For gamma-ray bursts (GRBs) with durations greater than two seconds (so-called long GRBs), the intrinsic prompt gamma-ray emission appears, on average, to last longer for bursts at lower redshifts. We explore the nature of this duration-redshift anti-correlation, describing systems and conditions in which this cosmological evolution could arise. In particular, we explore its dependence on metallicity of a massive star progenitor, as we can securely count on the average stellar metallicity to increase with decreasing redshift. Although higher metallicity/lower redshift stars lose mass and angular momentum through line-driven winds, in some cases these stars are able to form more extended accretion disks when they collapse, potentially leading to longer duration GRBs. We also examine how this duration-redshift trend may show up in interacting binary models composed of a massive star and compact object companion, recently suggested to be the progenitors of radio bright GRBs. Under certain conditions, mass loss and equation of state effects from higher metallicity, lower redshift massive stars can decrease the binary separation. This can then lead to spin-up of the massive star and allow for a longer duration GRB upon the massive star's collapse. Finally, the duration-redshift trend may also be supported by a relatively larger population of small-separation binaries born in situ at low redshift.
Studies of \textit{BATSE} bursts \citep{kouveliotou:93} have resulted in the widespread adoption of a two-group categorization: long bursts (those with durations $\geq 2$ seconds) and short bursts (those with durations $\leq 2$ seconds). This categorization, one must recall, used the observed $T_{90}$ time durations for bursts (during which 90\% of a burst's fluence is measured). In this work, we have explored two ideas: 1) a statistical search for a possible third, intermediate category of bursts (between the "short" and the "long" ones) among 2041 \textit{BATSE} GRBs and 757 \textit{Swift/BA…
Gamma-ray bursts (GRBs) show a bimodal distribution of durations, separated at a duration of ~2 s. Observations have confirmed the association of long GRBs with the collapse of massive stars. The origin of short GRBs is still being explored. We examine constraints on the emission region size in short and long GRBs detected by Fermi/GBM. We find that the emission region size during the prompt emission, R, and the burst duration, T$_{90}$, are consistent with the relation R ~ c x T$_{90}$, for both long and short GRBs. We find the characteristic size for the prompt emission region to be ~2 x 10$…
The intermediate-duration gamma-ray bursts (GRBs) identified in the data of the RHESSI satellite are investigated with respect to their spectral lags, peak count rates, redshifts, supernova observations, and star formation rates of their host galaxies. Standard statistical tests like Kolmogorov-Smirnov and Student t-test are used. It is discussed whether these bursts belong to the group of so-called short or long GRBs, or if they significantly differ from both groups.
We present a catalog of long duration bursts observed with the Joint European X-ray Monitor (JEM-X) and IBIS/ISGRI instruments onboard the INTEGRAL satellite. The fourteen bursts have e-folding times ranging from 55 s to ? 17 min, and are therefore classified as intermediate-duration bursts, caused by the ignition of an unusually thick helium layer. Though seven events have already been reported in literature, we have systematically re-analyzed the whole sample. We find three new photospheric radius expansion (PRE) bursts, which are not reported in the literature, allowing us to provide a new …
Gamma-ray bursts (GRBs) are detectable out to very large distances and as such are potentially powerful cosmological probes. Historically, the angular distribution of GRBs provided important information about their origin and physical properties. As a general population, GRBs are distributed isotropically across the sky. However, there are published reports that once binned by duration or redshift, GRBs display significant clustering. We have studied the redshift- and duration-dependent clustering of GRBs using proximity measures and kernel density estimation. Utilizing bursts detected by BATS…
The binary neutron star merger responsible for the gravitational wave event, GW170817, strengthened the merger association with short-duration gamma-ray bursts (SGRBs) following the detection of the SGRB counterpart, GRB 170817A. Here we consider the constraints on a population of local gamma-ray bursts with moderately short duration ($T_{90}<4 \textrm{ s}$) and within $d < 200 \textrm{ Mpc}$, that may have originated from similar compact binary mergers. Using well localised gamma-ray bursts from $\sim14.5 \textrm{ years}$ of Swift/Burst Alert Telescope monitoring, we find no events with high …
Gamma-ray bursts can be divided into three groups: short-, intermediate and long-duration bursts. While the progenitors of the short and long ones are relatively known, the progenitor objects of the intermediate-duration bursts are generally unknown, however, recent statistical studies suggest, that they should be related to the long-duration bursts. In this work we investigate whether there is a differ- ence between the global parameters of the X-ray flashes and intermediate-duration group of gamma-ray bursts. The statistical tests do not show any significant discrepancy regarding most of the…
Classification of gamma-ray bursts (GRBs) into groups has been intensively studied by various statistical tests in previous years. It has been suggested that there was a distinct group of GRBs, beyond the long and short ones, with intermediate durations. However, such a group is not securely confirmed yet. Strangely, concerning the spectral hardness, the observations from the Swift and RHESSI satellites give different results. For the Swift/BAT database it is found that the intermediate-duration bursts might well be related to so-called X-ray flashes (XRFs). On the other hand, for the RHESSI d…
We study the evolution with redshift of three measures of gamma-ray burst (GRB) duration ($T_{\rm 90}$, $T_{\rm 50}$ and $T_{\rm R45}$) in a fixed rest frame energy band for a sample of 232 Swift/BAT detected GRBs. Binning the data in redshift we demonstrate a trend of increasing duration with increasing redshift that can be modelled with a power-law for all three measures. Comparing redshift defined subsets of rest-frame duration reveals that the observed distributions of these durations are broadly consistent with cosmological time dilation. To ascertain if this is an instrumental effect, a …
It is generally believed that long-duration gamma-ray bursts (GRBs) are associated with massive star core-collapse, whereas short-duration GRBs are associated with mergers of compact star binaries. However, growing observations have suggested that oddball GRBs do exist, and multiple criteria (prompt emission properties, supernova/kilonova associations, and host galaxy properties) rather than burst duration only are needed to classify GRBs physically. A previously reported long-duration burst, GRB 060614, could be viewed as a short GRB with extended emission if it were observed at a larger dist…
The system of accretion disk and black hole is usually considered as the central engine of Gamma-ray Bursts (GRBs). It is usually thought that the disk in the central engine of GRBs is the advection-dominated accretion disk, which is developed from a massive (mass M_disk) torus at radius r_disk. We find a positive correlation between the isotropic gamma-ray energy E_iso and duration (so-called T_90) for GRBs. We interpret this correlation within the advection-dominated accretion disk model, associating E_iso and T_90 with M_ disk and viscous timescale respectively.
We numerically analyze the evolution of a long-duration gamma-ray burst jet as it leaves the progenitor star and propagates to the photospheric radius, where radiation can be released. We find that the interaction of the relativistic material with the progenitor star has influences well beyond the stellar surface. Tangential collimation shocks are observed throughout the jet evolution, out to about 100 stellar radii, which is the whole range of our simulation. We find that the jet is internally hot at the photospheric radius and we compute the photospheric emission. The photosphere is a very e…
Gamma-ray bursts (GRBs) are believed to belong to two classes and they are conventionally divided according to their durations. This classification scheme is not satisfied due to the fact that duration distributions of the two classes are heavily overlapped. We collect a new sample (153 sources) of GRBs and investigate the distribution of the logarithmic deviation of the $E_p$ value from the Amati relation. The distribution possesses an obvious bimodality structure and it can be accounted for by the combination of two Gaussian curves. Based on this analysis, we propose to statistically classif…
Relations linking the temporal or/and spectral properties of the prompt emission of gamma-ray bursts (hereafter GRBs) to the absolute luminosity are of great importance as they both constrain the radiation mechanisms and represent potential distance indicators. Here we discuss two such relations: the lag-luminosity relation and the newly discovered duration-luminosity relation of GRB pulses. We aim to extend our previous work on the origin of spectral lags, using the duration-luminosity relation recently discovered by Hakkila et al. to connect lags and luminosity. We also present a way to test…
We compare the redshifts, host galaxy metallicities, and isotropic (E_gamma,iso) and beaming-corrected (E_gamma) gamma-ray energy release of 16 long-duration gamma-ray bursts (LGRBs) at z < 1. From this comparison, we find no statistically significant correlation between host metallicity and redshift, E_gamma,iso, or E_gamma. These results are at odds with previous theoretical and observational predictions of an inverse correlation between gamma-ray energy release and host metallicity, as well as the standard predictions of metallicity-driven wind effects in stellar evolutionary models. We con…
The observed durations of prompt gamma-ray emission from gamma-ray bursts (GRBs) are often used to infer the progenitors and energetics of the sources. Inaccurate duration measurements will have a significant impact on constraining the processes powering the bursts. The "tip-of-the-iceberg" effect describes how the observed signal is lost into background noise; lower instrument sensitivity leads to higher measurement bias. In this study, we investigate how observing conditions, such as the number of enabled detectors, background level, and incident angle of the source relative to the detector …
Cosmological time dilation is a fundamental phenomenon in an expanding universe, which stresses that both the duration and wavelength of the emitted light from a distant object at the redshift $z$ will be dilated by a factor of $1+z$ at the observer. By using a sample of 139 \emph{Swift} long GRBs with known redshift ($z\leq8.2$), we measure the observed duration ($T_{90}$) in the observed energy range between $140/(1+z)$ keV and $350/(1+z)$ keV, corresponding to a fixed energy range of 140-350 keV in the rest frame. We obtain a significant correlation between the duration and the factor $1+z$…
Long-duration gamma-ray bursts (GRBs) are generally related to the core-collapse of massive stars. In the collapsar scenario, a rotating stellar-mass black hole (BH) surrounded by a hyperaccretion disk has been considered as one of the plausible candidates of GRB central engines. In this paper, we work on a sample including 146 long GRBs with significant jet break features in the multi-band afterglows. The jet opening angles can be then obtained by the jet break time. By asumming GRB jets powered by Blandford-Znajek (BZ) mechanism in the BH hyperaccretion system, we analyze the distributions o…
The prompt emission of Gamma Ray Bursts (GRBs) is usually well described by the Band function: two power-laws joined smoothly at a given break energy. In addition to the Band component, a few bursts (GRB941017, GRB090510, GRB090902B and GRB090926A) show clear evidence for a distinct high-energy spectral component, which in some cases evolves independently from the prompt keV component and is well described by a power-law (PL), sometimes with a cut-off energy; this component is found to have long duration, even longer than the burst itself for all the four bursts. Here we report the observation…
Ever since the insightful analysis of the durations of GRBs by [Kouveliotou:93], GRBs have most often been classified into two populations: "short bursts" (shorter than 2.0 seconds) and "long bursts" (longer than 2.0 seconds). However, recent works have suggested the existence of an intermediate population in the bursts observed by the Swift satellite. Moreover, some researchers have questioned the universality of the 2.0-second dividing line between short and long bursts: some bursts may be short but actually result from collapsars, the physical mechanism behind normally long bursts, and some…
The duration of the prompt emission of long gamma-ray bursts is generally considered to be fairly similar to the duration of the activity of the engine in the center of the progenitor star. Here, we investigate the relation between the duration of the engine activity and that of the observed light curve, using inputs from both numerical simulations and observations. We find that the observed burst duration is a good proxy for the engine duration after the time necessary for the jet to break out the star's surface is subtracted. However, the observed duration is a function of the viewing angle …
Two classes of gamma-ray bursts have been identified in the BATSE catalogs characterized by durations shorter and longer than about 2 seconds. There are, however, some indications for the existence of a third type of burst. Swift satellite detectors have different spectral sensitivity than pre-Swift ones for gamma-ray bursts. Therefore it is worth to reanalyze the durations and their distribution and also the classification of GRBs. Using The First BAT Catalog the maximum likelihood estimation was used to analyzed the duration distribution of GRBs. The three log-normal fit is significantly (99…
Long-duration gamma-ray bursts (LGRBs) are generally considered to originate from the massive collapsars. It is believed that the central engine of gamma-ray bursts (GRBs) is a neutrino-dominated accretion flow (NDAF) around a rotating stellar-mass black hole (BH). The neutrino annihilation above the NDAF is a feasible mechanism to power GRB. In this work, we analyse the distributions of the isotropic gamma-ray radiated energy and jet kinetic energy of 48 LGRBs. According to the NDAF and fireball models, we estimate the mean accreted masses of LGRBs in our sample to investigate whether the NDA…
Jets in long-duration $γ$-ray bursts (GRBs) have to drill through the collapsing star in order to break out of it and produce the $γ$-ray signal while the central engine is still active. If the breakout time is shorter for more powerful engines, then the jet-collapsar interaction acts as a filter of less luminous jets. We show that the observed broken power-law GRB luminosity function is a natural outcome of this process. For a theoretically motivated breakout time that scales with jet luminosity as $L^{-χ}$ with $χ\sim 1/3-1/2$, we show that the shape of the $γ$-ray duration distribution can …
Gamma-ray bursts are still not fully understood events. However, their exploration could provide a useful tool for a better understanding of the early Universe because they belong to the most distant and violent objects that astronomers know. This thesis tries to bring more information about a so-called group of intermediate-duration bursts claimed by different authors employing different data samples. Firstly, duration and spectral hardness properties of bursts from the Reuven Ramaty High-Energy Solar Spectroscopic Imager are statistically analysed. The obtained results bring a suspicion that…
Aiming to study GRB engine duration, we present numerical simulations to investigate collapsar jets. We consider typical explosion energy ($10^{52}$ erg) but different engine durations, in the widest domain to date from 0.1 to 100 s. We employ an AMR 2D hydrodynamical code. Our results show that engine duration strongly influences jet nature. We show that the efficiency of launching and collimating relativistic outflow increases with engine duration, until the intermediate engine range where it is the highest, past this point to long engine range, the trend is slightly reversed; we call this p…
Gamma-Ray Bursts (GRBs) are traditionally divided to long and short according to their durations (>/< 2 sec). It was generally believed that this reflects a different physical origin: Collapsars (long) and non-Collapsars (short). We have recently shown that the duration distribution of Collapsars is flat, namely independent of the duration, at short durations. Using this model for the distribution of Collapsars we determine the duration distribution of non-Collapsars and estimate the probability that a burst with a given duration (and hardness) is a Collapsar or not. We find that this probabil…
Gamma-ray burst light curves are characterized by marked variability, each showing unique properties. The origin of such variability, at least for a fraction of long GRBs, may be the result of an unsteady central engine. It is thus important to study the effects that an episodic central engine has on the jet propagation and, eventually, on the prompt emission within the collapsar scenario. Thus, in this study we follow the interaction of pulsed outflows with their progenitor stars with hydrodynamic numerical simulations in both two and three dimensions. We show that the propagation of unsteady…
The plateau in the duration distribution of long Gamma-Ray Bursts (LGRBs) provides a direct observational evidence for the Collapsar model. The plateau reflects the fact that the observed duration satisfies: $T_{90} = t_{e}-t_{b}$ where $t_{e}$ is the time that the central engine operates and $t_{b}$ is a threshold time, interpreted within the Collapsar model as the time it takes for the relativistic jet to penetrate the stellar envelope. Numerical simulation and macronova observations suggest that compact binary mergers involve mass ejection. If short-Gamma Ray Bursts (sGRBs) arise from such …
Until now the existence of extended emission is an intriguing property of short bursts. It is not clear what is the nature of the extended emission. It might be a rising x-ray afterglow, or it could be a manifestation of the prolonged activity of a central engine. We consider short duration gamma-ray bursts, emphasizing the common properties of short bursts and short burst with extended emission. Assuming that the extended emission with broad dynamic range is a common property of short bursts, we propose a two jet model which can describe both short main episode of hard spectra emission, speci…
We extend our study of energetic radio loud and quiet gamma-ray bursts (GRBs), suggesting these GRBs potentially come from two separate progenitor systems. We expand the sample from our previous paper (Lloyd-Ronning & Fryer, 2017) and find our results are strengthened - radio quiet GRBs have significantly shorter intrinsic prompt duration, and are also less energetic on average. However, the tenuous correlation between isotropic energy and intrinsic duration in the radio dark sample remains tenuous and is slightly weakened by adding more bursts. Interestingly, we find an anti-correlation betwe…
Gamma-ray bursts (GRBs) display a bimodal duration distribution, with a separation between the short- and long-duration bursts at about 2 sec. The progenitors of long GRBs have been identified as massive stars based on their association with Type Ic core-collapse supernovae, their exclusive location in star-forming galaxies, and their strong correlation with bright ultraviolet regions within their host galaxies. Short GRBs have long been suspected on theoretical grounds to arise from compact object binary mergers (NS-NS or NS-BH). The discovery of short GRB afterglows in 2005, provided the fir…
Several gamma-ray bursts (GRBs) last much longer (~hours) in gamma-rays than typical long GRBs (~ minutes), and recently it was proposed that these "ultra-long GRBs" may form a distinct population, probably with a different (e.g. blue supergiant) progenitor than typical GRBs. However, Swift observations suggest that many GRBs have extended central engine activities manifested as flares and internal plateaus in X-rays. We perform a comprehensive study on a large sample of Swift GRBs with XRT observations to investigate GRB central engine activity duration and to determine whether ultra-long GRB…
The discovery of a number of gamma-ray bursts with duration exceeding 1,000 seconds, in particular the exceptional case of GRB 111209A with a duration of about 25,000 seconds, has opened the question on whether these bursts form a new class of sources, the so called {\em ultra-long} GRBs, or if they are rather the tail of the distribution of the standard long GRB duration. In this Letter, using the long GRB sample detected by {\em Swift}, we investigate on the statistical properties of ultra-long GRBs and compare them with the overall long burst population. We discuss also on the differences o…
We report on a spectroscopic analysis of the X-ray emission from IGR J17062-6143 in the aftermath of its June 2020 intermediate duration Type I X-ray burst. Using the Neutron Star Interior Composition Explorer, we started observing the source three hours after the burst was detected with MAXI/GSC, and monitored the source for the subsequent twelve days. We observed the tail end of the X-ray burst cooling phase, and find that the X-ray flux is severely depressed relative to its historic value for a three day period directly following the burst. We interpret this intensity dip as the inner accre…
We investigate the intrinsic properties of a sample of bright (E_iso > 10^52 erg) gamma-ray bursts, comparing those with and without radio afterglows. We find that the sample of bursts with no radio afterglows has a significantly shorter mean intrinsic duration of the prompt gamma-ray radiation, and the distribution of this duration is significantly different from those bursts with a radio afterglow. Although the sample with no radio afterglow has on average lower isotropic energy, the lack of radio afterglow does not appear to be a result of simply energetics of the burst, but a reflection of…
A sample of 427 gamma-ray bursts from a database (February 2002 - April 2008) of the RHESSI satellite is analyzed statistically. The spectral lags and peak-count rates, which have been calculated for the first time in this paper, are studied completing an earlier analysis of durations and hardness ratios. The analysis of the RHESSI database has already inferred the existence of a third group with intermediate duration, apart from the so-called short and long groups. First aim of this article is to discuss the properties of these intermediate-duration bursts in terms of peak-count rates and spe…
Thermonuclear bursts from slowly accreting neutron stars (NSs) have proven difficult to detect, yet they are potential probes of the thermal properties of the neutron star interior. During the first year of a systematic all-sky search for X-ray bursts using the Gamma-ray Burst Monitor (GBM) aboard the Fermi Gamma-ray Space Telescope we have detected 15 thermonuclear bursts from the NS low-mass X-ray binary 4U 0614+09, when it was accreting at nearly 1% of the Eddington limit. We measured an average burst recurrence time of 12+/-3 d (68% confidence interval) between March 2010 and March 2011, c…
A long duration gamma-ray burst, GRB 160530A, was detected by the Compton Spectrometer and Imager (COSI) during the 2016 COSI Super Pressure Balloon campaign. As a Compton telescope, COSI is inherently sensitive to the polarization of gamma-ray sources in the energy range 0.2-5.0 MeV. We measured the polarization of GRB 160530A using 1) a standard method (SM) based on fitting the distribution of azimuthal scattering angles with a modulation curve, and 2) an unbinned, maximum likelihood method (MLM). In both cases, the measured polarization level was below the $99\%$ confidence minimum detectab…
Decades ago two classes of gamma-ray bursts were identified and delineated as having durations shorter and longer than about 2 s. Subsequently indications also supported the existence of a third class. Using maximum likelihood estimation we analyze the duration distribution of 888 Swift BAT bursts observed before October 2015. Fitting three log-normal functions to the duration distribution of the bursts provides a better fit than two log-normal distributions, with 99.9999% significance. Similarly to earlier results, we found that a fourth component is not needed. The relative frequencies of th…
One of the most intriguing features discovered by Swift is a plateau phase in the X-ray flux decay of about 70% of the afterglows of gamma-ray bursts (GRBs). The physical origin of this feature is still being debated. We constrain the proposed interpretations, based on the intrinsic temporal properties of the plateau phase. We selected and analyzed all the Swift/XRT GRB afterglows at known redshift observed between March 2005 and June 2008 featuring a shallow decay phase in their X-ray lightcurves. For our sample of 21 GRBs we find an anticorrelation of the logarithm of the duration of the sha…
[Abridged] By appealing to a Quark-Nova (QN; the explosive transition of a neutron star to a quark star) in the wake of a core-collapse Supernova explosion of a massive star, we develop a unified model for long duration Gamma-ray Bursts (LGRBs) and Fast Radio Bursts (FRBs). The time delay (years to decades) between the SN and the QN and, the fragmented nature (i.e. millions of chunks) of the relativistic QN ejecta are key to yielding a robust LGRB engine. In our model, a LGRB light-curve exhibits the interaction of the fragmented QN ejecta with a turbulent (i.e. filamentary and magnetically sa…
Gamma-ray bursts (GRBs) are divided into two classes according to their durations. We investigate if the softness of bursts plays a role in the conventional classification of the objects. We employ the BATSE (Burst and Transient Source Experiment) catalog and analyze the duration distributions of different groups of GRBs associated with distinct softness. Our analysis reveals that the conventional classification of GRBs with the duration of bursts is influenced by the softness of the objects. There exits a bimodality in the duration distribution of GRBs for each group of bursts and the time po…
We present broadband (gamma-ray, X-ray, near-infrared, optical, and radio) observations of the gamma-ray burst (GRB) 090709A and its afterglow in an effort to ascertain the origin of this high-energy transient. Previous analyses suggested that GRB 090709A exhibited quasi-periodic oscillations with a period of 8.06 s, a trait unknown in long-duration GRBs but typical of flares from soft gamma-ray repeaters. When properly accounting for the underlying shape of the power-density spectrum of GRB 090709A, we find no conclusive (> 3 sigma) evidence for the reported periodicity. In conjunction with t…
We present the results of a set of numerical simulations of long-duration gamma-ray burst jets aimed at studying the effect of a variable engine on the peak frequency of the photospheric emission. Our simulations follow the propagation of the jet inside the progenitor star, its break-out, and the subsequent expansion in the environment out to the photospheric radius. A constant and two step-function models are considered for the engine luminosity. We show that our synthetic light-curves follow a luminosity-peak frequency correlation analogous to the Golenetskii correlation found in long-durati…
We have conducted the first dedicated spectroscopic survey of long-duration gamma-ray burst (LGRB) host galaxies at z < 1, and use these observations along with data from the literature to determine a wide range of ISM properties and a statistically robust mass-metallicity relation. LGRBs have been proposed as possible tracers of star formation at high redshift; however, such an association is dependent on a thorough understanding of the relationship between LGRB progenitors and their host environments. In particular, the metallicity of LGRB host galaxies has become a matter of hot debate in r…
We present 2D high-resolution hydrodynamic simulations of the relativistic outflows of long-duration gamma-ray burst progenitors. We analyze the properties of the outflows at wide off-axis angles, produced by the expansion of the hot cocoon that surrounds the jet inside the progenitor star. We find that the cocoon emission at wide angles may have properties similar to those of the subclass of short-duration gamma-ray bursts with persistent X-ray emission. We compute the predicted duration distribution, redshift distribution, and afterglow brightness and we find that they are all in agreement w…
We present the results of radio observations from the eMERLIN telescope combined with X-ray data from Swift for the short-duration Gamma-ray burst (GRB) 200826A, located at a redshift of 0.71. The radio light curve shows evidence of a sharp rise, a peak around 4-5 days post-burst, followed by a relatively steep decline. We provide two possible interpretations based on the time at which the light curve reached its peak. (1) If the light curve peaks earlier, the peak is produced by the synchrotron self-absorption frequency moving through the radio band, resulting from the forward shock propagati…
