MAXI J1816-195: Swift Localization of this new transient
ATel #15421; J. A. Kennea (PSU), P. A. Evans (Leicester), H. Negoro (Nihon U.)
on 7 Jun 2022; 21:32 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Subjects: X-ray, Transient
Referred to by ATel #: 15425, 15426, 15427, 15431, 15437, 15445, 15458, 15467, 15470, 15481, 15769
MAXI reported the detection of a new transient source, MAXI J1816-195 on 2022 June 7 (ATEL #15418). In order to confirm and localize the transient, beginning 15:56:05UT on 2022 June 7, Swift performed a TOO observation consisting on 4 pointings to cover the MAXI error region, each consisting on 250s exposure in Photon Counting mode. A bright X-ray source was detected in the overlapping regions of two of these tiles at the following location, RA/Dec(J2000) = 274.20671, -19.63306, which is equivalent to:
RA(J2000) = 18h 16m 49.61s
Dec(J2000) = -19d 37m 59.0s,
with an estimated uncertainty of 3.7 arc-seconds radius (90% confidence). This location does not lie at the location of any known catalogued X-ray source, therefore we agree that this is a new transient source MAXI J1816-195. In addition, archival observations by Swift/XRT of this region taken in 2017 June 22, do not reveal any point source at this location, with an 3-sigma upper limit of 0.004 XRT counts/s.
We note that this source lies 8.4 arc-minutes from the source IGR J18172-1944, although typical errors on INTEGRAL sources are usually smaller, suggesting that this may be unrelated to the MAXI source.
The PC mode spectrum is well fit by an absorbed power-law with photon index = 1.3 +/- 0.2, with absorption N_H = 2.6 +/- 0.5 x 10^22 cm^-2. The flux uncorrected for absorption is 4.4 +/- 0.4 x 10^-9 erg/s/cm^2 (0.3 - 10 keV). During the two observations in which the target was observed, it shows evidence of linear brightening from 37 XRT count/s to 55 XRT count/s. Further observations will be needed to confirm this trend.
We do not detect the source in UVOT, and several stars are consistent with the localization, so we encourage follow-up to determine optical/IR counterparts.
Further observations of this transient by Swift are planned.
