Date: Wednesday 26-Feb-2025
Time: 11:30-12:30 pm
Location: PSC 1136
Speaker: Michael Moss (NASA GSFC)
Title: Understanding the Instrumental Bias of Durations and Fluences for High-z GRBs
Abstract: GRBs are the most powerful explosions in the universe. These catastrophic events are the signatures of highly relativistic material being jetted away from a compact object newly formed by either the core-collapse of a massive star or the merger of a compact binary system. Due to their incredible luminosities, GRBs can be detected across the entire observable universe and can be used as cosmological probes. We investigate how measurements of Gamma-Ray Burst (GRB) prompt emission duration and fluences are affected by increasing distance to the source. We selected a sample of 26 bright GRBs with measured redshifts π§ < 1 observed by the Burst Alert Telescope (BAT) on board the Neil Gehrels Swift Observatory (Swift). We simulated what BAT would have observed if the GRB were at larger redshifts up until the point the burst signal was no longer detectable above background and measured the duration and fluence of the simulated count light curves. As expected, we found that almost all durations (fluences) measured for simulated high-π§ GRBs were shorter (less) than their true durations (energies). The underestimations are due to low signal-to-noise emission being lost into the background, i.e., the so-called βtip-of-the-iceberg" effect. The amount of signal lost depends on the profile and intensity of the synthetic light curve, making the true signal unrecoverable without prior knowledge of the underlying light curve and, due to the uniqueness of GRB light curve profiles, means that there is no common behavior in the evolution of the measured durations with redshift. We then compared our simulated high-π§ sample (i.e., π§ > 3) to a sample of observed high-π§ bursts and found that the two samples were consistent with being drawn from the same underlying population. This implies that (i) prompt emission durations and fluences of high-z GRBs observed by Swift/BAT may all be underestimations, sometimes by up to an order of magnitude or a factor of βΌ 2, respectively, and (ii) GRBs do not require any parameter evolution with increasing redshift.
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