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A radio galaxy as possible counterpart of IGR J21247+5058

ATel #235; M. Ribo (CEA Saclay, France), J. A. Combi (IAR, Argentina), I. F. Mirabel (CEA Saclay, France and IAFE-CONICET, Argentina)
on 15 Feb 2004; 20:50 UT
Credential Certification: Marc Ribo (mribo@discovery.saclay.cea.fr)

Subjects: Radio, Infra-Red, Optical, X-ray, Gamma Ray, AGN, Binary, Black Hole, Quasar

Within the 2 arcmin-radius position error circle of the recently discovered INTEGRAL source IGR J21247+5058 (ATEL #229) is located the core of the bright radio source 4C 50.55 (also known as GPSR 93.319+0.394, KR2, NRAO 659 or BG 2122+50, among other names). The core has a flat radio spectrum with a peak flux density of 237 mJy/beam at 1.4 GHz. It is at the center of an elongated structure of 10 x 3 arcmin that ends in two large radio lobes that have peak flux densities of 288 mJy/beam (NW) and 92 mJy/beam (SE), and spectral indexes alpha~-0.6 (where S_nu is proportional to nu^+alpha), compatible with optically thin synchrotron radiation (see NVSS contour plot). The morphology of 4C 50.55 is typical of a radio galaxy, and the comparison among published radio data shows no significant changes in flux and morphology during the last 30 years. These properties are consistent with an extragalactic source, although, to our knowledge, no conclusive optical counterpart of a galaxy host has ever been reported, probably due to its location close to the Galactic plane (l=+93.32, b=+0.39).

The estimated J2000.0 ICRS position of the radio core from the NVSS map and data in the literature is RA=21h24m39.3s (+/-0.1s), DEC=+50d58'26" (+/-1"). Coincident with this position there is the IR source 2MASS 21243932+5058259 (see K-band 2MASS plot), with coordinates RA=21h24m39.32784s, DEC=+50d58'25.9284", and magnitudes J=13.27, H=12.38, K=11.37. The optical counterpart of this IR source has average magnitudes B=16.9 and R=15.1 in the USNO B1.0 catalog. The photometry of the IR/optical counterpart is not compatible with a stellar spectrum. There is no catalogued ROSAT or EGRET source coincident with IGR J21247+5058. Optical and X-ray observations are planned to confirm the extragalactic nature of the source and to study its spectrum in softer X-rays.