Swift X-ray monitoring observations of the Galactic center have resumed after Sun constraints
ATel #16436; N. Degenaar, R. Wijnands (University of Amsterdam), M. T. Reynolds (Ohio State University, University of Michigan), J. M. Miller (University of Michigan), J. A. Kennea (Penn State University), on behalf of a larger collaboration
on 9 Feb 2024; 08:28 UT
Credential Certification: Nathalie Degenaar (degenaar@uva.nl)
Subjects: X-ray, Binary, Black Hole, Neutron Star, Transient
Starting on 2024 February 3, Swift resumed X-ray monitoring of the Galactic center through daily 1.0-ks exposures (for a description of the program, see Degenaar et al. 2015, JHEA 7, 137). Within the ~20x20 arcmin region around Sgr A* covered by our campaign, the only X-ray transient that is currently active is AX J1745.6-2901.
The bursting and eclipsing neutron star low-mass X-ray binary AX J1745.6-2901 is located approximately 1.5 arcmin to the southwest of the supermassive black hole Sgr A*. In the 1-ks exposure taken on February 3, it is detected at a net count rate of 0.12 +/- 0.01 c s-1 and has an X-ray spectrum that can be described by an absorbed power law model with a power-law index of 1.24 +/- 0.37 (for a fixed absorption column density of 2E23 cm-2). The resulting 2-10 keV unabsorbed flux is (3.53 +0.13 -1.4)e-11 erg cm-2 s-1. For an assumed distance of 8 kpc, this translates into a luminosity of 2.7e35 erg s-1.
AX J1745.6-2901 started a new outburst in 2023 June (ATel #16106) and remained active in the XRT monitoring data since. Several long outbursts reaching up to 2-10 keV luminosities of several times e36 erg s-1 and lasting many months/years have been seen from this transient over the past 2 decades (e.g., Degenaar et al. 2015; ATels #14378, #9196).
Our daily Swift/XRT observations of the Galactic center are continuing and quick-look results are immediately posted at the Swift Sgr A* Monitoring Campaign Website: http://www.swift-sgra.com
