ON THE NATURE OF THE HARD X-RAY SOURCE IGR J2018+4043

摘要

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) x 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) x 10~(-12) ergs cm~(-2) s~(-1) (90% confidence level) at α = 20~h18~m38.55~s, 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 N_H = 6.1_(2.2)~(+3.2) x 10~(22) 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.