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A soft X-ray flare from XMMSL1 J202406.4+260926

ATel #3485; Richard Saxton (XMM SOC / ESAC, Madrid Spain), Andrew Read (Leicester University, U. K.), Pilar Esquej (Centro de Astrobiologia, CSIC-INTA, Torrejon de Ardoz, Spain)
on 15 Jul 2011; 07:23 UT
Credential Certification: Richard Saxton (richard.saxton@sciops.esa.int)

Subjects: X-ray, Request for Observations, Transient

We report the discovery of a large, 15 ct/s, soft X-ray flux from XMMSL1 J202406.4+260926 in an XMM-Newton slew on May 22nd 2011. The source position, RA:20 24 06.4 DEC:+26 09 26 (1-sigma error radius of 8") has been observed in two earlier slews in 2005 and 2009, without detecting the source (upper limits of 0.8 and 0.7 ct/s respectively). A very faint object, 1RXS J202406.6+260918, is catalogued in the ROSAT ALL-Sky Survey with a count rate of 0.032 c/s, which equates to a flux 60x fainter than that seen on May 22nd. A rudimentary slew spectrum, made from the 70 photons of the XMM-Newton slew detection, is consistent with a background AGN but only if the intrinsic flux (0.2-2 keV) is high (1-2x10E-10 ergs/s/cm2) and the power-law slope quite steep (2.7-4.1). We consider it more likely that the source lies in our galaxy, and tentatively identify it with the brightest optical object in the error circle, USNO-B1.0 1161-0489239, with B1 mag=14.55, R1 mag=12.96. We welcome further observations, particulary with optical telescopes, to ascertain the true nature of the object.