# Astronomy:Multi-messenger astronomy

Short description: Coordinated observation and interpretation of disparate "messenger" signals, created by different astrophysical processes

Multi-messenger astronomy is astronomy based on the coordinated observation and interpretation of disparate "messenger" signals. Interplanetary probes can visit objects within the Solar System, but beyond that, information must rely on "extrasolar messengers". The four extrasolar messengers are electromagnetic radiation, gravitational waves, neutrinos, and cosmic rays. They are created by different astrophysical processes, and thus reveal different information about their sources.

The main multi-messenger sources outside the heliosphere are expected to be compact binary pairs (black holes and neutron stars), supernovae, irregular neutron stars, gamma-ray bursts, active galactic nuclei, and relativistic jets.[1][2][3] The table below lists several types of events and expected messengers.

Detection from one messenger and non-detection from a different messenger can also be informative.[4]

Event type Electromagnetic Cosmic rays Gravitational waves Neutrinos Example
Solar flare yes yes - - SOL1942-02-28[5]
Supernova yes - predicted[6] yes SN 1987A
Neutron star merger yes - yes predicted[7] GW170817
Blazar yes possible - yes TXS 0506+056
Tidal disruption event yes possible possible yes possibly AT2019dsg[8]

## Networks

The Supernova Early Warning System (SNEWS), established in 1999 at Brookhaven National Laboratory and automated since 2005, combines multiple neutrino detectors to generate supernova alerts. (See also neutrino astronomy).

The Astrophysical Multimessenger Observatory Network (AMON),[9] created in 2013,[10] is a broader and more ambitious project to facilitate the sharing of preliminary observations and to encourage the search for "sub-threshold" events which are not perceptible to any single instrument. It is based at Pennsylvania State University.

## Milestones

• 1940s: Some cosmic rays are identified as forming in solar flares.[5]
• 1987: Supernova SN 1987A emitted neutrinos that were detected at the Kamiokande-II, IMB and Baksan neutrino observatories, a couple of hours before the supernova light was detected with optical telescopes.
• August 2017: A neutron star collision in the galaxy NGC 4993 produced the gravitational wave signal GW170817, which was observed by the LIGO/Virgo collaboration. After 1.7 seconds, it was observed as the gamma ray burst GRB 170817A by the Fermi Gamma-ray Space Telescope and INTEGRAL, and its optical counterpart SSS17a was detected 11 hours later at the Las Campanas Observatory, then by the Hubble Space Telescope and the Dark Energy Camera. Ultraviolet observations by the Neil Gehrels Swift Observatory, X-ray observations by the Chandra X-ray Observatory and radio observations by the Karl G. Jansky Very Large Array complemented the detection. This was the first gravitational wave event observed with an electromagnetic counterpart, thereby marking a significant breakthrough for multi-messenger astronomy.[11] Non-observation of neutrinos was attributed to the jets being strongly off-axis.[12] On 9 December 2017, astronomers reported a brightening of X-ray emissions from GW170817/GRB 170817A/SSS17a.[13][14]
• September 2017 (announced July 2018): On September 22, the extremely-high-energy[15] (about 290 TeV) neutrino event IceCube-170922A[16] was recorded by the IceCube Collaboration,[17][18] which sent out an alert with coordinates for the possible source. The detection of gamma rays above 100 MeV by the Fermi-LAT Collaboration[19] and between 100 GeV and 400 GeV by the MAGIC Collaboration[20] from the blazar TXS 0506+056 (reported September 28 and October 4, respectively) was deemed positionally consistent with the neutrino signal.[21] The signals can be explained by ultra-high-energy protons accelerated in blazar jets, producing neutral pions (decaying into gamma rays) and charged pions (decaying into neutrinos).[22] This is the first time that a neutrino detector has been used to locate an object in space and a source of cosmic rays has been identified.[21][23][24][25][26]
• October 2019 (announced February 2021): On October 1, a high energy neutrino was detected at IceCube and follow-up measurements in visible light, ultraviolet, x-rays and radio waves identified the tidal disruption event AT2019dsg as possible source.[8]

## References

1. Bartos, Imre; Kowalski, Marek (2017). Multimessenger Astronomy. IOP Publishing. doi:10.1088/978-0-7503-1369-8. ISBN 978-0-7503-1369-8. Bibcode2017muas.book.....B.
2. Franckowiak, Anna (2017). "Multimessenger Astronomy with Neutrinos". Journal of Physics: Conference Series 888 (12009): 012009. doi:10.1088/1742-6596/888/1/012009. Bibcode2017JPhCS.888a2009F.
3. Branchesi, Marica (2016). "Multi-messenger astronomy: gravitational waves, neutrinos, photons, and cosmic rays". Journal of Physics: Conference Series 718 (22004): 022004. doi:10.1088/1742-6596/718/2/022004. Bibcode2016JPhCS.718b2004B.
4. Abadie, J. (2012). "Implications for the origins of GRB 051103 from the LIGO observations". The Astrophysical Journal 755 (1): 2. doi:10.1088/0004-637X/755/1/2. Bibcode2012ApJ...755....2A.
5. Spurio, Maurizio (2015). Particles and Astrophysics: A Multi-Messenger Approach. Astronomy and Astrophysics Library. Springer. p. 46. doi:10.1007/978-3-319-08051-2. ISBN 978-3-319-08050-5.
6. Supernova Theory Group: Core-Collapse Supernova Gravitational Wave Signature Catalog
7. "No neutrino emission from a binary neutron star merger". 16 October 2017. Retrieved 20 July 2018.
9. Smith, M.W.E. (May 2013). "The Astrophysical Multimessenger Observatory Network (AMON)". Astroparticle Physics 45: 56–70. doi:10.1016/j.astropartphys.2013.03.003. Bibcode2013APh....45...56S.
10. Landau, Elizabeth; Chou, Felicia; Washington, Dewayne; Porter, Molly (16 October 2017). "NASA Missions Catch First Light from a Gravitational-Wave Event". NASA. Retrieved 17 October 2017.
11. Albert, A. (16 Oct 2017). "Search for high-energy neutrinos from binary neutron star merger GW170817 with ANTARES, IceCube, and the Pierre Auger Observatory". The Astrophysical Journal 850 (2): L35. doi:10.3847/2041-8213/aa9aed. Bibcode2017ApJ...850L..35A.
12. Haggard, Daryl; Ruan, John J.; Nynka, Melania; Kalogera, Vicky; Evans, Phil (December 9, 2017). "LIGO/Virgo GW170817: Brightening X-ray Emission from GW170817/GRB170817A/SSS17a - ATel #11041". The Astronomer's Telegram. Retrieved December 9, 2017.
13. Margutti, R.; Fong, W.; Eftekharl, T.; Alexander, E.; Chornock, R. (December 7, 2017). "LIGO/Virgo GW170817: Chandra X-ray brightening of the counterpart 108 days since merger - ATel #11037". The Astronomer's Telegram. Retrieved December 9, 2017.
14. Finkbeiner, A. (2017-09-22). "The New Era of Multimessenger Astronomy". Scientific American 318 (5): 36–41. doi:10.1038/scientificamerican0518-36. PMID 29672499.
15. https://gcn.gsfc.nasa.gov/gcn/gcn3/21916.gcn3
16. IceCube Collaboration (2018-07-12). "Neutrino emission from the direction of the blazar TXS 0506+056 prior to the IceCube-170922A alert". Science 361 (6398): 147–151. doi:10.1126/science.aat2890. PMID 30002248. Bibcode2018Sci...361..147I.
17. Mirzoyan, Razmik (2017-10-04). "ATel #10817: First-time detection of VHE gamma rays by MAGIC from a direction consistent with the recent EHE neutrino event IceCube-170922A". Astronomerstelegram.org. Retrieved 2018-07-16.
18. Aartsen (12 July 2018). "Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A". Science 361 (6398): eaat1378. doi:10.1126/science.aat1378. PMID 30002226. Bibcode2018Sci...361.1378I.
19. De Angelis, Alessandro; Pimenta, Mario (2018). Introduction to particle and astroparticle physics (multimessenger astronomy and its particle physics foundations). Springer. doi:10.1007/978-3-319-78181-5. ISBN 978-3-319-78181-5.
20. Aartsen (12 July 2018). "Neutrino emission from the direction of the blazar TXS 0506+056 prior to the IceCube-170922A alert". Science 361 (6398): 147–151. doi:10.1126/science.aat2890. PMID 30002248. Bibcode2018Sci...361..147I.
21. "Neutrino that struck Antarctica traced to galaxy 3.7bn light years away". The Guardian. July 12, 2018. Retrieved July 12, 2018.
22. "Source of cosmic 'ghost' particle revealed". BBC. July 12, 2018. Retrieved 12 July 2018.