Swift J001159.1+522440: Swift detection of an X-ray and UV transient.
ATel #17128; P. A. Evans, K. L. Page, S. Srivastava (U. Leicester), S. R. Oates (U. Lancaster), D. B. Malesani (DAWN/NBI and Radboud), S. Campana and B. Sbarufatti (INAF-OAB)
on 3 Apr 2025; 17:48 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Phil Evans (pae9@star.le.ac.uk)
Subjects: Ultra-Violet, X-ray
Referred to by ATel #: 17137
In data collected between 00:02:45 UT and 23:02:23 UT on 2025 March 28, Swift-XRT serendipitously detected an uncatalogued X-ray source, Swift J001159.1+522440, at RA, Dec = 2.9932, 52.4122 degrees, which is equivalent to:
RA (J2000) = 00h 11m 58.36s
Dec(J2000) = +52d 24' 44.0"
with an uncertainty of 4.2 arcsec (radius, 90% confidence). The source has an initial count-rate of (9.99 +/- 2.45)×10-3 ct/sec, which decayed to 3.95 (+1.54, -1.26)×10-3 ct s-1 over the next ~30 ks. Its spectrum can be modelled with an absorbed power-law with a poorly-constrained column of <6e21 cm-2 and a photon index of 1.3 (+0.7, -0.4). Using this spectrum, the peak count-rate corresponds to a 0.3-10 keV observed flux of (4.76 ± 1.17)×10-13 erg cm-2 s-1. The field has been previously observed by Swift, with no X-ray detection to a 3-sigma upper limit of 5.8×10-3 ct s-1.
Swift-UVOT also detects the source in the new data but not historically. Previous UVOT observations were taken in the u, uvm2, and uvw2 filters; the new data were in uvm2. In the previous observation (2012 July 14) the source was undetected with a 3-sigma upper limit of 20.28 in the uvm2 filter; in the new data it is clearly detected with a magnitude of 19.58±0.07, i.e. it has brightened by at least 0.7 magnitudes. The 3-sigma upper limits from the historical observations were 19.51 in u, and 19.46 in uvw2.
The source has no counterpart in SIMBAD and is not in the ALLWISE AGN catalogue, but corresponds to an extended object seen in archival Pan-STARRs data. Archival ZTF data show the source to have risen by ~1 magnitude in the r band and 0.5 magnitudes in the g filter since ~ mid 2018.
Follow up observations are strongly encouraged.
Swift J001159.1+522440 in LSXPS
