SRG discovery of SRGA J181414.6-225604 == SRGe J181415.1-225617 - possible Galactic X-ray transient

ATel #14510; I. Mereminskiy(1), A. Semena(1), A. Lutovinov(1), S. Molkov(1), A. Tkachenko(1), M. Gilfanov(1, 2), P. Medvedev(1), R. Sunyaev (1, 2) (1: IKI RAS, Moscow, Russia; 2: MPA, Garching, Germany)
on 4 Apr 2021; 21:33 UT
Credential Certification: Ilya Mereminskiy (i.a.mereminskiy@gmail.com)

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On Apr 1, 2021, during the third SRG all-sky survey, the Mikhail Pavlinsky ART-XC telescope on board the SRG observatory discovered a bright X-ray source at RA, Dec = 273.5611, -22.9345 (J2000) with a 90% error radius of 15". The source was detected with the X-ray flux of ~4x10^-11 ergs cm^-2 s^-1 in the 4-12 keV energy band. No objects were detected by ART-XC at that position in the first two surveys in 2020.

Simultaneously, the source was also detected by SRG/eROSITA, which provided an improved position at 273.56301, -22.93807 (J2000), with an uncertainty radius of 9" (95%). The eROSITA data suggest a fairly absorbed and hard spectrum with NH=1.4x10²² (error interval of (0.1-4.6)x10²² at 90% confidence), photon index Gamma=0.5 (error interval of -0.9 - 2.7) and 0.5-6 keV flux of ~6.4x10^-12, compatible with the hard X-ray flux, observed by ART-XC.

A faint absorbed source with several times smaller flux was also found at this position in the SRG/eROSITA data of the first two sky surveys.

Given the absorption and location of the source close to the Galactic bulge we tentatively propose the source to be a Galactic X-ray binary.

We note also that there is an archival X-ray source in XMM-Newton slew survey (XMM-SSC, 2017), labelled as XMMSL2 J181414.6-225613, located in 8" from the derived position, inside the eROSITA 95% localization region. The source was observed once in 2010 at a flux level of 3x10^-12 erg cm^-2 s^-1 in the 0.2-12 keV band.

There are several IR and optical sources of different magnitudes inside the eROSITA localization region. Additionally, according to the GAIA data there are no local sources with estimated distances below few kpc, implying that the intrinsic luminosity of the source is about 10³⁴ erg s^-1 or higher.

Multiwavelength observations are urged to uncover the nature of this hard transient. We will organize X-ray and optical observations as soon as there will be visibility.

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 the Proton rocket. ART-XC has been renamed 'Mikhail Pavlinsky ART-XC telescope' in honor of its first PI, Dr. Mikhail Pavlinsky, who passed away in July 2020.