Swift follow-up observations of IceCube-200107A: Identification of a X-ray high state for 4FGL J0955.1+3551
ATel #13395; F. Krauss, T. Gregoire, D. B. Fox, J. Kennea (PSU), P. Evans (U Leicester)
on 9 Jan 2020; 19:23 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Felicia Krauss (Felicia.Krauss@psu.edu)
Subjects: X-ray, Neutrinos, AGN, Blazar
We have observed the positions of the two Fermi/LAT sources (Garrappa et al., GCN Circ. 26669), positionally coincident with the IceCube neutrino event IceCube-200107A (GCN Circ. 26655) with the Neil Gehrels Swift Observatory X-ray Telescope (XRT). We detect the blazar 4FGL J0955.1+3551 with an observed 2-10 keV flux of 4.7 (± 0.8)×10-12 erg cm-2 s-1 (2-10 keV). A spectrum constructed from these data can be well described by an absorbed power law with N_H=5.3×10^20 cm-2 (wilm abundances, vern cross-sections), and a photon index of 1.8 (+0.23, -0.13).
These data were also mentioned in ATel #13394.
This object has been previously observed by Swift/XRT, and its historical behavior can be seen in the
2SXPS catalogue (Evans et al., 2019): https://www.swift.ac.uk/2SXPS/2SXPS%20J095507.8%2B355100 . Our recent observations are significantly brighter than the average flux in archival data: 1.78 (+0.14, -0.13) × 10-12 erg cm-2 s-1 (observed 2-10 keV flux), although the historical light curve does show that the source flux was gradually increasing in 2012-3. The catalogued ROSAT flux of this source (as 1RXS J095508.2+355054) is 0.11 ct/sec which, assuming the above spectrum, corresponds to a 2-10 keV observed flux of ~1.9 × 10-12 erg cm-2 s-1; therefore we suggest that this source is currently in a high state. Further observations of this source are strongly recommended.
The other source reported in GCN Circ. 26669 (4FGL J0957.8+3423) was not detected in our observations, with a 3σ upper limit of 0.010 ct/sec (0.3-10 keV). Assuming a standard spectrum (N_H=3×1020, Gamma=1.7) this corresponds to a observed 2-10 keV flux upper limit of 2.7 × 10-13 erg cm-2 s-1. This source has not been previously covered by Swift/XRT observations.
