NuSTAR detects a source consistent with the location of the transient Swift J174610-290018
ATel #17132; B. Grefenstette (Caltech), K. Forster (Caltech), S. Zhang (MSU), K. Mori (Columbia)
on 5 Apr 2025; 20:57 UT
Credential Certification: Brian Grefenstette (Bwgref@srl.caltech.edu)
Subjects: X-ray, Black Hole, Neutron Star, Transient
During an observation of the Galactic Center on 2025-04-04 (NuSTAR Program 10022, PI S Zhang), in the first 18-ks of exposure NuSTAR clearly detected a point source at a location that is consistent with that of Swift J174610-290018 (ATEL #16481). The NuSTAR SOC routinely checks for the presence of new transients when this does not conflict with the science of the program of the PI.
The NuSTAR 3-10 keV positions from the two telescopes are:
FPMA:
R.A.: 17:46:10
Dec.: -29:00:08.780
and
FPMB:
R.A.: 17:46:10.8549
Dec.: -29:00:14.5
...with systematic uncertainty in the astrometry of a roughly 5-arcsec. These are offset from the positions reported by Neil-Gehrels Swift/XRT in Feb 2024 (ATEL #16481) by 9 and 6-arcsec, respectively. We therefore propose that this is a re-brightening of this transient source.
We also checked recent NuSTAR observations of the Galactic Center on 2025-03-09 (NuSTAR Program 10090, PI K. Mori) and do not see the source in the quicklook images, implying that this source brightened between the two NuSTAR observations.
Using counts extracted from a source region 30-arcsec from the centroids, we find that the source is clearly detected in the 3-10 keV band and is well fit by an absorbed, soft spectrum that is alternatively well-fit by a soft power-law (Gamma>2) or a hot diskbb (Tin > 2 keV), though these parameters are poorly constrained and degenerate with the amount of absorption. With Nh == 20e22 cm^-2 for comparison with the Swift analysis and using a tbabs(po) model we find (fitting over the 3-10 keV) range:
Gamma: 2.6 ± 0.2
...and a 3-10 keV flux of 4.7 - 5.2e-12 ergs / sec / cm^2. This is comparable to the flux found in 2024 by Swift.
Further observations are planned for ongoing programs that will be able to monitor the flux at this location over the coming weeks but we encourage follow-up with other observatories.
