Burst Remnant Research Articles

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.

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.

Remnants from Gamma‐Ray Bursts

We model the intermediate-time evolution of a jetted gamma-ray burst (GRB) as two blobs of matter colliding with the interstellar medium. We follow the hydrodynamic evolution of this system numerically and calculate the bremsstrahlung and synchrotron images of the remnant. We find that for a burst energy of 1051 ergs the remnant becomes spherical after ~5000 yr, when it has collected ~50 M☉ of interstellar mass. This result is independent of the exact details of the GRB, such as the opening angle. After this time a gamma-ray burst remnant has an expanding sphere morphology. The similarity to a supernova remnant makes it difficult to distinguish between the two at this stage. The expected number of nonspherical gamma-ray burst remnants is ~0.05 per galaxy for a beaming factor of 0.01 and a burst energy of 1051 ergs. Our results suggest that the double-shell object DEM L316 is not a GRB remnant.

Analytic Light Curves of Gamma‐Ray Burst Afterglows: Homogeneous versus Wind External Media

Assuming an adiabatic evolution of a Gamma-Ray Burst (GRB) remnant interacting with an external medium, we calculate the injection, cooling, and absorption break frequencies, and the afterglow flux for plausible orderings of the break and observing frequencies. The analytical calculations are restricted to a relativistic remnant and, in the case of collimated ejecta, to the phase where there is an insignificant lateral expansion. Results are given for both a homogeneous external medium and for a wind ejected by the GRB progenitor. We compare the afterglow emission at different observing frequencies, for each type of external medium. It is found that observations at sub-millimeter frequencies during the first day provide the best way of discriminating between the two models. By taking into account the effect of inverse Compton scatterings on the electron cooling, a new possible time-dependence of the cooling break is identified. The signature of the up-scattering losses could be seen in the optical synchrotron emission from a GRB remnant interacting with a pre-ejected wind, as a temporary mild flattening of the afterglow decay. The up-scattered radiation itself should be detected in the soft X-ray emission from GRB remnants running into denser external media, starting few hours after the main event.

The Dynamics and Light Curves of Beamed Gamma‐Ray Burst Afterglows

The energy requirements of gamma-ray bursts have in past been poorly constrained because of three major uncertainties: the distances to bursts, the degree of burst beaming, and the efficiency of gamma-ray production. The first of these has been resolved, with both indirect evidence (the distribution of bursts in flux and position) and direct evidence (redshifted absorption features in the afterglow spectrum of GRB 970508) pointing to cosmological distances. We now wish to address the second uncertainty. Afterglows allow a statistical test of beaming, described in an earlier paper. In this paper, we modify a standard fireball afterglow model to explore the effects of beaming on burst remnant dynamics and afterglow emission. If the burst ejecta are beamed into angle ζm, the burst remnant's evolution changes qualitatively once its bulk Lorentz factor Γ 1/ζm: before this, Γ declines as a power law of radius, while afterward, it declines exponentially. This change results in a broken power-law light curve whose late-time decay is faster than expected for a purely spherical geometry. These predictions disagree with afterglow observations of GRB 970508. We explored several variations on our model, but none seems to be able to change this result. We therefore suggest that this burst is unlikely to have been highly beamed and that its energy requirements were near those of isotropic models. More recent afterglows may offer the first practical applications for our beamed models.

Overall Evolution of Realistic Gamma-Ray Burst Remnant and Its Afterglow

Conventional dynamic model of gamma-ray burst remnants is found to be incorrect for adiabatic blastwaves during the non-relativistic phase. A new model is derived, which is shown to be correct for both radiative and adiabatic blastwaves during both ultra-relativistic and non-relativistic phases. Our model also takes the evolution of the radiative efficiency into account. The importance of the transition from the ultra-relativistic phase to the non-relativistic phase is stressed.

How to Tell a Jet from a Balloon: A Proposed Test for Beaming in Gamma-Ray Bursts

If gamma ray bursts are highly collimated, the energy requirements of each event may be reduced by several (~ 4-6) orders of magnitude, and the event rate increased correspondingly. Extreme conditions in gamma ray bursters lead to highly relativistic motions (bulk Lorentz factors Gamma > 100). This results in strong forward beaming of the emitted radiation in the observer's rest frame. Thus, all information on gamma ray bursts comes from those ejecta emitted in a narrow cone (opening angle 1/Gamma) pointing towards the observer. We are at present ignorant of whether there are ejecta outside that cone or not. The recent detection of longer wavelength transients following gamma ray bursts allows an empirical test of whether gamma ray bursts are collimated jets or spherical fireballs. The bulk Lorentz factor of the burst ejecta will decrease with time after the event, as the ejecta sweep up the surrounding medium. Thus, radiation from the ejecta is beamed into an ever increasing solid angle as the burst remnant evolves. It follows that if gamma ray bursts are highly collimated, many more optical and radio transients should be observed without associated gamma rays than with them. Published supernova searches may contain enough data to test the most extreme models of gamma ray beaming. We close with a brief discussion of other possible consequences of beaming, including its effect on the evolution of burst remnants.