MAXI J0637-430 Not Detected by Swift in X-rays
ATel #13800; John A. Tomsick (UCB/SSL) & Hadar Lazar (UCB/SSL)
on 11 Jun 2020; 19:27 UT
Credential Certification: John A. Tomsick (jtomsick@ssl.berkeley.edu)
Subjects: X-ray, Black Hole, Transient
Following the report of a decline in the optical bandpass for the black hole candidate X-ray transient MAXI J0637-430 (Johar et al., ATEL#13779), we triggered a Swift X-ray Telescope (XRT) observation, which was carried out on 2020 June 10th. The XRT observation started at 16.0 h UT, and an exposure of 2040 seconds was obtained. The source was not detected, and the 90% confidence upper limit on the 0.5-10 keV flux is <1x10^-13 erg/cm2/s.
The previous Swift/XRT observation took place on April 16th, and the energy spectrum is well-described by a power-law. Assuming the low column density of ~3x10^20 cm-2 previously reported for MAXI J0637-430 (Thomas et al., ATEL#
13296), we find a power-law photon index of Gamma = 1.7+/-0.3 and a 0.5-10 keV flux of (2.0+0.6-0.4)x10^-12 erg/cm2/s on April 16th (90% confidence errors are given).
Thus, like the optical flux, the X-ray flux has dropped dramatically. Specifically, the X-ray flux has dropped by at least a factor of 15-20 in the past 2 months, and MAXI J0637-430 may be at or approaching its quiescent level.
We thank the Swift operations teams for support with the execution of these observations.
