MAXI J1727-203: Swift observation

ATel #11697; J. A. Kennea (PSU), A. Bahramian (Curtin), A. P. Beardmore (Leicester)
on 7 Jun 2018; 15:41 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)

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Starting on 06:55UT on June 7th, 2018, Swift began at target of opportunity of the likely black-hole candidate, MAXI J1727-203 (ATEL #11683, #11689, #11690, #11691, #11692, #11696). In 970s of Windowed Timing mode data, we detect a bright point source at a location consistent with the optical counterpart reported by GROND (ATEL #11690), confirming that that source is indeed MAXI J1723-203.

The Swift spectrum can be well fit by an absorbed power-law model plus a disk blackbody. The fitted parameters are N_H = 0.44 +/- 0.03 x 10²³ cm^-2, photon index = 2.5 +/- 0.2 and kT_in = 0.46 +/- 0.01. We note that these spectral parameters are similar to those reported from a NICER observation on June 5th, 2018, although with a hotter disk temperature.

Unfortunately the source lies partially outside of the WT field of view, making accurate estimation of the flux problematic, however, assuming the optical position and correcting for the missing part of the PSF, we find an X-ray flux of 3.9 x 10^-9 erg/s/cm² (0.5 - 10 keV, uncorrected for absorption).

Timing analysis of the XRT data shows no obvious signs of QPOs or periodicities.

The optical counterpart of MAXI J1727-203 is detected by UVOT, in all three filters in which it was observed, at v = 16.64 +/- 0.06, b = 17.05 +/- 0.05 and u = 17.42 +/- 0.05 (AB system).

Further observations are encouraged.