In order to identify the sources of the observed diffuse high-energy neutrino flux, it is crucial to discover their electromagnetic counterparts. To increase the sensitivity of detecting counterparts of transient or variable sources by telescopes with a limited field of view, IceCube began releasing alerts for single high-energy ( E ν > 60 TeV) neutrino detections with sky localisation regions of order 1° radius in 2016. We used Pan-STARRS1 to follow-up five of these alerts during 2016–2017 to search for any optical transients that may be related to the neutrinos. Typically 10–20 faint ( m i P1 ≲ 22.5 mag) extragalactic transients are found within the Pan-STARRS1 footprints and are generally consistent with being unrelated field supernovae (SNe) and AGN. We looked for unusual properties of the detected transients, such as temporal coincidence of explosion epoch with the IceCube timestamp, or other peculiar light curve and physical properties. We found only one transient that had properties worthy of a specific follow-up. In the Pan-STARRS1 imaging for IceCube-160427A (probability to be of astrophysical origin of ∼50%), we found a SN PS16cgx, located at 10.0′ from the nominal IceCube direction. Spectroscopic observations of PS16cgx showed that it was an H-poor SN at redshift z = 0.2895 ± 0.0001. The spectra and light curve resemble some high-energy Type Ic SNe, raising the possibility of a jet driven SN with an explosion epoch temporally coincident with the neutrino detection. However, distinguishing Type Ia and Type Ic SNe at this redshift is notoriously difficult. Based on all available data we conclude that the transient is more likely to be a Type Ia with relatively weak Si II absorption and a fairly normal rest-frame r -band light curve. If, as predicted, there is no high-energy neutrino emission from Type Ia SNe, then PS16cgx must be a random coincidence, and unrelated to the IceCube-160427A. We find no other plausible optical transient for any of the five IceCube events observed down to a 5 σ limiting magnitude of m i P1 ≈ 22 mag, between 1 day and 25 days after detection.
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AMON Multimessenger Alerts: Past and Future
The Astrophysical Multimessenger Observatory Network (AMON) was founded to tie the world’s high-energy and multimessenger observatories into a single network, with the purpose to enable the discovering of multimessenger sources, to exploit these sources for purposes of astrophysics, fundamental physics, and cosmology, and to explore archival datasets for evidence of multimessenger source populations. Contributions of AMON to date include the GCN prompt alerts for likely-cosmic neutrinos, multiple follow-up campaigns for likely-cosmic neutrinos including the IceCube-170922A event, and several archival searches for transient and flaring γ + ν and ν + CR multimessenger sources. Given the new dawn of multimessenger astronomy recently realized with the detection of the neutron binary star merger and the possible γ + ν coincidence detection from the blazar TXS0506+056, in 2019, we are planning to commission several multimessenger alert streams, including GW + γ and high-energy γ + ν coincidence alerts. We will briefly summarize the current status of AMON and review our monitoring plans for high-energy and multimessenger AMON alerts during what promises to be a very exciting year for multimessenger astrophysics.
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- Award ID(s):
- 1708146
- NSF-PAR ID:
- 10092738
- Date Published:
- Journal Name:
- Galaxies
- Volume:
- 7
- Issue:
- 1
- ISSN:
- 2075-4434
- Page Range / eLocation ID:
- 19
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract High-energy neutrino and
γ -ray emission has been observed from the Galactic plane, which may come from individual sources and/or diffuse cosmic rays. We evaluate the contribution of these two components through the multimessenger connection between neutrinos andγ -rays in hadronic interactions. We derive maximum fluxes of neutrino emission from the Galactic plane usingγ -ray catalogs, including 4FGL, HGPS, 3HWC, and 1LHAASO, and measurements of the Galactic diffuse emission by Tibet ASγ and LHAASO. We find that the IceCube Galactic neutrino flux is larger than the contribution from all resolved sources when excluding promising leptonic sources such as pulsars, pulsar wind nebulae, and TeV halos. Our result indicates that the Galactic neutrino emission is likely dominated by the diffuse emission by the cosmic-ray sea and unresolved hadronicγ -ray sources. In addition, the IceCube flux is comparable to the sum of the flux of nonpulsar sources and the LHAASO diffuse emission especially above ∼30 TeV. This implies that the LHAASO diffuse emission may dominantly originate from hadronic interactions, either as the truly diffuse emission or unresolved hadronic emitters. Future observations of neutrino telescopes and air-showerγ -ray experiments in the Southern hemisphere are needed to accurately disentangle the source and diffuse emission of the Milky Way. -
Several tentative associations between high-energy neutrinos and astrophysical sources have been recently reported, but a conclusive identification of these potential neutrino emitters remains challenging. We explore the use of Monte Carlo simulations of source populations to gain deeper insight into the physical implications of proposed individual source–neutrino associations. In particular, we focus on the IC170922A–TXS 0506+056 observation. Assuming a null model, we find a 7.6% chance of mistakenly identifying coincidences between γ -ray flares from blazars and neutrino alerts in 10-year surveys. We confirm that a blazar–neutrino connection based on the γ -ray flux is required to find a low chance coincidence probability and, therefore, a significant IC170922A–TXS 0506+056 association. We then assume this blazar–neutrino connection for the whole population and find that the ratio of neutrino to γ -ray fluxes must be ≲10 −2 in order not to overproduce the total number of neutrino alerts seen by IceCube. For the IC170922A–TXS 0506+056 association to make sense, we must either accept this low flux ratio or suppose that only some rare sub-population of blazars is capable of high-energy neutrino production. For example, if we consider neutrino production only in blazar flares, we expect the flux ratio of between 10 −3 and 10 −1 to be consistent with a single coincident observation of a neutrino alert and flaring γ -ray blazar. These constraints should be interpreted in the context of the likelihood models used to find the IC170922A–TXS 0506+056 association, which assumes a fixed power-law neutrino spectrum of E −2.13 for all blazars.more » « less
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ABSTRACT The origin of cosmic high-energy neutrinos remains largely unexplained. For high-energy neutrino alerts from IceCube, a coincidence with time-variable emission has been seen for three different types of accreting black holes: (1) a gamma-ray flare from a blazar (TXS 0506+056), (2) an optical transient following a stellar tidal disruption event (TDE; AT2019dsg), and (3) an optical outburst from an active galactic nucleus (AGN; AT2019fdr). For the latter two sources, infrared follow-up observations revealed a powerful reverberation signal due to dust heated by the flare. This discovery motivates a systematic study of neutrino emission from all supermassive black hole with similar dust echoes. Because dust reprocessing is agnostic to the origin of the outburst, our work unifies TDEs and high-amplitude flares from AGN into a population that we dub accretion flares. Besides the two known events, we uncover a third flare that is coincident with a PeV-scale neutrino (AT2019aalc). Based solely on the optical and infrared properties, we estimate a significance of 3.6σ for this association of high-energy neutrinos with three accretion flares. Our results imply that at least ∼10 per cent of the IceCube high-energy neutrino alerts could be due to accretion flares. This is surprising because the sum of the fluence of these flares is at least three orders of magnitude lower compared to the total fluence of normal AGN. It thus appears that the efficiency of high-energy neutrino production in accretion flares is increased compared to non-flaring AGN. We speculate that this can be explained by the high Eddington ratio of the flares.
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The recent discoveries of high-energy cosmic neutrinos and gravitational waves from astrophysical objects have led to a new era of multimessenger astrophysics. In particular, electromagnetic follow-up observations triggered by these cosmic signals have proved to be highly successful and have brought about new opportunities in time-domain astronomy. We review high-energy particle production in various classes of astrophysical transient phenomena related to black holes and neutron stars, and discuss how high-energy emission can be used to reveal the underlying physics of neutrino and gravitational-wave sources.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/galaxies7010019
