TITLE:   GCN CIRCULAR
NUMBER:  31514
SUBJECT: Fermi-LAT-ANTARES 220121a Coincidence
DATE:    22/01/21 16:44:54 GMT
FROM:    Timothee Gregoire at Penn State  <tmg5746@psu.edu>

ANTARES 220121A: AMON + ANTARES Identification of a Low False-Alarm Rate 
High-Energy Neutrino + Fermi LAT Coincidence

C. F. Turley, D. B. Fox and T. Gregoire (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 21 January 2022 at 01:02:01 UT, we identified 
a low false alarm-rate (1.497 per year) coincidence between one ANTARES 
neutrino and one Fermi LAT photon. An alert was automatically generated 
and, after human review, distributed to AMON partner facilities and here 
publicly. Alert details are as follows:

     Date:  21 January 2022
     Time:  01:02:01 UT
     R.A.:  300.984 (J2000)
     Dec.:  -69.3334 (J2000)
     r_90:  0.109 deg (90%-containment)
     FAR:   1.497 yr-1

ANTARES 220121A is a high-energy neutrino-induced muon event detected by 
ANTARES (Ageron et al. 2011) with coordinates R.A. 307.21, Dec. -67.163 
(J2000) at 01:02:32 UT, and a p-value based on the number of hits used 
for the reconstruction of 0.7853, 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 was detected at 
01:01:30 UT with coordinates R.A. 301, Dec. -69.3347 (J2000) and energy 
16.0 GeV.  The best-fit localization and uncertainty for a point source 
yielding the ANTARES 220121A 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 0.668 years. There is no 
know GeV emitter (based on the Fermi-LAT 4FGL catalog) in the vicinity 
of the found coincidence. The nearest one is 4FGL J1956.6-7011 (with is 
1.06deg away).

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).

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

//////////////////////////////////////////////////////////////////////
TITLE: GCN/AMON NOTICE
NOTICE_DATE: Fri 21 Jan 2022 09:02:09 UT
NOTICE_TYPE: Fermi-LAT ANTARES coincidence
AMON_NUM: 1475022503
SRC_RA: 300.984d {+20h03m56.3s} (J2000),
         301.493d {+20h05m58.2s} (current),
         299.705d {+19h58m49.1s} (1950)
SRC_DEC: -69.3334d {-4h37m20.0s} (J2000),
          -69.2756d {-4h37m06.2s} (current),
          -69.474d {-4h37m53.8s} (1950)

SRC_ERROR90: 0.109 [deg, stat, 90% containment]
DISCOVERY_DATE: 19600 TJD;  021 DOY; 22/01/21 (yy/mm/dd)
DISCOVERY_TIME: 3721 SOD {1:02:01.400} UT
REVISION: 0
DELTA_T: 61.20 [sec]
SIGMA_T: 30.60 [sec]
FAR: 1.497 [yr^-1]
SUN_POSTN: 302.851d {+20h11m24s} -20.0102d {-20d00m37s}
SUN_DIST: 49.34 [deg] Sun_angle= 12.0584 [hr]
MOON_POSTN: 159.214d {+10h36m51s} 14.1667d {+14d10m00s}
MOON_DIST: 119.85 [deg]
GAL_COORDS: 326.13, -31.6249 [deg] galactic lon,lat of the event
COMMENTS: ALERT FROM FERMI-LAT ANTARES COINCIDENCE STREAM