Swift confirms HD 347929/1RXS J180724.2+194217 in X-ray outburst
ATel #5078; J. A. Kennea (PSU), P. A. Evans, A. P. Beardmore (Leicester), H. Krimm (CRESST/GSFC/USRA), P. Curran (Curtin), V. Mangano, P. Romano (INAF-IASFPA), H. Negoro (Nihon U), K. Yamaoka (Nagoya U)
on 21 May 2013; 02:54 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Subjects: X-ray, Star, Transient
We report on Swift follow-up observations of the MAXI detected transient (MAXI J1807+196; Negoro et al., ATEL #5057), tentatively associated with HD 347929/1RXS J180724.2+194217. Swift performed a 4-point tiling observation to cover the MAXI error circle, beginning May 20th, 2013 @ 18:30UT. All 4 fields were taken in Photon Counting mode with exposure times of 500s each. In one field we find a bright, piled-up source at the following location: RA/Dec(J2000) = 271.85049, 19.70624, which is equivalent to:
RA (J2000): 18h 07m 24.12s
Dec (J2000): +19d 42' 22.5''
with an estimate error of 2.2 arc-seconds radius (90% confidence). This position lies 0.4 arc-seconds from HD 347929/1RXS J180724.2+194217.
The pile-up corrected spectrum can be well fit with a power-law model, with photon index 1.9 +/- 0.2. The fitted column density is 0.8 +/- 0.4 x 1021 cm-2, consistent with the Galactic value (Kalberla et al. 2005). The flux in the 0.3-10 keV band is 3.1 +/- 0.3 x 10-10 erg cm2 s-1. We note that MAXI and Swift previously observed this source in outburst in 2010 (Kennea et al., ATEL #2701, Usui et al., ATEL #2700). The 2013 Swift/XRT flux is approximately four times higher than that observed in 2010 and ~20 times the ROSAT flux, showing that the source is clearly in outburst. There is no evidence of variability over the 500s observation
We find no other bright point sources in the MAXI error circle, and therefore conclude that MAXI J1807+196 is indeed HD 347929/1RXS J180724.2+194217, which is reported to be a possible RS CVn type star.