X-ray upper limits of GW151226 with MAXI

TL;DR

This study used MAXI to observe the GW151226 event's error region, setting upper limits on X-ray emissions and analyzing MAXI's sensitivity to potential long X-ray signals associated with short gamma-ray bursts.

Contribution

First to provide X-ray upper limits for GW151226 using MAXI and evaluate MAXI's sensitivity to X-ray emissions from GW-associated short gamma-ray bursts.

Findings

No significant X-ray transient detected in GW error region.

MAXI set a 3-sigma upper limit of 1.2 × 10^{-9} erg cm^{-2} s^{-1} in 2-20 keV.

Detected a low-significance short excess event post-GW trigger.

Abstract

The error region of the the gravitational-wave (GW) event GW151226 was observed with Monitor of All-sky X-ray Image (MAXI). MAXI was operated at the time of GW151226, and continuously observed to 4 minutes after the event. MAXI covered about 84% of the 90 percent error region of the GW event during the first 92 minutes orbit after the event. No significant X-ray transient was detected in the GW error region. A typical 3-$\sigma$ GSC upper limit for a scan is 1.2 $\times 10^{-9}$ ergs cm$^{-2}$ s$^{-1}$ in the 2-20 keV. The auto-detection (MAXI nova-search) systems detected a short excess event with a low significance (2.85$\sigma$) from 5257 s to 5260 s after the GW trigger. Finally, we discuss the sensitivity of MAXI to long X-ray emissions of short gamma-ray bursts, which are expected to accompany GW events.