Counting on Short Gamma-Ray Bursts: Gravitational-wave Constraints of Jet Geometry

Amanda Farah, Reed Essick, Zoheyr Doctor, Maya Fishbach, Daniel E. Holz

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The detections of GW170817 and GRB 170817A revealed that at least some short gamma-ray bursts (sGRB) are associated with the merger of neutron-star compact binaries. The gamma-rays are thought to result from the formation of collimated jets, but the details of this process continue to elude us. One important feature of gamma-ray bursts is the emission profile of the jet as a function of viewing angle. We present two related methods to measure the effective angular width, θB, of sGRB jets using gravitational-wave (GW) and gamma-ray data, assuming all sGRBs have the same angular dependence for their luminosities. The first is a counting experiment that requires minimal knowledge about each event, beyond whether or not they were detected in gamma-rays. The second method uses GW and electromagnetic data to estimate parameters of the source. We additionally outline a model-independent method to infer the full jet structure of sGRBs using a nonparametric approach. Applying our methods to GW170817 and GW190425, we find weak constraints on the sGRB luminosity profile. We project that with 5 and 100 binary neutron star detections, the counting method would constrain the relative uncertainty in θB to within 51% and 12%, respectively. Incorporating GW parameter estimation provides only marginal improvements. We conclude that the majority of the information about jet structure comes from the relative sensitivities of GW and gamma-ray detectors as encoded in simple counting experiments.

Original languageEnglish (US)
Article number108
JournalAstrophysical Journal
Issue number2
StatePublished - Jun 1 2020

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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