GRB 190114C light curves

Observations begin 31s after the onset of the GRB and continue until ~7000s postburst. The light curves reveal a chromatic break at ~400-500s, with initial temporal decay {alpha}=1.669+/-0.013 flattening to {alpha}~1 postbreak, which we model as a combination of reverse and forward shock components with magnetization parameter R_B_~70.

The observed polarization degree decreases from 7.7%+/-1.1% to 2%-4% 52-109s postburst and remains steady at this level for the subsequent ~2000s at a constant position angle. Broadband spectral energy distribution modeling of the afterglow confirms that GRB 190114C is highly obscured (A_v,HG_=1.49+/-0.12mag; N_H,HG_=(9.0+/-0.03)x10^22^cm^-2^). We interpret the measured afterglow polarization as intrinsically low and dominated by dust -in contrast to the P>10% measured previously for other GRB reverse shocks-with a small contribution from polarized prompt photons in the first minute.