectral continuum below 200 MeV which can be attributed to neutral pion emission. Confirming the hadronic origin of the gamma-ray emission near 100 MeV is then of the greatest importance. Our paper is focused on a global re-assessment of all available data and models of particle acceleration in W44, with the goal of determining on a firm ground the hadronic and leptonic contributions to the overall spectrum. We also present new gamma-ray and CO NANTEN2 data on W44, and compare them with recently published AGILE and Fermi data. Our analysis strengthens previous studies and observations of the W44 complex environment and provides new information for a more detailed modeling. In particular, we determine that the average gas density of the regions emitting 100 MeV - 10 GeV gamma-rays is relatively high (n= 250 - 300 cm^-3). The hadronic interpretation of the gamma-ray spectrum of W44 is viable, and supported by strong evidence. It implies a relatively large value for the average magnetic field (B > 10^2 microG) in the SNR surroundings, sign of field amplification by shock-driven turbulence. Our new analysis establishes that the spectral index of the proton energy distribution function is p1 = 2.2 +/- 0.1 at low energies and p2 = 3.2 +/- 0.1 at high energies. We critically discuss hadronic versus leptonic-only models of emission taking into account simultaneously radio and gamma-ray data. We find that the leptonic models are disfavored by the combination of radio and gamma-ray data. Having determined the hadronic nature of the gamma-ray emission on firm ground, a number of theoretical challenges remains to be addressed.