Swift Observations of the Stellar-mass Black Hole GS 1354-645 in Outburst
ATel #17583; Jon M. Miller (Univ. of Michigan)
on 7 Jan 2026; 18:10 UT
Credential Certification: Jon Miller (jonmm@umich.edu)
Subjects: X-ray, Binary, Black Hole
GS 1354-645 is a transient X-ray binary system that harbors a
stellar-mass black hole. Following recent MAXI reports of renewed
activity in this source (ATEL #17563), Swift rapidly observed the
target to verify the outburst. Observations started on January 7,
2026 at 01:01:03 UTC.
The XRT observation was obtained in photon counting mode, and the
image reveals a bright source at the known position of GS 1354-645.
The source is bright enough to cause significant photon pile-up.
Extracting events from a region that excludes the central 18 arc
seconds of the event distribution still results in a sensitive
spectrum with over 4000 counts in 704 s of exposure.
Fits to the XRT spectrum suggest a column density of NH = 1.4 +/- 0.2
E+22 cm^-2, an inner disk temperature of kT = 0.18 +/- 0.02 keV, and a
flux of F = 2.9 E-9 erg/cm^2/s (0.5-10 keV) for an assumed power-law
index of Gamma = 1.40.
MeerKAT has also detected radio emission from GS 1354-645 (ATEL
#17582). It is likely that the source is in a rising hard state.
