SRGt J071522.1-191609: SRG/eROSITA discovery of a bright transient X-ray source

ATel #13657; A. Gokus (ECAP/FAU), A. Rau (MPE), J. Wilms (ECAP/FAU), L. Ducci (IAAT), O. Koenig, P. Weber (both ECAP/FAU), Th. Boller, A. Malyali (both MPE)
on 23 Apr 2020; 20:30 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Arne Rau (arau@mpe.mpg.de)

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During the first all-sky survey (eRASS:1), the eROSITA instrument on board the Russian/German Spektrum-Roentgen-Gamma (SRG) mission discovered a new, bright X-ray source, SRGt J071522.1-191609, localized to

RA(J2000) = 07:15:22.15
Dec(J2000) = -19:16:09.4

with an estimated uncertainty of 5" radius (incl. systematics).

The discovery was made by the eROSITA Near-Real Time Analysis Transit Search when the position entered the eROSITA Field of View for the first time on 2020-04-19 at UTC 01:28 hours (MJD 58958.06). The source remained at constant brightness (0.2-10 keV countrate ~1.3 cnt/s) during the following four scans over the position until 2020-04-19 17:30 hours (MJD 58958.73).

The X-ray spectrum with a total exposure of 243s can be described equally well by an absorbed power-law model with a slope of 2.1+/-0.6 and N_H=(11.7+/-1.1) x 10^21 cm^-2. and an absorbed disk-blackbody model with kT=1.3+/-0.5 keV and N_H=(7.5+/-1.8) x10^21 cm^-2 (uncertainties are given at 90% confidence level.) The equivalent neutral Hydrogen column density is roughly consistent with the Galactic foreground value towards this position (7.2 x10^21 cm^-2; HI4PI Collaboration, N. Ben Bekhti et al., 2016).

The resulting fluxes in the 0.2-2 keV and 0.2-10 keV bands are 2.6+/-0.3) x10^-12 erg/cm^2/s^1 and 1.3+/-0.4) x10^-11 erg/cm^2/s^1, respectively. No source was detected at this position during the ROSAT all-sky survey with an 0.2-2keV upper limit of 4.2 x10^-13 erg cm^{-2} s^{-1}, assuming the best-fit parameters from the power law fit. This suggests a brightening by at least a factor of ~ 12 since the ROSAT all-sky survey nearly 30 years ago. Upper limits where calculated using http://xmmuls.esac.esa.int/upperlimitserver/.

No obvious candidate optical counterpart was identified in archival optical and near-IR observations. As the nature of the transient remains open, we strongly encourage multi-wavelength follow-up observations.