K. M. Jayasurya | Searcharxiv

arXiv2026

Exploring the multi-wavelength properties of the high energetic event ZTF20abbiixp/GRB 200524A: from prompt emission to afterglow

We conducted a comprehensive multi-wavelength analysis of a high energetic long-duration ZTF20abbiixp / GRB~200524A detected by \textit{Fermi} Gamma Ray Burst Monitor (GBM). Our study combines extended high-energy observations from multiple space-based observatories including \textit{Fermi} with broadband afterglow data spanning X-ray to radio wavelengths, complemented by extensive photometric and spectroscopic follow-up from several ground-based optical facilities worldwide like 3.6-m Devasthal Optical Telescope (DOT). ZTF20abbiixp / GRB~200524A exhibits almost negligible spectral lag, likely arising from the presence of multiple overlapping emission episodes, a property uncommon among long-duration bursts. The burst additionally shows a clear intensity-tracking evolution of the prompt-emission spectral parameters. The broadband afterglow light curve best fits with a broken powerlaw with a break at $10^{5}$ s since the GBM trigger. The electron powerlaw index (p) calculated from the temporal and spectral slopes fail to distinguish between a interstellar medium and a wind environment. Our custom-developed afterglow model fits the panchromatic data well, combining forward shock (FS) and reverse shock (RS) emission. The RS contribution required to fit the early time optical data. The inferred afterglow model parameters suggest that ZTF20abbiixp / GRB~200524A is a high energetic burst expanding into a dense ISM environment, with a relatively large value of the fraction of energy going to accelerating electron and magnetic field ($ε_B$).

astro-ph.HE↗

arXiv2026

Photometric and late-time spectropolarimetric observations of GRB 250129A afterglow

Gamma-Ray Burst (GRB) afterglows arise from the interaction of relativistic ejecta with the circumburst medium and are observed across the electromagnetic spectrum. Afterglow polarisation is expected at early and late phases depending on the presence of reverse shocks (RS) and the observer's viewing geometry relative to the jet. Polarimetric observations of GRB afterglows provide a unique diagnostic tool to probe the geometry and structure of magnetic fields in the emitting region, which cannot be inferred from photometric or spectroscopic data alone. We report late-time (~19 hours post-burst) spectropolarimetric observations of GRB 250129A using the Southern African Large Telescope (SALT). The data reveal a hint of linear polarisation, with no evidence for rotation in the polarisation angle across wavelengths. Polarisation is typically expected during the early afterglow (<100 s) when the RS dominates. However, multi-wavelength modelling shows no indication of RS contribution at late times. Modelling incorporating both forward shock (FS) and RS components confirms that the RS fades rapidly after ~100 s. The afterglow emission is best explained by an off-axis viewing geometry of a jet with a Gaussian core and wings evolving in a uniform density environment. GRB 250129A thus provides rare observational evidence linking late-time polarisation to jet geometry and structure.

astro-ph.HE↗