Searching for High-energy Neutrinos from Supernovae with IceCube and an Optical Follow-up Program

In violent astrophysical processes high-energy neutrinos of TeV to PeV energies are expected to be produced along with the highest energy cosmic rays. The acceleration of nuclei to very high energies is assumed to takes place in astrophysical shocks and neutrinos are produced in the interaction of these cosmic rays with ambient baryons or photons. The neutrinos then escape the acceleration region and propagate through space without interaction, while the nuclei are deflected in magnetic fields and no longer carry information about their source position. Unlike gamma-rays, neutrinos are solely produced in hadronic processes and can therefore reveal the sources of charged cosmic rays. The IceCube neutrino detector, which is located at the geographical South Pole, has been build to detect these high-energy astrophysical neutrinos. The deep clear Antarctic ice is instrumented with light sensors on a grid, thus forming a Cherenkov particle detector, which is capable of detecting charged particles induced by neutrinos above 100 GeV. Transient neutrino sources such as Gamma-Ray Bursts (GRBs) and Supernovae (SNe) are hypothesized to emit bursts of high-energy neutrinos on a time-scale of ≤ 100 s. While GRB neutrinos would be produced in the high relativistic jets driven by the central engine, corecollapse SNe might host soft-relativistic jets which become stalled in the outer layers of the progenitor star and lead to an efficient production of high-energy neutrinos. This work aims for an increased sensitivity for these neutrinos and for a possible identification of their sources. Towards this goal, a low-threshold optical follow-up program for neutrino multiplets detected with IceCube has been implemented. If a neutrino multiplet – i.e. two or more neutrinos from the same direction within 100 s – is found by IceCube a trigger is sent to the Robotic Optical Transient Search Experiment (ROTSE). The 4 ROTSE telescopes immediately start an observation program of the corresponding region of the sky in order to detect a possible optical counterpart to the neutrino events. Complementary to previous transient neutrino searches, which have been performed offline on IceCube data on source regions and time windows provided by gamma-ray satellites, this neutrino search is applied – for the first time – in real time to neutrino data at the South Pole. It is sensitive to transient objects, including those which are gamma-ray dark or not detected by gamma-ray satellites. In addition to a gain in sensitivity, the optical observations may allow the identification of the transient neutrino source, be it a SN, a GRB or any other transient phenomenon producing an optical signal. Hence, it enables to test the hypothesis of soft relativistic jets in SNe and may shed light on the connection between GRBs, SNe and relativistic jets. The content of this work are the development and implementation of the optical follow-up program as well as the analysis of the data collected in the first year of operation. No statistically significant excess in the rate of neutrino multiplets has been observed and furthermore no coincidence with an optical counterpart was found. However, for the first time stringent limits can be set on current models predicting a high-energy neutrino flux from soft relativistic hadronic jets in core-collapse SNe. It can be concluded that a sub-population of SNe with jets with a typical Lorentz boost factor of 10 and a jet energy of 3 × 1051 erg does not exceed 4:2% at 90% confidence.Suche nach Hoch-energetischen Neutrinos von Supernovae mit IceCube und einem Optischen Nachbeobachtungsprogramm In energiereichen astrophysikalischen Prozessen erwartet man die Produktion von Neutrinos mit Energien im TeV bis PeV Bereich Seite an Seite mit der Produktion der hochenergetischen komischen Strahlung. Die Beschleunigung der Kerne zu den gemessenen hohen Energien findet vermutlich in astrophysikalischen Schocks statt. In Wechselwirkungen mit den umgebenden Baryonen und Photonen werden dann Neutrinos produziert. Diese Neutrinos können die Beschleunigungsregion verlassen und propagieren ungehindert durch den Raum, während die Kerne in intergalaktischen Magnetfeldern abgelenkt werden und sich ihre Quellen somit nicht mehr zurück verfolgen lassen. Im Gegensatz zu Photonen werden Neutrinos ausschließlich in hadronischen Prozessen erzeugt und erlauben es so, die Quellen der kosmischen Strahlung zu identifizieren. Zum Nachweis dieser astrophysikalischen Neutrinos wurde am geographischen Südpol der Neutrinodetektor IceCube gebaut. Das tiefe antarktische Eis wurde dafür mit Lichtsensoren ausgestattet und auf diese Weise in einen Tscherenkov Teilchendetektor verwandelt, welcher geladene Teilchen nachweisen kann, die durch Neutrinos mit Energies oberhalb von 100 GeV induziert werden. Theoretische Modelle sagen vorher, dass transiente Neutrinoquellen wie Gammastrahlungsausbrüche (GRBs) und Supernovae (SNe) kurze Ausbrüche – sogenannte “Bursts” – von hochenergetischen Neutrinos auf einer Zeitskala von ≤ 100 s emittieren. Während GRB Neutrinos in hoch relativistischen Jets produziert werden, könnten Kernkollaps-Supernovae (CCSNs) einen schwach relativistischen Jet beherbergen, dem es nicht gelingt, die äußere Hülle des Vorgängersternes zu durchdringen, sondern der darin zum Stillstand kommt und so für effiziente Neutrinoproduktion sorgt. Ziel diese Arbeit ist die Verbesserung der Sensitivität für die Messung diese Neutrinos und die Identifikation ihrer Quellen. Dafür wurde ein optisches Nachverfolgungsprogramm für Neutrinomultipletts entwickelt, welche mit dem IceCube Neutrinodetektor gemessen werden. Falls ein Neutrinomultiplett – d.h. mindestens zwei Neutrinos aus der gleichen Richtung innerhalb von 100 s – von IceCube gefunden wird, wird ein Trigger an das Robotic Optical Transient Search Experiment (ROTSE) gesendet. Die vier ROTSE Teleskope starten unmittelbar ein Beobachtungsprogramm für die entsprechende Richtung am Himmel, um ein optisches Gegenstück zu den Neutrinoereignisse detektieren zu können. Im Gegensatz zu den bisher durchgeführten Suchen nach transienten Neutrinoquellen, welche offline durchgeführt und durch die von Gammastrahlensatelliten bereitgestellte Informationen getriggert werden, wird diese Analyse als bislang erste Analyse in Echtzeit auf Neutrinodaten am Südpol angewendet. Sie ermöglicht die Detektion von transienten Objekten, einschließlich solcher, die keine Gammastrahlen emittieren oder die nicht von Satelliten beobachtet werden können. Zusätzlich zu einer Verbesserung der Sensitivität können die optischen Beobachtungen eine Identifikation der Quelle erlauben, unabhängig davon, ob es sich um eine SN, einen GRB oder eine anderes transientes Phänomen handelt, das ein optisches Signal erzeugt. Folglich kann mit dieser Methode das Modell für schwach relativistische Jets in SNe getestet, sowie Aufschluß über die Verbindung zwischen GRBs, SNe und relativistischen Jets gegeben werden. Der Inhalt dieser Arbeit ist die Entwicklung und Durchführung des optischen Nachverfolgungsprogramms sowie die Analyse der Daten, welche während des ersten Jahres des Betriebs aufgenommen wurden. In den Daten wurde weder ein statistisch signifikanter Exzess der Neutrinomultiplettrate noch ein optisches Gegenstück zu einem der Neutrinomultipletts gefunden. Diese Analyse erlaubt daher zum ersten mal ein strenges Limit auf aktuelle Modelle zu setzen, welche einen Fluss hochenergetischer Neutrinos aus schwach relativistischen hadronischen Jets in Kernkollaps-Supernovae vorhersagen. Es kann mit einem Vertrauensintervall von 90% ausgeschlossen werden, dass die Subpopulation von SNe mit Jets mit typischen Lorentz Boost Faktoren von 10 und Jetenergien von 3 × 1051 erg 4:2% überschreitet. Komplette Version ist aus urheberrechtlichen Gründen vorübergehend gesperrt

High-Energy Emission from Interacting Supernovae: New Constraints on Cosmic-Ray Acceleration in Dense Circumstellar Environments

Supernovae (SNe) with strong interactions with circumstellar material (CSM) are promising candidate sources of high-energy neutrinos and gamma rays, and have been suggested as an important contributor to Galactic cosmic rays beyond 1 PeV. Taking into account the shock dissipation by a fast velocity component of SN ejecta, we present comprehensive calculations of the non-thermal emission from SNe powered by shock interactions with a dense wind or CSM. Remarkably, we consider electromagnetic cascades in the radiation zone and subsequent attenuation in the pre-shock CSM. A new time-dependent phenomenological prescription provided by this work enables us to calculate gamma-ray, hard X-ray, radio, and neutrino signals, which originate from cosmic rays accelerated by the diffusive shock acceleration mechanism. We apply our results to SN IIn 2010jl and SN Ib/IIn 2014C, for which the model parameters can be determined from the multi-wavelength data. For SN 2010jl, the more promising case, by using the the latest Fermi Large Area Telescope (LAT) Pass 8 data release, we derive new constraints on the cosmic-ray energy fraction, <0.05-0.1. We also find that the late-time radio data of these interacting SNe are consistent with our model. Further multi-messenger and multi-wavelength observations of nearby interacting SNe should give us new insights into the diffusive shock acceleration in dense environments as well as pre-SN mass-loss mechanisms.Comment: 16 pages, 10 figures, 3 tables, accepted for publication in ApJ. Results and conclusions unchange

Optically Informed Searches of High-Energy Neutrinos from Interaction-Powered Supernovae

The interaction between the ejecta of supernovae (SNe) of Type IIn and a dense circumstellar medium (CSM) can efficiently generate thermal UV/optical radiation and lead to the emission of neutrinos in the $1$-$10^{3}$ TeV range. We investigate the connection between the neutrino signal detectable at the IceCube Neutrino Observatory and the electromagnetic signal observable by optical wide-field, high-cadence surveys to outline the best strategy for upcoming follow-up searches. We outline a semi-analytical model that connects the optical lightcurve properties to the SN parameters and find that a large peak luminosity ($L_{\rm{peak}}\gtrsim 10^{43}$-$10^{44}$ erg) and an average rise time ($t_{\rm{rise}}\gtrsim 10$-$40$ days) are necessary for copious neutrino emission. Nevertheless, the most promising $L_{\rm{peak}}$ and $t_{\rm{rise}}$ are not sufficient to guarantee ideal conditions for neutrino detection. Comparable optical properties can be obtained for SN configurations that are not optimal for neutrino emission. Such ambiguous correspondence between the optical lightcurve properties and the number of IceCube neutrino events implies that relying on optical observations only, a range of expected neutrino events should be considered (e.g. the expected number of neutrino events can vary up to two orders of magnitude for some among the brightest SNe IIn observed by the Zwicky Transient Facility up to now, SN 2020usa and SN 2020in). In addition, the peak in the high-energy neutrino curve should be expected a few $t_{\rm{rise}}$ after the peak in the optical lightcurve. Our findings highlight that it is crucial to infer the SN properties from multi-wavelength observations rather than focusing on the optical band only to enhance upcoming neutrino searches.Comment: 20 pages, including 14 figures and 3 appendice

Leptohadronic Multimessenger Modeling of 324 Gamma-Ray Blazars

The origin of the diffuse astrophysical neutrino flux observed by the IceCube experiment is still under debate. In recent years there have been associations of neutrino events with individual blazars, which are active galaxies with relativistic jets pointing toward Earth, such as the source TXS 0506+056. From a theoretical perspective, the properties of these sources as neutrino emitters are not yet well understood. In this work we model a sample of 324 blazars detected by the Fermi Large Area Telescope (LAT), most of which are flat-spectrum radio quasars (FSRQs). This amounts to 34% of all FSRQs in the latest Fermi catalog. By numerically modelling the interactions of cosmic-ray electrons and protons, we explain the emitted multi-wavelength fluxes from each source and self-consistently predict the emitted neutrino spectrum. We demonstrate that the optical and GeV gamma-ray broadband features are generally well described by electron emission. For 33% of the blazars in our sample, a description of the observed X-ray spectrum benefits from an additional component from proton interactions, in agreement with recent studies of individual IceCube candidate blazars. We conclude that blazars that are brighter in GeV gamma rays tend to have a higher neutrino production efficiency but a lower best-fit baryonic loading. The predicted neutrino luminosity shows a positive correlation with the observed GeV gamma-ray flux and with the predicted MeV gamma-ray flux. By extrapolating the results for this sample, we show that the diffuse neutrino flux from the population of gamma-ray-bright blazars may be at the level of about 20% of the IceCube flux, in agreement with current limits from stacking analyses. We discuss the implications of our results for future neutrino searches and suggest promising sources for potential detections with future experiments.Comment: Submitted to A&A. Contains 28 pages, 13 figures. Results available online in machine-readable format (see caption of Tab. B.1.

Multi-wavelength and neutrino emission from blazar PKS 1502+106

In July of 2019, the IceCube experiment detected a high-energy neutrino from the direction of the powerful blazar PKS 1502+106. We perform multi-wavelength and multi-messenger modeling of this source, using a fully self-consistent one-zone model that includes the contribution of external radiation fields typical of flat-spectrum radio quasars (FSRQs). We identify three different activity states of the blazar: one quiescent state and two flaring states with hard and soft gamma-ray spectra. We find two hadronic models that can describe the multi-wavelength emission during all three states: a leptohadronic model with a contribution from photo-hadronic processes to X-rays and gamma rays, and a proton synchrotron model, where the emission from keV to 10 GeV comes from proton synchrotron radiation. Both models predict a substantial neutrino flux that is correlated with the gamma-ray and soft X-ray fluxes. Our results are compatible with the detection of a neutrino during the quiescent state, based on event rate statistics. We conclude that the soft X-ray spectra observed during bright flares strongly suggest a hadronic contribution, which can be interpreted as additional evidence for cosmic ray acceleration in the source independently of neutrino observations. We find that more arguments can be made in favor of the leptohadronic model vis-a-vis the proton synchrotron scenario, such as a lower energetic demand during the quiescent state. However, the same leptohadronic model would be disfavored for flaring states of PKS 1502+106 if no IceCube events were found from the direction of the source before 2010, which would require an archival search.Comment: 14 pages, 5 figure

Multiwavelength Search for the Origin of IceCube's Neutrinos

The origin of astrophysical high-energy neutrinos detected by the IceCube Neutrino Observatory remains a mystery to be solved. In this paper we search for neutrino source candidates within the 90% containment area of 70 track-type neutrino events recorded by the IceCube Neutrino Observatory. By employing the Fermi-LAT 4FGL-DR2, the Swift-XRT 2SXPS, and the CRATES catalogs, we identify possible gamma-ray, X-ray, and flat-spectrum radio candidate sources of track-type neutrinos. We find that based on the brightness of sources and their spatial correlation with the track-type IceCube neutrinos, the constructed neutrino samples represent special populations of sources taken from the full Fermi-LAT 4FGL-DR2/Swift-XRT 2SXPS/CRATES catalogs with similar significance (2.1σ, 1.2σ, 2σ at 4.8 GHz, 2.1σ at 8.4 GHz, respectively, assuming 50% astrophysical signalness). After collecting redshifts and deriving subsamples of the CRATES catalog complete in the redshift-luminosity plane, we find that the 4.8 GHz (8.4 GHz) subsample can explain between 4% and 53% (3% and 42%) of the neutrinos (90% C.L.), when the probability of detecting a neutrino is proportional to the (k-corrected) radio flux. The overfluctuations indicate that a part of the sample is likely to contribute and that more sophisticated schemes in the source catalog selection are necessary to identify the neutrino sources at the 5σ level. Our selection serves as a starting point to further select the correct sources

ASAS-SN follow-up of IceCube high-energy neutrino alerts

We report on the search for optical counterparts to IceCube neutrino alerts released between April 2016 and August 2021 with the All-Sky Automated Survey for SuperNovae (ASAS-SN). Despite the discovery of a diffuse astrophysical high-energy neutrino flux in 2013, the source of those neutrinos remains largely unknown. Since 2016, IceCube has published likely-astrophysical neutrinos as public realtime alerts. Through a combination of normal survey and triggered target-of-opportunity observations, ASAS-SN obtained images within 1 hour of the neutrino detection for 20% (11) of all observable IceCube alerts and within one day for another 57% (32). For all observable alerts, we obtained images within at least two weeks from the neutrino alert. ASAS-SN provides the only optical follow-up for about 17% of IceCube's neutrino alerts. We recover the two previously claimed counterparts to neutrino alerts, the flaring-blazar TXS 0506+056 and the tidal disruption event AT2019dsg. We investigate the light curves of previously-detected transients in the alert footprints, but do not identify any further candidate neutrino sources. We also analysed the optical light curves of Fermi 4FGL sources coincident with high-energy neutrino alerts, but do not identify any contemporaneous flaring activity. Finally, we derive constraints on the luminosity functions of neutrino sources for a range of assumed evolution models

The Zwicky Transient Facility: System Overview, Performance, and First Results

The Zwicky Transient Facility (ZTF) is a new optical time-domain survey that uses the Palomar 48 inch Schmidt telescope. A custom-built wide-field camera provides a 47 deg 2 field of view and 8 s readout time, yielding more than an order of magnitude improvement in survey speed relative to its predecessor survey, the Palomar Transient Factory. We describe the design and implementation of the camera and observing system. The ZTF data system at the Infrared Processing and Analysis Center provides near-real-time reduction to identify moving and varying objects. We outline the analysis pipelines, data products, and associated archive. Finally, we present on-sky performance analysis and first scientific results from commissioning and the early survey. ZTF’s public alert stream will serve as a useful precursor for that of the Large Synoptic Survey Telescope

The Zwicky Transient Facility: Science Objectives

The Zwicky Transient Facility (ZTF), a public–private enterprise, is a new time-domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg2 field of view and an 8 second readout time. It is well positioned in the development of time-domain astronomy, offering operations at 10% of the scale and style of the Large Synoptic Survey Telescope (LSST) with a single 1-m class survey telescope. The public surveys will cover the observable northern sky every three nights in g and r filters and the visible Galactic plane every night in g and r. Alerts generated by these surveys are sent in real time to brokers. A consortium of universities that provided funding (“partnership”) are undertaking several boutique surveys. The combination of these surveys producing one million alerts per night allows for exploration of transient and variable astrophysical phenomena brighter than r∼20.5 on timescales of minutes to years. We describe the primary science objectives driving ZTF, including the physics of supernovae and relativistic explosions, multi-messenger astrophysics, supernova cosmology, active galactic nuclei, and tidal disruption events, stellar variability, and solar system objects. © 2019. The Astronomical Society of the Pacific

Kilonova Luminosity Function Constraints Based on Zwicky Transient Facility Searches for 13 Neutron Star Merger Triggers during O3

We present a systematic search for optical counterparts to 13 gravitational wave (GW) triggers involving at least one neutron star during LIGO/Virgo's third observing run (O3). We searched binary neutron star (BNS) and neutron star black hole (NSBH) merger localizations with the Zwicky Transient Facility (ZTF) and undertook follow-up with the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. The GW triggers had a median localization area of 4480 deg², a median distance of 267 Mpc, and false-alarm rates ranging from 1.5 to 10⁻²⁵ yr⁻¹. The ZTF coverage in the g and r bands had a median enclosed probability of 39%, median depth of 20.8 mag, and median time lag between merger and the start of observations of 1.5 hr. The O3 follow-up by the GROWTH team comprised 340 UltraViolet/Optical/InfraRed (UVOIR) photometric points, 64 OIR spectra, and three radio images using 17 different telescopes. We find no promising kilonovae (radioactivity-powered counterparts), and we show how to convert the upper limits to constrain the underlying kilonova luminosity function. Initially, we assume that all GW triggers are bona fide astrophysical events regardless of false-alarm rate and that kilonovae accompanying BNS and NSBH mergers are drawn from a common population; later, we relax these assumptions. Assuming that all kilonovae are at least as luminous as the discovery magnitude of GW170817 (−16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than −16.6 mag (the extrapolated peak magnitude of GW170817) and fade at a rate of 1 mag day⁻¹ (similar to GW170817), the joint probability of zero detections is 7%. If we separate the NSBH and BNS populations based on the online classifications, the joint probability of zero detections, assuming all kilonovae are brighter than −16.6 mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, no more than 10⁻⁴, or φ > 30° to be consistent with our limits. We look forward to searches in the fourth GW observing run; even 17 neutron star mergers with only 50% coverage to a depth of −16 mag would constrain the maximum fraction of bright kilonovae to <25%