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Optical and X-ray Observations of IGR J20187+4041 in the Error Circle of the Variable AGILE Source in Cygnus

ATel #1498; J. P. Halpern (Columbia U.)
on 29 Apr 2008; 23:52 UT
Credential Certification: Jules Halpern (jules@astro.columbia.edu)

Subjects: Optical, X-ray, AGN

Referred to by ATel #: 1518, 1547, 1584, 1585, 1597, 1623

With regard to the galaxy 2MASX J20183871+4041003 that was mentioned by Longo et al. (ATel #1492) in connection with a variable AGILE source, I note that this galaxy was first identified with the INTEGRAL source IGR J2018+4043 (=IGR J20187+4041) by Kennea et al. (ATel #788) and Bykov et al. (2006, ApJ, 649, L21) using the Swift XRT. (See also Ajello et al., ATel #1497). While these authors noted the proximity of the unidentified EGRET source 3EG J2020+4017, the galaxy is actually outside the EGRET error box. The claim by Bykov et al. that 2MASX J20183871+404100 has blazar-like characteristics, which was repeated by Iyudin et al. (2007, A&A, 468, 919), is not based on any physical property of the galaxy. In particular, it does not host a compact radio source, and other defining blazar signatures such as polarized optical continuum and high-amplitude variability have not been reported. The hypothesis that 2MASX J20183871+4041003 is a blazar because of its association with 3EG J2020+4017 is circular. While the variable AGILE source may or may not be identical to 3EG J2020+4017, a relationship of the AGILE source to 2MASX J20183871+4041003 is problematic for similar reasons.

I obtained an I-band image of 2MASX J20183871+4041003 on the MDM 2.4m telescope (see link below) on 2006 June 29. Despite partly cloudy conditions and Galactic extinction AI~4, a bulge and disk are clearly resolved, indicating that it is probably a nearby (z<0.1) Seyfert galaxy. In contrast, blazars are normally found in elliptical galaxies. In particular, this bright galaxy cannot be at z=1.5+/-0.2 as concluded by Iyudin et al. (2007). Optical and/or IR spectra are needed to determine the classification and redshift of 2MASX J20183871+4041003.

A new Swift XRT observation of IGR J20187+4041 was obtained on 2008 April 29. In 1880 s of quicklook data I measure a count rate of 0.026+/-0.004 s^-1 from 2MASX J20183871+404100, consistent with 0.021+/-0.002 s^-1 measured by Bykov et al. in 2006 March. Thus, there is no X-ray evidence of current blazar activity from this source.

Optical Image