On the Nature of the Hard X-Ray Source IGR J2018+4043

Abstract

We found a very likely counterpart to the recently discovered hard X-ray source IGR J2018+4043 in the multiwavelength observations of the source field. The source, originally discovered in the 20-40 keV band, is now confidently detected also in the 40-80 keV band, with a flux of (1.4 ± 0.4) × 10-11 ergs cm-2 s-1. A 5 ks Swift observation of the IGR J2018+4043 field revealed a hard pointlike source with an observed 0.5-10 keV flux of 3.4-0.8+0.7 × 10-12 ergs cm-2 s-1 (90% confidence level) at α = 20 h18m38.s55, δ = +40°41′00. ″4 (with a 4.″2 uncertainty). The combined Swift-INTEGRAL spectrum can be described by an absorbed power-law model with photon index Γ = 1.3 ± 0.2 and NH = 6.1-2.2+3.2 × 1022 cm-2. In archival optical and infrared data we found a slightly extended and highly absorbed object at the Swift source position. There is also an extended VLA 1.4 GHz source peaked at a beamwidth distance from the optical and X-ray positions. The observed morphology and multiwavelength spectra of IGR J2018+4043 are consistent with those expected for an obscured accreting object, i.e., an AGN or a Galactic X-ray binary. The identification suggests possible connection of IGR J2018+4043 to the bright γ-ray source GEV J2020+4023 detected by COS B and CGRO EGRET. © 2006. The American Astronomical Society. All rights reserved.