GCN Circular 26915

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 ANTARES 200127A: AMON + ANTARES Identification of a Low False-Alarm
Rate High-Energy Neutrino + Fermi LAT Coincidence


C. F. Turley and D. B. Fox (for AMON https://www.amon.psu.edu/) +
M. Ageron (CNRS/CPPM) A.Coleiro (Univ. de Paris/APC), D. Dornic
(CNRS/CPPM), A. Kouchner (Univ. de Paris/APC ) (for ANTARES) report:

"During operations of the AMON ANTARES neutrino + Fermi LAT gamma-ray
multimessenger alerts, at 2020 January 27 at 18:52:02.9 UT, we identified
a low false alarm-rate (1 per 4.04 years) coincidence between a single
ANTARES neutrino and two Fermi LAT photons. An alert was automatically
generated and, after human review, distributed to AMON partner
facilities at 2020 January 28, 02:09 UT. We are now reporting this
alert publicly. Alert details are as follows:

    Date:  27 January 2020
    Time:  18:52:02.95 UT
    R.A.:  16:01:47.1 (J2000)
    Dec.: -52:57:28.6 (J2000)
    r_90:  0.233 deg (90%-containment)
    FAR:   0.25 yr-1

ANTARES 200127A is a high-energy neutrino-induced muon event detected
by ANTARES (Ageron et al. 2011) with coordinates R.A. 16:16:33,
Dec. -53:36:46.8 (J2000) at 18:55:05 UT, and a p-value based on the
number of hits used for the reconstruction of 0.433, which relates
to the deposited energy.

The minimum false alarm rate coincidence from our analysis associates
this neutrino with two Fermi LAT photons. The first photon was detected at
18:49:25.9 UT with coordinates R.A. 16:01:47.52, Dec. -52:57:19.44 (J2000)
and energy 33.28 GeV. The second photon was detected at 18:51:37.9 UT with
coordinates R.A. 16:00:34.08, Dec -52:37:48.00 (J2000) and energy 2.18 GeV.
The best-fit localization and uncertainty for a point source yielding the
ANTARES 200127 neutrino and the photon is as quoted above. The false alarm
rate for ANTARES neutrino + Fermi LAT gamma-ray coincidences of this quality
or better is 1 per 4.036 years. We notice that this Fermi-LAT-ANTARES
coincidence is spatially matching the 50% credible region of the GW
event S200128d but preceded it by approximately 7.5 hours.

Details of the ANTARES + Fermi LAT coincidence search procedures are
provided in Ayala Solares et al. (AMON + ANTARES) 2019 (ApJ 886 (2019)
98, ArXiv:1904.06420). False alarm rates are established from 73,000
years of simulated observation and take into account the point spread
functions of the associated neutrino + photons, the known backgrounds
at this sky position, the energy of the neutrino, and the energies of
the Fermi LAT photons (within broad ranges).

The AMON alert for this coincidence is provided in GCN Alert format
below."

//////////////////////////////////////////////////////////////////////
TITLE: GCN/AMON NOTICE
NOTICE_DATE: Mon 27 Jan 2020 18:52:02.95 UT
NOTICE_TYPE: Fermi-LAT ANTARES coincidence
AMON_NUM: 1441204786
SRC_RA: 240.4463d {+16h 01m 47.1s} (J2000),
240.8313d {+16h 03m 19.5s} (current),
239.4871d {15:57:56.9} (1950)
SRC_DEC: -52.9579d {-52d 57��� 29"} (J2000),
-53.0125d {-53d 00��� 45"} (current),
-52.8186d {-52d 49' 07"} (1950)

SRC_ERROR90: 0.233 [deg, stat, 90% containment]
DISCOVERY_DATE: 18875 TJD;  27 DOY; 20/01/27 (yy/mm/dd)
DISCOVERY_TIME: 67922 SOD {18:52:02.95} UT
REVISION: 0
DELTA_T: 339.09 [sec]
SIGMA_T: 139.56 [sec]
FAR: 0.2478 [yr^-1]
SUN_POSTN: 309.754d {+20h 39m 01s} -18.431d {-18d 25��� 52"}
SUN_DIST: 62.98 [deg] Sun_angle= 4.20 [hr] (West of Sun)
MOON_POSTN: 346.433d {+23h 05m 44s} -10.925d {-10d 55��� 31"}
MOON_DIST: 90.67 [deg]
GAL_COORDS: 329.416, +0.233  [deg] galactic lon,lat of the event
COMMENTS: ALERT FROM FERMI-LAT ANTARES COINCIDENCE STREAM

 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Colin F. Turley
860-685-1260 Cell
cft114@psu.edu email

Department of Physics, Penn State University
104 Davey Lab, Box 52
University Park, PA 16802-6300