ALMA and RATIR observations of GRB131030A

TL;DR

This study presents ALMA and RATIR observations of GRB131030A, providing deep limits on afterglow emission, identifying a nearby submillimeter source, and modeling the afterglow with relativistic hydrodynamics, while also characterizing the host galaxy.

Contribution

First ALMA 345-GHz observation of GRB131030A's afterglow, combined with multiwavelength data, to model the afterglow and analyze the host galaxy and nearby sources.

Findings

Deep ALMA limit constrains afterglow and host galaxy emission.

Identification of a faint submillimeter source near the GRB.

Host galaxy has low IR luminosity and star formation rate.

Abstract

We report on the first open-use based Atacama Large Millimeter/submm Array (ALMA) 345-GHz observation for the late afterglow phase of GRB131030A. The ALMA observation constrained a deep limit at 17.1 d for the afterglow and host galaxy. We also identified a faint submillimeter source (ALMAJ2300-0522) near the GRB131030A position. The deep limit at 345 GHz and multifrequency observations obtained using {\it Swift} and RATIR yielded forward shock modeling with a two-dimensional relativistic hydrodynamic jet simulation and described X-ray excess in the afterglow. The excess was inconsistent with the synchrotron self-inverse Compton radiation from the forward shock. The host galaxy of GRB131030A and optical counterpart of ALMAJ2300-0522 were also identified in the SUBARU image. Based on the deep ALMA limit for the host galaxy, the 3-$\sigma$ upper limits of IR luminosity and the star formation rate (SFR) is estimated as $L_{IR}<1.11\times10^{11} L_{\odot}$ and SFR$<18.7$ ($M_{\odot}$~yr$^{-1}$), respectively. Although the separation angle from the burst location (3.5 arcsec) was rather large, ALMAJ2300-0522 may be one component of the GRB131030A host galaxy, according to previous host galaxy cases.