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Swift/XRT confirmation of HD 347929/1RXS J180724.2+194217 in X-ray outburst

ATEL # 2701; J. A. Kennea (PSU), K. Yamoaka (Aoyama Gakuin U.), H. Krimm (CRESST/GSFC/USRA), P. Curran (UCL-MSSL), V. Mangano (INAF-IASFPA), P. Romano (INAF-IASFPA) and P. Evans (U. Leicester)
on 29 Jun 2010; 3:53 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Jamie A. Kennea (

Subjects: X-ray, Transients

At 00:13UT on June 29th, 2010 Swift/XRT began a 1ks target of opportunity observation of the field of a MAXI reported transient (Usui et al., ATEL #2700). We find inside the MAXI error circle a single bright X-ray source, at the coordinates, RA, Dec (J2000) = 271.8506, +19.7055, which is equivalent to:

RA(J2000) = 18h 07m 24.15s,
Dec(J2000) = +19d 42m 20.0s,

with an estimated uncertainty of 3.5 arc-seconds radius (90% confidence). This location lies 10.6 arc-minutes from the center of the 12 arcminute MAXI error circle, and 3.1 arcseconds from HD 347929 (AKA 1RXS J180724.2+194217), reported to be a possible RS CVn type star, confirming the counterpart of this MAXI X-ray transient proposed by Usui et al. (ATEL #2700).

The spectrum of the source is well fit by a absorbed power-law model, with a photon index of 2.3 +/- 0.25 and a absorption column of 1.8 +/- 0.6 x 1021 cm-2. slightly in excess of the expected galactic value of 6.63 x 1020 cm-2 (Kalberla et al. 2005). The lightcurve shows no significant variability during the XRT observation. The fitted flux of the source is 7.8 +/- 0.8 x 10-11 erg/cm2/s (0.3-10 keV, uncorrected for absorption), and approximately 1.3 x 10-11 erg/cm2/s (0.3-10 keV) corrected for absorption, approximately 5 times brighter than the flux of 1RXS J180724.2+194217 reported in the ROSAT All-Sky Bright Source Catalogue (Voges et al., 1999). 

Analysis of these data were performed using the techniques described by Evans et al. (2009, MNRAS, 2009, 397, 1177).

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