INTEGRAL joins multi-messenger campaign to study high-energy neutrino source
Astrophysical neutrinos provide a window into high-energy cosmic-ray interactions
occurring at their source. While the existence of high-energy astrophysical
neutrinos had been revealed by the IceCube neutrino observatory in 2013, no
potential neutrino sources had been identified thus far.
On September 22, 2017, IceCube detected a high-energy neutrino event of
potential astrophysical origin, named IceCube-170922A, and promptly alerted the
astronomical community to enable the search for an electromagnetic counterpart.
The direction of the neutrino was consistent with that of the blazar TXS 0506+056,
which at the time the neutrino was detected was in a high-emission state in the
GeV gamma-ray band as reported by the Fermi-LAT telescope. Follow-up observations
with the MAGIC telescopes resulted in the first detection of the source in
very-high-energy gamma rays. The significance of the correlation between the
neutrino and the flaring blazar has been estimated to be at the 3 sigma level,
providing first evidence for an astrophysical high-energy neutrino source. The
archival analysis of IceCube neutrinos has revealed an increase in the neutrino
rate from the direction of the blazar in 2014-2015, providing additional evidence
to the claim.
INTEGRAL participated in the follow-up campaign of IceCube-170922A that involved
14 other observatories spanning the electromagnetic spectrum to identify the counterpart.
Data from the SPI-ACS and IBIS/Veto instruments onboard INTEGRAL were used to set
upper limits on short X-ray bursts from the direction of the neutrino around the
time of the detection, while serendipitous observations with the ISGRI instrument
were used to set constraints on the flux from the blazar in the 20-250 keV range.
The image above shows the spectral energy distribution of TXS 0506+056 across
17 orders of magnitude in energy, with data collected up to two weeks after the
detection of the neutrino. Flux measurements from source detections are shown as
markers with error bars and upper limits are indicated as colored bands. For
comparison, the muon neutrino flux necessary to produce one event in IceCube over
0.5 (solid line) and 7.5 (dashed line) years is shown in black. The inset shows the
neutrino event as observed by the IceCube detector.
This exciting result is the first evidence for the existence of an astrophysical
source of high-energy neutrinos and continued observations could reveal more
potential counterparts to IceCube events. As IceCube is sensitive to neutrinos
across the entire sky, the sensitivity and large field of view of INTEGRAL makes
it a great follow-up instrument for this type of searches.
Credits: Marcos Santander (University of Alabama, USA), Volodymyr Savchenko (ISDC, University of Geneva, Switzerland).
References:
"Multimessenger observations of a flaring blazar coincident with high-energy
neutrino IceCube-170922A",
The IceCube Collaboration, Fermi-LAT, MAGIC, AGILE, ASAS-SN, HAWC, H.E.S.S.,
INTEGRAL, Kanata, Kiso, Kapteyn, Liverpool Telescope, Subaru, Swift/NuSTAR,
VERITAS, VLA/17B-403 teams
Science 13 Jul 2018, Vol. 361, Issue 6398
DOI: 10.1126/science.aat1378
(https://doi.org/10.1126/science.aat1378)
"Neutrino emission from the direction of the blazar TXS 0506+056 prior to
the IceCube-170922A alert",
The IceCube Collaboration
Science 13 Jul 2018, Vol. 361, Issue 6398, pp. 147-151
DOI: 10.1126/science.aat2890
(https://doi.org/10.1126/science.aat2890)
