The detection of a long flaring activity from blazar TXS 0506+056 in temporal and spatial coincidence with the energetic neutrino IceCube-170922A provided evidence about the photo-hadronic interactions in this source. However, analysis of the archival neutrino and multi-wavelength data from the direction of this blazar between September 2014 and March 2015 revealed a "neutrino flare" without observing quasi-simultaneous activity in the gamma-ray bands, posing challenges to established models. Electron-positron ($e^\pm$) pairs generated from the accretion disks have been amply proposed as a mechanism of bulk acceleration of sub-relativistic and relativistic jets. These pairs annihilate inside the source producing a line around the electron mass which is expected to be blueshifted in the observed frame (on Earth) and redshifted in the frame of the dissipation region of the jet. The redshifted photons in the dissipation region interact with accelerated protons, producing high-energy neutrinos that contribute significantly to the diffuse neutrino flux in the $\sim$ 10 - 20 TeV energy range in connection with gamma-rays from photo-pion process which can be detected by future MeV orbiting satellites. Based on this phenomenological model we can explain the "neutrino flare" reported in 2014-2015.
Motivated by the observation of a $>290$ TeV muon neutrino by IceCube, coincident with a $\sim$6 month-long $γ$-ray flare of the blazar TXS 0506+056, and an archival search which revealed $13 \pm 5$ further, lower-energy neutrinos in the direction of the source in 2014-2015, we discuss the likely contribution of blazars to the diffuse high-energy neutrino intensity, the implications for neutrino emission from TXS 0506+056 based on multi-wavelength observations of the source, and a multi-zone model that allows for sufficient neutrino emission so as to reconcile the multi-wavelength cascade cons…
For the first time since the discovery of high-energy cosmic neutrinos by IceCube, a multimessenger campaign identified a distant gamma ray blazar, TXS 0506+056, as the source of a high-energy neutrino. The extraordinary brightness of the blazar despite its distance suggests that it may belong to a special class of sources that produce cosmic rays. Moreover, over the last 10 years of data, the high-energy neutrino flux from the source is dominated by a previous neutrino flare in 2014, which implies that flaring sources strongly contribute to the cosmic ray flux. We investigate the contribution…
Recent detection of the neutrino event, IceCube-170922A by IceCube observatory from the Blazar TXS 0506+056 in the state of enhanced gamma ray emission indicates for acceleration of cosmic rays in the blazar jet. The non-detection of the broadline emission in the optical spectrum of TXS 0506+056 and other BL Lac objects suggests that external photons emissions are weak and hence photo-meson (p-gamma) interaction may not be a favored mechanism for high energy neutrino production. The lack of broadline signatures also creates doubt about the presence of a high density cloud in the vicinity of th…
Recently the IceCube collaboration and 15 other collaborations reported the spatial and temporal coincidence between the neutrino event IceCube-170922A and the radio-TeV activity of the blazar TXS 0506+056. Their further analysis on 9.5 years of IceCube data discovered neutrino flare between September 2014 and March 2015, when TXS 0506+056 is however in "quiescent" state. We analyze the Fermi-LAT data in that direction, and find another bright GeV source PKS 0502+049, which is at an angle of $1.2^{\circ}$ from TXS 0506+056, with strong activties during the neutrino flare. No other bright GeV s…
We discuss possible interpretations of the neutrinos observed from the AGN blazar TXS 0506+056 in the multi-messenger and multi-wavelength context, including both the 2014-15 and 2017 neutrino flares. While the neutrino observed in September 2017 has to describe contemporary data in e.g. the X-ray and VHE gamma-ray ranges, data at the 2014-15 excess are much sparser. We demonstrate that in both cases the simplest possible one-zone AGN blazar models face challenges. While the 2017 flare can be well interpreted by considering more sophisticated source geometries, the 2014-15 flare is much harder…
The origin of magnetic fields in the universe is an open problem. Seed magnetic fields possibly produced in early times may have survived up to the present day close to their original form, providing an untapped window to the primeval universe. The recent observations of high-energy neutrinos from the blazar TXS 0506+056 in association with an electromagnetic counterpart in a broad range of wavelengths can be used to probe intergalactic magnetic fields via the time delay between the neutrinos and gamma rays as well as the time dependence of the gamma-ray fluxes. Using extensive three-dimension…
Parsec-scale polarimetry and kinematics of a spine-sheath jet in the neutrino-blazar TXS 0506+056
Julius-Maximilians-Universität Würzburg（维尔茨堡大学）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；Joint Institute for VLBI ERIC（甚长基线干涉测量联合研究所）；GFZ Helmholtz Centre for Geosciences（GFZ赫尔姆霍兹地学研究中心）；Instituto de Astrofísica de Andalucía-CSIC（安达卢西亚天体物理研究所-CSIC）；Denison University（丹尼森大学）；Purdue University（普渡大学）
We report on the radio brightening of the blazar TXS 0506+056 (at $z=0.3365$), supporting its identification as source of the high-energy (HE) neutrino IC-170922A by the IceCube Neutrino Observatory. MOJAVE/VLBA data indicate its radio brightness abruptly increasing since January 2016. When decomposing the total radio flux density curve (January 2008 - July 2018) provided by the Owens Valley Radio Observatory into eight Gaussian flares, the peak time of the largest flare overlaps with the HE neutrino detection, while the total flux density exhibits a threefold increase since January 2016. We r…
We report results of a multiband monitoring campaign of the flat spectrum radio quasar TXS 0536+145 at redshift 2.69. This source was detected during a very high gamma-ray activity state in 2012 March by the Large Area Telescope on board Fermi, becoming the gamma-ray flaring blazar at the highest redshift detected so far. At the peak of the flare the source reached an apparent isotropic gamma-ray luminosity of 6.6 x 10^49 erg/s which is comparable to the values achieved by the most luminous blazars. This activity triggered radio-to-X-rays monitoring observations by Swift, Very Long Baseline Ar…
We investigate whether the emission of neutrinos observed in 2014-15 from the direction of the blazar TXS 0506+056 can be accommodated with leptohadronic multi-wavelength models of the source commonly adopted for the 2017 flare. While multi-wavelength data during the neutrino flare are sparse, the large number of neutrino events ($13\pm5$) challenges the missing activity in gamma rays. We illustrate that two to five neutrino events during the flare can be explained with leptohadronic models of different categories: a one-zone model, a compact core model, and an external radiation field model. …
The physical nature of the mechanism responsible for the emission of neutrinos in active galactic nuclei (AGN) has been matter of debate in the literature, with relativistic jets of radio-loud AGNs as possible candidates to be the sources of high energy neutrinos. The most prominent candidate so far is the blazar TXS 0506+056, which is found to be associated with the neutrino event IceCube-170922A. Furthermore, the IceCube reported an excess of neutrinos towards TXS 0506+056 between September 2014 and March 2015, even though this association needs additional investigation, considering the pres…
The recent observation of high-energy neutrinos from the 2017 flare of the blazar TXS~0506+056, together with counterparts across the whole electromagnetic spectrum, opens up new possibilities for investigating the properties of this class of objects as well as the traversed medium. Propagation effects such as the attenuation of the very-high-energy gamma-ray component by the extragalactic background light are well known, and usually taken into account when fitting spectral energy distributions of objects. Other effects such as those of intergalactic magnetic fields are, however, often neglect…
On 22nd of September 2017 the IceCube collaboration sent an alert for an EHE (Extreme High Energy) event, corresponding to the reconstruction of a muonic neutrino (IC-170922A) with energy $\sim 290$ TeV. A multi-wavelength follow-up campaign associated this neutrino event with a gamma-ray flaring state of the BL Lac TXS 0506+056 located at z=0.3365. From the same position of the sky a muonic neutrino excess is observed in a time window of 110 days around 13th of December 2014. These observations together suggest TXS 0506+056 as a possible neutrino emitter. We report here a long term gamma-ray …
The observation of a very-high-energy neutrino by IceCube (IceCube-170922A) and its association with the flaring blazar TXS 0506+056 provided the first multimessenger observations of blazar jets, demonstrating the important role of protons in their dynamics and emission. In this paper, we present SOPRANO (https://www.amsdc.am/soprano), a new conservative implicit kinetic code which follows the time evolution of the isotropic distribution functions of protons, neutrons and the secondaries produced in photo-pion and photo-pair interactions, alongside with the evolution of photon and electron/pos…
IceCube discovered a flux of cosmic neutrinos originating in extragalactic sources with an energy density close to that in gamma rays and cosmic rays. A multimessenger campaign triggered by the coincident observation of a gamma-ray flare and a 290-TeV IceCube neutrino pinpointed the cosmic-ray accelerator TXS 0506+056. Subsequently, the IceCube archival data revealed a 3-month burst of 13 cosmic neutrinos in 2014-15 that dominates the neutrino flux of the source over the 9.5 years of observations. The original identification of the source as a blazar was puzzling because it requires a major ac…
The IceCube report of a $\sim 3.5σ$ excess of $13\pm5$ neutrino events in the direction of the blazar TXS 05056+056 in 2014-2015 and the 2017 detection of a high-energy neutrino, IceCube-170922A, during a gamma-ray flare from the same blazar, have revived the interest in scenarios for neutrino production in blazars. We perform comprehensive analyses on the long-term electromagnetic emission of TXS 05056+056 using optical, X-ray, and gamma-ray data from the All-Sky Automated Survey for Supernovae (ASAS-SN), the Neil Gehrels Swift Observatory (Swift), the Monitor of All-sky X-ray Image (MAXI), a…
TXS 0506+056, a source of the extreme energy neutrino event, IceCube-170922A, was observed on 22 September 2017. The Fermi-LAT detector reported high energy (HE) $γ$-ray flare between 100 MeV and 100 GeV starting from 15 September 2017 from this source. Several attempts to trace the very high energy (VHE) gamma-ray counterparts around the IceCube-170922A resulted in no success. Only after 28 September, the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes observed the first VHE gamma-rays from the blazar above 100 GeV. The $\sim$ 41 hr survey resulted in VHE-$γ$ ray activity til…
The IceCube collaboration reported a $\sim 3.5σ$ excess of $13\pm5$ neutrino events in the direction of the blazar TXS 0506+56 during a $\sim$6 month period in 2014-2015, as well as the ($\sim3σ$) detection of a high-energy muon neutrino during an electromagnetic flare in 2017. We explore the possibility that the 2014-2015 neutrino excess and the 2017 multi-messenger flare are both explained in a common physical framework that relies on the emergence of a relativistic neutral beam in the blazar jet due to interactions of accelerated cosmic rays (CRs) with photons. We demonstrate that the neutr…
A high-energy neutrino event detected by IceCube on 22 September 2017 was coincident in direction and time with a gamma-ray flare from the blazar TXS 0506+056. Prompted by this association, we investigated 9.5 years of IceCube neutrino observations to search for excess emission at the position of the blazar. We found an excess of high-energy neutrino events with respect to atmospheric backgrounds at that position between September 2014 and March 2015. Allowing for time-variable flux, this constitutes 3.5σ evidence for neutrino emission from the direction of TXS 0506+056, independent of and pri…
In this work, we investigate the 2014-2015 neutrino flare associated with the blazar TXS 0506+056 and a recently discovered muon neutrino event IceCube-200107A in spatial coincidence with the blazar 4FGL J0955.1+3551, under the framework of a two-zone radiation model of blazars where an inner/outer blob close to/far from the supermassive black hole are invoked. An interesting feature that the two sources share in common is that no evidence of GeV gamma-ray activity is found during the neutrino detection period, probably implying a large opacity for GeV gamma rays in the neutrino production reg…
The evidence for joint gamma and neutrino emission from the blazar TXS 0506+056 has renewed interest in blazars as neutrino sources. The detection of neutrinos from blazars can be seen as the smoking gun for the presence of relativistic protons in blazar's jets, and can thus help identify blazars, and active galactic nuclei in general, as cosmic-ray accelerators. In this contribution I first introduce blazars and blazar hadronic models, and then present the results of the multi-messenger modeling of both the 2017 gamma-neutrino flare, and the 2014-2015 neutrino-only flare of TXS 0506+056. For …
A high-energy muon neutrino event, IceCube-170922A, was recently discovered in both spatial and temporal coincidence with a gamma-ray flare of the blazar TXS 0506+056. It has been shown, with standard one-zone models, that neutrinos can be produced in the blazar jet via hadronic interactions, but with a flux which is mostly limited by the X-ray data. In this work, we explore the neutrino production from TXS 0506+056 by invoking two physically distinct emission zones in the jet, separated by the broad line region (BLR). Using the Doppler-boosted radiation of the BLR as the target photon field, …
Recent studies with IceCube have shown signs of a time-integrated flux of astrophysical neutrinos from point-like sources such as TXS 0506+056 and NGC 1068. Time-variability of this neutrino emission from TXS 0506+056 has been studied extensively by assuming a temporal profile of the possible flare(s) or searching for temporal neutrino correlation with other electromagnetic counterparts. However, experimental evidence of the temporal profile of an astrophysical neutrino signal, besides the TXS 0506+056 source, remains lacking. In this study, we present a new KS-test based method for investigat…
The detection of the high-energy neutrino IC-170922A in spatial (within the error region) and temporal flare activity correlation with the blazar TXS 0506+056 allowed these objects to be considered as progenitor sources of neutrinos. Besides this, no more detection of this kind was reported. Some other neutrinos detected by IceCube show a spatial correlation (within the error region) from other Fermi-LAT detected sources. However, these objects did not show a flare activity like TXS 0506+056. Assuming a lepto-hadronic scenario through p$γ$ interactions, this work describes the SED in some obje…
On September 18, 2022, an alert by ceCube indicated that a ~170TeV neutrino arrived in directional coincidence with the blazar TXS 0506+056. This event adds to two previous ones: a neutrino alert from its direction on September 22, 2017, and a 3sigma signature of a dozen neutrinos in 2014/2015. deBruijn 2020 showed that these two previous neutrino emission episodes could be due to a supermassive binary black hole (SMBBH) where jet precession close to final coalescence results in periodic emission. This model predicted a new emission episode consistent with the September 18, 2022 neutrino obser…
The recent detection of possible neutrino emission from the blazar TXS 0506+056 was the first high-energy neutrino associated with an astrophysical source, making this special type of active galaxies promising neutrino emitters. The fact that two distinct episodes of neutrino emission were detected with a separation of around 3 years suggests that emission could be periodic. Periodic emission is expected from supermassive binary black hole systems due to jet precession close to the binary's merger. Here we show that if TXS 0506+056 is a binary source then the next neutrino flare could occur be…
In 2017, IceCube detected a high energy neutrino in coincidence with the blazar TXS 0506+056. In a follow up analysis of archival data, evidence for previous neutrino emission from the blazar during 2014-15 was found. In this analysis, we investigate whether other blazars might have had episodes of neutrino emission. We use a 5-year sample of muon-neutrino data and the same timedependent algorithm that was used for the archival analysis of TXS 0506+056, applying it to all of the objects in the northern sky listed in the Fermi 3LAC catalog. We fit for the most significant neutrino flare from ea…
We present the dissection in space, time, and energy of the region around the IceCube-170922A neutrino alert. This study is motivated by: (1) the first association between a neutrino alert and a blazar in a flaring state, TXS 0506+056; (2) the evidence of a neutrino flaring activity during 2014 - 2015 from the same direction; (3) the lack of an accompanying simultaneous $γ$-ray enhancement from the same counterpart; (4) the contrasting flaring activity of a neighbouring bright $γ$-ray source, the blazar PKS 0502+049, during 2014 - 2015. Our study makes use of multi-wavelength archival data acc…
Recent results from IceCube regarding TXS 0506+056 suggest the presence of neutrino flares that are not temporally coincident with a significant corresponding gamma ray flare. Such flares are particularly difficult to identify, as their presence must be inferred from the temporal distribution of neutrino data alone. Here we present the results of using a novel method to search for all such flares across the entire neutrino sky in 10 years of IceCube data, using both Gaussian and box-shaped flare hypotheses. Unlike for past searches, that looked for only the most significant neutrino flare in t…
A neutrino outburst between September 2014 and March 2015 was discovered from the blazar TXS 0506+056 by an investigation of $9.5$ years of IceCube data, while the blazar was in a quiescent state during the outburst with a gamma-ray flux only about one-fifth of the neutrino flux. In this work, we give a possible interpretation of the abnormal feature by proposing that the neutrino outburst originates from the interaction between a relativistic jet and a dense gas cloud formed via the tidally disrupted envelope of a red giant being blown apart by the impact of the jet. Gamma-ray photons and ele…
MAGIC collaboration has recently analyzed data from a long-term multiwavelength campaign of the $γ$-ray blazar TXS 0506+056. In December 2018, it was flaring in the very-high-energy (VHE; $E>100$ GeV) $γ$-ray band, but no simultaneous neutrino event was detected. We model the observed spectral energy distribution (SED), using a one-zone leptohadronic emission. We estimate the neutrino flux through the restriction from observed X-ray flux on the secondary radiation due to hadronic cascade, initiated by protons with energy $E_p \lesssim 0.1$ EeV. We assume ultrahigh-energy cosmic rays (UHECRs; $…
Following the detection of a $\sim$300 TeV neutrino potentially associated with the flaring blazar TXS 0506+056, an excess of neutrinos around its position in 2014-2015 was revealed by IceCube. However, its contemporaneous quiescence in $γ$-rays is challenging to interpret consistently. Meanwhile, the blazar PKS 0502+049, positioned within the neutrino localization uncertainties, was seen to be flaring in $γ$-rays. We show that dense, line-emitting gas clouds that interact with its jet and induce cosmic ray acceleration and hadronuclear interaction can plausibly explain the 2014-2015 neutrino …
Relativistic antiparticles can be created in high-energy nuclear interactions; thus, detection of antiparticles in an astrophysical source can tell us something remarkable about the underlying high-energy processes and nuclear interactions. However, once created, the antiparticles remain a minor fraction of their conjugant normal particles, so the detection of the antiparticles represents a big science challenge. To address this challenge we employ imaging and polarimetry of microwave radiation produced as the positrons gyrate in the ambient magnetic field. The key property of the radiation us…
We consider implications of high-energy neutrino emission from blazar flares, including the recent event IceCube-170922A and the 2014-2015 neutrino flare that could originate from TXS 0506+056. First, we discuss their contribution to the diffuse neutrino intensity taking into account various observational constraints. Blazars are likely to be subdominant in the diffuse neutrino intensity at sub-PeV energies, and we show that blazar flares like those of TXS 0506+056 could make <1-10 percent of the total neutrino intensity. We also argue that the neutrino output of blazars can be dominated by th…
From Variability to SED Modeling: A Multiwavelength Study of the Neutrino Blazar TXS 0506+056
School of Physics and Astronomy, Beijing Normal University（北京师范大学物理学院）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天文与天体物理研究所）；College of Intelligent Systems Science and Engineering, Hubei Minzu University（湖北民族大学智能系统科学与工程学院）
We attempt to present a multiwavelength variability and correlation study as well as detailed multi-waveband spectral characteristics of the May 2021 $γ$-ray flare of the blazar source TXS 1700+685. The multi-wavelength observation from \textit{Fermi}-LAT, \textit{Swift}-XRT/UVOT as well as radio archival data are used for our spectro-temporal investigation. We estimate the variability time-scale of the source from the flux doubling time in different flaring regions detected in \textit{Fermi}-LAT observation and the shortest variability time is used to put a constraint on the minimum Doppler f…
Blazar jets are extreme environments, in which relativistic proton interactions with an ultraviolet photon field could give rise to photopion production. High-confidence associations of individual high-energy neutrinos with blazar flares could be achieved via spatially and temporally coincident detections. In 2017, the track-like, extremely high-energy neutrino event IC 170922A was found to coincide with increased $γ$-ray emission from the blazar TXS 0506+056, leading to the identification of the most promising neutrino point source candidate so far. We calculate the expected number of neutrin…
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-yea…
Although many high-energy neutrinos detected by the IceCube telescope are believed to have anextraterrestrial origin, their astrophysical sources remain a mystery. Recently, an unprecedenteddiscovery of a high-energy muon neutrino event coincident with a multiwavelength flare from ablazar, TXS 0506+056, shed some light on the origin of the neutrinos. It is usually believed that ablazar is produced by a relativistic jet launched from an accreting supermassive black hole (SMBH).Here we show that the high-energy neutrino event can be interpreted by the inelastic hadronuclearinteractions between t…
The blazar TXS 0506+056 got into the spotlight of the astrophysical community in September 2017, when a high-energy neutrino detected by IceCube (IceCube-170922A) was associated at the 3 $σ$ level to a $γ$-ray flare from this source. This multi-messenger photon-neutrino association remains, as per today, the most significant one ever observed. TXS 0506+056 was a poorly studied object before the IceCube-170922A event. To better characterize its broad-band emission, we organized a multi-wavelength campaign lasting 16 months (November 2017 to February 2019), covering the radio-band (Metsähovi, OV…
Recently the IceCube collaboration detected very high energy (VHE) neutrinos and associated them with the blazar \txs{}, raising a possible association of VHE neutrinos with this and other individual blazars. Very Long Baseline Interferometry (VLBI) is so far the only technique enabling the imaging of the innermost jet at milli-arcsec resolution (parsec scale), where the high energy emission possibly originates from. Here, we report on the radio properties of the parsec scale jet in \txs{} derived from the analysis of multi-epoch multi-frequency archive VLBI data. The half opening angle of the…
Based on the magnetar model, we have studied in detail the processes of neutrino cooling of an electron--positron plasma generating an SGR giant flare and the influence of the magnetar magnetic field on these processes. Electron--positron pair annihilation and synchrotron neutrino emission are shown to make a dominant contribution to the neutrino emissivity of such a plasma. We have calculated the neutrino energy losses from a plasma-filled region at the long tail stage of the SGR 0526--66, SGR 1806--20, and SGR 1900+14 giant flares. This plasma can emit the energy observed in an SGR giant fla…
The detection of a high-energy neutrino from the flaring blazar TXS 0506+056 and the subsequent discovery of a neutrino excess from the same direction have strengthened the hypothesis that blazars are cosmic neutrino sources. The lack, however, of $γ$-ray flaring activity during the latter period challenges the standard scenario of correlated $γ$-ray and high-energy neutrino emission in blazars. We propose instead that TeV-PeV neutrinos are produced in coincidence with X-ray flares that are powered by proton synchrotron radiation. In this case, neutrinos are produced by photomeson interactions…
Broad-band temporal and spectral study of TeV blazar TXS 0518+211
Physical Research Laboratory（物理研究实验室）；Indian Institute of Science Education and Research Mohali（印度科学教育研究所穆扎法尔纳加尔分校）；Aryabhatta Research Institute of Observational Sciences (ARIES)（阿亚恩博达观测科学研究所）；Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交大李政道研究所）；Indian Institute of Technology Gandhinagar（甘地纳加尔印度理工学院）
The sources of IceCube neutrinos are as yet unknown. The multi-messenger observation of their emission in $γ$-rays can be a guide to their identification, as exemplified by the case of TXS 0506+056. We suggest a new method of searching for $γ$-rays with Imaging Air Cherenkov Telescopes from sources in coincidence with possible astrophysical neutrinos. We propose that searches of $γ$-rays are extended, from the current practice of only a few days, to up to one month from a neutrino alert. We test this strategy on simulated sources modeled after the blazar \emph{TXS 0506+056-like}, emitting neut…
Blazar TXS 0506+056 is the main candidate for a coincident neutrino and gamma-ray flare event. In this paper, we present a detailed kinetic lepto-hadronic emission model capable of producing a photon and neutrino spectrum given a set of parameters. Our model includes a range of large-scale geometries and both dynamical and steady-state injection models for electrons and protons. We link this model with a Markov Chain Monte Carlo sampler to obtain a powerful statistical tool that allows us to both fit the Spectral Energy Distribution and study the probability density functions and correlations …
