TITLE: GCN CIRCULAR NUMBER: 23641 SUBJECT: IceCube-190104A: Swift-XRT observations DATE: 19/01/08 12:35:11 GMT FROM: Azadeh Keivani at Columbia U A. Keivani (Columbia U.), P.A. Evans (U. Leicester), D.B. Fox (PSU), J.A. Kennea (PSU), D.F. Cowen (PSU), J.P. Osborne (U. Leicester), F.E. Marshall (GSFC), Marcos Santander (U. Alabama), Miguel Mostafa (PSU), and Hugo Ayala (PSU) report: Swift has observed the field of the IceCube HESE neutrino candidate IceCube-190104A (revision 1, https://gcn.gsfc.nasa.gov/gcn3/23605.gcn3), utilizing its on-board 37-point tiling pattern to cover a region centered on R.A., Dec. (J2000) = (357.98d, -26.65d), with a radius of approximately 1.1 degrees. Swift first started observing the initial location of the IceCube-190104A, ~3 hours after the neutrino arrival time: R.A., Dec. (J2000) = (359.3299d, -25.3659d) with an angular uncertainty of 0.42d, 50% containment (revision 0, https://gcn.gsfc.nasa.gov/gcn/notices_amon/68269692_131999.amon), using a 19-point tiling pattern. Upon receiving the GCN Circular update from the IceCube collaboration on the event refined direction and localization, Swift slewed to observe the new position with a 37-point tiling. Swift-XRT collected ~400 s per field of PC mode data per tile. The new observations were taken between 14:47:27 UT on 2019 January 4 and 10:22:20 UT on 2019 January 5, and covered 3.8 square degrees. There is a patch of diffuse X-ray emission around R.A. 23h 51m 39.27s, Dec. -26d 05’ 05.2” which gives rise to multiple spurious point-source detections; upon review, however, there is no evidence of point-like X-ray sources in this region. SIMBAD reports the galaxy [CKS2006] 11 at this position. The diffuse X-rays likely come from the galaxy cluster Abell 2667 (located at R.A. 23h 51m 39.37s, Dec. -26d 05’ 02.7”). A single point-like X-ray source is detected at R.A. 23h 50m 29.68s, Dec. -26d 20’ 45.2” with an uncertainty of 5.4” (90% conf. radius). This matches the catalogued X-ray source XMMSL2 J235029.0-262037 with its current flux at 2.4-sigma below the catalogued level from XMM-Newton Slew Survey Source Catalogue. SIMBAD lists a QSO ([VV2006] J235029.6-262046) at 2.7" from the XRT position for this source; the object is a broad-line quasar at redshift z=0.217 with M_i~-23 mag and L_X~10^44 erg s^-1 (Jones et al. 2009, MNRAS, 399 683). Its mean XRT count rate from our observations is 1.3(+0.6, -0.5)e-2 ct s^-1. The 3-sigma upper limit on the count rate in the rest of the field is 0.02 ct s^-1, which corresponds to a 0.3-10 keV flux of 8.0e-13 erg cm^-2 s^-1 for a typical AGN spectrum (NH=3e20 cm^-2, Gamma=1.7).