[vsnet-grb-info 21542] IceCube-190104A: Swift-XRT observations

[GCN Circulars]

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  <azadeh.keivani at columbia.edu>

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).