J-GEM Follow-Up Observations to Search for an Optical Counterpart of The First Gravitational Wave Source GW150914

TL;DR

This paper reports on optical follow-up observations by the J-GEM collaboration to find electromagnetic counterparts to the first gravitational wave source GW150914, using wide-field and galaxy-targeted surveys across multiple telescopes, but finds no associated transients.

Contribution

It presents the first coordinated multi-telescope optical follow-up search for GW150914, detailing survey strategies, depths, and the non-detection of counterparts, advancing follow-up methodologies.

Findings

No transient sources associated with GW150914 were detected.

Survey depths reached approximately 18.3 to 18.9 magnitude.

The probability of the source being in the observed area was very low.

Abstract

We present our optical follow-up observations to search for an electromagnetic counterpart of the first gravitational wave source GW150914 in the framework of the Japanese collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM), which is an observing group utilizing optical and radio telescopes in Japan, as well as those in New Zealand, China, South Africa, Chile, and Hawaii. We carried out a wide-field imaging survey with Kiso Wide Field Camera (KWFC) on the 1.05-m Kiso Schmidt telescope in Japan and a galaxy-targeted survey with Tripole5 on the B&C 61-cm telescope in New Zealand. Approximately 24 deg2 regions in total were surveyed in i-band with KWFC and 18 nearby galaxies were observed with Tripole5 in g-, r-, and i-bands 4-12 days after the gravitational wave detection. Median 5-sigma depths are i~18.9 mag for the KWFC data and g~18.9 mag, r~18.7 mag, and i~18.3 mag for the Tripole5 data. Probability for a counterpart to be in the observed area is 1.2% in the initial skymap and 0.1% in the final skymap. We do not find any transient source associated to an external galaxy with spatial offset from its center, which is consistent with the local supernova rate. We summarize future prospects and ongoing efforts to pin down electromagnetic counterparts of binary black hole mergers as well as neutron star mergers.