Swift GC monitoring program detection of low luminosity outburst a new source: Swift J174610-290018

ATel #16481; Mark Reynolds (Ohio State/U. Michigan), Natalie Degenaar (U. Amsterdam), Rudy Wijnands (U. Amsterdam), Jon Miller (U. Michigan), Jamie Kennea (Penn State) on behalf of a larger collaboration.
on 24 Feb 2024; 02:35 UT
Credential Certification: Mark Reynolds (reynolds.1362@osu.edu)

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In a 0.92 ks Neil-Gehrels Swift/XRT observation of the Galactic center (Degenaar et al. 2013, 2015) on 2024 Feb 22nd (20:33 UT), excess point-like X-ray emission is detected at a position of
ra : 17 46 10.4
dec: -29 00 17.6
with a 90% uncertainty radius of 5". We denote this source Swift J174610-290018.

Source counts are extracted from a 18" radius circular region centered on the source position, with background extracted from a neighboring source free region. Due to the intrinsic faintness of the source (~24 net counts), we carry out a restricted spectral fit. When characterized with a powerlaw (tbabs*pow with Nh == 20e22 cm^-2; Gamma == 1.8), an observed flux of fx = (6.1 +\- 2.4)e-12 erg/s/cm2 (90% conf, 2-10 keV) is measured. For an assumed distance of 8 kpc, this corresponds to a luminosity of Lx ~ 4.7e34 erg/s.

Two cataloged X-ray sources lie near this position as reported in the Chandra source catalog (Evans et al. 2010). These are CXO J174610.7-290019 (at a separation of 4.3") with a flux of fx = (9 +0.1 -1.3)e-15 erg/s/cm2 (0.5 - 7.0 keV) and 2CXO J174609.8-290010 at a separation of 10.4" and with a flux of fx = (1.7 +\- 0.4)e-14 erg/s/cm2 (0.5 - 7.0 keV). XMM-Newton has also detected a variable source near this position on multiple occasions: 4XMM J174610.7-290020 (at a separation of 5-6", Webb et al. 2020), with fluxes varying from fx ~ (9.1 +\- 0.2)e-13 erg/s/cm2 -- (8.9 +\- 0.9)e-15 erg/s/cm2 (0.2 - 12.0 keV). These source fluxes are >10x lower than what we measure for Swift J174610-290018.

The current detection is the first detection of a source at this position by Swift, and suggests an outburst may be underway. Given the separation w.r.t. the known cataloged sources above, Swift J174610-290018 may be a new X-ray transient. Further observations to determine the nature of this source are encouraged.

We thank the Swift team for their ongoing support of this program.

References:
Evans et al., 2010, ApJS, 189, 37
Degenaar et al., 2013, ApJ, 769, 155
Degenaar et al., 2015, JHEAp, 7, 137
Webb et al., 2020 A&A, 641A 136