This is the fifth and final part of the Multi-Messenger Astronomy series. We conclude with the events where multiple cosmic messengers have been detected simultaneously — the landmark cases that defined the field.
SN 1987A: the first multi-messenger event
SN 1987A — the supernova in the Large Magellanic Cloud on February 23, 1987 — was the first event detected in multiple cosmic messengers. Two were caught:
Neutrinos: A 13-second burst of 24 events spread across three detectors (Kamiokande-II in Japan, IMB in Ohio, Baksan in Russia). The burst arrived about 3 hours before any visible light.
Photons: Optical signature visible as a supernova in the LMC about 3 hours after the neutrino burst. Subsequent observation continued for decades, mapping the expansion of the remnant.
(Gravitational waves were not detected — LIGO didn’t exist yet at appropriate sensitivity. Cosmic-ray emission from a single supernova at 168,000 light-years is unmeasurable at Earth.)
The event combined four insights:
- Half a century of core-collapse-supernova theory was confirmed in 24 events.
- The 99% energy emission as neutrinos was directly measured.
- The timing offset — neutrinos arriving first, photons hours later — confirmed predictions about the optical depths of the collapsing star.
- The neutron-star formation was indirectly inferred (no compact-object signature has yet been detected in SN 1987A’s remnant, leaving open whether a neutron star formed and is hidden, or collapse went to a black hole).
Koshiba won the 2002 Nobel Prize for the Kamiokande detection, with SN 1987A as a central piece.
GW170817: the optical follow-up paradigm
August 17, 2017. LIGO and Virgo detected a binary neutron-star inspiral signal lasting about 100 seconds. The detection was identified within seconds. Multiple alerts went out.
The Fermi Gamma-ray Burst Monitor and INTEGRAL detected a short gamma-ray burst about 1.7 seconds after the neutron-star merger time. Direction consistent with the gravitational-wave region.
Within 11 hours, optical telescopes identified the new transient: a “kilonova” called AT 2017gfo, in the galaxy NGC 4993 at 40 megaparsecs. Subsequent observations included ultraviolet, infrared, X-ray (Chandra and others), and radio (VLA, MeerKAT) data over months.
Neutrinos: IceCube, Super-Kamiokande, ANTARES, and Baikal-GVD all looked for coincident neutrino events. None was detected. Upper limits were set.
The combined picture established:
- Binary neutron-star mergers produce short gamma-ray bursts. Theoretical prediction confirmed.
- Heavy elements form in mergers. The kilonova emission spectrum showed signatures of lanthanide and actinide radioactive decay — confirming the prediction that mergers are the dominant astrophysical site of $r$-process heavy-element synthesis (gold, platinum, uranium).
- A standard-siren measurement of the Hubble constant. The gravitational-wave distance combined with the host-galaxy redshift produced a $H_0 \approx 70$ km/s/Mpc measurement, in tension with neither the CMB nor the local distance-ladder values.
GW170817 won the 2017 Breakthrough Prize for multi-messenger astrophysics.
TXS 0506+056: the neutrino follow-up paradigm
September 22, 2017 (six weeks after GW170817). IceCube reconstructed a single muon-track event at high energy. The reconstructed direction pointed to a specific known blazar: TXS 0506+056, 3.7 billion light-years away.
Within hours, alerts triggered observation by 18 telescopes worldwide. The optical and gamma-ray follow-up showed that TXS 0506+056 was in a flaring state — its gamma-ray luminosity was elevated by a factor of ~5 over its quiescent level. The neutrino arrived in the middle of this flare.
Retrospective analysis of IceCube data from 2014-2015 found a previously-overlooked cluster of muon tracks from the TXS direction. Combined with the 2017 event, the evidence for TXS 0506+056 as a real cosmic neutrino source reached high statistical significance.
The campaign established:
- The first individually-identified extragalactic cosmic neutrino source.
- Blazars as hadronic accelerators — the simultaneous gamma-ray + neutrino flare implies cosmic-ray proton acceleration in the jet.
- The multi-messenger alert infrastructure works — coordinated response across 18 observatories worldwide produced the identification within days.
TXS 0506+056 is the textbook example of how neutrino astronomy now operates as a working observational science.
What we’ve learned
These three events combined illustrate the power of multi-messenger observation:
SN 1987A: established neutrino astronomy as a working discipline. Showed that core-collapse theory was right. Established the timing-offset technique for catching early supernova phases.
GW170817: established gravitational-wave astronomy as multi-messenger ready. Confirmed neutron-star mergers as heavy-element sites. Demonstrated the optical-follow-up paradigm.
TXS 0506+056: established neutrino astronomy as source-identifying. Confirmed blazars as hadronic accelerators. Demonstrated the real-time alert paradigm.
What’s coming
The infrastructure for multi-messenger campaigns has matured. SNEWS, AMON, GCN (Gamma-ray Coordinates Network), and Astronomer’s Telegram all coordinate alerts. Most major observatories have automated follow-up protocols.
Anticipated multi-messenger events in the next decade:
A galactic core-collapse supernova (expected once per ~30-50 years; the last visible one was Kepler’s supernova in 1604). Would produce neutrinos + gravitational waves + photons. Modern detectors are ready.
More binary neutron-star mergers. LIGO O4 and beyond should detect dozens. Some will have electromagnetic counterparts; the closer ones may produce detectable neutrino coincidence.
More IceCube-triggered blazar/AGN alerts. Currently ~1 per year of high-significance alerts. With IceCube-Gen2, this rate increases substantially.
The first detection of a tidal-disruption event in neutrinos and gravitational waves. Several candidates have been associated with IceCube events but none has been definitively confirmed.
A possibly-detectable kilonova-merger combining all messengers: a future binary neutron-star merger within ~100 Mpc could potentially produce gravitational waves + photons across all wavelengths + neutrinos, if such mergers actually emit detectable neutrino fluxes.
This concludes the Multi-Messenger Astronomy series. For the chronological context of how each messenger came online, see the Neutrino History series. For the detector technology behind each detection, see Detector Deep Dives. For where neutrinos come from in the cosmic picture, see Sources of Neutrinos.
Frequently asked
Which events have produced multi-messenger observations?
Three landmark events define the field: SN 1987A (1987, neutrinos + photons), GW170817 (2017, gravitational waves + photons across all wavelengths), and TXS 0506+056 (2017, neutrinos + photons across all wavelengths from a single AGN). Each combined different messengers and produced fundamental insights inaccessible to any single observable.
What did each event teach us?
SN 1987A confirmed core-collapse-supernova theory and established neutrino astronomy. GW170817 confirmed neutron-star mergers as heavy-element production sites and that mergers produce short gamma-ray bursts. TXS 0506+056 identified the first individually-resolved extragalactic cosmic-neutrino source and established blazars as hadronic accelerators.
Why are multi-messenger events so rare?
Each messenger has different detection requirements, sky coverage, and sensitivity. Coincident detection requires that a source be bright enough in all relevant channels and that all detectors be operating at the right time. For weak signals, post-hoc temporal coincidence may not exceed background. The infrastructure for rapid alert distribution is relatively new — only now is the field set up to recognize multi-messenger coincidences in real time.
What would the next event look like?
Three plausible candidates: (1) a galactic core-collapse supernova, which would produce neutrinos + gravitational waves + photons simultaneously; (2) a binary neutron-star merger close enough that both gravitational-wave and neutrino emission are detectable; (3) another high-energy IceCube-triggered alert from a flaring blazar or AGN with detected gamma-ray counterpart. The first two would be once-per-decade events; the third happens roughly annually.
Cite this article 5 formats
APA
Neutrino Times Editorial Team. (2026, March 31). Multi-Messenger Astronomy — Part 5: When messengers combine — SN 1987A, GW170817, TXS 0506+056. Neutrino Times. https://neutrino-times.com/articles/multi-messenger-part-5-combined-events/
Chicago
Neutrino Times Editorial Team. "Multi-Messenger Astronomy — Part 5: When messengers combine — SN 1987A, GW170817, TXS 0506+056." Neutrino Times, March 31, 2026. https://neutrino-times.com/articles/multi-messenger-part-5-combined-events/.
MLA
Neutrino Times Editorial Team. "Multi-Messenger Astronomy — Part 5: When messengers combine — SN 1987A, GW170817, TXS 0506+056." Neutrino Times, 31 Mar. 2026, https://neutrino-times.com/articles/multi-messenger-part-5-combined-events/.
BibTeX
@misc{neutrino-times-multi-messenger-part-5-combined-events,
author = {Neutrino Times Editorial Team},
title = {Multi-Messenger Astronomy — Part 5: When messengers combine — SN 1987A, GW170817, TXS 0506+056},
howpublished = {Neutrino Times},
year = {2026},
month = {mar},
url = {https://neutrino-times.com/articles/multi-messenger-part-5-combined-events/},
note = {Accessed: 2026-03-31}
} RIS
TY - GEN TI - Multi-Messenger Astronomy — Part 5: When messengers combine — SN 1987A, GW170817, TXS 0506+056 AU - Neutrino Times Editorial Team PY - 2026 DA - 2026-03-31 PB - Neutrino Times UR - https://neutrino-times.com/articles/multi-messenger-part-5-combined-events/ ER -