Short-hard Bursts Research Articles

GRB 180418A: A Possibly Short Gamma-Ray Burst with a Wide-angle Outflow in a Faint Host Galaxy

Abstract We present X-ray and multiband optical observations of the afterglow and host galaxy of GRB 180418A, discovered by Swift/BAT and Fermi/GBM. We present a reanalysis of the GBM and BAT data deriving durations of the prompt emission of T 90 ≈ 2.56 and 1.90 s, respectively. Modeling the Fermi/GBM catalog of 1405 bursts (2008–2014) in the hardness–T 90 plane, we obtain a probability of ≈60% that GRB 180418A is a short-hard burst. From a combination of Swift/XRT and Chandra observations, the X-ray afterglow is detected to ≈38.5 days after the burst and exhibits a single power-law decline with F X ∝ t −0.98. Late-time Gemini observations reveal a faint r ≈ 25.69 mag host galaxy at an angular offset of ≈0.″16. At the likely redshift range of z ≈ 1–2.25, we find that the X-ray afterglow luminosity of GRB 180418A is intermediate between short and long gamma-ray bursts (GRBs) at all epochs during which there are contemporaneous data and that GRB 180418A lies closer to the E γ,peak–E γ,iso correlation for short GRBs. Modeling the multiwavelength afterglow with the standard synchrotron model, we derive the burst explosion properties and find a jet opening angle of θ j ≳ 9°–14°. If GRB 180418A is a short GRB that originated from a neutron star merger, it has one of the brightest and longest-lived afterglows along with an extremely faint host galaxy. If, instead, the event is a long GRB that originated from a massive star collapse, it has among the lowest-luminosity afterglows and lies in a peculiar space in terms of the hardness–T 90 and E γ,peak–E γ,iso planes.

Universal afterglow of supernovaless gamma-ray bursts

The well-sampled afterglows of gamma ray bursts (GRBs) not associated with a supernova (SN) explosion, can be scaled down to a simple dimensionless universal formula, which describes well their temporal behavior. Such SN-less GRBs include short hard bursts (SHBs) and long SN-less GRBs. The universal temporal behavior of their afterglows is that expected from a pulsar wind nebula powered by the rotational energy loss of the newly born pulsar.

Infrared Emission from Kilonovae: The Case of the Nearby Short Hard Burst GRB 160821B

Abstract We present constraints on Ks-band emission from one of the nearest short hard gamma-ray bursts, GRB 160821B, at z = 0.16, at three epochs. We detect a red relativistic afterglow from the jetted emission in the first epoch but do not detect any excess kilonova emission in the second two epochs. We compare upper limits obtained with Keck I/MOSFIRE to multi-dimensional radiative transfer models of kilonovae, that employ composition-dependent nuclear heating and LTE opacities of heavy elements. We discuss eight models that combine toroidal dynamical ejecta and two types of wind and one model with dynamical ejecta only. We also discuss simple, empirical scaling laws of predicted emission as a function of ejecta mass and ejecta velocity. Our limits for GRB 160821B constrain the ejecta mass to be lower than 0.03 M ⊙ for velocities greater than 0.1 c. At the distance sensitivity range of advanced LIGO, similar ground-based observations would be sufficiently sensitive to the full range of predicted model emission including models with only dynamical ejecta. The color evolution of these models shows that I–K color spans 7–16 mag, which suggests that even relatively shallow infrared searches for kilonovae could be as constraining as optical searches.

IS THE LATE NEAR-INFRARED BUMP IN SHORT-HARD GRB 130603B DUE TO THE LI-PACZYNSKI KILONOVA?

Short-hard gamma-ray bursts (GRBs) are widely believed to be produced by the merger of two binary compact objects, specifically by two neutron stars or by a neutron star orbiting a black hole. According to the Li-Paczynski kilonova model, the merger would launch sub-relativistic ejecta and a near-infrared/optical transient would then occur, lasting up to days, which is powered by the radioactive decay of heavy elements synthesized in the ejecta. The detection of a late bump using the {\em Hubble Space Telescope} ({\em HST}) in the near-infrared afterglow light curve of the short-hard GRB 130603B is indeed consistent with such a model. However, as shown in this Letter, the limited {\em HST} near-infrared lightcurve behavior can also be interpreted as the synchrotron radiation of the external shock driven by a wide mildly relativistic outflow. In such a scenario, the radio emission is expected to peak with a flux of $\sim 100 \mu$Jy, which is detectable for current radio arrays. Hence, the radio afterglow data can provide complementary evidence on the nature of the bump in GRB 130603B. It is worth noting that good spectroscopy during the bump phase in short-hard bursts can test validity of either model above, analogous to spectroscopy of broad-lined Type Ic supernova in long-soft GRBs.

A RADIO-SELECTED SAMPLE OF GAMMA-RAY BURST AFTERGLOWS

We present a catalog of radio afterglow observations of gamma-ray bursts (GRBs) over a 14 year period from 1997 to 2011. Our sample of 304 afterglows consists of 2995 flux density measurements (including upper limits) at frequencies between 0.6 GHz and 660 GHz, with the majority of data taken at 8.5 GHz frequency band (1539 measurements). We use this dataset to carry out a statistical analysis of the radio-selected sample. The detection rate of radio afterglows has stayed unchanged almost at 31% before and after the launch of the {\em Swift} satellite. The canonical long-duration GRB radio light curve at 8.5 GHz peaks at 3-6 days in the source rest frame, with a median peak luminosity of $10^{31}$ erg s$^{-1}$ Hz$^{-1}$. The peak radio luminosities for short-hard bursts, X-ray flashes and the supernova-GRB classes are an order of magnitude or more fainter than this value. There are clear relationships between the detectability of a radio afterglow and the fluence or energy of a GRB, and the X-ray or optical brightness of the afterglow. However, we find few significant correlations between these same GRB and afterglow properties and the peak radio flux density. We also produce synthetic light curves at centimeter (cm) and millimeter (mm) bands using a range of blastwave and microphysics parameters derived from multiwavelength afterglow modeling, and we use them to compare to the radio sample. Finding agreement, we extrapolate this behavior to predict the cm and mm behavior of GRBs observed by the Expanded Very Large Array and the Atacama Large Millimeter Array.

Short γ-ray bursts and gravitational waves from dynamically formed merging binaries

Merging binary systems consisting of two collapsed objects are among the most promising sources of high frequency gravitational wave, GW, signals for ground based interferometers. Double neutron star or black hole/neutron star mergers are also believed to give rise to short hard bursts, SHBs, a subclass of gamma ray bursts. SHBs might thus provide a powerful way to infer the merger rate of two-collapsed object binaries. Under the hypothesis that most SHBs originate from double neutron star or black hole/neutron star mergers, we outline here a method to estimate the incidence of merging events from dynamically formed binaries in globular clusters and infer the corresponding GW event rate that can be detected with Advanced LIGO/Virgo. In particular a sizeable fraction of detectable GW events is expected to be coincident with SHBs. The beaming and redshift distribution of SHBs are reassessed and their luminosity function constrained by using the results from recent SHBs observations. We confirm that a substantial fraction of SHBs goes off at low redshifts, where the merging of systems formed in globular clusters through dynamical interactions is expected.

Swift-BAT results on the prompt emission of short bursts

This is a brief review of short hard bursts (SHBs) from previous missions and from Swift-BAT; in particular, a review of the developing class of gamma-ray bursts which are similar to SHBs in that they have the short hard initial spike (0.1 to a few seconds), but that they also have a long extended phase of soft emission (50-200s). Further, we suggest that a class of events discovered by Horvath in the T90 versus hardness ratio plane is this SHB with extended emission.

Prospects of LIGO for constraining inclination of merging compact binaries associated with three-dimensionally localized short-hard GRBs

We study prospects of a method to constrain the inclination of a coalescing compact binary by detecting its gravitational waves associated with a three-dimensionally localized (direction and distance) short-hard gamma-ray burst. We take advantage of a synergy of these two observations, and our method can be applied even with a single interferometer. For a nearly face-on binary the inclination angle $I$ can be constrained in the range $1\ensuremath{-}{\mathrm{SNR}}^{\ensuremath{-}1}\ensuremath{\le}\mathrm{cos}I\ensuremath{\le}1$ (SNR: the signal-to-noise ratio of gravitational wave detection), provided that the error of the distance estimation is negligible. This method would help us to study properties of the short-hard bursts, including potentially collimated jetlike structures as indicated by recent observation.

Comparison of VSB from BATSE, KONUS and SWIFT

We. show the locations of the SWIFT Short Hard Bursts (SHB) with afterglows on the galactic map and compare with the Very Short Bursts (VSB) BATSE events. As we have pointed out before, there is an excess of events in the galactic map of BATSE VSB events. We note that none of VSB SWIFT era events fall into this cluster. More SWIFT events are needed to check this claim. We also report a new study with KONUS data of the VSB sample with an average energy above 90keV showing a clear excess of events below 100 ms duration (T 90 ) that have large mean energy photons. We suggest that VSB themselves consist of two subclasses: a fraction of events have peculiar distribution properties and have no detectable counter parts, as might be expected for exotic sources such as primordial black holes.

GRB 060313: A New Paradigm for Short‐Hard Bursts?

We report the simultaneous observations of the prompt emission in the gamma-ray and hard X-ray bands by the Swift BATand the Konus-Wind instruments of the short-hard burst, GRB 060313. The observations reveal multiple peaks in both the gamma-ray and hard X-ray bands suggesting a highly variable outflow from the central explosion. We also describe the early-time observations of the X-ray and UV/optical afterglows by the Swift XRT and UVOT instruments. The combination of the X-ray and UV/optical observations provides the most comprehensive light curves to date of a short-hard burst at such an early epoch. The afterglows exhibit complex structure with different decay indices and flaring. This behavior can be explained by the combination of a structured jet, radiative loss of energy, and decreasing microphysics parameters occurring in a circumburst medium with densities varying by a factor of approximately two on a length scale of 10 17 cm. These density variations are normally associated with the environment of a massive star and inhomogeneities in its windy medium. However, the mean density of the observed medium (n � 10 � 4 cm 3 ) is much less than that expected for a massive star. Although the collapse of a massive star as theoriginofGRB060313isunlikely,themergerofacompactbinaryalsoposesproblemsforexplainingthebehavior of this burst. Two possible suggestions for explaining this scenario are that some short bursts may arise from a mechanism that does not invoke the conventional compact binary model, or that soft late-time central engine activity is producing UV/optical but no X-ray flaring.

On the possibility of identifying the short hard burst GRB 051103 with a giant flare from a soft gamma repeater in the M81 group of galaxies

The light curve, energy characteristics, and localization of the short hard burst GRB 051103 are considered. Evidence for identifying this event with a giant flare from a soft gamma repeater in the nearby M81 group of interacting galaxies is discussed.

The BATSE-Swift luminosity and redshift distributions of short-duration GRBs

We compare the luminosity function and rate inferred from the BATSE peak flux distribution of short hard bursts (SHBs) with the redshift and luminosity distributions of SHBs observed by Swift/HETE II. While the Swift/HETE II SHB sample is incompatible with the SHB population that follows the star formation rate, it is compatible with an SHB rate that reflects a distribution of delay times after the SFR. This would be the case if SHBs were associated with binary neutron star mergers. The available data allows, however, different interpretations. For example, a population whose rate is independent of the redshift fits the data very well. The implied SHB rates that we find range from ∼8 to ∼30 h 3 70 Gpc -3 yr -1 . This rate, which is comparable to the rate of neutron star mergers estimated from statistics of binary pulsars, is a much higher rate than what was previously estimated. We stress that our analysis, which is based on observed SHBs, is limited to bursts with luminosities above 10 49 erg/s. Weaker bursts may exist, but if so they are hardly detected by BATSE of Swift, so their rate is very weakly constrained by current observations.

The Galaxy Hosts and Large‐Scale Environments of Short‐Hard Gamma‐Ray Bursts

The rapid succession of discoveries of short-duration hard-spectrum gamma-ray bursts (GRBs) has led to unprecedented insights into the energetics of the explosion and nature of the progenitors. Yet short of the detection of a smoking gun, such as a burst of coincident gravitational radiation or a Li-Paczynski minisupernova, it is unlikely that a definitive claim can be made for the progenitors. As was the case with long-duration soft-spectrum GRBs, however, the expectation is that a systematic study of the hosts and locations of short GRBs could begin to yield fundamental clues as to their nature. We present an aggregate study of the host galaxies of short-duration hard-spectrum GRBs. In particular, we present the Gemini-North and Keck discovery spectra of the galaxies that hosted three short GRBs and a moderate-resolution (R ≈ 6000) spectrum of a fourth host. We find that these short-hard GRBs originate in a variety of low-redshift (z < 1) environments that differ substantially from those of long-soft GRBs, both on individual galaxy scales and on galaxy-cluster scales. Specifically, three of the bursts are found to be associated with old and massive galaxies with no current (<0.1 M☉ yr-1) or recent star formation. Two of these galaxies are located within a cluster environment. These observations support an origin from the merger of compact stellar remnants, such as double neutron stars or a neutron star-black hole binary. The fourth event, in contrast, occurred within a dwarf galaxy with a star formation rate exceeding 0.3 M☉ yr-1. Therefore, it appears that like supernovae of Type Ia, the progenitors of short-hard bursts are created in all galaxy types, suggesting a corresponding class with a wide distribution of delay times between formation and explosion.

Most Short-Hard Gamma-Ray Bursts Are Not in Moderately Bright Nearby Host Galaxies

The recent discovery by the Swift and HETE-2 satellites of X-ray afterglows from five short-hard bursts (SHBs) has lead to a simple picture in which SHBs have a typical isotropic burst energy of around 1050 ergs and in which the bursters are in normal L* host galaxies at nearby distances with redshifts of around 0.2. In this Letter, I compare this simple picture with evidence from five SHBs detected in 1978-1979, for which their observed median peak fluxes were ~100 times brighter than the 2005 events and for which their positional error regions are empty of galaxies to deeper limits than the associated galaxies for the 2005 events. For example, GRB 790406 had a peak flux of 5 × 10-5 ergs s-1, and its error box is empty to 23.29 mag; GRB 050509B had a peak flux of 2 × 10-7 ergs s-1, and its associated galaxy is 18.60 mag. Independent of redshift for either set of SHBs, the set from 1978 to 1979 has a ratio of burst luminosity to host galaxy luminosity that differs by almost 2 orders of magnitude when compared with the set from 2005. A Student's t-test produces a probability of less than 2.7% that the two sets are drawn from the same parent population. The explanation for the very different properties of the two sets of SHBs might be due to (1) chance coincidence in the 2005 associations, (2) two different populations, (3) the ejection of the progenitors from their original galaxy, and (4) a very broad burst luminosity function. Each of these four explanations has problems, and the true explanation is likely some combination of these.

Closing in on a Short‐Hard Burst Progenitor: Constraints from Early‐Time Optical Imaging and Spectroscopy of a Possible Host Galaxy of GRB 050509b

The localization of the short-duration, hard-spectrum gamma-ray burst GRB 050509b by the Swift satellite was a watershed event. We report the discovery of the probable host galaxy, a bright elliptical galaxy at z = 0.2248. This is the first known redshift and host of a short-hard GRB and shows that at least some short-hard GRBs are cosmological in origin. We began imaging the GRB field 8 minutes after the burst and continued for 8 days. We present a reanalysis of the XRT afterglow and report the absolute position of the GRB. Based on positional coincidences, the GRB and the elliptical are likely to be physically related, unlike any known connection between a long-duration GRB and an early-type galaxy. Similarly unique, GRB 050509b likely also originated from within a rich cluster of galaxies with detectable diffuse X-ray emission. We demonstrate that while the burst was underluminous, the ratio of the blast wave energy to the γ-ray energy is consistent with that of long-duration GRBs. Based on this analysis, on the location of the GRB (40 ± 13 kpc from the putative host), on the galaxy type (elliptical), and the lack of a coincident supernova, we suggest that there is now observational support for the hypothesis that short-hard bursts arise during the merger of a compact binary. We limit the properties of any Li-Paczyński "minisupernova" that is predicted to arise on ~1 day timescales. Other progenitor models are still viable, and new Swift bursts will undoubtedly help to further clarify the progenitor picture.

The afterglow and elliptical host galaxy of the short γ-ray burst GRB 050724

Despite a rich phenomenology, gamma-ray bursts (GRBs) are divided into two classes based on their duration and spectral hardness--the long-soft and the short-hard bursts. The discovery of afterglow emission from long GRBs was a watershed event, pinpointing their origin to star-forming galaxies, and hence the death of massive stars, and indicating an energy release of about 10(51) erg. While theoretical arguments suggest that short GRBs are produced in the coalescence of binary compact objects (neutron stars or black holes), the progenitors, energetics and environments of these events remain elusive despite recent localizations. Here we report the discovery of the first radio afterglow from the short burst GRB 050724, which unambiguously associates it with an elliptical galaxy at a redshift z = 0.257. We show that the burst is powered by the same relativistic fireball mechanism as long GRBs, with the ejecta possibly collimated in jets, but that the total energy release is 10-1,000 times smaller. More importantly, the nature of the host galaxy demonstrates that short GRBs arise from an old (> 1 Gyr) stellar population, strengthening earlier suggestions and providing support for coalescing compact object binaries as the progenitors.

The afterglow of GRB 050709 and the nature of the short-hard γ-ray bursts

The final chapter in the long-standing mystery of the gamma-ray bursts (GRBs) centres on the origin of the short-hard class of bursts, which are suspected on theoretical grounds to result from the coalescence of neutron-star or black-hole binary systems. Numerous searches for the afterglows of short-hard bursts have been made, galvanized by the revolution in our understanding of long-duration GRBs that followed the discovery in 1997 of their broadband (X-ray, optical and radio) afterglow emission. Here we present the discovery of the X-ray afterglow of a short-hard burst, GRB 050709, whose accurate position allows us to associate it unambiguously with a star-forming galaxy at redshift z = 0.160, and whose optical lightcurve definitively excludes a supernova association. Together with results from three other recent short-hard bursts, this suggests that short-hard bursts release much less energy than the long-duration GRBs. Models requiring young stellar populations, such as magnetars and collapsars, are ruled out, while coalescing degenerate binaries remain the most promising progenitor candidates.

Discovery of the short γ-ray burst GRB 050709

Gamma-ray bursts (GRBs) fall into two classes: short-hard and long-soft bursts. The latter are now known to have X-ray and optical afterglows, to occur at cosmological distances in star-forming galaxies, and to be associated with the explosion of massive stars. In contrast, the distance scale, the energy scale and the progenitors of the short bursts have remained a mystery. Here we report the discovery of a short-hard burst whose accurate localization has led to follow-up observations that have identified the X-ray afterglow and (for the first time) the optical afterglow of a short-hard burst; this in turn led to the identification of the host galaxy of the burst as a late-type galaxy at z = 0.16 (ref. 10). These results show that at least some short-hard bursts occur at cosmological distances in the outskirts of galaxies, and are likely to be caused by the merging of compact binaries.

Formation Rates of Black Hole Accretion Disk Gamma‐Ray Bursts

While many models have been proposed for GRBs, those currently favored are all based upon the formation of and/or rapid accretion into stellar mass black holes. We present population synthesis calculations of these models using a Monte Carlo approach in which the many uncertain parameters intrinsic to such calculations are varied. We estimate the event rate for each class of model as well as the propagation distance for those having significant delay between formation and burst production, i.e., double neutron star (DNS) mergers and black hole-neutron star (BH/NS) mergers. For reasonable assumptions regarding the many uncertainties in population synthesis, we calculate a daily event rate in the universe for i) merging neutron stars: ~100/day; ii) neutron-star black hole mergers: ~450/day; iii) collapsars: ~10,000/day; iv) helium star black hole mergers: ~1000/day; and v) white dwarf black hole mergers: ~20/day. The range of uncertainty in these numbers however, is very large, typically two to three orders of magnitude. These rates must additionally be multiplied by any relevant beaming factor and sampling fraction (if the entire universal set of models is not being observed). Depending upon the mass of the host galaxy, half of the DNS and BH/NS mergers will happen within 60kpc (for a Milky-Way massed galaxy) to 5Mpc (for a galaxy with negligible mass) from the galactic center. Because of the delay time, neutron star and black hole mergers will happen at a redshift 0.5 to 0.8 times that of the other classes of models. Information is still lacking regarding the hosts of short hard bursts, but we suggest that they are due to DNS and BH/NS mergers and thus will ultimately be determined to lie outside of galaxies and at a closer mean distance than long complex bursts (which we attribute to collapsars).