SRG discovery of SRGA J124404.1-632232 = SRGE J124403.8-632231 - possible Galactic X-ray transient

ATel #14357; A. Semena(1), V. Doroshenko (2), V. Arefiev (1), A. Lutovinov (1), C. Maitra(3), I. Mereminskiy (1), S. Molkov (1), A. Rau (3), P. Weber (4), J. Wilms (4) (1: IKI RAS, Moscow, Russia; 2: U. of Tuebingen, Tuebingen, Germany, 3: MPE, Garching, Germany, 4: ECAP and Remeis-Observatory, Bamberg, Germany)
on 29 Jan 2021; 20:00 UT
Credential Certification: Ilya Mereminskiy (i.a.mereminskiy@gmail.com)

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On Jan 27, 2021, during the third consecutive all-sky survey, the Mikhail Pavlinsky ART-XC telescope on board the SRG observatory discovered a bright X-ray source at RA, Dec = 191.0172deg, -63.3756deg (J2000) with a 90% error radius of 25". The source was detected with the X-ray flux of ~10^-11 ergs cm^-2 s^-1 in the 4-12 keV energy band. No sources were detected by ART-XC at that position in the first two surveys in 2020.

Simultaneously, the source was also detected by the SRG/eROSITA telescope, providing an enhanced position of
RA(J2000) = 191.01604deg (12h 44m 3.8s)
DEC(J2000)=-63.37555deg (-63d 22' 32")
with an uncertainty radius of 8" (3 sigma).

Inspection of the previous eROSITA scans over this position found the source to be detected both in eRASS1 (Jan 2020) and eRASS2 (Jul 2020). A joint fit to eROSITA spectra from all three surveys reveals no significant variations in spectral shape, which can be approximated as an absorbed power law with photon index of ~1.4, absorption column of ~2.4x10²² cm^-2, consistent with the Galactic foreground absorption in this direction, and observed flux of 1.5, 0.4, and 3.1x10^-12 ergs cm^-2 s^-1 in 0.2-5 keV energy band respectively.

The eROSITA position is consistent with the bright, reddened NIR/optical star 2MASS 12440380-6322320, for which the GAIA DR3 distance estimate is available (approx. 5.8 kpc, Bailer-Jones et al., 2021). Given the low Galactic latitude of the transient (b=-0.51 degree), and its obscured, hard X-ray spectrum, we tentatively propose it to be the new Galactic HMXB. The source also was detected earlier by Swift/XRT (2SXPS J124403.6-632234, Evans et al., 2020), at a flux level of 2x10^-12 ergs cm^-2 s^-1 in 0.3-10 keV band.

Multiwavelength observations are urged to uncover the nature of this hard transient. Follow-up NuSTAR observations of the source are scheduled for Jan, 30-31.

ART-XC and eROSITA are X-ray telescopes on board the SRG observatory which was launched from the Baikonur cosmodrome on 13 July 2019 by a Proton rocket. ART-XC has been renamed 'Mikhail Pavlinsky ART-XC telescope', after the tragic loss of its former PI, Dr. Mikhail Pavlinsky, who passed away in July 2020.