*5.2. Time-Resolved Measurements*

Time-resolved analysis was performed on a range of different GRBs by different collaborations. POLAR only found hints of an evolving PA for two GRBs in their catalog, GRB 170114A and 170101A [187]. Out of the 14 GRBs studied by POLAR, these are the only

two with a single fast-rising exponential decay (FRED)-like structure. Such GRBs are of interest as they are typically considered to originate from a single emission region with no contamination from multiple overlapping pulses that complicate the analysis. For any other GRB in the POLAR catalog, all being multi-pulsed, no signs of an evolving PA were found. It is possible that the PA varies between different overlapping pulses, and integrating over different temporal segments of the emission episode results in an approximately fixed PA and also a lower PD due to cancellations. Alternatively, it is equally possible that the PA does not vary between pulses for many GRBs and that the PD is intrinsically low.

The data of POLAR do not allow to determine the nature of the PA evolution for the two GRBs for which hints of it were found. The data are compatible with both random variations as well as a single 90◦ change [104]. Finer time binning or higher statistics within the time bins are required to fully resolve this.

Both the IBIS, GAP, and AstroSAT CZTI collaborations have reported an evolution of the PA over more complex GRBs consisting either of multiple separated pulses (100826A, 160325A) or overlapping pulses (041219A, 160821A) [231,236,239,242]. For both 100826A and 160821A, the evolution is reported to be compatible with PA changes of 90◦ . For 160325A, for which a high PD was found in time-integrated analysis presented in [188], the time-resolved analysis found that the first emission episode showed no or low polarization, whereas the second episode showed a PD above 43% with a 1.5 *σ* confidence level. For 041219A, the evolution in PA during the first emission period could explain the low PD observed with time-integrated analysis.

Neither GAP nor AstroSAT has reported any studies of PA evolution for GRBs with FRED-like pulses. Therefore, similar to the time-integrated polarization, currently existing results do not allow to draw any strong conclusions for PA evolution. This is due to the limited number of measurements, lower precision, as well as the disagreement between results found by different groups.
