INTEGRAL observations of the gamma-ray binary 1FGL J1018.6-5856

TL;DR

This study reports the detection of gamma-ray binary 1FGL J1018.6-5856 using INTEGRAL observations, revealing phase-dependent variability and potential anti-correlation with GeV emissions, contributing to understanding its high-energy behavior.

Contribution

First INTEGRAL-based detection and analysis of 1FGL J1018.6-5856, highlighting phase-dependent X-ray variability and its relation to gamma-ray emissions.

Findings

Detection at 5.4 sigma significance in 18-40 keV band

Evidence of phase-dependent variability in X-ray emission

Possible anti-correlation with GeV gamma-ray periodicity

Abstract

The Fermi-LAT collaboration has recently reported that one of their detected sources, namely, 1FGL J1018.6-5856, is a new gamma-ray binary similar to LS 5039. This has prompted efforts to study its multi-frequency behavior. In this report, we present the results from 5.78-Ms INTEGRAL IBIS/ISGRI observations on the source 1FGL J1018.6-5856. By combining all the available INTEGRAL data, a detection is made at a significance level of 5.4 sigma in the 18-40 keV band, with an average intensity of 0.074 counts/s . However, we find that, there is non-statistical noise in the image that effectively reduces the significance to about 4 sigma and a significant part of the signal appears to be located in a 0.2-wide phase region, at phases 0.4-0.6 (where even the corrected significance amounts to 90% of the total signal found). Given the scarcity of counts, a variability is hinted at about 3 sigma at the hard X-rays, with an anti-correlation with the Fermi-LAT periodicity. Should this behavior be true, it would be similar to that found in LS 5039, and prompt observations with TeV telescopes at phases anti-correlated with the GeV maximum.