MAXI J1348-630: Swift XRT localization, possible periodicity

ATel #12434; J. A. Kennea (PSU) and H. Negoro (Nihon U)
on 27 Jan 2019; 00:49 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)

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Following the reporting of a new X-ray transient, MAXI J1348-630 (Yatabe et al., ATEL #12425), and it's subsequent detection by Swift's Burst Alert Monitor (BAT), as reported by D'Elia et al (GCN #23795 and #23796), Swift performed a 1ks Target of Opportunity observation of this transient in Photon Counting mode, in order to accurately localize it. Analysis of the XRT data find a bright uncatalogued X-ray source the following location: RA/Dec(J2000) = 207.05305, -63.27411,

RA(J2000) = 13h 48m 12.73s,
Dec(J2000) = -63d 16m 26.8s,

with an error radius of 1.7 arc-seconds (90% confidence), this lies 1.9 arc-seconds from the optical transient reported by Denisenko et al. (ATEL #12430), and although the position lies slightly outside of the 90% error region, we believe that this unambiguously confirms that the optical transient is related to MAXI J1348-630. This optical transient is also detected by Swift's UVOT.

Due to the BAT detection reported in GCN #23795, we also have XRT data in Windowed Timing mode. The WT spectra, can be well fit by a power-law spectrum with photon index = 1.32 +/- 0.02, and a flux of 4 x 10^-9 erg/s/cm^2 (0.5 - 10 keV).

In addition we have performed a timing analysis of the WT data, and found evidence of a possible periodicity around 9.8s (or perhaps at 4.9s). The estimated pulse fraction from folding at this period is low (6%). The light-curve folded at 9.8s has a sinusoidal shape, suggesting that MAXI J1348-630 may harbor an X-ray pulsar. Follow-up observations are strongly encouraged in order to determine if this period is real.