TITLE:   GCN CIRCULAR
NUMBER:  20890
SUBJECT: IceCube-170312A: Swift-XRT observations
DATE:    17/03/17 14:59:20 GMT
FROM:    Azadeh Keivani at PSU  <keivani@psu.edu>

A. Keivani (PSU), P.A. Evans (U. Leicester), J.A. Kennea (PSU), D.B.
Fox (PSU), G. Tesic (PSU), D.F. Cowen (PSU), J.P. Osborne (U.
Leicester) and M.W.E. Smith (JPL) report on behalf of the
Swift-IceCube collaboration:

Swift has observed the field of the IceCube HESE neutrino,
IceCube-170312A (https://gcn.gsfc.nasa.gov/gcn3/20857.gcn3), utilizing
the on-board
19-point tiling pattern to cover a region centered on RA,Dec (J2000) =
(304.7300, -26.2380), with a radius of approximately 0.8 degrees.

Swift-XRT collected ~800 s per field of PC mode data per tile. The
observations were taken between 15:51:22 on 2017-03-12 and 05:04:48 on
2017-03-13 (i.e. from 7.3 ks to 54.9 ks after the neutrino trigger),
and covered 2.1 square degrees.

Five X-ray sources are detected in the observations. One of these
corresponds to a known X-ray emitter, and others are faint objects
well below the RASS limits, therefore we do not consider any of them
to be likely counterparts to the IceCube trigger. We conclude that we
have not discovered a transient X-ray event associated with the
IceCube trigger.

The 3-sigma upper limit on the count rate in the rest of the field is
0.01 ct s^-1, which corresponds to a 0.3-10 keV flux of 4.1e-13 erg
cm^-2 s^-1 for a typical AGN spectrum (NH=3e20cm^-2, Gamma=1.7).
Overlaps between the different tiles accounts for 0.5 square degrees:
in these regions the 3-sigma upper limit is .007 ct s^-1,
corresponding to 2.9e-13 erg cm^-2 s^-1.

Details of the five detected X-ray sources are below. All fluxes are
0.3-10 keV and assume the same AGN spectrum as above.

Source 1
========
RA:          20h 21m 21.41s = 305.33920d 	
Dec:         -26d 01' 32.3" = -26.02565d
Error:       6.3 arcsec (90% confidence radius)
Count rate:  (2.8 [+0.8, -0.7]) x 10^-2 ct s^-1
Flux:        (1.1 [+0.3, -0.2]) x 10^-12 erg cm^-2 s^-1
Notes:       Matches known X-ray source: 1RXS J202121.5-260149 (from
ROSAT/RASSFSC), 16.7102046720847" away.

Source 2
========
RA:          20h 21m 54.52s = 305.47717d
Dec:         -26d 04′ 12.0″ = -26.07000d
Error:       4.9 arcsec (90% confidence radius)
Count rate:  (2.1 +/- 0.6) x 10^-2 ct s^-1
Flux:        (8.6 +/- 2.5) x 10^-13 erg cm^-2 s^-1

Source 3
========
RA:          20h 18m 26.48s = 304.61032d
Dec:         -26d 50′ 24.6″ = -26.84017d
Error:       6.5 arcsec (90% confidence radius)
Count rate:  (1.0 [+0.6, -0.4]) x 10^-2 ct s^-1
Flux:        (4.1 [+2.5, -1.6]) x 10^-13 erg cm^-2 s^-1

Source 4
========
RA:          20h 16m 34.69s = 304.14452d
Dec:         -26d 38′ 56.6″ = -26.64904d
Error:       5.8 arcsec (90% confidence radius)
Count rate:  (1.6 [+0.6, -0.5]) x 10^-2 ct s^-1
Flux:        (6.6 [+2.5, -2.1]) x 10^-13 erg cm^-2 s^-1

Source 5
========
RA:          20h 19m 25.94s = 304.85809d
Dec:         -26d 06′ 09.9″ = -26.10276d
Error:       5.5 arcsec (90% confidence radius)
Count rate:  (6.4 [+3.5, -2.6]) x 10^-2 ct s^-1
Flux:        (2.6 [+1.4, -1.1]) x 10^-12 erg cm^-2 s^-1

[GCN OPS NOTE(17mar17): Per author's request, the Subject line
now includes the event designation and the type of observation.]