Continued Swift Monitoring of the Stellar-mass Black Hole GX 339-4
ATel #17653; J. M. Miller, I. Chan, I. Dumitrascu, M. Lopez (Univ. of Michigan)
on 8 Feb 2026; 16:46 UT
Credential Certification: Jon Miller (jonmm@umich.edu)
Subjects: X-ray, Binary, Black Hole, Transient
GX 339-4 is a stellar-mass black hole that has recently been observed
in a hard state outburst (ATEL #17484). We report on the most recent X-ray
monitoring observation with the Neil Gehrels Swift Observatory. ObsID
00016552122 started on February 4, 2026, at 08:03:07 UTC. A total
exposure of 640 seconds was obtained using the XRT, operated in
"windowed timing" mode. We derived a spectrum and response files in
the standard manner, grouped the data to require at least 15 counts
per bin, and made simple fits across the 0.7-10.0 keV band using XSPEC.
Fits to the spectrum with an absorbed power-law model give a column
density of N_H = 6 +/- 1 E+21 cm^-2, a photon index of Gamma = 1.4 +/-
0.1, and a normalization of 2.1 +/- 0.3 E-3 ph/cm^2/s/keV at 1 keV.
This translates to an absorbed flux of 1.6 +/- 0.2 E-10 erg/cm^2/s
(0.5-10.0 keV), or an unabsorbed flux of 1.9 E-10 erg/cm^2/s.
Assuming a distance of 8 kpc, this corresponds to a luminosity of L =
1.5 +/- 0.1 E+36 erg/s. For a black hole mass of 5.8 solar masses
(Hynes et al. 2003), this corresponds to an Eddington fraction of
0.002.
The source continues a slow decay through the low/hard state.
References
Hynes, R., et al., 2003, ApJ, 583, L95
