Counting on Short Gamma-Ray Bursts: Gravitational-Wave Constraints of Jet Geometry. (arXiv:1912.04906v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Farah_A/0/1/0/all/0/1">Amanda Farah</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Essick_R/0/1/0/all/0/1">Reed Essick</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Doctor_Z/0/1/0/all/0/1">Zoheyr Doctor</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fishbach_M/0/1/0/all/0/1">Maya Fishbach</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Holz_D/0/1/0/all/0/1">Daniel E. Holz</a>
The detection of GW170817 in gravitational waves and gamma rays revealed that
short gamma-ray bursts are associated with the merger of neutron-stars. Gamma
rays are thought to result from the formation of collimated jets, but the
details of this process continue to elude us. One fundamental observable is the
emission profile of the jet as a function of viewing angle. We present two
methods to measure the effective angular width, $theta_B$, of short gamma-ray
burst (sGRB) jets using gravitational wave and gamma-ray data, assuming all
sGRBs have the same angular dependence for their luminosities. The first is a
counting experiment, where we combine the known detection thresholds of the
LIGO/Virgo and Fermi Gamma Ray Burst Monitor detectors to infer parameters of
systems that are detected in gravitational waves. This method requires minimal
knowledge about each event, beyond whether or not they were detected in
gamma-rays. The second method uses additional information from the
gravitational-wave and electromagnetic data to estimate parameters of the
source, and thereby improve constraints on jet properties. Applying our methods
to GW170817, we find only weak constraints on the sGRB luminosity profile, with
statistical uncertainty dominating differences between models. We also analyze
simulated events from future observing runs, and find that with 5 and 100 BNS
detections, the counting method constrains the relative uncertainty in
$theta_B$ to within 51% and 12%, respectively. Incorporating
gravitational-wave parameter estimation would further tighten these constraints
to 43% and 9.6%. In the limit of many detections, incorporating parameter
estimation achieves only marginal improvements; we conclude that the majority
of the information about jet structure comes from the relative sensitivities of
gravitational-wave and gamma-ray detectors as encoded in simple counting
experiments.
The detection of GW170817 in gravitational waves and gamma rays revealed that
short gamma-ray bursts are associated with the merger of neutron-stars. Gamma
rays are thought to result from the formation of collimated jets, but the
details of this process continue to elude us. One fundamental observable is the
emission profile of the jet as a function of viewing angle. We present two
methods to measure the effective angular width, $theta_B$, of short gamma-ray
burst (sGRB) jets using gravitational wave and gamma-ray data, assuming all
sGRBs have the same angular dependence for their luminosities. The first is a
counting experiment, where we combine the known detection thresholds of the
LIGO/Virgo and Fermi Gamma Ray Burst Monitor detectors to infer parameters of
systems that are detected in gravitational waves. This method requires minimal
knowledge about each event, beyond whether or not they were detected in
gamma-rays. The second method uses additional information from the
gravitational-wave and electromagnetic data to estimate parameters of the
source, and thereby improve constraints on jet properties. Applying our methods
to GW170817, we find only weak constraints on the sGRB luminosity profile, with
statistical uncertainty dominating differences between models. We also analyze
simulated events from future observing runs, and find that with 5 and 100 BNS
detections, the counting method constrains the relative uncertainty in
$theta_B$ to within 51% and 12%, respectively. Incorporating
gravitational-wave parameter estimation would further tighten these constraints
to 43% and 9.6%. In the limit of many detections, incorporating parameter
estimation achieves only marginal improvements; we conclude that the majority
of the information about jet structure comes from the relative sensitivities of
gravitational-wave and gamma-ray detectors as encoded in simple counting
experiments.
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