A two-component jet model for the optical plateau in the afterglow of GRB 191221B

Abstract

The long gamma-ray burst GRB 191221B has abundant observations in X-ray, optical and radio bands. In the literature, the observed optical light curve of GRB 191221B displays a plateau around 0.1-day, which is rather peculiar in gamma-ray bursts. Here we performed detailed analysis of the observational data from Swift/UVOT, VLT and LCO, obtained the light curve of the multi-band afterglow of GRB 191221B. By examining optical, ultraviolet, X-ray, and radio data for this event, we demonstrate that an on-axis two-component jet model can explain the observations. Our analysis suggests that the narrow component has an initial Lorentz factor of 400 and a jet opening half-angle of $1.4^{\circ }$, while the wide component has an initial Lorentz factor of 25 and a jet opening half-angle of $2.8^{\circ }$. The narrow jet dominates the early decay, whereas the wider jet causes the optical plateau and dominates late decay. According to this model, the reason for the absence of the X-ray plateau is due to the steeper spectral index of the wide component, resulting in a less significant flux contribution from the wide jet in the X-ray bands than in the optical bands. Moreover, we have explained the inconsistency in the decay indices of the UVOT and Rc-band data around 2000 seconds using reverse shock emission.

10 pages, 7 figures, Accepted by the Monthly Notices of the Royal Astronomical Society

References in corpus (13)

• Gamma-Ray Bursts: Progress, Problems & Prospects
• A Comprehensive Radio View of the Extremely Bright Gamma-Ray Burst 130427A
• On Dust Extinction of Gamma-ray Burst Host Galaxies
• A two component jet model for the X-ray afterglow flat segment in short GRB 051221A
• The Two-Component Afterglow of Swift GRB 050802
• The Possibility of Modeling the Very High Energy Afterglow of GRB 221009A in a Wind Environment
• Off-axis jet scenario for early afterglow emission of low-luminosity gamma-ray burst GRB 190829A
• Spectropolarimetry and photometry of the early afterglow of the gamma-ray burst GRB191221B
• Optical Observations of GRB 050401 Afterglow : A case for Double Jet Model
• Simultaneous Radio and Optical Polarimetry of GRB 191221B Afterglow
• An optical-ultraviolet flare with absolute AB magnitude of -39.4 detected in GRB 220101A
• A study of gamma-ray burst afterglows as they first come into view of the Swift Ultraviolet and Optical Telescope
• Three-stage Collapse of the Long Gamma-Ray Burst from GRB 160625B Prompt Multiwavelength Observations