IceCube-181023A

The IceCube Collaboration (http://icecube.wisc.edu/) reports:

On 23 October 2018 UTC IceCube detected a track-like, very-high-energy 
event with a high probability of being of astrophysical origin. The 
event was identified by the ��Extremely High Energy (EHE) track event 
selection.�� The IceCube detector was in a normal operating state. EHE 
events typically have a neutrino interaction vertex that is outside the 
detector, produce a muon that traverses the detector volume, and have a 
high light level (a proxy for energy).

After the initial automated alert 
(https://gcn.gsfc.nasa.gov/notices_amon/53411354_131653.amon), more
sophisticated reconstruction algorithms have been applied offline, with 
the direction refined to:

Date: 18/10/23

Time: 16:37:32.65 UTC
RA: 270.18 (-1.70,+2.00 deg ��90% PSF containment) J2000
Dec: -8.57 ��(-1.30,+1.25 deg 90% PSF containment) J2000

The closest sources to this position among Fermi-LAT catalogs 3FGL, 
2FGL, and 3FGL and Roma-BZCat is the unassociated source 3FGL 
J1804.5-0850 (1.3 degrees from best fit refined direction). ��We 
encourage follow-up of this alert by ground and space-based instruments 
to help identify a possible astrophysical source for the candidate neutrino.


The original GCN Notice contained an incorrect statement that ���this EHE 
event is the same as the previously reported HESE event.����� This is a 
unique EHE alert trigger and unrelated to previously reported HESE alerts.


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

S. Buson (Univ. of Wuerzburg), S. Garrappa (DESY-Zeuthen),  S. Cutini (Univ. of Perugia) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the very high-energy IC181023A neutrino event (GCN 23375
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 ) 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 2018-10-23 16:37:32.65 UTC (T0) with J2000 position RA = 270.18 (-1.70,+2.00) deg, Decl. = -8.57 (-1.30,+1.25) deg 90% PSF containment. One cataloged >100 MeV gamma-ray source is located within the 90% IC181014A localization error, at a distance of roughly 0.97deg. This is the unassociated object 3FGL J1804.5-0850 (Ackermann et al. 2015, ApJS, 810, 14). Based on a preliminary analysis of the LAT data over the past month, this object is not significantly detected in gamma-rays. 
 
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 (0.1 - 300 GeV) within the IC181023A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.2 fixed) for a point source at the IceCube best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.4e-8 (< 1.2e-8)  ph cm^-2 s^-1 for a 1-month (6-month) integration time before T0.

Within the error circle for the direction of the neutrino, 0.3deg offset from the best-fit IC181023A position, a ~4 sigma excess of gamma rays, Fermi J1801-0849, was detected in an analysis of the integrated LAT data (0.1 - 300 GeV) between 2008-08-04 and 2018-03-16. Assuming a power-law spectrum, the candidate gamma-ray source has best-fit localization of RA: 270.42  Dec:  -8.82 (0.14 deg 99% containment) with best fit spectral parameters flux = (7 +/- 3)e-9 ph cm^-2 s^-1, index = 2.3 +/- 0.1. This region is located near the Galactic plane, where the emission of the gamma-ray diffuse background is bright and might present some structure.

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. Buson (sara.buson at gmail.com), S. Garrappa (simone.garrappa at desy.de) and S. Cutini (sara.cutini at pg.infn.it).
 
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.

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-181023A
(https://gcn.gsfc.nasa.gov/gcn3/23375.gcn3
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 ) in a time range of
2 days centered on the alert event time (2018-10-22 16:37:32 UTC
to 2018-10-24 16:37:32 UTC) during which IceCube was collecting
good quality data. Excluding the event that prompted the alert, 2
additional track-like events are found in spatial coincidence with
the 90% PSF containment of IceCube-181023A. We find that these
data are well described by atmospheric background expectations, with
a p-value of 1.0. Accordingly, these data would represent a time-integrated
muon-neutrino flux upper limit assuming an E^-2 spectrum (E^2 dN/dE) at
the 90% CL of 9.71 x 10^-5 TeV cm^-2  for this observation period.

A subsequent search was performed to include the previous month of
data (2018-09-23 16:37:32 UTC to 2018-10-24 16:37:32 UTC). In
this case, we report a p-value of 1.0, consistent with no significant
excess of track events, and a corresponding time-integrated
muon-neutrino flux upper limit assuming an E^-2 spectrum (E^2 dN/dE)
at the 90% CL of 2.66 x 10^-4 TeV cm^-2.

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

V.Lipunov, V.Kornilov, N.Tiurina, E. Gorbovskoy, A.Kuznetsov, D.Zimnukhov, D.Kuvshinov, P.Balanutsa, V.Vladimirov,  D.Vlasenko
Lomonosov Moscow State University, Physics Department, SAI

N.M.Budnev, O. Gres, Yu.Ishmuhametova
Irkutsk State University (API ISU)

D. Buckley,
South African Astronomical Observatory (SAAO)

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias (IAC)

A. Tlatov, V.Senik, D. Dormidontov
Kislovodsk Solar Station of the Pulkovo Observatory

R. Podesta, F. Podesta, C. Lopez, C.Francile
Observatorio Astronomico Felix Aguilar (OAFA)

H.Levato,
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

A. Gabovich, V. Yurkov, Yu. Sergienko
Blagoveschensk Educational State University (BSPU)

MASTER Global Robotic Net started automatically IC181023A alert (from
socket coordinates)  observations  22 sec after notice time (MASTER-Tavrida) and
continued 1 day later as  IceCube-181023A (Blaufuss et al.GCN 23375,Pizzuto et al. GCN 23380
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 ) inspection  at MASTER-Kislovodsk.

MASTER-Tavrida robotic telescope (MASTER Net: Lipunov et.al.  2010, Advances in Astronomy, vol. 2010, 30L  http://www.hindawi.com/journals/aa/2010/349171/),
located in Lomonosov MSU, SAI Crimean astronomical station,
was pointed automatically to the  IC181023A error-box (taken from the socket)
22 sec after notice time and 66 sec after trigger time at 2018-10-23 16:38:38 UT.
We observed this socket error-box with unfiltered mlim=18.3 and not found 
new OT, connected with EHE neutrino astrophysical source.

The galactic latitude b =  7 deg., longitude l = 19 deg.
The observations made on zenit distance = 68 deg.
The sun  altitude  was -20.7 deg.
The moon (99 % bright part) was 21 deg. above the horizon. The distance 
between  moon and  object was 109 deg.


MASTER-Kislovodsk started IceCube-181023A (Blaufuss et al.GCN 23375 (RA:270.18 (-1.70,+2.00 deg); Dec: -8.57 (-1.30,+1.25 deg))
  inspection  with  mlim=17.0 between clouds  at 2018-10-24 15:31:39 UT

The observations made on zenit distance = 63 deg.
The moon (100 % bright part) was 11 deg. above the horizon. The distance  between  moon and  object was 121 deg.
The sun  altitude  was -15.2 deg.

Observations and more accurate reduction will be continued.
This message may be cited

Ignacio Taboada (Georgia Tech) and Israel Martinez (University of Maryland) report on behalf of the HAWC collaboration (https://www.hawc-observatory.org/collaboration/):

On 2018/10/23 16:37:32.65 UTC IceCube detected a track-like, very-high-energy event with a high probability of being of astrophysical origin, at RA=270.18d and Dec=-8.57d (J2000) as reported in GCN circular 23375
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 .

The event was not in the field of view of HAWC, so we analyze the data in three timescales:

*We searched for a steady source in archival data from November 2014 to April 2018.  Assuming a spectral index of -2.5 we searched in the reported 90% PSF containment circle.The maximum significance is 2.6 sigma at RA=270.62d and Dec=-8.88d. We estimate the number of trials to be ~100. We set an upper limit 95% CL on gamma rays for this period of:

E^2 dN/dE = 1.1e-12 (E/TeV)^-0.5 TeV cm^-2 s^-1.

*We searched using data corresponding to the month previous to the IceCube-181023A alert (2018-09-25 21:48 to 2018-10-25 00:41 UTC). Using the same spectral index and search window, the maximum significance is 1.6 sigma at RA=269.34d and Dec=-9.22d. We set an upper limit 95% CL on gamma rays for this period of:

E^2 dN/dE = 3.9e-12 (E/TeV)^-0.5 TeV cm^-2 s^-1.

*We also performed a study using data corresponding to the two nearest transits of IceCube-181023A in HAWC's field of view (2018/10/22 12:35:33 to 2018/10/24 00:55:13 UTC). Using the same spectral index and search window, the maximum significance is 2.1 sigma at RA=269.69d and Dec=-9.29d. We set an upper limit 95% CL on gamma rays for this period of:

E^2 dN/dE = 4.0e-11 (E/TeV)^-0.5 TeV cm^-2 s^-1.

HAWC is a very-high-energy gamma-ray observatory located in Central Mexico at latitude 19 deg North. It operates 24 hours per day 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.