MAXI J0636+146: Swift/XRT localization
ATel #9710; J. A. Kennea (PSU), P. A. Evans, A. P. Beardmore (U Leicester), H. A. Krimm (CRESST/GSFC/USRA), P. Romano (INAF-IASFPA), K. Yamaoka (Nagoya U.), M. Serino (RIKEN) and H. Negoro (Nihon U.)
on 4 Nov 2016; 14:25 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Subjects: X-ray, Transient
As a result of the MAXI discovery of a new transient source, MAXI J0636+146 (Negoro et al., ATEL #9707), Swift performed a target-of-opportunity observation of the MAXI error region starting at 06:12 on November 4, 2016, approximately 4 hours after the MAXI trigger. In order to cover the MAXI error region, Swift performed a 7-point tiling observation, with approximately 300s exposure per tile. In these data we find a bright, X-ray point source at the following coordinates: RA/Dec(J2000) = 99.35075, 14.63145, which is equivalent to:
RA(J2000) = 06h 37m 24.18s,
Dec(J2000) = +14d 37m 53.2s,
with an estimated error of 2.5 arc-seconds radius (90% confidence). This position lies inside of the reported MAXI error ellipse. The position does not match the position of any previously catalogued X-ray point source in a search of the Simbad database. An optical source with V=14.9 lies 5.6 arc-seonds away from the X-ray localization, outside of the error radius, and no optical counterpart is detected in UVOT u-band imaging that is consistent with the XRT error region.
The X-ray source is moderately bright, with an XRT count rate of 0.46 +/- 0.06 count/s. The spectrum is well fit by an absorbed power-law model, with photon index = 2.6 +/- 0.8 and N_H consistent with the Galactic value of 4.5 x 10^21 cm^-1 (Willingale et al., 2013). The model fitted observed flux is 1.5 x 10-11 erg/s/cm2 (0.5 - 10 keV). Although this is significantly fainter than the MAXI peak flux of 51 +/- 13 mCrab (4.0-10 keV), the source was seen to fade rapidly by MAXI, so this lower flux is consistent with this.
Follow-up observations of this object are encouraged in order to determine the source type.