INTEGRAL and SRG/ART-XC observations of the rise of Swift J1727.8-1613
ATel #16217; R. A. Sunyaev(1, 2), I. A. Mereminskiy (1), S. V. Molkov (1), A. N. Semena (1), V. A. Arefiev (1), R. A. Krivonos(1), V. V. Levin (1), A. A. Lutovinov (1), A. E. Shtykovsky (1), A. Yu. Tkachenko(1) (1: IKI RAS, Moscow, Russia; 2: MPA, Garching, Germany)
on 29 Aug 2023; 18:00 UT
Credential Certification: Ilya Mereminskiy (i.a.mereminskiy@gmail.com)
Subjects: X-ray, Black Hole, Transient
During the routine observations of the Galactic Center region (PI: Sunyaev) INTEGRAL observed the field of the new Galactic X-ray transient Swift J1727.8-1613 (GCN# #34541, #34537, ATel #16205, #16207) - candidate microquasar (ATel #16208, #16211).
First set of data (rev. 2676) was obtained during the rapid rise of the optical emission from the source that was observed by ATLAS (ATel #16209) on 2023-08-20. We obtained an upper limit on the source brightness at the 18 mCrab level (4 sigma, the 30-60 keV energy band). In subsequent observations (over 2023-08-24..26) the source showed a rapid rise in hard X-rays (30-60 keV) from ~400 mCrab up to ~5 Crab.
We have initiated a follow-up observation with the Mikhail Pavlinsky ART-XC telescope onboard the SRG mission. The observation was performed on 2023-08-27 and lasted for approx. 45 ks. The source spectrum is hard and could be described as an absorbed powerlaw with NH=2.3x1021 cm-2 (fixed, ATel #16207) and Γ~1.7 in the 5-15 keV band. In line with Swift/BAT findings (ATel #16215) we also found strong QPO at 0.43 Hz along with low-frequency noise. Presumably, QPO at even lower frequencies (around 0.2 Hz) was seen in the INTEGRAL IBIS and SPI data on 2023-08-26, although more complicated analysis needed to study it in detail.
Additional ToO observations of the source are planned to be performed with ART-XC soon.