Optical Observations of GRB 050401 Afterglow : A case for Double Jet Model

TL;DR

This paper presents optical observations and modeling of GRB 050401's afterglow, proposing a double jet model to explain its unique multi-band features, including a break in X-ray light curve and differing optical and X-ray decay behaviors.

Contribution

It introduces a two-component jet model for GRB 050401's afterglow, explaining complex light curve features and comparing it with the first double jet case, GRB 030329.

Findings

X-ray light curve shows a break at ~0.06 day with no spectral evolution.

Optical emission remains smooth without a break.

Model successfully reproduces multi-band afterglow features.

Abstract

The afterglow of GRB 050401 presents several novel and interesting features : [1] An initially faster decay in optical band than in X-rays. [2] A break in the X-ray light curve after $\sim$ 0.06 day with an unusual slope after the break. [3] The X-ray afterglow does not show any spectral evolution across the break while the R band light curve does not show any break. We have modeled the observed multi-band evolution of the afterglow of GRB 050401 as originating in a two component jet, interpreting the break in X-ray light curve as due to lateral expansion of a narrow collimated outflow which dominates the X-ray emission. The optical emission is attributed to a wider jet component. Our model reproduces all the observed features of multi-band afterglow of GRB 050401. We present optical observations of GRB 050401 using the 104-cm Sampurnanand Telescope at ARIES, Nainital. Results of the analysis of multi-band data are presented and compared with GRB 030329, the first reported case of double jet.