INTEGRAL detection of past hard X-ray activity from SRGA J144459.2-60420 before its discovery
ATel #16493; Vito Sguera (INAF-OAS Bologna, Italy), Lara Sidoli (INAF-IASF Milano, Italy)
on 29 Feb 2024; 10:20 UT
Credential Certification: Lara Sidoli (sidoli@lambrate.inaf.it)
Subjects: X-ray, Transient
Referred to by ATel #: 16507
Following the report of the discovery of SRGA J144459.2-60420 on 21 Feb 2024 by the Mikhail Pavlinsky ART-XC telescope onboard the SRG observatory (ATel #16464), we analyzed INTEGRAL data searching for eventual hard X-ray activity during a few months before its discovery. We found out that the source was already active in December 2023, as significantly detected by INTEGRAL during observations performed from 15 to 16 Dec 2023, for an effective on-source exposure time of 3.2 ks. The source was detected at 7.2 sigma level (25-60 keV) with an average flux of 25.0+/-3.5 mCrab. No detection was obtained in the higher energy band 60-100 keV, and the relative 3 sigma upper limit is 32 mCrab. The IBIS/ISGRI spectrum is best fit by a power law model with photon index equal to 3.3(+1.3,-1), the corresponding 25-60 keV (18-60 keV) flux is 1.8E-10 erg cmE-2 sE-1 (3.3E-10 erg cmE-2 sE-1). The timing of this hard X-ray activity is in agreement with the 2-10 keV detection by MAXI/GSC from 9 to 14 Dec 2023 (ATel #16483).
