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Lowly polarized light from a highly magnetized jet of GRB 190114C
- Source :
- ApJ, 892, 2 (2020)
- Publication Year :
- 2019
-
Abstract
- We report multi-color optical imaging and polarimetry observations of the afterglow of the first TeV- detected gamma-ray burst, GRB 190114C, using RINGO3 and MASTER II polarimeters. Observations begin 31 s after the onset of the GRB and continue until $\sim 7000\,$s post-burst. The light curves reveal a chromatic break at $\sim 400- 500\,$s, with initial temporal decay $\alpha = 1.669 \pm 0.013$ flattening to $\alpha \sim 1$ post-break, which we model as a combination of reverse and forward-shock components, with magnetization parameter $R_{\rm B} \sim 70$. The observed polarization degree decreases from $7.7 \pm 1.1\%$ to $2-4\%$ during $52-109\,$s post-burst and remains steady at this level for the subsequent $\sim 2000$-s, at constant position angle. Broadband spectral energy distribution modeling of the afterglow confirms GRB 190114C is highly obscured (A$_{\rm v, HG} = 1.49 \pm 0.12 \,$mag; N$_{\rm H, HG}= (9.0 \pm 0.3) \times 10^{22}\,$cm$^{-2}$). We interpret the measured afterglow polarization as intrinsically low and dominated by dust, in contrast to ${\rm P} >10\%$ measured previously for other GRB reverse shocks, with a small contribution from polarized prompt photons in the first minute. We test whether 1st and higher-order inverse Compton scattering in a magnetized reverse shock can explain the low optical polarization and the sub-TeV emission but conclude neither is explained in the reverse shock Inverse Compton model. Instead, the unexpectedly low intrinsic polarization degree in GRB 190114C can be explained if large-scale jet magnetic fields are distorted on timescales prior to reverse shock emission.<br />Comment: The full photometry data is available in the journal publication
- Subjects :
- Astrophysics - High Energy Astrophysical Phenomena
Subjects
Details
- Database :
- arXiv
- Journal :
- ApJ, 892, 2 (2020)
- Publication Type :
- Report
- Accession number :
- edsarx.1911.08499
- Document Type :
- Working Paper
- Full Text :
- https://doi.org/10.3847/1538-4357/ab7248