[vsnet-grb-info 22305] IceCube-190503A: Swift-XRT Follow-up Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24404
SUBJECT: IceCube-190503A: Swift-XRT Follow-up Observations
DATE:    19/05/06 10:59:53 GMT
FROM:    Azadeh Keivani at Columbia U  <azadeh.keivani at columbia.edu>

A. Keivani (Columbia U.), D. B. Fox (PSU), P. A. Evans (U. Leicester), J.
A. Kennea (PSU), M. Santander (U. Alabama), & F. Krauss (GRAPPA/API,
University of Amsterdam) report:


The Neil Gehrels Swift Observatory observed the field of the IceCube EHE
astrophysical neutrino candidate event IceCube-190503A (revision 1,
https://gcn.gsfc.nasa.gov/gcn3/24378.gcn3) beginning May 3, 20:14:26 UT
(2.85 hours after the neutrino arrival time).

Swift utilized its onboard 19-point tiling pattern to cover a region
centered on R.A., Dec. (J2000) = 120.28d, +6.35d, with a radius of
approximately 0.8 deg; estimated 90%-containment radii for this event are
0.57 deg  to 0.77 deg depending on position angle. Swift-XRT collected ~800
s per field of PC mode data per tile between 20:17:30 UT on 3 May and
10:51:09 UT on 4 May. Data have been reduced using the analysis approach
and software routines of Evans et al. 2014 (ApJS, 210, 8).

Several X-ray sources are detected in these observations, most of which are
previously uncataloged and relatively low in flux, consistent with
expectations for serendipitous (unrelated) sources over a region of this
extent. A few sources with a false positive rate of ~1% look like real
X-ray sources. However, none of them look promising to be IceCube-190503A
counterparts due to their low flux and lack of variability.

Excluding identified sources, the 3-sigma upper limit on the count rate of
any point-like counterpart over the rest of the tiled region is 0.01 ct
s^-1, which corresponds to a 0.3-10 keV flux of 4.0e-13 erg cm^-2 s^-1 for
a typical AGN spectrum (nH=3e20 cm^-2, Gamma=1.7).

Coordinates and count rates for the X-ray sources are provided below.

Source, RA, Dec, Error_90 (arcsec), XRT count rate (ct s^-1)

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#1: 120.75962d, 7.01880d, 11.2, 1.0 (+0.5, -0.4) e-2

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#2: 120.56238d, 6.63466d, 5.2, --

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#3: 119.80197d, 7.11136d, 6.7, 1.1 (+0.6, -0.4) e-2

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#4: 120.49133d, 6.05997d, 6.7, 9 (+6, -4) e-3

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#5: 119.81789d, 6.45455d, 6.3, 1.0 (+0.5, -0.4) e-2

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#6: 120.14345d, 6.13111d, 7.8, 4.6 (+4.4, -2.7) e-3