Two
papers published this week in the journal Science have for
the first time provided evidence for a known blazar as a
source of high-energy neutrinos detected by the IceCube
observatory. The papers are available at this address
and here.
This blazar, designated by astronomers as TXS 0506+056, was
first singled out following a neutrino alert sent by IceCube
on Sept. 22, 2017 (IC170922A). More information are given on
the IceCube
website (see also the Press
Conference).
Thanks
to sharing of information by the IceCube collaboration
before the public release, the ANTARES Collaboration was
able to perform three different searches for neutrino
candidates associated with IC170922A or from the direction
of TXS 0506+056. The first one refers to the online
follow-up associated with IC170922A. The second is based on
the standard likelihood method employed by the Collaboration
to search for point-like neutrino sources. The third uses
the information from the time-dependent analysis performed
by the IceCube collaboration, which reports a bursting
activity centered on December 13, 2014, as input for an
ANTARES dedicated analysis. The results of these searches
are presented in an article submitted to The Astrophysical
Journal, available
here and on arXiv.
The online follow-up and the time-dependent analysis yield
no events related to the source. The time-integrated study
performed over a period from 2007 to 2017 fits 1.03 signal
events, which corresponds to a p-value of 3.4%. TXS 0506+056
consequently appears as the third most significant source
among the 107 scrutinised by ANTARES. Accounting for all
trials, the p-value rises up to 87%.
 |
 |
Left
: a blazar is accelerating protons that produce
pions, which produce neutrinos and gamma rays. Neutrinos
are always the result of a hadronic reaction such as the
one displayed here. Gamma rays can be produced in both
hadronic and electromagnetic interactions (Credit :
IceCube/NASA). Right : a high-energy neutrino
detected by IceCube on Sept. 22, 2017, with an estimated
energy of 290 TeV. The neutrino event display shows a
muon, created by the interaction of a neutrino with the
ice very close to IceCube, which leaves a track of light
while crossing the detector. In this display, the light
collected by each sensor is shown with a colored sphere.
The color gradient, from red to green/blue, shows the
time sequence (Credit: IceCube Collaboration).
 |
Distribution of ANTARES events in the (RA, DEC)
coordinates around the position of TXS 0506+056. The
inner (outer) green line depicts the one (five) degree
distance from the position source location, indicated as
a gray star. The red point denotes a shower-like event,
whereas the blue points indicate track-like events. The
dashed circles around the events indicate the angular
error estimate. Different shades of red and blue
correspond to the values assumed by the energy
estimators, the right legend shows the color scales. The
number of hits is used for shower-like events and a
parameter ρ for track-like events.
The ANTARES Collaboration thanks the IceCube Collaboration for the sharing of information before the public release. ANTARES congratulates the IceCube Collaboration for what seems to be a new major step forward in the multi-messenger era !