Rapid-response 1.3 mm Observations of GRB 260127A with the Submillimeter Array

TL;DR

This paper reports the earliest millimeter observations of GRB 260127A using the SMA, revealing rapid flux decline and providing insights into afterglow emission mechanisms.

Contribution

First rapid-response 1.3 mm observations of a GRB with SMA, capturing early afterglow behavior within 12.6 minutes of detection.

Findings

Detected a 6.9 mJy source consistent with X-ray afterglow position

No emission detected 1.9 days later with a 0.70 mJy upper limit

Indicates the 1.3 mm light curve declined at least as fast as t^{-0.5}

Abstract

We present the results from rapid-response 1.3 mm observations of GRB 260127A using the Submillimeter Array (SMA). SMA arrived on-source 12.6 minutes after the initial detection by the Neil Gehrels Swift Observatory, representing the earliest millimeter/submillimeter observations of a GRB to date. From these observations, we find a source with flux density $6.9\pm1.7$ mJy, consistent with the X-ray afterglow position but slightly offset from the optical afterglow position (2.7'' offset, with the SMA detection having a 90% confidence radial position uncertainty of 0.9''). Subsequent observations 1.9 days later show no sources of emission, with a $3\sigma$ upper limit of 0.70 mJy. If the SMA detection is associated with GRB 260127A, we infer that the 1.3 mm light curve for GRB 260127A declined at least as fast as $t^{-0.5}$, suggesting that peak brightness of the event at this wavelength was reached in under a day. We discuss how these findings may be consistent with both forward shock and reverse shock afterglow scenarios, and implications for future millimeter/submillimeter observations of GRBs on these timescales.