SRG/ART-XC detection of the possible new outburst of AX J1820.5-1434

ATel #18082; I. Mereminskiy(1), A. Semena(1), A. Lutovinov(1), S. Molkov(1), A. Tkachenko(1) (1:IKI RAS, Moscow)
on 29 Sep 2026; 13:22 UT
Credential Certification: Andrey Semena (san@iki.rssi.ru)

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During the observations of the Galactic Plane on Sept. 28, 2026, the Mikhail Pavlinsky ART-XC telescope onboard the SRG observatory detected a bright X-ray source at the position of RA, Dec = 275.1232, -14.5692 (estimated 90% containment radius of 10''), with the observed X-ray flux in 4-12 keV of (7.9+-0.2)x10^-11 erg cm-2 s-1. No sources were detected in this region during previous all-sky surveys by the ART-XC, indicating a brightening of at least an order of magnitude.

Next to the boundary of the error region, at 15” offset, there is a known heavily absorbed transient HMXB AX J1820.5-1434, previous detection of this source at similar fluxes was in 2018, when it was observed by Swift/XRT. Given the positional coincidence and strong variability we tentatively identify the ART-XC detection as a new outburst of AX J1820.5-1434, although additional observations are needed to confirm the association.

We encourage follow-up X-ray and NIR-IR observations of this interesting source.

The Mikhail Pavlinsky ART-XC telescope is the X-ray telescope on board the SRG observatory which was launched from the Baikonur cosmodrome on 13 July 2019 by the Proton rocket.