INTEGRAL observations of GW170104

TL;DR

This study used INTEGRAL data to set upper limits on gamma-ray and X-ray emissions from GW170104, constraining possible electromagnetic counterparts and challenging previous claims of detection.

Contribution

It provides the first comprehensive upper limits on high-energy emission from GW170104 using INTEGRAL's full localization capability, refining constraints on gamma-ray counterparts.

Findings

INTEGRAL set upper limits on gamma-ray emission from GW170104.

The INTEGRAL results do not confirm the AGILE/MCAL gamma-ray counterpart.

The gamma-ray to gravitational wave energy ratio is constrained to less than 2.6x10^-5.

Abstract

We used data from the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) to set upper-limits on the ${\gamma}$-ray and hard X-ray prompt emission associated with the gravitational wave event GW170104, discovered by the LIGO/Virgo collaboration. The unique omni-directional viewing capability of the instruments on-board INTEGRAL allowed us to examine the full 90% confidence level localization region of the LIGO trigger. Depending on the particular spectral model assumed and the specific position within this region, the upper limits inferred from the INTEGRAL observations range from F${\gamma}$=1.9x10-7 erg cm-2 to F${\gamma}$=10-6 erg cm-2 (75 keV - 2 MeV energy range). This translates into a ratio between the prompt energy released in ${\gamma}$-rays along the direction to the observer and the gravitational wave energy of E${\gamma}$/EGW <2.6x10-5 . Using the INTEGRAL results, we can not confirm the ${\gamma}$-ray proposed counterpart to GW170104 by the AGILE team with the MCAL instrument. The reported flux of the AGILE/MCAL event, E2, is not compatible with the INTEGRAL upper limits within most of the 90% LIGO localization region. There is only a relatively limited portion of the sky where the sensitivity of the INTEGRAL instruments was not optimal and the lowest allowed fluence estimated for E2 would still be compatible with the INTEGRAL results. This region was also observed independently by Fermi/GBM and AstroSAT, from which, as far as we are aware, there are no reports of any significant detection of a prompt high-energy event.