//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27612 SUBJECT: IceCube-200421A - IceCube observation of a high-energy neutrino candidate event DATE: 20/04/21 03:10:12 GMT FROM: Erik Blaufuss at U. Maryland/IceCube The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 21 April, 2020 at 00:35:24.24 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_Bronze alert stream. The threshold astrophysical neutrino purity for Bronze alerts is 30% . This alert has an estimated false alarm rate of 2.8 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/133985_60770138.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 21 April 2020 Time: 00:35:24.24 UT RA: 87.93 (+3.44/- 2.83 (+1.88/-1.64) deg 90% (50%) PSF containment) J2000 Dec: 8.23 (+2.09/-1.84 (+1.25/-1.19) deg 90% (50%) PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. There are no Fermi 4FGL or 3FHL catalog sources in the 50% uncertainty region. The nearest gamma-ray source in either catalog is 4FGL J0545.0+0613 at RA: 86.27 deg, Dec: 6.23 deg (2.59 deg away from the best-fit event position). The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27613 SUBJECT: IceCube-200421A: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation DATE: 20/04/21 10:30:17 GMT FROM: Alexander Lutovinov at Space Research Inst.,IKI Alexander Lutovinov (IKI, Russia),  Enrico Bozzo, V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland) J. Rodi (IAPS-Roma, Italy) A. Coleiro (APC, France) S. Mereghetti (INAF IASF-Milano, Italy) on behalf of the INTEGRAL multi-messenger collaboration: https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration Using combination of INTEGRAL all-sky detectors (following [1]): SPI/ACS, IBIS/Veto, and IBIS we have performed a search for a prompt gamma-ray counterpart of unknown (GCN 27612). At the time of the event (2020-04-21 00:35:24 UTC, hereafter T0), INTEGRAL was operating in nominal mode. The peak of the event localization probability was at an angle of 162 deg with respect to the spacecraft pointing axis. This orientation implies strongly suppressed (3.7% of optimal) response of ISGRI, near-optimal (85% of optimal) response of IBIS/Veto, and strongly suppressed (38% of optimal) response of SPI-ACS. The background within +/-300 seconds around the event was rather stable (excess variance 1.3). We have performed a search for any impulsive events in INTEGRAL SPI- ACS (as described in [2]), IBIS, and IBIS/Veto data. We do not detect any significant counterparts and estimate a 3-sigma upper limit on the 75-2000 keV fluence of 4.9e-07 erg/cm^2 (within the 50% probability containment region of the source localization) for a burst lasting less than 1 s with a characteristic short GRB spectrum (an exponentially cut off power law with alpha=-0.5 and Ep=600 keV) occurring at any time in the interval within 300 s around T0. For a typical long GRB spectrum (Band function with alpha=-1, beta=-2.5, and Ep=300 keV), the derived peak flux upper limit is ~5e-07 (9.2e-08) erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range. We report for completeness and in order of FAP, all excesses identified in the search region. We find: 2 possibly associated excesses: T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP 3.07 | 1.15 | 3.6 | 0.553 +/- 0.152 +/- 0.186 | 0.0163 40 | 9.5 | 3.5 | 2.09 +/- 0.526 +/- 0.703 | 0.033 2 likely background excesses: T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP -36.6 | 1.5 | 3.3 | 0.433 +/- 0.133 +/- 0.146 | 0.307 -119 | 0.35 | 4.6 | 1.25 +/- 0.277 +/- 0.419 | 0.668 All results quoted are preliminary. This circular is an official product of the INTEGRAL Multi-Messenger team. [1] Savchenko et al. 2017, A&A 603, A46 [2] Savchenko et al. 2012, A&A 541A, 122S //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27614 SUBJECT: IceCube Alert 200421.02: Global MASTER-Net observations report DATE: 20/04/21 13:39:10 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov, D. Cheryasov (Lomonosov Moscow State University, SAI, Physics Department), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA), H.Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University) MASTER-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the IceCube Alert 200421.02 (trigger No 60770138,05h 57m 01.20s , +07d 54m 25.2s, R=0.61) errorbox 45894 sec after notice time and 45943 sec after trigger time at 2020-04-21 13:21:07 UT, with upper limit up to 15.6 mag. Observations started at twilight. The observations began at zenith distance = 68 deg. The sun altitude is -10.4 deg. The galactic latitude b = -8 deg., longitude l = 200 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1341229 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 45973 | 2020-04-21 13:21:07 | MASTER-Tunka | (05h 51m 49.84s , +08d 17m 27.8s) | C | 60 | 15.3 | 46053 | 2020-04-21 13:22:27 | MASTER-Tunka | (05h 59m 58.32s , +08d 19m 28.6s) | C | 60 | 15.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27615 SUBJECT: IceCube-200421A: not observable by Fermi-GBM DATE: 20/04/21 20:16:14 GMT FROM: Rachel Hamburg at UAH R. Hamburg (UAH) and P. Veres (UAH) report on behalf of the Fermi-GBM Team: For the IceCube high-energy neutrino candidate event 200421A (GCN 27612), the reported position: RA: 87.93 (+3.44/-2.83 deg 90% PSF containment) J2000 Dec: 8.23 (+2.09/-1.84 deg 90% PSF containment) J2000 was occulted by the Earth for Fermi-GBM from approximately from 16.2 minutes prior until 18.1 minutes after event time. Therefore, the GBM observations are not constraining for prompt gamma-ray emission. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27617 SUBJECT: IceCube-200421A: No significant detection in HAWC DATE: 20/04/21 21:18:04 GMT FROM: Hugo Ayala at Pennsylvania State University Hugo Ayala (Penn State) reports on behalf of the HAWC collaboration (http://www.hawc-observatory.org/collaboration): On 2020/04/21 00:35:24 UTC, the IceCube collaboration reported a track-like very-high-energy event that has a high probability of being an astrophysical neutrino, IceCube-200421A. Location is at RA: 87.93 (+3.49/-2.83 deg 90% PSF containment) J2000 Dec: 8.23 (+2.09/-1.84 deg 90% PSF containment) J2000 (GCN circular 27612). We performed two types of analyses for the follow-up. The first is for a steady source in archival data and the second is a search for a transient source. We assume a power-law spectrum with an index of -2.3 for both analyses. Search for a steady source in archival data: The archival data spans from November 2014 to May 2018. We searched inside the reported IceCube error region. The highest significance, 2.83 sigma (-0.43 post-trials), is at RA 87.19 deg, Dec +7.37 deg (+-0.21 deg 68% containment) J2000. We set a time-integrated 95% CL upper limit on gamma rays at the maximum position of: E^2 dN/dE = 2.82e-13 (E/TeV)^-0.3 TeV.cm^-2.s^-1 Search for a transient source. Since the IceCube event fall inside the HAWC field of view, we report on the result during the transit of the IceCube position. Data acquisition started on 2020/04/20 19:23:55 UTC and ended 2020/04/21 01:24:32 UTC. The most significant location, with 3.28 sigma (1.53 post-trials), is at RA 85.05 deg, Dec +8.5 (+-0.23 deg 68% containment) deg (J2000). We set a time-integrated 95% CL upper limit at the position of maximum significance of: E^2 dN/dE = 1.3.e-11 (E/TeV)^-0.3 TeV.cm^-2.s^-1 HAWC is a very-high-energy gamma-ray observatory operating in Central Mexico at latitude 19 deg. north. Operating day and night with over 95% duty cycle, HAWC has an instantaneous field of view of 2 sr and surveys 2/3 of the sky every day. It is sensitive to gamma rays from 300 GeV to 100 TeV. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27619 SUBJECT: IceCube-200421A: No Neutrino Counterpart in ANTARES data DATE: 20/04/22 06:25:17 GMT FROM: Antoine Kouchner at ANTARES Collaboration Alexis Coleiro (APC/Universite de Paris) and Damien Dornic (CPPM/CNRS) on behalf of the ANTARES Collaboration.

Using data from the ANTARES detector, we have performed a follow-up analysis of the recently reported single track-like event IceCube-200117A (GCN 27612< https://gcn.gsfc.nasa.gov/gcn3/27612.gcn3>). The original reconstructed origin was 25.0 degrees below the horizon for ANTARES.
No up-going muon neutrino candidate events were recorded at the location of the IceCube event coordinates (accounting for the reported uncertainties) during a +/- 1h time-window centered on the IceCube event time, and over which the potential source remained visible all time. A search over an extended time window of +/- 1 day has also yielded no detection (45% visibility).
This leads to a preliminary 90% confidence level upper limit on the muon-neutrino fluence from a point source of 15 GeV.cm^-2 over the energy range 3.9 TeV – 4.0 PeV (the range corresponding to 5-95% of the detectable flux) for an E^-2 power-law spectrum, and 27 GeV.cm^-2 (720 GeV - 380 TeV) for an E^-2.5 spectrum.
ANTARES > is the largest undersea neutrino detector (Mediterranean Sea) and it is primarily sensitive to astrophysical neutrinos in the TeV-PeV energy range. At 10 TeV, the median angular resolution for muon neutrinos is about 0.5 degrees. In the range 1-100 TeV ANTARES has a competitive sensitivity to this position in the sky. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27620 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-200421A DATE: 20/04/22 09:03:56 GMT FROM: Simone Garrappa at DESY S. Garrappa (DESY-Zeuthen) and S. Buson (Univ. of Wuerzburg) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC200421A neutrino event (GCN 27612) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2020-04-21 00:35:24.24 UT (T0) with J2000 position RA = 87.93 (+3.44, - 2.83) deg, Decl. = 8.23 (+2.09, -1.84) deg 90% PSF containment. No cataloged >100 MeV gamma-ray sources are located within the 90% IC200421A localization error. We searched for the existence of intermediate (months to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC200421A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IceCube best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2e-9 ph cm^-2 s^-1 for ~11-years (2008-08-04 / 2020-04-21 UTC), < 8e-9 (< 5e-8) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this source the Fermi-LAT contact persons are S. Garrappa (simone.garrappa at desy.de ) and S. Buson (sara.buson at uni-wuerzburg.de ). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27624 SUBJECT: IceCube-200421A: Upper limits from a search for additional neutrino events in IceCube DATE: 20/04/22 15:24:07 GMT FROM: Alex Pizzuto at ICECUBE/U of Wisconsin The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search for additional track-like muon neutrino events arriving from the direction of IceCube-200421A (https://gcn.gsfc.nasa.gov/gcn3/27612.gcn3) in a time range of 2 days centered on the alert event time (2020-04-20 00:35:24.24 UTC to 2020-04-22 00:35:24.240 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, one additional track-like event is found in spatial coincidence with the 90% containment region of IceCube-200421A. We find that these data are consistent with atmospheric background expectations, with a p-value of 1.0. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/ dE = 3.8 x 10^-5 TeV cm^-2 at 90% CL, under the assumption of an E^-2 power law. 90% of events IceCube would detect from a source at this declination with an E^-2 spectrum are approximately between 1 TeV and 2 PeV. A subsequent search was performed to include the month of data prior to the alert event (2020-03-21 00:35:24.24 UTC to 2020-04-22 00:35:24.240 UTC). In this case, we report a p-value of 1.0, consistent with no significant excess of track-like events, and a corresponding time-integrated muon-neutrino flux upper limit assuming an E^-2 spectrum (E^2 dN/dE) of 8.4 x 10^-5 TeV cm^-2 at the 90% CL. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu.