Swift Monitoring of the Black Hole Candidate EXO 1846-031
ATel #13344; S. Kim, B. Tetarenko, J. M. Miller (Univ. of Michigan)
on 10 Dec 2019; 15:43 UT
Credential Certification: Jon Miller (jonmm@umich.edu)
Subjects: X-ray, Binary, Black Hole, Transient
We report on X-ray monitoring observations of the X-ray binary and stellar-mass black hole candidate EXO 1846-031, obtained with the Neil Gehrels Swift Observatory. The source was detected to be in outburst with MAXI on 2019-07-23, after 34 years in quiescence (ATEL #12968), and confirmed with Swift (ATEL #12969). Soon thereafter, the source was also detected in radio with the VLA (ATEL #12977) and then MEERKAT (ATEL #12992). A pointed observation with NuSTAR revealed a strong disk reflection spectrum and evidence of a disk wind (ATEL #13012), and observations with NICER revealed Type-C quasi-periodic oscillations (ATELs #12976, #13036). Each of these phenomena is typical of a stellar-mass black hole in outburst.
We are in the process of studying the disk and coronal emission through Swift/XRT monitoring observations of this outburst. The table below details the results of spectral fits with a simple disk blackbody plus power-law model, modified by line-of-sight absorption in the Milky Way, for three example observations:
Date, Exposure, kT, Gamma, Flux
2019-08-17, 1.37 ks, 0.82(4) keV, 2.0(2), 2.6 E-8 erg/cm^2/s
2019-08-18, 1.37 ks, 0.88(3) keV, 2.4(2), 2.1 E-8 erg/cm^2/s
2018-08-25, 1.36 ks, 0.66(7) keV, 2.9(9), 4.3 E-8 erg/cm^2/s
These parameters are broadly consistent with the "steep power-law" or "very high" state. We are continuing to analyze the monitoring observations and expect to report on the evolution of the disk and corona in EXO 1846-031 in a future paper.
