GCN Circular 24405

IceCube-190504A: Swift-XRT Follow-up Observations

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 HESE
astrophysical neutrino candidate event IceCube-190504A (revision 1,
https://gcn.gsfc.nasa.gov/gcn3/24392.gcn3
Not found
 
 
) beginning May 4, 20:09:37 UT
(1.74 hours after the neutrino arrival time).

Swift utilized its onboard 19-point tiling pattern to cover a region
centered on R.A., Dec. (J2000) = 65.7866d, -37.4431d, with a radius of
approximately 0.8 deg; estimated 90%-containment radius for this event is
1.23 deg. Swift-XRT collected ~800 s per field of PC mode data per tile
between 20:12:40 UT on 4 May and 09:08:01 UT on 5 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. The highest-significance X-ray source is located at R.A. 66.17568d,
Dec. -37.93938d (J2000), 35 arcmin away from the neutrino direction, and
matches the known (SIMBAD) X-ray source QSO B0422-380 (1.4 arcsec away) as
well as 1SXPS J042442.5-375618 (6 arcsec away). We recover it at a mean
observed XRT count rate of 3.2 (+0.8, -0.7) e-2 ct s^-1, consistent with
(1.5-sigma above) the cataloged flux from 1SXPS. Although the brightness of
this object does not look significantly elevated over the previous Swift
observations, it is catalogued as a blazar and would be interesting if
there is other electromagnetic emission from this source. Fermi-LAT has
reported (GCN Circular #24401) significant emission at gamma ray over a
timescale of one week before the neutrino arrival time (at a flux level
consistent with the 10 years average) but no recent remarkable activity at
gamma rays.

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, count rates, and possible counterparts for the X-ray sources
are provided below.

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

------------------------------------------------------------------------------------------------------------------

#1: 66.17568d, -37.93938d, 7.9, 3.2 (+0.8, -0.7) e-2, QSO B0422-380 (1.4
arcsec away) & 1SXPS J042442.5-375618 (6 arcsec away)

------------------------------------------------------------------------------------------------------------------

#2: 66.39382d, -37.70566d, 6.6, 1.3 (+0.7, -0.5) e-2, 1RXS J042532.5-374212
(25.4 arcsec away)

------------------------------------------------------------------------------------------------------------------

#3: 65.19589d, -37.26399d, 9.5, 1.0 (+0.6, -0.4) e-2, 1RXS J042449.3-365537
(13.2 arcsec away)

------------------------------------------------------------------------------------------------------------------

#4: 66.20972d, -36.92833d, 6.3, 1.4 (+0.6, -0.5) e-2, --

------------------------------------------------------------------------------------------------------------------

#5: 65.70905d, -37.94807d, 7.5, 1.2 (+0.6, -0.5) e-2, --

------------------------------------------------------------------------------------------------------------------

#6: 66.39458d, -37.70534d, 7.9, 1.3 (+0.7, -0.5) e-2, 1RXS J042532.5-374212
(27.1 arcsec away)

------------------------------------------------------------------------------------------------------------------

#7: 65.29548d, -38.09169d, 10.5, 1.3 (+0.6, -0.5) e-2, 1RXS
J042110.9-380533 (2.9 arcsec away)