Strong NIR emission following the long duration GRB 211211A: Dust heating as an alternative to a kilonova

Abstract

The prolonged near infrared (NIR) emission observed following the long duration GRB 211211A is inconsistent with afterglow emission from the shock driven into the circum-stellar medium (CSM), and with emission from a possible underlying supernova. It has therefore been suggested that the observed NIR flux is the signature of a kilonova -- a radioactive ejecta that is similar to the outcome of the binary neutron star merger GW170817. We propose here an alternative plausible explanation. We show that the NIR flux is consistent with thermal emission from dust, heated by UV and soft X-ray radiation produced by the interaction of the GRB jet plasma with the CSM. This NIR emission was predicted by Waxman & Draine for GRBs residing near or withing massive molecular clouds. The dust NIR emission scenario is consistent with a GRB at $z\lesssim1$. Inspection of the environment of GRB 211211A suggests that there are at least two host-galaxy candidates, one at $z=0.076$ and the other at $z=0.459$. The $z=0.459$ possibility is also consistent with the non-detection of a supernova signature in the light curve of the GRB afterglow, and with a typical GRB $\gamma$-ray energy for the fluence of GRB 211211A.