Follow-up of the IceCube neutrino source candidate TXS 0506-056


The ANTARES and HESS collaborations have followed-up the IceCube observation of a first possible high-energy neutrino source candidate, and the APC groups have had a strong role in these searches.

The IceCube Collaboration has reported, in a press conference at the US National Science Foundation on July 12th 2018, a correlation between high-energy neutrinos and the blazar known as TXS0506+056. This object was first brought to attention following a neutrino alert sent by IceCube on Sept. 22nd 2017 (IC170922A). About 20 observatories on Earth and in space have participated to a large multi-messenger effort to follow-up the alert on their data streams and to search for correlation in archival data. Two papers [1, 2] have been published reporting these results.


The IceCube track-like event IC170922A, which was detected and reconstructed in the IceCube detector on September 22nd 2017 as arriving from approximate equatorial coordinates RA=77.43+1.3-0.8 and δ = 5.72+0.7-0.4 with an estimated energy of 290 TeV, which triggered a large-scale multi-messenger search for its counterpart. (Credit: the IceCube Collaboration)


High-energy neutrino search: ANTARES analyses


The IceCube collaboration shared some restricted information with the ANTARES Collaboration in compliance with a Memorandum of Understanding. Three different searches for neutrino candidates associated with IC170922A or from the direction of TXS 0506+056 were performed by ANTARES:

  • The first search refers to the online follow-up associated with IC170922A.
  • The second one is based on the standard method employed by the Collaboration to search for a time-integrated directional excess from point-like neutrino sources.
  • The third one uses the information from the time-dependent analysis performed by the IceCube Collaboration, which reports a neutrino-bursting activity centered on December 13, 2014, as input for an ANTARES dedicated study.

The results of the searches are presented in a submitted journal article [3]. The online follow-up and the time-dependent analysis yield no events related to the source and to the neutrino flare reported by the IceCube Collaboration . The time-integrated study, performed over 10 years of ANTARES data taking from 2007 to 2017, reports 1.03 fitted signal events from the region around TXS 0506+056, which corresponds to a pre-trial p-value of 3.4%. TXS 0506+056 consequently appears as the third most significant source among the 107 scrutinised by ANTARES for the period 2007-2015. Accounting for all trials, the p-value rises up to 87%.


ANTARES track- (blue) and shower-like (red) events in the proximity of TXS 0506+056 (indicated as a star a the center of the sky-map) over ten years of data taking. The dashed circles around the events indicate the estimated error on the direction reconstruction. The color code shows the energy estimator of each individual event.


High-energy gamma-ray search: Observation with HESS


Combined observations of various cosmic messengers might indeed provide the missing pieces of information about the violent phenomena at the origin of high-energy cosmic rays. High-energy gamma rays play an important role in this context. The H.E.S.S. collaboration has been participating in multi-messenger observations for the past several years, in close collaboration with both of the major neutrino telescopes, IceCube and ANTARES.

On September 22, 2017: at 20:54:30.43 Coordinated Universal Time (UTC), a high-energy neutrino of about 290TeV (IceCube-170922A) was detected by the IceCube neutrino telescope. An alert was distributed to observatories around the globe within 1 minute. The direction of the neutrino (reconstructed to an area of about 1sq deg and consistent with the location of a known gamma-ray blazar TXS 0506+056) became visible at the location of the H.E.S.S. observatory in Namibia around 4 hours later and follow-up observations were started (cf. Astronomer Telegram ATEL #10787). Additional observations were obtained on subsequent nights but no gamma-ray emission could be detected from the region. Upper limits at 7.5×10-12 erg / cm2 /s (95% C.L.) on the gamma-ray flux level were subsequently derived.


Significance map of the H.E.S.S. observation in the region of TXS 0506+056


To go further:


The IceCube Collaboration Website:

The ANTARES Collaboration Website:

The H.E.S.S. Observatory Website:


[1] “Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A,” The IceCube, Fermi-LAT, MAGIC, AGILE, ASAS-SN, HAWC, H.E.S.S, INTEGRAL, Kanata, Kiso, Kapteyn, Liverpool telescope, Subaru, Swift/NuSTAR, VERITAS, and VLA/17B-403 teams, Science 361. DOI:10.1126/science.aat1378

[2] “Neutrino emission from the direction of the blazar TXS 0506+056 prior to the IceCube-170922A alert,” IceCube Collaboration: M.G. Aartsen et al. Science 361. DOI:10.1126/science.aat2890

[3] “Search for neutrinos from TXS 0506+056 with the ANTARES telescope”, ANTARES Collaboration: A. Albert et al.,