English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

GRB 230307A is the second brightest gamma-ray burst (GRB) ever detected over50 years of observations and has a long duration in the prompt emission. Twogalaxies 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 $\sim0.2\operatorname{-}0.3$ arcsec from the GRB position (with a projected distanceof $\sim 1\operatorname{-}2 \, \rm kpc$); 2) a nearby ($z= 0.065$) spiralgalaxy, located at an offset of 30 arcsec (with a projected distance of $\sim40 \, \rm kpc$). Though it has been found that the brightest GRBs are readilydetected in GeV emission by the Fermi Large Area Telescope (LAT), we find noGeV afterglow emission from GRB 230307A. Combining this with the optical andX-ray afterglow data, we find that a circum-burst density as low as $\sim10^{-5} \operatorname{-} 10^{-4}~{\rm cm^{-3}}$ is needed to explain thenon-detection of GeV emission and the multi-wavelength afterglow data,regardless of the redshift of this GRB. Such a low-density disfavors theassociation of GRB 230307A with the high-redshift star-forming galaxy, sincethe proximity of the GRB position to this galaxy would imply a higher-densityenvironment. Instead, the low-density medium is consistent with thecircumgalactic medium, which agrees with the large offset between GRB 230307Aand the low-redshift galaxy. This points to the compact stellar merger originfor GRB 230307A, consistent with the detection of an associated kilonova.

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