2nd XRISM follow-up observation of the black hole X-ray binary GS 1354-64
ATel #17697; D. Miura (U. of Tokyo), K. Fukushima, Y. Kanemaru, S. Ogawa, Y. Uchida, T. Yoneyama (JAXA/ISAS), C. Baluta (NASA/GSFC), Y. Terada (Saitama U.), E. Costantini (SRON), M. Guainazzi (ESA/ESTEC), R. Kelley (NASA/GSFC), K. Matsushita (TUS), R. Petre, B. Williams (NASA/GSFC), H. Yamaguchi, S. Watanabe (JAXA/ISAS), M. Tashiro (Saitama U.)
on 24 Feb 2026; 05:24 UT
Credential Certification: Kotaro Fukushima (kxfukushima@gmail.com)
Subjects: X-ray, Black Hole, Transient
Referred to by ATel #: 17724
XRISM has observed the black hole X-ray binary GS 1354-64 from 2026-02-19T17:24:00 to 2026-02-20T21:14:00 (UTC), using 49 ks exposure time in the Director's Discretionary Time (DDT) allocation for XRISM Cycle 2.
MAXI/GSC found a new outburst for this target on 2025-12-25 (ATel #17563). Since then, multi-wavelength follow-up observations were carried out (ATels #17582, #17583, #17586, #17611, #17612, #17618). XRISM observed GS 1354-64 as a DDT target from 2026-01-20T03:37:00 to 2026-01-23T04:00:00 (ATel #17625). After the XRISM follow-up observation, the transition to the soft state has been confirmed for this source (ATels #17638, #17650, #17673). Then, the second DDT observation of GS 1354-64 was requested and carried out as above.
We fit the 1.8–12 keV Resolve spectrum, extracted from quick-look events, with TBabs × (diskbb + powerlaw) and determine the disc temperature to be kTin = 1.032 +/- 0.011 keV, and the power-law index to be Γ = 2.683 +/- 0.017, with an unabsorbed X-ray flux of F2–13 keV = (5.634 +/- 0.005) × 10-9 erg s-1cm-2. The absorption column density is fixed as NH = 1.40 × 1022 cm-2 (ATel #17583). The current total flux is substantially contributed by the disc component at about 30%, whereas previous XRISM observation indicated a mere fraction of about 3%.
Follow-up observations are encouraged.
