On the Nature of the Hard X-Ray Source IGR J2018+4043
Kennea, J. A.; Terrier, R.; Rauw, G.; Hermsen, W.; De Becker, M.; Pavlov, G. G.; Renaud, M.; Bykov, A. M.; Krassilchtchikov, A. M.; Uvarov, Yu. A.; Bloemen, H.; Lebrun, F.; Swings, J. -P.; Kaastra, J.; Dubner, G. M.; Giacani, E. B.
Russia, United States, Argentina, Netherlands, France, Belgium
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+0.7-0.8×10-12 ergs cm-2 s-1 (90% confidence level) at α=20h18m38.55 s, δ=+40deg41'00.4" (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+3.2-2.2×1022 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.