Time-Domain Dust Astrophysics. II. TransRAT: Time-Dependent Grain Alignment and Disruption by Cosmic Transients and Their Observational Signatures
Abstract
We introduce {\it TransRAT}, a self-consistent time-domain framework that follows the coupled dynamical response of dust to transient irradiation and predicts its observable signatures. We apply {\it TransRAT} to a Type~IIP supernova illuminating a one-zone molecular cloud. Radiative heating raises the grain temperature, modifying the magnetic susceptibility and Larmor precession, while the enhanced radiation field accelerates radiative precession and can switch the alignment axis from the magnetic field (B-RAT) to the radiation direction (k-RAT). Simultaneously, strong RATs align grains faster than gas randomization, extending {\it fast alignment} to smaller grain sizes, and disrupt large grains through RAT disruption (RAT-D), irreversibly modifying the grain size distribution. As the transient fades, the alignment axis returns to bf B at a rate controlled by the magnetic susceptibility, whereas the enhanced aligned-grain population and RAT-D-modified grain size distribution can persist long after the radiation has faded- referred to as \emph{physical memory effects}. The time-dependent evolution of grain alignment and disruption produces distinctive observational signatures: a flare in extinction and thermal dust polarization followed by a RAT-D-induced dip; a blueward shift of the polarization peak λmax; a polarization-angle rotation equal to the projected bf B--bf k separation (45∘ for our adopted geometry) when RAT-D removes large high-J aligned grains and leaves low-J grains aligned with kRAT followed by angle reverberation as alignment returns to bf B; and a non-monotonic evolution of RV. The persistent observational manifestations of the transient irradiation, including enhanced polarization, blueshifted λmax, modified RV, and polarization-angle evolution, constitute \emph{fossil imprints} of past cosmic transients.
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BibTeX
@misc{hoang2026timedomain,
title = {{Time-Domain Dust Astrophysics. II. TransRAT: Time-Dependent Grain Alignment and Disruption by Cosmic Transients and Their Observational Signatures}},
author = {Thiem Hoang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.09555},
eprint = {2609.09555},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.09555},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Time-Domain Dust Astrophysics. II. TransRAT: Time-Dependent Grain Alignment and Disruption by Cosmic Transients and Their Observational Signatures
AU - Thiem Hoang
PY - 2026
DA - 2026/09/09
PB - arXiv
DO - 10.48550/arxiv.2609.09555
UR - https://arxiv.org/abs/2609.09555
AB - We introduce {\it TransRAT}, a self-consistent time-domain framework that follows the coupled dynamical response of dust to transient irradiation and predicts its observable signatures. We apply {\it TransRAT} to a Type~IIP supernova illuminating a one-zone molecular cloud. Radiative heating raises the grain temperature, modifying the magnetic susceptibility and Larmor precession, while the enhanced radiation field accelerates radiative precession and can switch the alignment axis from the magnetic field (B-RAT) to the radiation direction (k-RAT). Simultaneously, strong RATs align grains faster than gas randomization, extending {\it fast alignment} to smaller grain sizes, and disrupt large grains through RAT disruption (RAT-D), irreversibly modifying the grain size distribution. As the transient fades, the alignment axis returns to bf B at a rate controlled by the magnetic susceptibility, whereas the enhanced aligned-grain population and RAT-D-modified grain size distribution can persist long after the radiation has faded- referred to as \emph{physical memory effects}. The time-dependent evolution of grain alignment and disruption produces distinctive observational signatures: a flare in extinction and thermal dust polarization followed by a RAT-D-induced dip; a blueward shift of the polarization peak λ_max; a polarization-angle rotation equal to the projected bf B--bf k separation (45^∘ for our adopted geometry) when RAT-D removes large high-J aligned grains and leaves low-J grains aligned with kRAT followed by angle reverberation as alignment returns to bf B; and a non-monotonic evolution of R_V. The persistent observational manifestations of the transient irradiation, including enhanced polarization, blueshifted λ_max, modified R_V, and polarization-angle evolution, constitute \emph{fossil imprints} of past cosmic transients.
ER -