| Name: Sitha K Jagan |
| Affiliation: Indian Institute of Space Science and Technology (IIST) |
| Conference ID: ASI2026_915 |
| Title: Investigating Jet Structure in Gamma-Ray Bursts Using Early Rising Optical Afterglows |
| Abstract Type: Poster |
| Abstract Category: High Energy Phenomena, Fundamental Physics and Astronomy |
| Author(s) and Co-Author(s) with Affiliation: Sitha K Jagan(Indian Institute of Space Science and Technology, Trivandrum 695547, Kerala, India), Lekshmi Resmi(Indian Institute of Space Science and Technology, Trivandrum 695547, Kerala, India) |
| Abstract: Early optical afterglows of gamma-ray bursts (GRBs) provide important constraints on the structure of relativistic jets and the angle at which they are observed. Recent work by Chakyar & Resmi (2025) showed that delayed optical peaks and slowly rising light curves can be used to identify off-axis and structured GRB jets, based on a limited sample. Motivated by this study, we present an ongoing analysis aimed at extending these results to a larger sample to understand the distribution of viewing angles and jet structure across bursts.
From an initial sample of 495 GRB afterglows obtained from the SLAC optical afterglow light curve database, we identified 44 well-sampled early-rising light curves with known redshifts through visual inspection of the sample for the present analysis. Optical afterglow light curves for these events have been examined to identify clear rising phases, and rest-frame luminosity–time profiles are being generated to study their rise behaviour, peak times, and luminosity distributions.
The present work focuses on investigating whether systematic trends emerge among GRBs with rising optical afterglows that may be linked to jet structure or viewing angle. In the next stage, we will complete the sample with X-ray and radio data for these GRBs. The multi-wavelength light curves will be modelled using the VEGAS afterglow model, which calculates the synchrotron emission from the afterglow and incorporates Bayesian parameter estimation to infer jet geometry and key microphysical parameters.
GRB jet structure is linked to the jet launching mechanism. Viewing angle constraints are essential to obtain the true rate and energetics of GRBs. This study aims to place stronger constraints on GRB jet structure by combining a statistically meaningful sample with multi-wavelength afterglow modelling, and by linking early optical signatures with the behaviour of GRB afterglows at later times. |
