Duration Gamma-ray Bursts Research Articles

Investigation of redshift- and duration-dependent clustering of gamma-ray bursts

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 BATSE, Fermi/GBM and Swift/BAT, we found marginal evidence for clustering in very short duration GRBs lasting less than 100 ms. Our analysis provides little evidence for significant redshift-dependent clustering of GRBs.

Exploring the canonical behaviour of long gamma-ray bursts using an intrinsic multiwavelength afterglow correlation

In this paper we further investigate the relationship, reported by Oates et al., 2012, between the optical/UV afterglow luminosity (measured at restframe 200s) and average afterglow decay rate (measured from restframe 200s onwards) of long duration Gamma-ray Bursts (GRBs). We extend the analysis by examining the X-ray light curves, finding a consistent correlation. We therefore explore how the parameters of these correlations relate to the prompt emission phase and, using a Monte Carlo simulation, explore whether these correlations are consistent with predictions of the standard afterglow model. We find significant correlations between: $\rm log\;L_{O,200\rm{s}}$ and $\rm log\;L_{X,200\rm{s}}$; $\alpha_{O,>200\rm{s}}$ and $\alpha_{X,>200\rm{s}}$, consistent with simulations. The model also predicts relationships between $\rm log\;E_{iso}$ and $\rm log\;L_{200\rm{s}}$, however, while we find such relationships in the observed sample, the slope of the linear regression is shallower than that simulated and inconsistent at $\gtrsim 3\sigma$. Simulations also do not agree with correlations observed between $\rm log\;L_{200\rm{s}}$ and $\alpha_{>200\rm{s}}$, or $\rm log\;E_{iso}$ and $\alpha_{>200\rm{s}}$. Overall, these observed correlations are consistent with a common underlying physical mechanism producing GRBs and their afterglows regardless of their detailed temporal behaviour. However, a basic afterglow model has difficulty explaining all the observed correlations. This leads us to briefly discuss alternative more complex models.

Radio afterglow rebrightening: evidence for multiple active phases in gamma-ray burst central engines

The rebrightening phenomenon is an interesting feature in some X-ray, optical, and radio afterglows of gamma-ray bursts (GRBs). Here, we propose a possible energy-supply assumption to explain the rebrightenings of radio afterglows, in which the central engine with multiple active phases can supply at least two GRB pulses in a typical GRB duration time. Considering the case of double pulses supplied by the central engine, the double pulses have separate physical parameters, except for the number density of the surrounding interstellar medium (ISM). Their independent radio afterglows are integrated by the ground detectors to form the rebrightening phenomenon. In this work, we firstly simulate diverse rebrightening light curves under consideration of different and independent physical parameters. Using this assumption, we also give our best fit to the radio afterglow of GRB 970508 at three frequencies of 1.43, 4.86, and 8.46 GHz. We suggest that the central engine may be active continuously at a timescale longer than that of a typical GRB duration time as many authors have suggested, and that it may supply enough energy to cause the long-lasting rebrightenings observed in some GRB afterglows.

GAMMA-RAY BURSTS TRACE UV METRICS OF STAR FORMATION OVER 3 <z< 5

We present the first uniform treatment of long duration gamma-ray burst (GRB) host galaxy detections and upper limits over the redshift range 3<z<5, a key epoch for observational and theoretical efforts to understand the processes, environments, and consequences of early cosmic star formation. We contribute deep imaging observations of 13 GRB positions yielding the discovery of eight new host galaxies. We use this dataset in tandem with previously published observations of 31 further GRB positions to estimate or constrain the host galaxy rest-frame ultraviolet (UV; 1600 A) absolute magnitudes M_UV. We then use the combined set of 44 M_UV estimates and limits to construct the M_UV luminosity function (LF) for GRB host galaxies over 3<z<5 and compare it to expectations from Lyman break galaxy (LBG) photometric surveys with the Hubble Space Telescope. Adopting standard prescriptions for the luminosity dependence of galaxy dust obscuration (and hence, total star formation rate), we find that our LF is compatible with LBG observations over a factor of 600x in host luminosity, from M_UV = -22.5 mag to >-15.6 mag, and with extrapolations of the assumed Schechter-type LF well beyond this range. We review proposed astrophysical and observational biases for our sample, and find they are for the most part minimal. We therefore conclude, as the simplest interpretation of our results, that GRBs successfully trace UV metrics of cosmic star formation over the range 3<z<5. Our findings suggest GRBs are providing an accurate picture of star formation processes from z ~3 out to the highest redshifts.

The Life and Death of Massive Stars in the Starburst Galaxy I Zw 18

AbstractMassive stars at low metallicity are strong candidates for two of the most energetic explosions in the Universe: long duration gamma-ray bursts and superluminous supernovae. But what is the reason these explosions prefer low metallicity environments? To answer this question, we investigate how massive stellar evolution proceeds in low metallicity environments.

The mass of the neutrino-dominated accretion disks in short gamma-ray bursts

The coalesence of compact binary systems might be the plausible candidate to power short Gamma-Ray Bursts (GRBs), since in this scenario a low mass disk can be formed, and the lifetime of the disk is comparable to the duration of the short GRBs. After merger, a neutrino-dominated accretion flow (NDAF) surrounding a stellar-mass black hole (BH) will be formed and neutrino-antineutrino annihilation above the disk may power short GRBs. The results of the simulation show that the disk mass of the NDAF has a limit after merger events. So the question is: can annihilations of neutrinos from NDAFs owning such disk masses power all the observed short GRBs? Using the current short GRB observational data and fireball model, we estimate the disk mass of the NDAF. The neutrino annihilation luminosity as a function of BH spin and accretion rate is fitted from the global solutions of NDAFs. The results show that the estimation of the disk mass mainly depends on its output energy, jet opening angle, and central BH characteristic of GRBs. And some short GRBs require massive disks, which approach or exceed the limits in simulations. If the precise value of jet opening angle is considered, the real requirements of the disk masses will be much larger than the present results, since we use only the lower limit of them in the calculation. These results reflect that the neutrino annihilation process is deficient to power short GRBs. We suggest that there may exit other magnetohydrodynamic processes or some mechanisms to increase the efficiency of the neutrino emission, and then provide energy to power short GRBs.

THE MILLISECOND MAGNETAR CENTRAL ENGINE IN SHORT GRBs

One favored progenitor model for short duration gamma-ray bursts (SGRBs) is the coalescence of two neutron stars (NS-NS). One possible outcome of such a merger would be a rapidly spinning, strongly magnetized neutron star (known as a millisecond magnetar). These magnetars may be "supra-massive", implying they would collapse to black holes after losing centrifugal support due to magnetic dipole spindown. By systematically analyzing the BAT-XRT light curves of all short GRBs detected by {\em swift}, we test how well the data are consistent with this central engine model of short GRBs. We find that the so-called "extended emission" observed with BAT in some short GRBs are fundamentally the same component as the "internal X-ray plateau" as observed in many short GRBs, which is defined as a plateau in the lightcurve followed by a very rapid drop. Based on how likely a short GRB hosts a magnetar, we characterize the entire {\em Swift} short GRB sample into three categories: the "internal plateau" sample, the "external plateau" sample, and the "no plateau" sample. The derived magnetar surface magnetic field $B_{\rm p}$ and the initial spin period $P_0$ fall into the reasonable range. No GRBs in the internal plateau sample have the total energy exceeding the maximum energy budget of a millisecond magnetar. Assuming that the rapid fall time at the end of the internal plateau is the collapse time of a supra-massive magnetar to a black hole, and applying the measured mass distribution of NS-NS systems in our Galaxy, we constrain the neutron star equation of state (EOS). The data suggest that the NS equation of state is close to the GM1 model, which has a maximum non-rotating NS mass $M_{\rm TOV} \sim 2.37 M_\odot$.

SN 2013dx associated with GRB 130702A: a detailed photometric and spectroscopic monitoring and a study of the environment

Long duration gamma-ray bursts (GRBs) and broad-line, type Ic supernovae (SNe) are strongly connected. We aim at characterizing SN 2013dx, associated with GRB\,130702A, through sensitive and extensive ground-based observational campaigns in the optical-IR band. We monitored the field of the Swift GRB 130702A (redshift z = 0.145) using the 8.2-m VLT, the 3.6-m TNG and the 0.6-m REM telescopes during the time interval between 4 and 40 days after the burst. Photometric and spectroscopic observations revealed the presence of the associated Type Ic SN 2013dx. Our multi-band photometry allowed the construction of a bolometric light curve.} The bolometric light curve of SN 2013dx resembles that of 2003dh (associated with GRB 030329), but is ~10% faster and ~25% dimmer. From this we infer a synthesized 56Ni mass of ~0.2 solar masses. The multi-epoch optical spectroscopy shows that the SN 2013dx behavior is best matched by SN 1998bw, among the other well-known low-redshift SNe associated with GRBs and XRFs, and by SN 2010ah, an energetic Type Ic SN not associated with any GRB. The photospheric velocity of the ejected material declines from ~2.7X10^4 km/s at 8 rest frame days from the explosion, to ~3.5X10^3 km/s at 40 days. These values are extremely close to those of SN1998bw and 2010ah. We deduce for SN 2013dx a kinetic energy of ~35X10^51 erg, and an ejected mass of ~7 solar masses. This suggests that the progenitor of SN2013dx had a mass of ~25 solar masses, i.e., 15-20% less massive than that of SN 1998bw. Finally, we performed a study of the SN 2013dx environment, through spectroscopy of the closeby galaxies. 9 out of the 14 inspected galaxies lie within 0.03 in redshift from z=0.145, indicating that the host of GRB 130702A/SN 2013dx belongs to a group of galaxies, an unprecedented finding for a GRB-associated SN and, to our knowledge, for long GRBs in general.

Implications of Possible Alternate Scenarios for Short and Long Duration GRBs

Gamma-ray bursts (GRB) are the most luminous physical phenomena in the universe, consisting of flashes of gamma rays that last from seconds to hours. In this paper we look at possible alternate scenarios for both short and long duration GRBs. We consider scenarios for short duration GRBs,which could explainwhy fewer GRBs are observed than what is expected. Also a new class of objects (dark matter objects) is proposed as possible candidate for short duration GRBs which eliminates the baryon load problem, which could also provide a possible scenario for the formation of sub- stellar black holes, distinct from the usual Hawking black hole.We also consider a new model (dubbed the Smashnova model)where an SN can trigger a GRB.In case of long duration GRBs, we propose the possibility of a GRB triggering the collapse of a WR or RG star in a binary system producing an SN, and typical signatures. We also discuss GRBs from population III stars of ~500 �� at high redshifts,and argue that collapse of such high mass stars does not lead to GRBs. Observational implications for the above scenarios are briefly explained.

Systematic Spectral Lag Analysis of Swift Known-zGRBs

The difference of photon arrival time, which is known as spectral lag, is well known characteristics of gamma-ray bursts (GRBs). In particular, long duration GRBs show a soft lag which means that high energy photons arrive earlier than soft photons. The lag-luminosity relation is the empirical relationship between the isotropic peak luminosity and the spectral lag. We calculated the spectral lags for 40 known redshift GRBs observed bySwiftaddition to the previous 31 GRB samples. We confirmed that most of our samples follow the lag-luminosity relation. However, we noticed that there are some GRBs which show a significant scatter from the relation. We also confirm that the relationship between the break time and the luminosity of the X-ray afterglow (so-called Dainotti relation) extends up to the lag-luminosity relation.

A real-time fast radio burst: polarization detection and multiwavelength follow-up

Fast radio bursts (FRBs) are one of the most tantalizing mysteries of the radio sky; their progenitors and origins remain unknown and until now no rapid multiwavelength follow-up of an FRB has been possible. New instrumentation has decreased the time between observation and discovery from years to seconds, and enables polarimetry to be performed on FRBs for the first time. We have discovered an FRB (FRB 140514) in real-time on 14 May, 2014 at 17:14:11.06 UTC at the Parkes radio telescope and triggered follow-up at other wavelengths within hours of the event. FRB 140514 was found with a dispersion measure (DM) of 562.7(6) cm$^{-3}$ pc, giving an upper limit on source redshift of $z \lesssim 0.5$. FRB 140514 was found to be 21$\pm$7% (3-$\sigma$) circularly polarized on the leading edge with a 1-$\sigma$ upper limit on linear polarization $<10%$. We conclude that this polarization is intrinsic to the FRB. If there was any intrinsic linear polarization, as might be expected from coherent emission, then it may have been depolarized by Faraday rotation caused by passing through strong magnetic fields and/or high density environments. FRB 140514 was discovered during a campaign to re-observe known FRB fields, and lies close to a previous discovery, FRB 110220; based on the difference in DMs of these bursts and time-on-sky arguments, we attribute the proximity to sampling bias and conclude that they are distinct objects. Follow-up conducted by 12 telescopes observing from X-ray to radio wavelengths was unable to identify a variable multiwavelength counterpart, allowing us to rule out models in which FRBs originate from nearby ($z < 0.3$) supernovae and long duration gamma-ray bursts.

Investigating signatures of cosmological time dilation in duration measures of prompt gamma-ray burst light curves

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 similar analysis of Fermi/GBM data for the 57 bursts detected by both instruments is conducted, but inconclusive due to small number statistics. We then investigate under-populated regions of the duration redshift parameter space. We propose that the lack of low-redshift, long duration GRBs is a physical effect due to the sample being volume limited at such redshifts. However, we also find that the high-redshift, short duration region of parameter space suffers from censorship as any Swift GRB sample is fundamentally defined by trigger criteria determined in the observer frame energy band of Swift/BAT. As a result, we find that the significance of any evidence for cosmological time dilation in our sample of duration measures typically reduces to $<2\sigma$.

A search forFermibursts associated with supernovae and their frequency of occurrence

Context: Observations suggest that the major fraction of long duration gamma-ray bursts (GRBs) are connected with broad-lines supernovae Ib/c, (SNe-Ibc). The presence of GRB-SNe is revealed by rebrightenings emerging from the optical GRB afterglow $10$--$15$ days, in the rest-frame of the source, after the prompt GRB emission. Aims: \textit{Fermi}-GBM has a field of view (FoV) which is about 6.5 times larger than the FoV of \textit{Swift}, therefore we expect that a number of GRB-SN connections have been missed due to lack of optical and X-ray instruments on board of \textit{Fermi}, which are essential to reveal SNe associated with GRBs. This fact has motivated our search in the \textit{Fermi} catalogue for possible GRB-SN events. Methods: The search for possible GRB-SN associations follows two requirements: (1) SN should fall inside the \textit{Fermi}-GBM error box of the considered long GRB, and (2) this GRB should occur within $20$ days before the SN event. Results: We have found $5$ cases, within $z<0.2$ fulfilling the above reported requirements. One of them, GRB 130702A-SN 2013dx, was already known as GRB-SN association. We have analyzed the remaining $4$ cases and we concluded that three of them are, very likely, just random coincidences, due to the \textit{Fermi}-GBM large error box associated with each GRB detection. We found one GRB possibly associated with a SN 1998bw-like, GRB 120121B/SN 2012ba. Conclusions: The very low redshift of GRB 120121B/SN 2012ba ($z = 0.017$) implies a low isotropic energy of this burst ($E_{iso} = 1.39 \times 10^{48}$) erg. We then compute the rate of \textit{Fermi} low-luminosity GRBs connected with SNe to be $\rho_{0,b} \leq 770\ $Gpc$^{-3}$yr$^{-1}$. We estimate that \textit{Fermi}-GBM could detect $1$--$4$ GRBs-SNe within $z \leq 0.2$ in the next 4 years.

The dynamics of a highly magnetized jet propagating inside a star

The collapsar model explains the association of long duration gamma-Ray Bursts (GRBs) with stellar collapse. It involves a relativistic jet that forms at the core of a collapsing massive star. The jet penetrates the stellar envelope and the prompt GRB emission is produced once the jet is well outside the star. Most current models for generation of relativistic jets involve Poynting flux dominated outflows. We explore here the propagation of such a jet through a stellar envelope. The jet forms a bow shock around it. Energy dissipation at the head of this shock supplies energy to a cocoon that surrounds the jet. This cocoon exerts pressure on the jet and collimates it. While this description resembles the propagation of a hydrodynamic jets there are significant qualitative differences. Two Strong shocks, the reverse shock that slows down the hydrodynamic jet and the collimation shock that collimates it, cannot form within the Poynting flux dominated jet. As a result this jet moves much faster and dissipates much less energy while it crosses the stellar envelope. We construct here a simple analytic model that explores, self consistently, the jet-cocoon interaction and dynamics. Using this model we determine the properties of the jet, including its velocity, propagation time and shape.

HOW LONG DOES A BURST BURST?

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 GRBs are unusual events. We define burst duration t_burst based on both gamma-ray and X-ray light curves rather than using gamma-ray observations alone. We find that t_burst can be reliably measured in 343 GRBs. Within this "good" sample, 21.9% GRBs have t_burst >=10^3 s and 11.5% GRBs have t_burst >=10^4 s. There is an apparent bimodal distribution of t_burst in this sample. However, when we consider an "undetermined" sample (304 GRBs) with t_burst possibly falling in the gap between GRB duration T_90 and the first X-ray observational time, as well as a selection effect against t_burst falling into the first Swift orbital "dead zone" due to observation constraints, the intrinsic underlying t_burst distribution is consistent with being a single component distribution. We found that the existing evidence for a separate ultra-long GRB population is inconclusive, and further multi-wavelength observations are needed to draw a firmer conclusion. We also discuss the theoretical implications of our results. In particular, the central engine activity duration of GRBs is generally much longer than the gamma-ray T90 duration and it does not even correlate with T90. It would be premature to make a direct connection between T90 and the size of the progenitor star.

LONG GAMMA-RAY BURSTS TRACE THE STAR FORMATION HISTORY

We show that if the broad-line supernova explosions of type Ic (SNeIc) produce the bulk of the observed long duration gamma ray bursts (LGRBs), which include the high luminosity GRBs, low luminosity GRBs and X-ray flashes (XRFs), and if LGRBs have the geometry assumed in the cannonball (CB) model of LGRBs, then their rate measured by Swift and their redshift distribution are consistent with the star formation rate (SFR) over the entire range of redshifts where the SFR has been measured with sufficient accuracy.

Spectroscopy of the short-hard GRB 130603B

Short duration gamma-ray bursts (SGRBs) are thought to be related to the violent merger of compact objects, such as neutron stars or black holes, which makes them promising sources of gravitational waves. The detection of a 'kilonova'-like signature associated to the Swift-detected GRB 130603B has suggested that this event is the result of a compact object merger. Our knowledge on SGRB has been, until now, mostly based on the absence of supernova signatures and the analysis of the host galaxies to which they cannot always be securely associated. Further progress has been significantly hampered by the faintness and rapid fading of their optical counterparts (afterglows), which has so far precluded spectroscopy of such events. Afterglow spectroscopy is the key tool to firmly determine the distance at which the burst was produced, crucial to understand its physics, and study its local environment. Here we present the first spectra of a prototypical SGRB afterglow in which both absorption and emission features are clearly detected. Together with multiwavelength photometry we study the host and environment of GRB 130603B. From these spectra we determine the redshift of the burst to be z = 0.3565+/-0.0002, measure rich dynamics both in absorption and emission, and a substantial line of sight extinction of A_V = 0.86+/-0.15 mag. The GRB was located at the edge of a disrupted arm of a moderately star forming galaxy with near-solar metallicity. Unlike for most long GRBs (LGRBs), N_HX / A_V is consistent with the Galactic ratio, indicating that the explosion site differs from those found in LGRBs. The merger is not associated with the most star-forming region of the galaxy; however, it did occur in a dense region, implying a rapid merger or a low natal kick velocity for the compact object binary.

A NEW STANDARD PULSAR MAGNETOSPHERE

In view of recent efforts to probe the physical conditions in the pulsar current sheet, we revisit the standard solution that describes the main elements of the ideal force-free pulsar magnetosphere. The simple physical requirement that the electric current contained in the current layer consists of the local electric charge moving outward at close to the speed of light, yields a new standard solution for the pulsar magnetosphere everywhere ideal force-free except in the current layer. The main elements of the new solution are a) the pulsar spindown rate of the aligned rotator is 23% times larger than that of the orthogonal vacuum rotator, b) only 60% of the magnetic flux that crosses the light cylinder opens up to infinity, c) the electric current closes along the other 40% which gradually converges to the equator, d) this transfers 40% of the total pulsar spindown energy flux in the equatorial current sheet which is then dissipated in the acceleration of particles and in high-energy electromagnetic radiation, e) there is no separatrix current layer. Our solution is a minimum free-parameter solution in that the equatorial current layer is electrostatically supported against collapse and thus does not require a thermal particle population. In that respect, it is one more step toward the development of a new standard solution. We discuss the implications for intermittent pulsars and long duration gamma-ray bursts. We conclude that the physical conditions in the equatorial current layer determine the global structure of the pulsar magnetosphere.

THE ORTHOGONAL GAMMA-RAY BURST MODEL

We explore the analogy between a rotating magnetized black hole and an axisymmetric pulsar and derive its electromagnetic spindown after its formation in the core collapse of a supermassive star. The spindown shows two characteristic phases, an early Blandford-Znajek phase that lasts a few hundred seconds, and a late pulsar-like afterglow phase that lasts much longer. During the first phase, the spindown luminosity decreases almost exponentially, whereas during the afterglow phase it decreases as t^{-a} with 1<a<1,5. We associate our findings with long duration gamma-ray bursts (GRB) and compare with observations.

Long gamma ray bursts from binary black holes

We consider a scenario for the longest duration gamma ray bursts, resulting from the collapse of a massive rotating star in a close binary system with a companion black hole. The primary black hole born during the core collapse is first being spun up and increases its mass during the fallback of the stellar envelope just after its birth. As the companion black hole enters the outer envelope, it provides an additional angular momentum to the gas. After the infall and spiral-in towards the primary, the two black holes merge inside the circumbinary disk. The second episode of mass accretion and high final spin of the post-merger black hole prolongs the gamma ray burst central engine activity. The observed events should have two distinct peaks in the electromagnetic signal, separated by the gravitational wave emission. The gravitational recoil of the burst engine is also possible.