Spectropolarimetry and photometry of the early afterglow of the gamma-ray burst GRB191221B

Abstract

We report on results of spectropolarimetry of the afterglow of the long gamma-ray burst GRB 191221B, obtained with SALT/RSS and VLT/FORS2, as well as photometry from two telescopes in the MASTER Global Robotic Network, at the MASTER-SAAO (South Africa) and MASTER-OAFA (Argentina) stations. Prompt optical emission was detected by MASTER-SAAO 38 s after the alert, which dimmed from a magnitude (white-light) of ~10 to 16.2 mag over a period of ~10 ks, followed by a plateau phase lasting ~10 ks and then a decline to ~18 mag after 80 ks. The light curve shows complex structure, with four or five distinct breaks in the power-law decline rate. SALT/RSS linear spectropolarimetry of the afterglow began ~2.9 h after the burst, during the early part of the plateau phase of the light curve. Absorption lines seen at ~6010 Å and 5490 Å are identified with the Mg II 2799 Å line from the host galaxy at z=1.15 and an intervening system located at z=0.96. The mean linear polarisation measured over 3400-8000 Å was ~1.5% and the mean equatorial position angle theta ~65 degrees. VLT/FORS2 spectropolarimetry was obtained ~10 h post-burst, during a period of slow decline (alpha = -0.44), and the polarisation was measured to be p = 1.2% and theta = 60 degrees. Two observations with the MeerKAT radio telescope, taken 30 and 444 days after the GRB trigger, detected radio emission from the host galaxy only. We interpret the light curve and polarisation of this long GRB in terms of a slow-cooling forward-shock.

Accepted for publication in MNRAS on 19 June 2021; 14 pages, 6 figures

References in corpus (18)

• The Physics of Gamma-Ray Bursts and Relativistic Jets
• Fast radio bursts as synchrotron maser emission from decelerating relativistic blast waves
• Ten per cent polarized optical emission from GRB 090102
• Evolution of the polarization of the optical afterglow of the gamma-ray burst GRB 030329
• Circular polarization in the optical afterglow of GRB 121024A
• Multiwavelength analysis of the intriguing GRB 061126: the reverse shock scenario and magnetization
• Gamma Ray Bursts in the Swift-Fermi Era
• A Comprehensive Radio View of the Extremely Bright Gamma-Ray Burst 130427A
• The POLAR Gamma-Ray Burst Polarization Catalog
• On the existence of a reverse shock in magnetized GRB ejecta
• Constraining the magnetic field structure in collisionless relativistic shocks with a radio afterglow polarization upper limit in GW170817
• Large Interstellar Polarisation Survey. LIPS I: FORS2 spectropolarimetry in the Southern Hemisphere
• Spectropolarimetry of SN 2006aj at 9.6 days
• Signatures of photon and axion-like particle mixing in the gamma-ray burst jet
• The Synchrotron Polarization in Decaying Magnetic Field in Gamma-Ray Bursts
• Multi-Wave band Synchrotron Polarization of Gamma-Ray Burst Afterglows
• Polarization constraints on the geometry of the magnetic field in the external shock of gamma-ray bursts
• On the Polarized Absorption Lines in Gamma-ray Burst Optical Afterglows

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