GCN Circular 26674

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ANTARES 200108A: AMON + ANTARES Identification of a 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 8 at 09:30:14 UT, we identified
a low false alarm-rate (2.39 per year) coincidence between a single
ANTARES neutrino and one Fermi LAT photon. An alert was automatically
generated and, after human review, distributed to AMON partner
facilities at 2020 January 8, 15:04 UT. We are now reporting this
alert publicly. Alert details are as follows:

    Date:  8 January 2020
    Time:  09:30:14.48 UT
    R.A.:  02:53:55.6 (J2000)
    Dec.: -18:04:02 (J2000)
    r_90:  0.832 deg (90%-containment)
    FAR:   2.387 yr-1

ANTARES 200108A is a high-energy neutrino-induced muon event detected
by ANTARES (Ageron et al. 2011) with coordinates R.A. 02:53:47.8,
Dec. -18:07:23 (J2000) at 09:25:12 UT, and a p-value based on the
number of hits used for the reconstruction of 0.0269, which relates
to the deposited energy.

The minimum false alarm rate coincidence from our analysis associates
this neutrino with one Fermi LAT photon. The photon is detected at
09:35:16.96 UT with coordinates R.A. 02:54:06.79, Dec. -18:01:00.12
(J2000) and energy 778.3 MeV. The best-fit localization and
uncertainty for a point source yielding the ANTARES 200108A 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 0.419 years.

Details of the ANTARES + Fermi LAT coincidence search procedures are
provided in Ayala Solares et al. 2019 (ApJ 886, 98). 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).

This nearest LAT source to this transient is 3FGL J0251.1-1829, which
is 0.77 deg away, within the 90%-containment region for this
coincidence.

We provide the associated AMON alert for this coincidence in GCN Alert
format, below."

//////////////////////////////////////////////////////////////////////
TITLE: GCN/AMON NOTICE
NOTICE_DATE: Wed 08 Jan 2020 09:30:14.48 UT
NOTICE_TYPE: Fermi-LAT ANTARES coincidence
AMON_NUM: 1440223121
SRC_RA: 43.4818d {+02h 53m 55.6s} (J2000),
43.7129 d{+02h 54m 51.1s} (current),
42.9035d {02:51:36.8} (1950)
SRC_DEC: -18.0673d {-18d 04��� 02"} (J2000),
17.9866d {-17d 59��� 12"} (current),
-18.2702d {-18d 16' 13"} (1950)

SRC_ERROR90: 0.832 [deg, stat, 90% containment]
DISCOVERY_DATE: 18856 TJD;  8 DOY; 20/01/082 (yy/mm/dd)
DISCOVERY_TIME: 34214 SOD {01:42:52.783} UT
REVISION: 0
DELTA_T: 604.96 [sec]
SIGMA_T: 302.48 [sec]
FAR: 2.387 [yr^-1]
SUN_POSTN: 289.0042d {+19h 16m 01s} -22.2867d {-22d 17��� 12"}
SUN_DIST: 104.29 [deg] Sun_angle= 6.95 [hr] (East of Sun)
MOON_POSTN: 79.4917d {+05h 17m 58s} +21.4503 {+21d 27��� 01"}
MOON_DIST: 53.03 [deg]
GAL_COORDS: 201.6015, -60.4037  [deg] galactic lon,lat of the event
COMMENTS: ALERT FROM FERMI-LAT ANTARES COINCIDENCE STREAM

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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