Kavli Affiliate: Nicola Omodei
| First 5 Authors: Rahul Gupta, Rahul Gupta, , ,
| Summary:
We present a comprehensive multiwavelength analysis of GRB 240825A, a bright
gamma-ray burst (GRB) detected by Fermi and Swift, with a prompt duration
($T_rm 90$ ~ 4 sec in 50-300 keV) near the boundary separating short and
long GRBs, prompting a detailed investigation into its classification and
progenitor. Using classical prompt metrics (duration, minimum variability
timescale (MVT), lag, and spectral hardness) and modern classification
techniques (machine-learning (ML) based t-SNE, support vector machine,
energy-hardness-duration, and $epsilon equiv E_gamma,mathrmiso,52 /
E_p,z,2^5/3$), we find GRB 240825A exhibits hybrid characteristics. The
short MVT (13.830 $pm$ 1.574 ms), rest-frame duration, and ML-based
classification indicate a merger-like or ambiguous nature, while its energetics
and position on the Amati relation favor a collapsar origin. We conducted deep
optical and NIR photometric and spectroscopic late-time search for an
associated supernova (SN)/kilonova (KN) and the host galaxy using 10.4 m GTC
and 8.4 m binocular LBT telescopes. No bright SN (like SN 1998bw) is detected
down to stringent limits (e.g., $m_r > 26.1$ mag at 17.59 days), despite a
redshift of $z$ = 0.659 measured from GTC spectroscopy. Host galaxy SED
modeling with Prospector indicates a massive, dusty, and star-forming
galaxy-typical of collapsar GRB hosts, though with low sSFR and large offset.
We compare these findings with hybrid events like GRB 211211A, GRB 230307A, GRB
200826A, including SNe-GRBs, and conclude that GRB 240825A likely originated
from a massive star collapse, with the associated supernova obscured by a dusty
host environment or low luminosity SN with absolute magnitude M$_V$ fainter
than -18.0. This study emphasizes the need for multiwavelength follow-up and a
multi-layered classification to determine GRB progenitors.
| Search Query: ArXiv Query: search_query=au:”Nicola Omodei”&id_list=&start=0&max_results=3