Time-Domain Dust Astrophysics. I. Polarization Flares, Polarization-Angle Reverberation, and Fossil Imprints in Supernova-Illuminated Clouds

Abstract

Cosmic transients can enhance the local radiation field on timescales of days to months. Using the time-domain \TransRAT\ framework, which self-consistently follows grain heating, alignment, rotational disruption, and switching of the alignment axis between the magnetic field ({\bf B}) and the radiation direction ({\bf k}), we predict the time-dependent dust polarization of a dense cloud, represented by a homogeneous one-zone model, illuminated by a Type~IIP supernova over a range of source--cloud distances. We identify four key signatures. First, for $D\lesssim 1$~pc, a \emph{polarization flare} develops within days to weeks, marked by sharp increases in both thermal dust polarization and extinction-polarization efficiency; this is followed by a \emph{polarization dip} as radiative torque disruption (RAT-D) destroys the large aligned grains. Second, the peak wavelength of extinction polarization, ${\lambda }_{\max }$, shifts blueward as the minimum aligned-grain size decreases. Third, the transition from B-RAT to k-RAT produces an abrupt \emph{polarization-angle rotation} of up to $45^{\circ }$ in our fiducial geometry. Fourth, as the transient fades, the return to B-RAT generates a \emph{polarization-angle reverberation} governed by Larmor precession. At $D>1$~pc, SN-induced polarization properties can persist long after the radiation has faded. These {\it fossil imprints} offer the most practical near-term observational test: clouds near supernova remnants younger than the relaxation timescale of $\sim 10t_{\mathrm{gas}}$ with $t_{\mathrm{gas}}$ gas damping time, should exhibit elevated polarization and blueshifted ${\lambda }_{\max }$ today. Time-dependent dust polarization can therefore probe dust physics, dust properties, and pristine pre-shock magnetic fields in real time, while fossil imprints preserve a record of past explosions.

12 pages, 6 figures; minor revisions