Time-integrated polarizations in GRB prompt phase via the Multi-window interpretation

Abstract

The multi-window observations, including the light curve and the evolutions of the spectral peak energy ($E_p$), the polarization degree (PD) and the polarization angle (PA), are used to infer the model parameters to predict the time-integrated PD in gamma-ray burst (GRB) prompt phase. We select 23 GRBs co-detected by Fermi/GBM and polarization detectors (i.e., GAP, POLAR and AstroSat). In our multi-window fitting, the light curve, $E_p$ curve, PD curve and PA curve are interpreted simultaneously under the synchrotron radiation model in ordered magnetic fields (i.e., the aligned-fields case and the toroidal-fields case). For the bursts with abrupt PA rotations, the predicted time-integrated PD of the aligned-fields case roughly matches the corresponding observed best fit value, while it is higher for the toroidal-fields case. For the bursts without abrupt PA rotation(s), the predicted PDs of the aligned-fields case and the toroidal-fields case are comparable and could interpret the observational data equally well. For GRB 170206A, its observed time-resolved and time-integrated PDs are comparable and both smaller than our predicted upper limits in ordered magnetic fields. So mixed magnetic fields, i.e., the magnetic fields with both ordered and random components, should be reside in the radiation regions of this burst. Except 1 out of the total 23 bursts, the predicted time-integrated PDs, which are around $\sim44\%$ for the aligned-fields case and around $49\%$ for the toroidal-fields case, are consistent with the corresponding observed values. Therefore, consistent with the former study, the models with synchrotron radiation in ordered magnetic fields could interpret most of the current polrization data within $1\sigma$ error bar.