Gamma-ray Burst Remnants Research Articles

Is the birth of PSR J0538+2817 accompanied by a gamma-ray burst?

ABSTRACT Recently, the Five-hundred-meter Aperture Spherical radio Telescope measured the three-dimensional velocity of PSR J0538+2817 with respect to its associated supernova remnant S147 and found a possible spin–velocity alignment for this pulsar. Here, we show that the high velocity and the spin–velocity alignment of this pulsar can be explained by the so-called electromagnetic rocket mechanism. In this framework, the pulsar is kicked in the direction of the spin axis, which naturally explains the spin–velocity alignment. We scrutinize the evolution of the pulsar and show that the kick process can create a highly relativistic jet at the opposite direction of the kick velocity. The lifetime and energetics of the jet is estimated. It is argued that the jet can generate a gamma-ray burst (GRB). The long-term dynamical evolution of the jet is calculated. It is found that the shock radius of the jet should expand to about 32 pc at present, which is well consistent with the observed radius of the supernova remnant S147 (32.1 ± 4.8 pc). Additionally, our calculations indicate that the current velocity of the GRB remnant should be about 440 km s−1, which is also roughly consistent with the observed blast-wave velocity of the remnant of S147 (500 km s−1).

Constraining the Nuclear Equation of State via Gravitational-wave Radiation of Short Gamma-Ray Burst Remnants

Abstract The observed internal plateau of X-ray emission in some short gamma-ray bursts (GRBs) suggests the formation of a remnant supramassive magnetar following a double neutron star (NS) merger. In this paper, we assume that the rotational energy is lost mainly via gravitational-wave radiation instead of magnetic dipole (MD) radiation, and present further constraints on the NS nuclear equation of state (EoS) via mass quadrupole deformation and r-mode fluid oscillations of the magnetar. We present two short GRBs with measured redshifts, 101219A and 160821B, whose X-ray light curves exhibit an internal plateau. This suggests that a supramassive NS may survive as the central engine. By considering 12 NS EoSs, within the mass quadrupole deformation scenario we find that the GM1, DD2, and DDME2 models give an M p band falling within the 2σ region of the proto-magnetar mass distribution for ε = 0.01. This is consistent with the constraints from the MD radiation dominated model of rotational energy loss. However, for an r-mode fluid oscillation model with α = 0.1 the data suggest that the NS EOS is close to the Shen and APR models, which is obviously different from the MD radiation dominated and mass quadrupole deformation cases.

Multiwaveform cross-correlation search method for intermediate-duration gravitational waves from gamma-ray bursts

Gamma-ray Bursts (GRBs) are flashes of gamma-rays thought to originate from rare forms of massive star collapse (long GRBs), or from mergers of compact binaries (short GRBs) containing at least one neutron star (NS). The nature of the post-explosion / post-merger remnant (NS versus black hole, BH) remains highly debated. In ~50% of both long and short GRBs, the temporal evolution of the X-ray afterglow that follows the flash of gamma-rays is observed to "plateau" on timescales of 100-10000 s since explosion, possibly signaling the presence of energy injection from a long-lived, highly magnetized NS (magnetar). The Cross-Correlation Algorithm (CoCoA) proposed by [R. Coyne et. al., (2016)] aims to optimize searches for intermediate-duration (100-10000s) gravitational waves (GWs) from GRB remnants. In this work, we test CoCoA on real data collected with ground-based GW detectors. We further develop the detection statistics on which CoCoA is based to allow for multi-waveform searches spanning a physically-motivated parameter space, so as to account for uncertainties in the physical properties of GRB remnants.

Non-detection of fast radio bursts from six gamma-ray burst remnants with possible magnetar engines

ABSTRACT The analogy of the host galaxy of the repeating fast radio burst (FRB) source FRB 121102 and those of long gamma-ray bursts (GRBs) and superluminous supernovae (SLSNe) has led to the suggestion that young magnetars born in GRBs and SLSNe could be the central engine of repeating FRBs. We test such a hypothesis by performing dedicated observations of the remnants of six GRBs with evidence of having a magnetar central engine using the Arecibo telescope and the Robert C. Byrd Green Bank Telescope (GBT). A total of ∼20 h of observations of these sources did not detect any FRB from these remnants. Under the assumptions that all these GRBs left behind a long-lived magnetar and that the bursting rate of FRB 121102 is typical for a magnetar FRB engine, we estimate a non-detection probability of 8.9 × 10−6. Even though these non-detections cannot exclude the young magnetar model of FRBs, we place constraints on the burst rate and luminosity function of FRBs from these GRB targets.

Observationally constraining gravitational wave emission from short gamma-ray burst remnants

Observations of short gamma-ray bursts indicate ongoing energy injection following the prompt emission, with the most likely candidate being the birth of a rapidly rotating, highly magnetized neutron star. We utilize X-ray observations of the burst remnant to constrain properties of the nascent neutron star, including its magnetic field-induced ellipticity and the saturation amplitude of various oscillation modes. Moreover, we derive strict upper limits on the gravitational wave emission from these objects by looking only at the X-ray light curve, showing the burst remnants are unlikely to be detected in the near future using ground-based gravitational wave interferometers, such as Advanced LIGO.

Nuclear equation of state from observations of short gamma-ray burst remnants

The favoured progenitor model for short $\gamma$-ray bursts (SGRBs) is the merger of two neutron stars that triggers an explosion with a burst of collimated $\gamma$-rays. Following the initial prompt emission, some SGRBs exhibit a plateau phase in their $X$-ray light curves that indicates additional energy injection from a central engine, believed to be a rapidly rotating, highly magnetised neutron star. The collapse of this `protomagnetar' to a black hole is likely to be responsible for a steep decay in $X$-ray flux observed at the end of the plateau. In this letter, we show that these observations can be used to effectively constrain the equation of state of dense matter. In particular, we show that the known distribution of masses in binary neutron star systems, together with fits to the $X$-ray light curves, provide constraints that exclude the softest and stiffest plausible equations of state. We further illustrate how a future gravitational wave observation with Advanced LIGO/Virgo can place tight constraints on the equation of state, by adding into the picture a measurement of the chirp mass of the SGRB progenitor.

A search for diffuse X-ray emission from GeV-detected Galactic globular clusters

Recently, diffuse and extended sources in TeV gamma-rays as well as in X-rays have been detected in the direction of the Galactic globular cluster (GC) Terzan 5. Remarkably, this is among the brightest GCs detected in the GeV regime. The nature of both the TeV and the diffuse X-ray signal from Terzan 5 is not settled yet. These emissions most likely indicate the presence of several non-thermal radiation processes in addition to these giving rise to the GeV signal. The aim of this work is to search for diffuse X-ray emission from the GeV detected GCs M 62, NGC 6388, NGC 6541, M 28, M 80 and NGC 6139 to compare the obtained results with the signal detected from Terzan 5. This study will help to determine whether Terzan 5 stands out amongst other GC or whether a whole population of globular clusters feature similar properties. None of the six GCs show significant diffuse X-ray emission on similar scales as observed from Terzan 5 above the particle and diffuse galactic X-ray background components. The derived upper limits allow to assess the validity of different models that were discussed in the interpretation of the multi-wavelength data of Terzan 5. A scenario based on synchrotron emission from relativistic leptons provided by the millisecond pulsar population can not be securely rejected if a comparable magnetic field strength as in Terzan 5 is assumed for every GC. However, such a scenario seems to be unlikely for NGC 6388 and M 62. An inverse-Compton scenario relying on the presence of a putative GRB remnant with the same properties as the one proposed for Terzan 5 can be ruled out for all of the six GCs. Finally, the assumption that each GC hosts a source with the same luminosity as in Terzan 5 is ruled out for all GCs but NGC 6139. (abridged)

Finding short GRB remnants in globular clusters: the VHE gamma-ray source in Terzan 5

Globular cluster are believed to boost the rate of compact binary mergers which may launch a certain type of cosmological gamma-ray bursts (GRBs). Therefore globular clusters appear to be potential sites to search for remnants of such GRBs. The very-high-energy (VHE) gamma-ray source HESS J1747-248 recently discovered in the direction of the Galactic globular cluster Terzan 5 is investigated for being a GRB remnant. Signatures created by the ultra-relativistic outflow, the sub-relativistic ejecta and the ionizing radiation of a short GRB are estimated for an expected age of such a remnant of t > 10^4 years. The kinetic energy of a short GRB could roughly be adequate to power the VHE source in a hadronic scenario. The age of the proposed remnant estimated from its extension possibly agrees with the occurrence of such events in the Galaxy. Sub-relativistic merger ejecta could shock-heat the ambient medium. Further VHE observations can probe the presence of a break towards lower energies expected for particle acceleration in ultra-relativistic shocks. Deep X-ray observations would have the potential to examine the presence of thermal plasma heated by the sub-relativistic ejecta. The identification of a GRB remnant in our own Galaxy may also help to explore the effect of such a highly energetic event on the Earth.

THE HYDRODYNAMICS OF GAMMA-RAY BURST REMNANTS

This paper reports on the results of a numerical investigation designed to address how the initially anisotropic appearance of a GRB remnant is modified by the character of the circumburst medium and by the possible presence of an accompanying supernova (SN). Axisymmetric hydrodynamical calculations of light, impulsive jets propagating in both uniform and inhomogeneous external media are presented, which show that the resulting dynamics of their remnants since the onset of the non-relativistic phase is different from the standard self-similar solutions. Because massive star progenitors are expected to have their close-in surroundings modified by the progenitor winds, we consider both free winds and shocked winds as possible external media for GRB remnant evolution. Abundant confirmation is provided here of the important notion that the morphology and visibility of GRB remnants are determined largely by their circumstellar environments. For this reason, their detectability is highly biased in favor of those with massive star progenitors; although, in this class of models, the beamed component may be difficult to identify because the GRB ejecta is eventually swept up by the accompanying SN. The number density of asymmetric GRB remnants in the local Universe could be, however, far larger if they expand in a tenuous interstellar medium, as expected for some short GRB progenitor models. In these sources, the late size of the observable, asymmetric remnant could extend over a wide, possibly resolvable angle and may be easier to constrain directly.

HYPERNOVA AND GAMMA-RAY BURST REMNANTS AS TeV UNIDENTIFIED SOURCES

We investigate hypernova (hyper-energetic supernova) and gamma-ray burst (GRB) remnants in our Galaxy as TeV gamma-ray sources, particularly in the role of potential TeV unidentified sources, which have no clear counterpart at other wavelengths. We show that the observed bright sources in the TeV sky could be dominated by GRB/hypernova remnants, even though they are fewer than supernova remnants (SNRs). If this is the case, TeV SNRs are more extended (and more numerous) than deduced from current observations. In keeping with their role as cosmic ray accelerators, we discuss hadronic gamma-ray emission from pi^0 decay, from beta decay followed by inverse Compton emission, and propose a third, novel process of TeV gamma-ray emission arising from the decay of accelerated radioactive isotopes such as 56Co entrained by relativistic or semi-relativistic jets in GRBs/hypernovae. We discuss the relevant observational signatures which could discriminate between these three mechanisms.

A Detailed Study on the Equal Arrival Time Surface Effect in Gamma-Ray Burst Afterglows

Due to the relativistic motion of gamma-ray burst remnant and its deceleration in the circumburst medium, the equal arrival time surfaces at any moment are not spherical, rather, they are distorted ellipsoids. This will leave some imprints in the afterglows. We study the effect of equal arrival time surfaces numerically for various circumstances, i.e., isotropic fireballs, collimated jets, density jumps and energy injection events. For each case, a direct comparison is made between including and not including the effect. For isotropic fireballs and jets viewed on axis, the effect slightly hardens the spectra and postpones the peak time of the afterglows, but does not change the shapes of the spectra and light curves significantly. In the cases of a density jump or an energy injection, the effect smears out the variations in the afterglows markedly.

Constraining the environment of GRB 990712 through emission line fluxes

The energy output in the gamma-ray burst (GRB) prompt emission and afterglow phase is expected to photoionize the surrounding medium out to large radii. Cooling of this gas produces line emission, particularly strong in the optical, whose variability is a strong diagnostics of the gas density and geometry in the close environment of the burst. We present the results of a spectral time series analysis of the host galaxy of GRB 990712 observed up to ~6 years after the burst. We analyze the emission line fluxes together with those of the previous observations of the same GRB, in search for photoionization signatures. We find that the emission line fluxes show no variation within the uncertainities up to 6 years after the burst, and we use the measured line intensities to set a limit on the density of the gas within a few parsecs of the burst location. This is the first time that emission from cooling GRB remnants is probed on years time scales.

A Gamma-Ray Burst Remnant in Our Galaxy: HESS J1303-631

We present an investigation of the multiwavelength data on HESS J1303-631, an unidentified TeV source serendipitously discovered in the Galactic plane by the HESS collaboration. Our results strongly suggest the identification of this particular source as the remnant of a gamma-ray burst (GRB) that happened some few tens of thousands years ago in our Galaxy at a distance on the order of ≳10 kpc from us. We show through detailed calculations of particle diffusion, interaction, and radiation processes of relativistic particles in the interstellar medium that it is possible for a GRB remnant (GRBR) to be a strong TeV emitter with no observable synchrotron emission. We predict spectral and spatial signatures that would unambiguously distinguish GRBRs from ordinary supernova remnants, including (1) large energy budgets inferred from their TeV emission, but at the same time (2) suppressed fluxes in the radio through GeV wave bands; (3) extended center-filled emission with an energy-dependent spatial profile; and (4) possible elongation in the direction of the past pair of GRB jets. While GRBRs can best be detected by ground-based gamma-ray detectors, the future GLAST mission will play a crucial role in confirming the predicted low level of GeV emission.

The Large-Scale, Decelerating X-ray Jets from the Microquasar Xte J1550−564: Evidence for External Shocks Caused by the Jet-Ism Interaction?

Large-scale, decelerating, relativistic X-ray jets from microquasar XTE J1550—564 has been recently discovered with Chandra by Corbel et al. (2002). We find that the dynamical evolution of the approaching jet at the late time is consistent with the well-known Sedov evolutionary phase R ∝ t2/5. A trans-relativistic external shock dynamic model by analogy with the evolution of gammaray burst remnants, is shown to be able to fit the proper-motion data of the approaching jet reasonably well. The inferred interstellar medium density around the source is well below the canonical value nISM ∼ 1 cm−3. The rapidly fading X-ray emission can be interpreted as synchrotron radiation from the non-thermal electrons in the adiabatically expanding ejecta. These electrons were accelerated by the reverse shock (moving back into the ejecta) which becomes important when the inertia of the swept external matter leads to an appreciable slowing down of the original ejecta.

Analytical Light Curves in the Realistic Model for Gamma‐Ray Burst Afterglows

Afterglow light curves are constructed analytically for realistic gamma-ray burst remnants decelerating in either a homogeneous interstellar medium or a stellar wind environment, taking into account the radiative loss of the blast wave, which affects the temporal behaviors significantly. Inverse Compton scattering, which plays an important role when the energy equipartition factor epsilon(e) of electrons is much larger than that of the magnetic field (epsilon(B)), is considered. The inverse Compton effect prolongs the fast cooling phase markedly, during which the relativistic shock is semiradiative and the radiation efficiency is approximately constant, epsilon = epsilon(e). It is further shown that the shock is still semiradiative for quite a long time after it transits into the slow cooling phase because of a slow decreasing rate of the radiation efficiency of electrons. The temporal decaying index of the X-ray afterglow light curve in this semiradiative phase is (3p + 2 + 2epsilon)/(4 - epsilon) in the interstellar medium case and [3p - 2 - (p - 2)epsilon]/2(2 - epsilon) in the stellar wind case, where p is the distribution index of the shock-accelerated electrons. Taking p = 2.2-2.3 as implied from the common shock acceleration mechanism and assuming epsilon(e) similar to 1/3, the temporal index is more consistent with the observed (alpha(X)) similar to 1.3 than the commonly used adiabatic one. The observability of the inverse Compton component in soft X-ray afterglows is also investigated. To manifest as a bump or even dominant in the X-ray afterglows during the relativistic stage, the density must be larger than similar to1-10 cm(-3) in the interstellar medium case, or the wind parameter A(*) must be larger than similar to1 in the stellar wind case.

Extended GeV-TeV Emission around Gamma-Ray Burst Remnants and the Case of W49B

We investigate the high-energy photon emission around Gamma-Ray Burst (GRB) remnants caused by ultrahigh-energy cosmic rays (UHECRs) from the GRBs. We apply the results to the recent report that the supernova remnant W49B is a GRB remnant in our Galaxy. If this is correct, and if GRBs are sources of UHECRs, a natural consequence of this identification would be a detectable TeV photon emission around the GRB remnant. The imaging of the surrounding emission could provide new constraints on the jet structure of the GRB.

The slow decay of some radio afterglows - a puzzle for the simplest γ-ray burst fireball model

Abridged: The decay of half of the GRB radio afterglows with long temporal monitoring is significantly slower than at optical frequencies, contrary to what is expected in the simplest fireball model. We investigate four ways to decouple the radio and optical decays: an evolving index of the power-law distribution of the shock-accelerated electrons, the presence of a spectral break between the two domains, a structured outflow, and a long-lived reverse shock contribution to the afterglow emission. [...] In the fourth scenario, it is assumed that the radio afterglow emission arises in the reverse shock propagating in a steady stream of ejecta, which catch up with the decelerating GRB remnant. This scenario can accommodate the properties of the afterglows with slow radio decays and requires that the injected energy is less than or comparable to the initial fireball energy, while other afterglow parameters have reasonable values. For a jet, the transition to a semi-relativistic motion mitigates the radio decay, however this scenario would work only when the slower radio decay is observed well after the steeper optical fall-off. A structured outflow with a relativistic core, yielding a fast decaying optical emission, and a non-relativistic envelope, producing a slowly falling-off radio afterglow, is not a viable solution, as it fails to decouple the radio and optical decays.

THE INTERACTION BETWEEN GAMMA-RAY BURSTS AND THEIR ENVIRONMENT

Gamma-ray Bursts (GRBs) are the most energetic and most relativistic phenomenon in the Universe. Understanding the nature of their progenitors is among the primary efforts of current research in high energy astrophysics, and their unmatched luminosity and other properties makes them ideal cosmological probes. This review summarizes the observational effects resulting from the interaction between the longer-wavelength radiation accompanying GRBs and their close environment. In particular, it discusses signatures that, in addition to providing powerful clues on the GRB progenitors, can also shed light on the physical characteristics, such as metallicity and dust content, of the GRB host galaxies. The last part of the article reviews the long-term signatures imprinted in the medium after a GRB explosion, particularly focusing on how we can identify GRB remnants in our own and nearby galaxies, and what we can learn from their identification.

External Shock Model for the Large‐Scale, Relativistic X‐Ray Jets from the Microquasar XTE J1550−564

Large-scale, decelerating, relativistic X-ray jets due to material ejected from the black-hole candidate X-ray transient and microquasar XTE J1550-564 has been recently discovered with Chandra by Corbel et al. (2002). We find that the dynamical evolution of the eastern jet at the late time is consistent with the well-known Sedov evolutionary phase. A trans-relativistic external shock dynamic model by analogy with the evolution of gamma-ray burst remnants, is shown to be able to fit the observation data reasonably well. The inferred interstellar medium density around the source is well below the canonical value $n_ISM \sim 1 cm^{-3}$. We find that the emission from the continuously shocked interstellar medium (forward shock region) decays too slowly to be a viable mechanism for the eastern X-ray jet. However, the rapidly fading X-ray emission can be interpreted as synchrotron radiation from the non-thermal electrons in the adiabatically expanding ejecta. These electrons were accelerated by the reverse shock (moving back into the ejecta) which becomes important when the inertia of the swept external matter leads to an appreciable slowing down of the original ejecta. To ensure the dominance of the emission from the shocked ejecta over that from the forward shock region during the period of the observations, the magnetic field and electron energy fractions in the forward shock region must be far below equipartition. Future continuous, follow-up multi-wavelength observations of new ejection events from microquasars up to the significant deceleration phase should provide more valuable insight into the nature of the interaction between the jets and external medium.

Gamma-ray bursts: optical afterglows in the deep Newtonian phase

Gamma-ray burst remnants become trans-relativistic typically in days to tens of days, and they enter the deep Newtonian phase in tens of days to months, during which the majority of shock-accelerated electrons will no longer be highly relativistic. However, a small portion of electrons are still accelerated to ultra-relativistic speeds and are capable of emitting synchrotron radiation. The distribution function for electrons is re-derived here so that synchrotron emission from these relativistic electrons can be calculated. Based on the revised model, optical afterglows from both isotropic fireballs and highly collimated jets are studied numerically, and compared to analytical results. In the beamed cases, it is found that, in addition to the steepening due to the edge effect and the lateral expansion effect, the light curves are universally characterized by a flattening during the deep Newtonian phase.