The intrinsic X-ray emission of gamma-ray bursts (GRBs) is often found to be absorbed over and above the column density through our own Galaxy. The extra component is usually assumed to be due to ...absorbing gas lying within the host galaxy of the GRB itself. There is an apparent correlation between the equivalent column density of hydrogen, N
H,intrinsic (assuming it to be at the GRB redshift), and redshift, z, with the few z > 6 GRBs showing the greatest intrinsic column densities. We investigate the N
H, intrinsic-z relation using a large sample of Swift GRBs, as well as active galactic nuclei and quasar samples, paying particular attention to the spectral energy distributions of the two highest redshift GRBs. Various possible sample biases and systematics that might produce such a correlation are considered, and we conclude that the correlation is very likely to be real. This may indicate either an evolutionary effect in the host galaxy properties, or a contribution from gas along the line of sight, in the diffuse intergalactic medium (IGM) or intervening absorbing clouds. Employing a more realistic model for IGM absorption than in previous works, we find that this may explain much of the observed opacity at z 3 providing it is not too hot, likely between 105 and 106.5 K, and moderately metal enriched, Z ∼ 0.2 Z. This material could therefore constitute the warm-hot intergalactic medium. However, a comparable level of absorption is also expected from the cumulative effect of intervening cold gas clouds, and given current uncertainties it is not possible to say which, if either, dominates. At lower redshifts, we conclude that gas in the host galaxies must be the dominant contributor to the observed X-ray absorption.
Abstract
The discovery of GW170817 and GRB 170817A in tandem with AT 2017gfo cemented the connection between neutron star mergers, short gamma-ray bursts (GRBs), and kilonovae. To investigate short ...GRB observations in the context of diverse kilonova behavior, we present a comprehensive optical and near-IR catalog of 85 bursts discovered over 2005–2020 on timescales of ≲12 days. The sample includes previously unpublished observations of 23 bursts and encompasses both detections and deep upper limits. We identify 11.8% and 15.3% of short GRBs in our catalog with upper limits that probe luminosities lower than those of AT 2017gfo and a fiducial neutron star–black hole kilonova model (for pole-on orientations), respectively. We quantify the ejecta masses allowed by the deepest limits in our catalog, constraining blue and “extremely blue” kilonova components of 14.1% of bursts to
M
ej
≲ 0.01–0.1
M
⊙
. The sample of short GRBs is not particularly constraining for red kilonova components. Motivated by the large catalog, as well as model predictions of diverse kilonova behavior, we investigate modified search strategies for future follow-up to short GRBs. We find that ground-based optical and near-IR observations on timescales of ≳2 days can play a significant role in constraining more diverse outcomes. We expect future short GRB follow-up efforts, such as from the James Webb Space Telescope, to expand the reach of kilonova detectability to redshifts of
z
≈ 1.
We present Hubble Space Telescope (HST) and Chandra imaging, combined with Very Large Telescope MUSE integral field spectroscopy of the counterpart and host galaxy of the first binary neutron star ...merger detected via gravitational-wave emission by LIGO and Virgo, GW170817. The host galaxy, NGC 4993, is an S0 galaxy at z = 0.009783. There is evidence for large, face-on spiral shells in continuum imaging, and edge-on spiral features visible in nebular emission lines. This suggests that NGC 4993 has undergone a relatively recent ( 1 Gyr) "dry" merger. This merger may provide the fuel for a weak active nucleus seen in Chandra imaging. At the location of the counterpart, HST imaging implies there is no globular or young stellar cluster, with a limit of a few thousand solar masses for any young system. The population in the vicinity is predominantly old with 1% of any light arising from a population with ages < 500 Myr . Both the host galaxy properties and those of the transient location are consistent with the distributions seen for short-duration gamma-ray bursts, although the source position lies well within the effective radius ( r e ∼ 3 kpc), providing an re-normalized offset that is closer than ∼ 90 % of short GRBs. For the long delay time implied by the stellar population, this suggests that the kick velocity was significantly less than the galaxy escape velocity. We do not see any narrow host galaxy interstellar medium features within the counterpart spectrum, implying low extinction, and that the binary may lie in front of the bulk of the host galaxy.
We present the discovery of the optical afterglow and host galaxy of the Swift short-duration gamma-ray burst (SGRB) GRB 181123B. Observations with Gemini-North starting 9.1 hr after the burst reveal ...a faint optical afterglow with i 25.1 mag at an angular offset of 0 59 0 16 from its host galaxy. Using grizYJHK observations, we measure a photometric redshift of the host galaxy of . From a combination of Gemini and Keck spectroscopy of the host galaxy spanning 4500-18000 , we detect a single emission line at 13390 , inferred as Hβ at z = 1.754 0.001 and corroborating the photometric redshift. The host galaxy properties of GRB 181123B are typical of those of other SGRB hosts, with an inferred stellar mass of 9.1 × 109 M , a mass-weighted age of 0.9 Gyr, and an optical luminosity of 0.9L*. At z = 1.754, GRB 181123B is the most distant secure SGRB with an optical afterglow detection and one of only three at z > 1.5. Motivated by a growing number of high-z SGRBs, we explore the effects of a missing z > 1.5 SGRB population among the current Swift sample on delay time distribution (DTD) models. We find that lognormal models with mean delay times of 4-6 Gyr are consistent with the observed distribution but can be ruled out to 95% confidence, with an additional one to five Swift SGRBs recovered at z > 1.5. In contrast, power-law models with ∝t−1 are consistent with the redshift distribution and can accommodate up to 30 SGRBs at these redshifts. Under this model, we predict that 1/3 of the current Swift population of SGRBs is at z > 1. The future discovery or recovery of existing high-z SGRBs will provide significant discriminating power on their DTDs and thus their formation channels.
ABSTRACT We present late time multi-wavelength observations of Swift J1644+57, suggested to be a relativistic tidal disruption flare (TDF). Our observations extend to >4 years from discovery and show ...that 1.4 years after outburst the relativistic jet switched off on a timescale less than tens of days, corresponding to a power-law decay faster than t−70. Beyond this point weak X-rays continue to be detected at an approximately constant luminosity of LX ∼ 5 × 1042 erg s−1 and are marginally inconsistent with a continuing decay of t−5/3, similar to that seen prior to the switch-off. Host photometry enables us to infer a black hole mass of MBH = 3 × 106 M , consistent with the late time X-ray luminosity arising from sub-Eddington accretion onto the black hole in the form of either an unusually optically faint active galactic nucleus or a slowly varying phase of the transient. Optical/IR observations show a clear bump in the light curve at timescales of 30-50 days, with a peak magnitude (corrected for host galaxy extinction) of MR ∼ −22 to −23. The luminosity of the bump is significantly higher than seen in other, non-relativistic TDFs and does not match any re-brightening seen at X-ray or radio wavelengths. Its luminosity, light curve shape, and spectrum are broadly similar to those seen in superluminous supervnovae, although subject to large uncertainties in the correction of the significant host extinction. We discuss these observations in the context of both TDF and massive star origins for Swift J1644+5734 and other candidate relativistic tidal flares.
ABSTRACT We introduce the Swift Gamma-Ray Burst Host Galaxy Legacy Survey ("SHOALS"), a multi-observatory high-redshift galaxy survey targeting the largest unbiased sample of long-duration gamma-ray ...burst (GRB) hosts yet assembled (119 in total). We describe the motivations of the survey and the development of our selection criteria, including an assessment of the impact of various observability metrics on the success rate of afterglow-based redshift measurement. We briefly outline our host galaxy observational program, consisting of deep Spitzer/IRAC imaging of every field supplemented by similarly deep, multicolor optical/near-IR photometry, plus spectroscopy of events without preexisting redshifts. Our optimized selection cuts combined with host galaxy follow-up have so far enabled redshift measurements for 110 targets (92%) and placed upper limits on all but one of the remainder. About 20% of GRBs in the sample are heavily dust obscured, and at most 2% originate from Using this sample, we estimate the redshift-dependent GRB rate density, showing it to peak at and fall by at least an order of magnitude toward low (z = 0) redshift, while declining more gradually toward high ( ) redshift. This behavior is consistent with a progenitor whose formation efficiency varies modestly over cosmic history. Our survey will permit the most detailed examination to date of the connection between the GRB host population and general star-forming galaxies, directly measure evolution in the host population over cosmic time and discern its causes, and provide new constraints on the fraction of cosmic star formation occurring in undetectable galaxies at all redshifts.
Long-duration γ-ray bursts (GRBs) are associated with type Ic supernovae that are more luminous than average and that eject material at very high velocities. Less-luminous supernovae were not ...hitherto known to be associated with GRBs, and therefore GRB-supernovae were thought to be rare events. Whether X-ray flashes-analogues of GRBs, but with lower luminosities and fewer γ-rays-can also be associated with supernovae, and whether they are intrinsically 'weak' events or typical GRBs viewed off the axis of the burst, is unclear. Here we report the optical discovery and follow-up observations of the type Ic supernova SN 2006aj associated with X-ray flash XRF 060218. Supernova 2006aj is intrinsically less luminous than the GRB-supernovae, but more luminous than many supernovae not accompanied by a GRB. The ejecta velocities derived from our spectra are intermediate between these two groups, which is consistent with the weakness of both the GRB output and the supernova radio flux. Our data, combined with radio and X-ray observations, suggest that XRF 060218 is an intrinsically weak and soft event, rather than a classical GRB observed off-axis. This extends the GRB-supernova connection to X-ray flashes and fainter supernovae, implying a common origin. Events such as XRF 060218 are probably more numerous than GRB-supernovae.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present observations and analysis of the host galaxies of 23 heavily dust-obscured gamma-ray bursts (GRBs) observed by the Swift satellite during the years 2005-2009, representing all GRBs with an ...unambiguous host-frame extinction of A sub(V) > 1 mag from this period. Deep observations with Keck, Gemini, Very Large Telescope, Hubble Space Telescope, and Spitzer successfully detect the host galaxies and establish spectroscopic or photometric redshifts for all 23 events, enabling us to provide measurements of the intrinsic host star formation rates, stellar masses, and mean extinctions. Compared to the hosts of unobscured GRBs at similar redshifts, we find that the hosts of dust-obscured GRBs are (on average) more massive by about an order of magnitude and also more rapidly star forming and dust obscured. While this demonstrates that GRBs populate all types of star-forming galaxies, including the most massive, luminous systems at z approximately 2, at redshifts below 1.5 the overall GRB population continues to show a highly significant aversion to massive galaxies and a preference for low-mass systems relative to what would be expected given a purely star-formation-rate-selected galaxy sample. This supports the notion that the GRB rate is strongly dependent on metallicity, and may suggest that the most massive galaxies in the universe underwent a transition in their chemical properties ~9 Gyr ago. We also conclude that, based on the absence of unobscured GRBs in massive galaxies and the absence of obscured GRBs in low-mass galaxies, the dust distributions of the lowest-mass and the highest-mass galaxies are relatively homogeneous, while intermediate-mass galaxies (~10 super(9) M sub(middot in circle)) have diverse internal properties.
ABSTRACT
Compact binaries such as double neutron stars or a neutron star paired with a black hole, are strong sources of gravitational waves during coalescence and also the likely progenitors of ...various electromagnetic phenomena, notably short-duration gamma-ray bursts (SGRBs), and kilonovae. In this work, we generate populations of synthetic binaries and place them in galaxies from the large-scale hydrodynamical galaxy evolution simulation, eagle. With our zELDA code, binaries are seeded in proportion to star formation rate, and we follow their evolution to merger using both the bpass and cosmic binary stellar evolution codes. We track their dynamical evolution within their host galaxy potential, to estimate the galactocentric distance at the time of the merger. Finally, we apply observational selection criteria to allow comparison of this model population with the legacy sample of SGRBs. We find a reasonable agreement with the redshift distribution (peaking at 0.5 < z < 1), host morphologies, and projected galactocentric offsets (modal impact parameter ≲10 kpc). Depending on the binary simulation used, we predict $\sim 16\!-\!35{{\ \rm per\ cent}}$ of SGRB events would appear ‘host-less’, i.e. sources that merge with high impact parameters or have hosts fainter than the detection limit (H > 26).
The discovery of binary neutron star merger GW170817 from its gravitational wave (GW) signature, together with its accompanying electromagnetic (EM) emission spanning gamma‐ray to radio, marked the ...birth of GW + EM multimessenger astrophysics. The radioactively powered thermal kilonova, which dominated the ultraviolet to infrared in the hours to weeks after the merger, indicates that such mergers are the site of heavy‐element nucleosynthesis, likely extending to the third r‐process peak. The prompt gamma‐ray flash, and late‐time nonthermal (X‐ray to radio) emission, indicate that the merger also produced an ultrarelativistic jet, thus tying this event to the phenomena of short‐duration gamma‐ray bursts. In the future, observations of further mergers promise to establish their contribution to global nucleosynthesis, allow investigation of jet launching and structure, provide independent estimates of the cosmological parameters, constrain the neutron star equation of state, and address questions of fundamental physics.
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