AstroSat observation of current outburst of BHXB GX 339-4
ATel #16570; Vaibhav Sharma(Indian Institute of Technology, Kanpur), Akash Garg(IUCAA, Pune), J S Yadav(Indian Institute of Technology, Kanpur), Ranjeev Misra(IUCAA, Pune), Pankaj Jain(Indian Institute of Technology, Kanpur)
on 4 Apr 2024; 17:02 UT
Credential Certification: Akash Garg (akash.garg@iucaa.in)
Subjects: X-ray, Binary, Black Hole, Transient
AstroSat/LAXPC and AstroSat/SXT observed the low-mass black hole X-ray
binary GX 339-4 from MJD 60354.31 (February 14, 2024) to MJD 60355.99
(February 15, 2024) (obs 1) for 40 ksecs and from MJD 60390.39 (March 21,
2024) to MJD 60390.98 (March 21, 2024) (obs 2) for 30 ksecs during its
ongoing outburst reported by Swift/XRT (ATel #16260), MAXI/GSC (ATel #16424),
and NuSTAR (ATel #16425). The joint spectra (LAXPC and SXT) of both
observations were modeled in the energy range of 0.7-20.0 keV with disk and
comptonization components along with the Gaussian iron line. We found the
absorption column density nH to be ~5.7 x 10^21 cm-2. The power law photon
index is 2.11(-0.06,+0.06) for obs 1 and 2.27(-0.23,+0.22) for obs 2. The
inner disc temperature is ~0.85 keV during obs 1, which decreases to ~0.60
keV during obs 2. During obs 1, the unabsorbed flux was ~1.12e-8 erg s-1 cm-2
which decreased to ~3.61e-9 erg s-1 cm-2 during obs 2 in the energy range
0.7-20.0 keV.
We also performed a temporal analysis in the 3.0-30.0 keV energy range. A
low-frequency QPO at ~4.62 Hz with ~5.27% r.m.s. is present along with a
harmonic at ~9.20 Hz with ~3.24% r.m.s. in the power density spectrum during
the obs 1. We could not observe any feature in the power density spectrum
during the obs 2. We thank the AstroSat Time Allocation and operations teams
for quickly responding to the ToO proposal.
