//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28468 SUBJECT: IceCube-200921A: IceCube observation of a high-energy neutrino candidate event DATE: 20/09/21 20:36:22 GMT FROM: Cristina Lagunas Gualda at DESY The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 20/09/21 at 19:07:12.89 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 average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 1.586 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/134512_71996695.amon), more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 20/09/21 Time: 19:07:12.89 UT RA: 195.29 (+ 2.35 - 1.73 deg 90% PSF containment) J2000 Dec: 26.24 (+ 1.51 - 1.77 deg 90% 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 is one Fermi 4FGL/3FHL source located within the 90% localization region, 4FGL J1303.0+2434, located at RA: 195.76 deg, Dec: 24.58 deg (J2000), at a distance of 1.71 deg 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: 28469 SUBJECT: IceCube-200921A: Upper limits from Fermi-GBM Observations DATE: 20/09/22 02:48:51 GMT FROM: Rachel Hamburg at UAH R. Hamburg (UAH) reports on behalf of the Fermi-GBM team: For the IceCube high-energy neutrino candidate event IceCube-200921A (GCN 28468), at the event time Fermi-GBM was observing the reported neutrino location at: RA: 195.29 (+2.35 -1.73 deg 90% PSF containment) J2000 Dec: 26.24 (+1.51 -1.77 deg 90% PSF containment) J2000 There was no Fermi-GBM onboard trigger around the event time of the neutrino candidate. An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from +/-30 s around the neutrino candidate time. From this search, no significant signal was found related to IceCube-200921A. We set upper limits on impulsive gamma-ray emission. Using the representative soft, normal, and hard GRB-like templates described in arXiv:1612.02395, we set the following 3 sigma flux upper limits over 10-1000 keV (in units of 10^-6 erg/s/cm^2): Timescale Soft Normal Hard -------------------------------------- 0.128 s: 17. 34. 73. 1.024 s: 6.4 13. 21. 8.192 s: 2.2 2.5 1.4 These results are preliminary. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28470 SUBJECT: IceCube-200921A: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation DATE: 20/09/22 07:09:21 GMT FROM: Volodymyr Savchenko at ISDC,U of Geneve 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 IceCube-200921A (GCN 28468). At the time of the event (2020-09-21 19:07:12 UTC, hereafter T0), INTEGRAL was operating in nominal mode. The peak of the event localization probability was at an angle of 87 deg with respect to the spacecraft pointing axis. This orientation implies strongly suppressed (8.6% of optimal) response of ISGRI, strongly suppressed (31% of optimal) response of IBIS/Veto, and somewhat suppressed (63% of optimal) response of SPI-ACS. The background within +/-300 seconds around the event was very stable (excess variance 1.1). 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 2.9e-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 ~2.6e-07 (7.7e-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: 6 likely background excesses: T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP -3.86 | 0.25 | 3.8 | 0.752 +/- 0.217 +/- 0.316 | 0.0625 -14 | 0.9 | 3.7 | 0.381 +/- 0.114 +/- 0.16 | 0.0812 16.5 | 0.05 | 4.7 | 2.17 +/- 0.494 +/- 0.911 | 0.295 -43.9 | 0.7 | 3.2 | 0.379 +/- 0.129 +/- 0.159 | 0.832 239 | 0.95 | 3.9 | 0.412 +/- 0.111 +/- 0.173 | 0.858 -19.8 | 0.15 | 3.5 | 0.891 +/- 0.28 +/- 0.375 | 0.964 Note that FAP estimates (especially at timescales above 2s) may be possibly further affected by enhanced non-stationary local background noise. This list excludes any excesses for which FAP is close to unity. 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: 28480 SUBJECT: IceCube-200921A: no significant detection in HAWC observations DATE: 20/09/23 03:20:52 GMT FROM: Alberto Carraminana at AzTEC Alberto Carramiñana (INAOE) and Hugo Ayala (PSU) report on behalf of the HAWC collaboration (http://www.hawc-observatory.org/collaboration): On 2020/09/21 19:07:13 UTC, the IceCube collaboration reported a track-like very-high-energy event that has a moderate probability of being an astrophysical neutrino, IceCube-200921A. Location is at RA: 195.29 (+2.35/-1.73 deg 90% PSF containment) J2000 Dec: 26.24 (+1.51/-1.77 deg 90% PSF containment) J2000 (GCN circular 28468). 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 most significant location, with p-value 2.51e-04 (2.85e-02 post-trials), is at RA 193.67 deg, Dec +25.86 deg (±0.10 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 = 3.03e-13 (E/TeV)^-0.3 TeV.cm^-2.s^-1 - Search for a transient source: The event was in our field of view at the time reported. Data acquisition started on 2020/09/21 16:13:38 UTC and ended 2020/09/21 22:39:47 UTC. The most significant location, with p-value 2.02e-04 (2.30e-02 post-trials), is at RA 197.67 deg, Dec +25.82 deg (±0.17 deg 68% containment) J2000. We set a time-integrated 95% CL upper limit at the position of maximum significance of: E^2 dN/dE = 1.63e-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: 28481 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-200921A and detection of a new gamma-ray source, Fermi J1256.9+2630 DATE: 20/09/23 07:56:04 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 IC200921A neutrino event (GCN 28468) 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 2020-09-21 19:07:12.89 UT (T0) with J2000 position RA = 195.29 (+2.35, -1.73) deg, Decl. = 26.24 (+1.51, -1.77) deg 90% PSF containment. Three cataloged >100 MeV gamma-ray sources are located within the 90% IC200921A localization error (The Fourth Fermi-LAT catalog; The Fermi-LAT collaboration 2020, ApJS, 247, 33). These are 4FGL J1303.0+2434 (associated with the BL Lac object MG2 J130304+2434), 4FGL J1256.9+2736 (associated with the AGN  NGC 4839) and 4FGL J1310.6+2449 (associated with the BL Lac object CRATES J131038.52+244822.1). Based on a preliminary analysis of LAT data at timescales of 1-month and 1-day prior to T0, these objects are not significantly detected (>5sigma). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (>100 MeV) at the IC200921A best-fit position. 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 < 2.8e-10 ph cm^-2 s^-1 for ~12-years (2008-08-04 / 2020-09-21 UTC), < 3.7e-9 (< 6.1e-8) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. In the analysis of the ~12-years integrated LAT data (0.1 - 800 GeV), a 4.7 sigma new excess of gamma rays, Fermi J1256.9+2630, was detected 1.0 deg offset from the best-fit IC200921A position and within the 90% confidence localization of the direction of the neutrino. Assuming a power-law spectrum, the best-fit localization is (J2000) RA: 194.23 deg, Dec: 26.51 deg (7.4 arcmin 99% containment, 3.6 arcmin 68% containment). The gamma-ray best-fit spectral parameters are flux = (4+/-3)e-10 ph cm^-2 s^-1 and index = 1.8+/-0.2. In a preliminary analysis of the LAT data over 1-day and 1-month prior T0, Fermi J1256.9+2630 is not significantly detected in the LAT data. All values include the statistical uncertainty only. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For these observations 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: 28485 SUBJECT: IceCube-200921A: Upper limits from a search for additional neutrino events in IceCube DATE: 20/09/23 14:53:18 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-200921A (https://gcn.gsfc.nasa.gov/gcn3/28433.gcn3) in a time range of 2 days centered on the alert event time (2020-09-20 19:07:12.89 UTC to 2020-09-22 19:07:12.89 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero additional track-like events are found in spatial coincidence with the 90% containment region of IceCube-200921A. We accordingly derive a time-integrated muon-neutrino flux upper limit at the alert position of E^2 dN/ dE = 4.8 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 1 PeV. A subsequent search was performed to include the month of data prior to the alert event (2020-08-22 19:07:12.89 UTC to 2020-09-22 19:07:12.89 UTC). In this case, we report a p-value of 0.08, 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 7.6 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28487 SUBJECT: IceCube Alert 200921.80: Global MASTER-Net observations report DATE: 20/09/23 21:13:10 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), 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 200921.80 (trigger No 71996695,13h 00m 47.28s , +26d 25m 48.0s, R=0.51) errorbox 1 days 64942 sec after notice time and 1 days 65023 sec after trigger time at 2020-09-23 13:10:56 UT, with upper limit up to 17.4 mag. The observations began at zenith distance = 80 deg. The sun altitude is -20.2 deg. The galactic latitude b = 87 deg., longitude l = 13 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1445930 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 151514 | 2020-09-23 13:10:56 | MASTER-Tunka | (13h 01m 31.51s , +26d 37m 02.0s) | C | 180 | 17.1 | 151713 | 2020-09-23 13:14:15 | MASTER-Tunka | (13h 01m 36.54s , +26d 35m 50.5s) | C | 180 | 17.1 | 151913 | 2020-09-23 13:17:35 | MASTER-Tunka | (13h 01m 30.54s , +26d 34m 42.7s) | C | 180 | 17.4 | 152112 | 2020-09-23 13:20:54 | MASTER-Tunka | (13h 01m 36.71s , +26d 34m 39.1s) | C | 180 | 17.4 | 152311 | 2020-09-23 13:24:14 | MASTER-Tunka | (13h 01m 33.97s , +26d 36m 08.7s) | C | 180 | 16.9 | 152511 | 2020-09-23 13:27:33 | MASTER-Tunka | (13h 01m 34.00s , +26d 34m 54.3s) | C | 180 | 17.0 | 152710 | 2020-09-23 13:30:53 | MASTER-Tunka | (13h 01m 37.00s , +26d 35m 54.6s) | C | 180 | 16.9 | 152910 | 2020-09-23 13:34:12 | MASTER-Tunka | (13h 01m 31.81s , +26d 35m 18.6s) | C | 180 | 16.7 | 153109 | 2020-09-23 13:37:31 | MASTER-Tunka | (13h 01m 31.93s , +26d 36m 14.7s) | C | 180 | 16.5 | 153308 | 2020-09-23 13:40:51 | MASTER-Tunka | (13h 01m 38.44s , +26d 35m 09.0s) | C | 180 | 16.5 | 153508 | 2020-09-23 13:44:10 | MASTER-Tunka | (13h 01m 32.31s , +26d 34m 02.6s) | C | 180 | 16.4 | 153707 | 2020-09-23 13:47:30 | MASTER-Tunka | (13h 01m 38.05s , +26d 34m 17.3s) | C | 180 | 15.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.