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A. Neronov

Publications and source records attributed to A. Neronov.

At least 19 recordsLinked to original sources
arXiv2026

PeV extended emission around Galactic PeVatrons and echos of their flares

We notice that Galactic sources of PeV gamma-rays are generally expected to be surrounded by multi-degree-scale extended emission produced as a result of injection of electron-positron pairs in the interstellar medium from interactions of PeV gamma-rays with microwave photons. The surface brightness of such emission may be variable in time because of variability of the PeV emission power of its parent source. A flare of the parent source produces an ``echo'' spreading across the extended emission region that may be detectable on the time scales from decades to millennia. We consider a possibility that the very extended PeV source in the Cygnus region is the produced by the Cygnus X-3 PeV gamma-ray source, possibly being an echo of its past flare.

astro-ph.HE↗
arXiv2026

Pulsar based modeling of point spread function of Fermi Large Area Telescope

Sensitivity of searches for extended emission around gamma-ray sources is naturally limited by the precision of the knowledge of the Point Spread Function (PSF) of gamma-ray telescopes. Inaccuracies in the PSF models of the Fermi Large Area Telescope (LAT) can potentially lead to false positive detections of source extension. We explore uncertainties in the Fermi/LAT PSF by comparing the PSF models provided by the Fermi/LAT Instrument Response Functions (IRFs) with signals of bright pulsars. We compare the analytical PSF models of Fermi/LAT IRFs with pulsar data and fit the pulsar data with the same analytical model as in the Fermi/LAT IRFs to derive an improved set of PSF parameters. We then apply this revised PSF parameterisation to the search of extended emission around a blazar, Mrk 501. We find that the parameters of the analytical PSF models of Fermi/LAT IRFs are inconsistent with the pulsar data. We obtain an improved set of PSF parameters from the fits to pulsar data that is consistent with observations. We find no evidence of the previously reported extended signal around Mrk 501 if the revised PSF consistent with pulsar data is used in data analysis.

astro-ph.HE↗
arXiv2026

Revision of conservative lower bound on the intergalactic magnetic field from Fermi and Cherenkov telescope observations of extreme blazars

Joint observations of extreme blazars with Fermi Large Area Telescope (LAT) and Imaging Atmospheric Cherenkov telescopes (IACT) have been previously used to derive lower bounds on intergalactic magnetic field (IGMF). We update these previous bounds using a set of extreme blazars that are detected in the Very-High-Energy (VHE, photon energies above 100 GeV) band by both Fermi/LAT and IACTs. We measure IGMF-dependent suppression of secondary delayed gamma-ray flux from electron-positron pairs deposited in the intergalactic medium by VHE gamma-rays interacting with Extragalactic Background Light. From overall 22 extreme blazars detected by Fermi/LAT and IACTs in the VHE band, seven have their spectral characteristics inconsistent with the possibility of zero magnetic field along their lines of sight, even under the most restrictive assumption that the sources have only switched on at the start of VHE band observations. Adopting this assumption, we derive a "conservative" lower bound on the IGMF strength at the level of 2e-17 G. The tightest bound is imposed by the signal of 1ES 0502+675, a source that has not been considered in the IGMF analysis before. Our bound is comparable to the bound derived by MAGIC collaboration, but is weaker than that previously derived from analysis of Fermi/LAT and HESS telescope data, even though our dataset includes that data. We clarify the origin of this discrepancy.

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arXiv2026

Seyfert galaxy targets for KM3NeT neutrino telescope

Neutrino signal from a population of Seyfert galaxies has been detected by IceCube neutrino telescope in the muon neutrino channel that has sensitivity mostly to the Northern Hemisphere sources. This detection can be verified by KM3NeT telescope that has sensitivity also in the Southern Hemisphere. We define a catalog of Seyfert galaxies that are expected to be detectable with KM3NeT, assuming that the neutrino luminosity scales with the intrinsic hard X-ray luminosity of the sources. We find that four sources: NGC 1068, NGC 4151, NGC 4945 and Circinus galaxy, are detectable by KM3NeT, if their spectra follow either NGC 1068 or NGC 4151 spectral template based on IceCube data. We discuss uncertainties of the neutrino flux estimate, considering the Compton-thick nature of three of the four detectable sources: NGC 1068, NGC 4945 and Circinus. The limited catalog of the four sources can be used in KM3NeT source search to reduce the trial factor of analysis aimed at independent verification of the neutrino signal from Seyfert galaxies.

astro-ph.HE↗
arXiv2026

LISA and $γ$-ray telescopes as multi-messenger probes of a first-order cosmological phase transition

We study two possible cosmological consequences of a first-order phase transition in the temperature range of 1 GeV to $10^3$ TeV: the generation of a stochastic gravitational wave background (SGWB) within the sensitivity of the Laser Interferometer Space Antenna (LISA) and, simultaneously, primordial magnetic fields that would evolve through the Universe's history and could be compatible with the lower bound from $γ$-ray telescopes on intergalactic magnetic fields (IGMF) at present time. We find that, if even a small fraction of the kinetic energy in sound waves is converted into MHD turbulence, a first-order phase transition occurring at a temperature between 1 and $10^6$ GeV can give rise to an observable SGWB signal in LISA and, at the same time, an IGMF compatible with the lower bound from the $γ$-ray telescope MAGIC, for all proposed evolutionary paths of the magnetic fields throughout the radiation-dominated era (i.e., for both helical and non-helical magnetic fields). For the following fractions of energy density converted into turbulence, $\varepsilon_{\rm turb}=0.1$ and $1$, we provide the range of first-order phase transition parameters, together with the corresponding range of magnetic field strength $B$ and correlation length $λ$, that would lead to the SGWB and IGMF observable with LISA and MAGIC. The resulting magnetic field strength at recombination can also correspond to the one that has been proposed to induce baryon clumping, previously suggested as a possible way to ease the Hubble tension. In the limiting case $\varepsilon_{\rm turb} \ll 1$, the SGWB is only sourced by sound waves, but an IGMF is still generated. We find that for values as small as $\varepsilon_{\rm turb} \sim 10^{-13}$ or $10^{-9}$, respectively helical or non-helical magnetic fields can provide IGMF compatible with MAGIC's lower bound.

astro-ph.CO↗
arXiv2025

Diffuse gamma-ray and neutrino emission from the Milky Way and the local knee in the cosmic ray spectrum

The LHAASO observatory has recently measured details of the cosmic-ray (CR) spectrum in the knee region (1 -- 10 PeV) with unprecedented precision, including its average CR mass composition and the spectrum of the proton component. We use these precision measurements, combined with direct measurements of CRs by space-based detectors, to derive predictions for the spectrum of diffuse gamma-ray and neutrino emission from the interstellar medium under the assumption that the CR spectrum is universal throughout the Milky Way. We compare these predictions with the Fermi-LAT and LHAASO measurements of the diffuse gamma-ray flux from inner and outer Galactic Plane regions and with estimates of the neutrino flux based on the IceCube data for the same Galactic Plane regions. We notice that the model predictions exceed LHAASO gamma-ray measurements at energies above 100 TeV. This excess can be interpreted within a CR knee model assuming a "local PeV CR bubble''. Within this model, we infer the extension of the local PeV CR bubble of 1.5 +/- 0.3 kpc in the direction of the inner Galaxy and of 0.7+/-0.3 kpc toward the outer Galaxy.

astro-ph.HE↗
arXiv2025

Neutrino emission and corona heating induced by high-energy proton interactions in Seyfert galaxies

Recent detection of very-high-energy neutrino emission from Seyfert type active galactic nuclei (AGN) provides a new insight into the physics of the AGN central engines. We notice that if high-energy protons responsible for neutrino emission are accelerated close to the surface of the accretion disk, the neutrino flux may have no unambiguously identifiable electromagnetic counterpart. This is because the electromagnetic power released in interactions of high-energy protons would only contribute to the heating of the disk surface and corona above the disk, rather than escape from the source. Given that the heat deposited in the corona is released in the hard X-ray range we notice that there still might be an "indirect" electromagnetic counterpart of the neutrino signal: the hard X-ray flux variability may be strongly or weakly correlated with the neutrino flux variations, depending on the importance of the high-energy proton heating in the disk/corona heat balance. If heating by high-energy protons provides a sizable contribution to the overall corona heating rate, the overall flux of diffuse GeV neutrino background from Seyfert galaxies may be comparable to the X-ray background flux and the high-energy tail of this background can provide a sizable contribution to the astrophysical neutrino flux in the TeV band.

astro-ph.HE↗
arXiv2025

Catalog of very-high-energy emitting active galactic nuclei at high Galactic latitudes

Large number of Active Galactic Nuclei (AGN) producing Very-High-Energy (VHE) gamma-rays (energies above 100~GeV) has been revealed using observations with Imaging Atmospheric Cherenkov Telescopes (IACTs). However, our knowledge of the VHE emitting AGN population is limited in the absence of an unbiased sky survey. We use long exposure of Fermi Large Area Telescope (LAT) to perform a survey of VHE emitting AGN at Galactic latitudes |b|>10 degrees. We consider clustering of gamma-ray events with energies E>100 GeV around positions of AGN from the 4-th LAT source catalog to select sources detected in the VHE range. The VHE AGN catalog produced in this way contains overall 175 sources detected with high confidence and additional 100 sources detected at more than 3-sigma level. It is 90% complete at the flux limit 1.3e-12 erg/cm2s. Less than half of the source sample (71) are previously reported VHE emitters, other sources are new detections in the VHE band. The majority of VHE AGN detectable at the survey flux limit are BL Lac type objects. We find their luminosity function to derive their spatial density (6.5+/-0.5)e-7/ Mpc3 and the characteristic luminosity scale ~1e44 erg/s. Ten sources in the VHE AGN catalog are nearby radio galaxies and seven are flat spectrum radio quasars, while 20 sources are unclassified AGN. We also include in our catalog four unidentified sources that may or may not be VHE AGN. 63 source in the catalog are "extreme" blazars, with 41 of them being new VHE band detections. In spite of the fact that the VHE flux is heavily attenuated by the pair production in interactions with Extragalactic Background Light (EBL), the catalog includes 7 sources at redshift larger than 1. Some of these sources show peculiar hardening of the VHE band spectra that point either to errors in redshift determination, or to limitations of modeling of cosmological evolution of EBL.

astro-ph.HE↗
arXiv2025

Baryon asymmetry constraints on magnetic field from the Electroweak epoch

Decay of helical (hyper)magnetic fields that may have been present in the Universe during the Electroweak epoch can contribute to generation of the baryon asymmetry of the Universe. We revise constraints on the strength and correlation length of such fields from the requirement that their decay does not lead to over-production of the baryon asymmetry. We show that the helical fields with strength down to 1e-5 of the maximal possible strength during the Electroweak epoch should have had their correlation at least ~1e-6 of the Hubble radius during this epoch. For weaker fields this lower bound on the correlation length relaxes proportionally to the square of magnetic field strength. A field with parameters saturating the bound may actually be responsible for the baryon asymmetry observed today. We show that relic of such a field, surviving in the present day Universe in the form of intergalactic magnetic field detectable with Cherenkov Telescope Array Observatory, may have the strength up to 10-100 pG and can have parameters needed to affect the cosmological recombination and relax the Hubble tension. We also show that there is no constraint on the parameters of helical or non-helical magnetic fields stemming from the requirement that the baryon isocurvature perturbations produced by such fields during the Electroweak epoch are within the observational limits.

astro-ph.CO↗
arXiv2024

Revision of upper bound on volume-filling intergalactic magnetic fields with LOFAR

Magnetic fields present in the Large Scale Structure (LSS) of the Universe change polarization of radio waves arriving from distant extragalactic sources through the effect of Faraday rotation. This effect has been recently used to detect magnetic field in the LSS filaments based on the Rotation Measure data of the LOFAR Two-Meter Sky Survey (LoTSS). We notice that the same data also constrain the strength of the volume-filling magnetic field in the voids of the LSS. We use the LoTSS data to to derive an improved upper bound on the volume-filling field. The new upper bound provides an order of magnitude improvement on the previous Faraday rotation bounds. The new Faraday Rotation bound on the scale-invariant field that may originate from the epoch of inflation is also an order of magnitude lower than the bound on such field derived from the anisotropy analysis of the Cosmic Microwave Background.

astro-ph.CO↗
arXiv2024

Intergalactic magnetism in a gamma-ray beam as a model of Porphyrion

We estimate the magnetic field in the jets of the recently discovered 7 Mpc long Porphyrion system. We use non-detection of the system in gamma-rays to derive a lower bound on the co-moving magnetic field strength at the level of ~10 nG. This value is consistent with recent estimates of magnetic fields in the filaments of the Large Scale Structure. We discuss the possibility that, instead of being the extreme case of a radio jet formation scenario, Porphyrion actually traces a very-high-energy gamma-ray beam emitted by an active galactic nucleus. In such a model, jets do not need to spread into the voids of the Large Scale Structure to appear straight on a very large distance range, and several anomalies of the standard radio jet scenarios can be solved at once.

astro-ph.HE↗
arXiv2024

Energy dependence of the knee in the cosmic ray spectrum across the Milky Way

The all-particle spectrum of cosmic rays measured at Earth has a knee-like feature around 4 PeV. A priori, it is not clear if this is a local feature specific to the Solar neighbourhood in the Milky Way, or if it is a generic property of the Galactic cosmic-ray spectrum. We argue that combining gamma-ray and cosmic-ray data of LHAASO indicates that the knee is a local feature. In order to demonstrate this, we derive a model for the local cosmic-ray spectrum and composition, consistent with the recent LHAASO measurements of the all-particle spectrum and the mean logarithmic mass in the knee region. We calculate the spectrum of diffuse gamma-ray emission based on this model and find that the expected spectral shape of the diffuse gamma-ray flux disagrees with the LHAASO measurements of the diffuse gamma-ray emission in the 10-100 TeV energy range in the inner and outer Galaxy. We determine the break energy in the CR spectrum expected from these gamma-ray data and find it an energy ten times lower than obtained from local measurements.

astro-ph.HE↗
arXiv2024

Neutrino signal from Cygnus region of the Milky Way

Interactions of cosmic ray protons and nuclei in their sources and in the interstellar medium produce "hadronic" gamma-ray emission. Gamma-rays can also be of "leptonic" origin, i.e. originating from high-energy electrons accelerated together with protons. It is difficult to distinguish between hadronic and leptonic emission mechanisms based on gamma-ray data alone. This can be done via detection of neutrinos, because only hadronic processes lead to neutrino production. We use publicly available ten-year IceCube neutrino telescope dataset to demonstrate the hadronic nature of high-energy emission from the direction of Cygnus region of the Milky Way. We find a 3-sigma excess of neutrino events from an extended Cygnus Cocoon, with the flux comparable to the flux of gamma-rays in the multi-TeV energy range seen by HAWC and LHAASO telescopes.

astro-ph.HE↗
arXiv2024

Neutrino signal from a population of Seyfert galaxies

IceCube collaboration has previously reported an evidence for neutrino signal from a Seyfert galaxy NGC 1068. This may suggest that all Seyfert galaxies emit neutrinos. To test this hypothesis, we identify the best candidate neutrino sources among nearby Seyfert galaxies, based on their hard X-ray properties. Only two other sources, NGC 4151 and NGC 3079 are expected to be detectable in 10 years of IceCube data. We find an evidence (~3 sigma)} for neutrino signal from both sources in publicly available ten-year IceCube dataset. {Though neither source alone is above the threshold for discovery,} the chance coincidence probability to find the observed neutrino count excesses in the directions of the two out of two expected sources, in addition to the previously reported brightest source, is p<2.6e-7. This corresponds to a correlation between Seyfert galaxies and neutrino emission.

astro-ph.HE↗
arXiv2024

The second data release from the European Pulsar Timing Array: IV. Implications for massive black holes, dark matter and the early Universe

The European Pulsar Timing Array (EPTA) and Indian Pulsar Timing Array (InPTA) collaborations have measured a low-frequency common signal in the combination of their second and first data releases respectively, with the correlation properties of a gravitational wave background (GWB). Such signal may have its origin in a number of physical processes including a cosmic population of inspiralling supermassive black hole binaries (SMBHBs); inflation, phase transitions, cosmic strings and tensor mode generation by non-linear evolution of scalar perturbations in the early Universe; oscillations of the Galactic potential in the presence of ultra-light dark matter (ULDM). At the current stage of emerging evidence, it is impossible to discriminate among the different origins. Therefore, in this paper, we consider each process separately, and investigate the implications of the signal under the hypothesis that it is generated by that specific process. We find that the signal is consistent with a cosmic population of inspiralling SMBHBs, and its relatively high amplitude can be used to place constraints on binary merger timescales and the SMBH-host galaxy scaling relations. If this origin is confirmed, this is the first direct evidence that SMBHBs merge in nature, adding an important observational piece to the puzzle of structure formation and galaxy evolution. As for early Universe processes, the measurement would place tight constraints on the cosmic string tension and on the level of turbulence developed by first-order phase transitions. Other processes would require non-standard scenarios, such as a blue-tilted inflationary spectrum or an excess in the primordial spectrum of scalar perturbations at large wavenumbers. Finally, a ULDM origin of the detected signal is disfavoured, which leads to direct constraints on the abundance of ULDM in our Galaxy.

astro-ph.CO↗
arXiv2024

Pulsar timing array constraints on the cosmological magnetic field from quark confinement epoch

Recent evidence for the stochastic gravitational wave backgorund reported by the pulsar timing arrays (PTA) can be interpreted as a signal from the cosmological phase transition. We use up-to-date models of the gravitational wave power spectra to compare constraints on the parameters of the phase transition for the three different available PTA measurements and to work out a refined estimate of the cosmological magnetic field that should result from this transition. We find that the PTA data, combined with a constraint from the abundance of primordial black holes, are consistent with a possibility of a moderate strength first-order phase transition during quark confinement and yield a rather precise prediction for the initial parameters of the magnetic field, with the magnetic field energy density in near equipartition with photon energy density and correlation length close to one co-moving parsec.

astro-ph.CO↗