Radio follow-up of gravitational wave triggers during Advanced LIGO O1

TL;DR

This study reports on radio follow-up observations of gravitational wave events during LIGO's first observing run, aiming to identify electromagnetic counterparts and improve follow-up strategies.

Contribution

It provides the first radio follow-up results for LIGO O1 triggers, demonstrating the importance of combined optical and radio observations for counterpart identification.

Findings

No radio counterparts were found for binary black hole mergers.

Combining optical and radio data helps identify contaminating sources.

The results align with theoretical expectations for black hole merger radio signals.

Abstract

We present radio follow-up observations carried out with the Karl G. Jansky Very Large Array during the first observing run (O1) of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). A total of three gravitational wave triggers were followed up during the ~4 months of O1, from September 2015 to January 2016. Two of these triggers, GW150914 and GW151226, are binary black hole merger events of high significance. A third trigger, G194575, was subsequently declared as an event of no interest (i.e., a false alarm). Our observations targeted selected optical transients identified by the intermediate Palomar Transient Factory (iPTF) in the Advanced LIGO error regions of the three triggers, and a limited region of the gravitational wave localization area of G194575 not accessible to optical telescopes due to Sun constraints, where a possible high-energy transient was identified. No plausible radio counterparts to GW150914 and GW151226 were found, in agreement with expectations for binary black hole mergers. We show that combining optical and radio observations is key to identifying contaminating radio sources that may be found in the follow-up of gravitational wave triggers, such as emission associated to star formation and AGN. We discuss our results in the context of the theoretical predictions for radio counterparts to gravitational wave transients, and describe our future plans for the radio follow-up of Advanced LIGO (and Virgo) triggers.