TITLE: GCN CIRCULAR NUMBER: 26915 SUBJECT: Fermi-LAT-ANTARES coincidence DATE: 20/01/28 13:01:29 GMT FROM: Colin F Turley at AMON, Penn State U ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 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