Evidence for a compact stellar merger origin for GRB 230307A from Fermi-LAT and multi-wavelength afterglow observations

Abstract

GRB 230307A is the second brightest gamma-ray burst (GRB) ever detected over 50 years of observations and has a long duration in the prompt emission. Two galaxies are found to be close to the position of GRB 230307A: 1) a distant ($z\sim 3.87$) star-forming galaxy, located at an offset of $\sim 0.2-0.3$ arcsec from the GRB position (with a projected distance of $\sim 1-2\mathrm{kpc}$); 2) a nearby ($z=0.065$) spiral galaxy, located at an offset of 30 arcsec (with a projected distance of $\sim 40\mathrm{kpc}$). Though it has been found that the brightest GRBs are readily detected in GeV emission by the Fermi Large Area Telescope (LAT), we find no GeV afterglow emission from GRB 230307A. Combining this with the optical and X-ray afterglow data, we find that a circum-burst density as low as $\sim 10^{-5}-10^{-4}\mathrm{c}{\mathrm{m}}^{-3}$ is needed to explain the non-detection of GeV emission and the multi-wavelength afterglow data, regardless of the redshift of this GRB. Such a low-density disfavors the association of GRB 230307A with the high-redshift star-forming galaxy, since the proximity of the GRB position to this galaxy would imply a higher-density environment. Instead, the low-density medium is consistent with the circumgalactic medium, which agrees with the large offset between GRB 230307A and the low-redshift galaxy. This points to the compact stellar merger origin for GRB 230307A, consistent with the detection of an associated kilonova.

14 pages, 6 figures. The article has been accepted and the statistical comparison of the offset between long and short bursts has been added

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Cited by in corpus (8)

• What Powered the Kilonova-Like Emission After GRB 230307A in the Framework of a Neutron Star-White Dwarf Merger?
• A set of distinctive properties ruling the prompt emission of GRB 230307A and other long γ-ray bursts from compact object mergers
• Repeated partial disruptions in a WD-NS or WD-BH merger modulate the prompt emission of long-duration merger-type GRBs
• GRB minimum variability timescales with Fermi/GBM
• How Do Nuclear Isomers Influence the Gamma-Ray Bursts in Binary Neutron Star Mergers?
• Discovery and Analysis of Afterglows from Poorly Localised GRBs with the Gravitational-wave Optical Transient Observer (GOTO) All-sky Survey
• Kilonova and progenitor properties of merger-driven gamma-ray bursts
• GOTO identification and broadband modelling of the counterpart to the SVOM GRB 250818B