GRB 140102A: Insight into Prompt Spectral Evolution and Early Optical Afterglow Emission

TL;DR

This paper analyzes multi-wavelength data of GRB 140102A, revealing insights into its prompt spectral evolution, early optical afterglow from reverse shock, and host galaxy properties, advancing understanding of GRB shock physics and environments.

Contribution

It provides detailed modeling of the reverse and forward shocks in GRB 140102A, including shock parameters and host galaxy characterization, with comparisons to other GRBs.

Findings

Early optical afterglow consistent with reverse shock emission in a thin shell scenario.

Spectral peak energy tracks intensity during the first episode of prompt emission.

Host galaxy is a high-mass, star-forming galaxy at redshift ~2.8.

Abstract

We present and perform a detailed analysis of multi-wavelength observations of \thisgrb, an optical bright GRB with an observed reverse shock (RS) signature. Observations of this GRB were acquired with the BOOTES-4 robotic telescope, the \fermi, and the \swift missions. Time-resolved spectroscopy of the prompt emission shows that changes to the peak energy (\Ep) tracks intensity and the low-energy spectral index seems to follow the intensity for the first episode, whereas this tracking behavior is less clear during the second episode. The fit to the afterglow light curves shows that the early optical afterglow can be described with RS emission and is consistent with the thin shell scenario of the constant ambient medium. The late time afterglow decay is also consistent with the prediction of the external forward shock (FS) model. We determine the properties of the shocks, Lorentz factor, magnetization parameters, and ambient density of \thisgrb, and compare these parameters with another 12 GRBs, consistent with having RS produced by thin shells in an ISM-like medium. The value of the magnetization parameter ($R_{\rm B} \approx 18$) indicates a moderately magnetized baryonic dominant jet composition for \thisgrb. We also report the host galaxy photometric observations of \thisgrb obtained with 10.4m GTC, 3.5m CAHA, and 3.6m DOT telescopes and find the host (photo $z$ = $2.8^{+0.7}_{-0.9}$) to be a high mass, star-forming galaxy with a star formation rate of $20 \pm 10 \msun$ $\rm yr^{-1}$.