Time varying polarized gamma-rays from GRB 160821A: evidence for ordered magnetic fields

Abstract

GRB 160821A is the third most energetic gamma ray burst observed by the {\it Fermi} gamma-ray space telescope. Based on the observations made by Cadmium Zinc Telluride Imager (CZTI) on board {\it AstroSat}, here we report the most conclusive evidence to date of (i) high linear polarization ($66_{-27}^{+26}\%$; $5.3\sigma$ detection), and (ii) variation of its polarization angle with time happening twice during the rise and decay phase of the burst at $3.5\sigma$ and $3.1\sigma$ detections respectively. All confidence levels are reported for two parameters of interest. These observations strongly suggest synchrotron radiation produced in magnetic field lines which are highly ordered on angular scales of $1/\Gamma$, where $\Gamma$ is the Lorentz factor of the outflow.

12 pages, 6 figures, accepted for publication in The Astrophysical Journal Letters

References in corpus (31)

• The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission
• The Fermi Gamma-Ray Burst Monitor
• Gamma-Ray Bursts
• Polarization of the prompt gamma-ray emission from the gamma-ray burst of 6 December 2002
• Detection of a Thermal Spectral Component in the Prompt Emission of GRB 100724B
• GRB110721A: An extreme peak energy and signatures of the photosphere
• Detection of Gamma-Ray Polarization in Prompt Emission of GRB 100826A
• Statistical Properties of Gamma-Ray Burst Polarization
• Re-Analysis of Polarization in the Gamma-ray flux of GRB 021206
• The Most Probable Cause for the High Gamma-Ray Polarization in GRB 021206
• Magnetic Structures in Gamma-Ray Burst Jets Probed by Gamma-Ray Polarization
• Physics of Gamma-Ray Bursts Prompt Emission
• Variable polarization measured in the prompt emission of GRB 041219A using IBIS on board INTEGRAL
• Gamma-Ray Burst Polarization: Limits from RHESSI Measurements
• Time-resolved Analysis of Fermi GRBs with Fast and Slow-Cooled Synchrotron Photon Models
• Compton drag as a mechanism for very high linear polarization in Gamma-Ray Bursts
• Fermi and Swift Gamma-Ray Burst Afterglow Population Studies
• The polarized Gamma-Ray Burst GRB 061122
• GRB 140206A: the most distant polarized Gamma-Ray Burst
• Detailed polarization measurements of the prompt emission of five Gamma-Ray Bursts
• The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks
• The Bright and the Slow -- GRBs 100724B \& 160509A with high-energy cutoffs at $\lesssim 100$MeV
• Variable jet properties in GRB110721A: Time resolved observations of the jet photosphere
• High Energy Polarimetry of Prompt GRB Emission
• Time-Resolved GRB Polarization with POLAR and GBM
• High energy emission and polarisation limits for the INTEGRAL burst GRB 061122
• AstroSat CZT Imager observations of GRB 151006A: timing, spectroscopy, and polarisation study
• Synchrotron emission in GRBs observed by Fermi: Its limitations and the role of the photosphere
• AstroSat-CZTI detection of variable prompt emission polarization in GRB 171010A
• Violation of synchrotron line of death by the highly polarized $GRB160802A$
• Polarization signature of gamma-ray bursts from fragmented fireballs

Cited by in corpus (26)

• The POLAR Gamma-Ray Burst Polarization Catalog
• Prompt emission polarimetry of Gamma Ray Bursts with ASTROSAT CZT-Imager
• Hard X-ray polarization catalog for a 5-year sample of Gamma-Ray Bursts using AstroSat CZT-Imager
• Bayesian Time-Resolved Spectroscopy of Multi-Pulsed GRBs: Variations of Emission Properties amongst Pulses
• The Fraction of Gamma-ray Bursts with an Observed Photospheric Emission Episode
• Temporal Evolution of Prompt GRB Polarization
• Synchrotron-Self-Compton radiation from magnetically-dominated turbulent plasmas in relativistic jets
• The Synchrotron Polarization in Decaying Magnetic Field in Gamma-Ray Bursts
• Photospheric Prompt Emission From Long Gamma Ray Burst Simulations -- II. Spectropolarimetry
• Spectro-polarimetric analysis of prompt emission of GRB 160325A: jet with evolving environment of internal shocks
• Multi-wavelength study of the luminous GRB 210619B observed with Fermi and ASIM
• Rotation of polarization angle in gamma-ray burst prompt phase
• Multi-Wave band Synchrotron Polarization of Gamma-Ray Burst Afterglows
• Observational characteristics of radiation-mediated shocks in photospheric gamma-ray burst emission
• The polarization-angle flip in GRB prompt emission
• Onset of particle acceleration during the prompt phase in gamma-ray bursts as revealed by synchrotron emission in GRB160821A
• A detailed time-resolved and energy-resolved spectro-polarimetric study of bright GRBs detected by AstroSat CZTI in its first year of operation
• Gamma-Ray Polarimetry
• Prospects of measuring Gamma-ray Burst Polarisation with the Daksha mission
• Gamma-ray Polarimetry of Transient Sources with POLAR
• Spectro-polarimetry of GRB 180427A: evidence for distinct emission sites with varying polarisation
• Adding Gamma-ray Polarimetry to the Multi-Messenger Era
• Extending the energy range of AstroSat-CZTI up to 380 keV with Compton Spectroscopy
• Episode-wise spectro-polarimetry of GRB 220107A: Testing the hypothesis of evolving radiation mechanisms
• Sub-MeV spectroscopy with AstroSat-CZT Imager for Gamma Ray Bursts
• Time-integrated polarizations in GRB prompt phase via the Multi-window interpretation