arXiv subjects

Emma Kun

Publications and source records attributed to Emma Kun.

At least 19 recordsLinked to original sources

arXiv2026

Correlation Between Hard X-Ray and Cosmic Neutrino Sources: From Obscured AGN to Blazars

The origin of high-energy astrophysical neutrinos remains a key open question in multimessenger astrophysics. A correlation between unabsorbed hard X-ray and high-energy neutrino luminosity has been reported in six active galactic nuclei with the highest individual IceCube significances, linking neutrino production to compact, photon-rich environments near supermassive black holes. We study whether the threshold-near IceCube excesses associated with seven NuSTAR-observed blazars are statistically consistent with that relation. Calibrating the $L_\mathrm{hX}$-$L_\nu$ relation on the six published sources via a Bayesian regression with errors on both axes, the slope is consistent with $\beta = 1$ and the intrinsic scatter is $\sim 0.6$\,dex. All seven new blazars are posterior-predictively consistent with this calibration ($\chi^2_7 = 1.58$, $p = 0.98$) under the working hypothesis that the published IceCube $\hat{n}_s$ values reflect the signal. A null-injection test confirms that, at the present calibration sample size, the consistency test does not by itself adjudicate between signal and selected-background origins. A distance-free $L_\mathrm{hX}/L_\nu$ ratio diagnostic places both populations within the photohadronic prediction band, statistically indistinguishable. Two diagnostics that control the common $d_L^{\,2}$ distance bias, a redshift-partial rank correlation ($\tau|z = 0.69$, $\sim\!2.7\,\sigma$) and a flux-space permutation test on the 13-source joint sample ($p = 6.3\times10^{-4}$, $3.23\,\sigma$), indicate a residual $L_\mathrm{hX}$-$L_\nu$ association beyond the distance-induced trend. We interpret these results as a conditional consistency check; a detection-level statement requires either an enlarged calibration set or an X-ray-weighted IceCube stacking likelihood with internal data.

astro-ph.HE↗

arXiv2026

Upstream neutrino production and delayed jet emission in the blazar GB6 J1542+6129

We present a multimessenger case study of the blazar GB6 J1542+6129, examining whether its multiwavelength behavior is consistent with neutrino production in a compact region near the central black hole, or with the parsec-scale radio jet. We perform a multimessenger analysis combining ~17 years of Fermi-LAT gamma-ray data with ~14 years of VLBI/MOJAVE. These are compared to the temporal properties of a suspected IceCube neutrino flare with a duration of $147^{+110}_{-25}$ days, enabling a direct test of spatial and causal connections between neutrino and electromagnetic emission regions. We find that the suspected neutrino flare appears to precede both a $\gamma$-ray flare and a pronounced increase in the VLBI core Doppler factor by up to ~1 year. The duration of the post-flare $\gamma$-ray activity is comparable to that of the neutrino flare, which, in our framework, is consistent with both signatures originating from a single propagating disturbance whose temporal structure is preserved during the propagation. The gamma-ray spectral energy distribution remains consistent in shape across the full, flare, and post-flare intervals, indicating stable particle acceleration conditions. The temporal ordering, taken at face value, places the neutrino production site upstream of the VLBI core. The observations of GB6 J1542+6129 are consistent with a disturbance-driven, multi-zone scenario in which neutrinos are produced in a compact, photon-rich inner region upstream of the parsec-scale VLBI core, plausibly at the coronal region, while the same disturbance later enhances Doppler-boosted leptonic emission once it reaches the radio core. While the data alone do not strictly establish this scenario on a population level, they show how time-domain multimessenger observations of a single AGN can localize neutrino emission relative to the parsec-scale radio jet in a particular source.

astro-ph.HE↗

arXiv2026

Characterizing Gamma-Radio Delayed Flaring Activity from Blazars

Flaring activity from the jets of active galactic nuclei has been studied for several decades, closely related to the loading and evolution of the jet. In this work, we focus on the sub-hundred parsec jet region, well traced by non-thermal radio and gamma-ray emission. Only in recent years have light curves capturing the decade-long behavior of such sources become available for a large ensemble of objects. While previous studies have focused on a direct correlation or few-month lag between gamma-ray and radio activity, recent neutrino-bright blazars observed by the IceCube Neutrino Observatory present multi-year delays between initial gamma-ray activity and subsequent radio flares. In this work, we search for similar-timescale correlations between Fermi-LAT gamma-ray data and RATAN-600 radio data from ~100 blazars. We consider two gamma-ray bands, 100 MeV-1 GeV and 1 GeV-500 GeV, as well as the integral band, to compare correlations between potential opaque and unabsorbed regions of the jet. Gaussian process modeling is used for smooth light curve function prediction. We also analyze morphological AGN core data from the MOJAVE survey, forming a sub-selection to better illustrate potential dependence on location. In the broader selection, several sources exhibit delayed flares on the order of 1-3 years. In the stacked analysis, we find the highest correlation for a radio delay on the order of 180 days. The stacked correlation resulting from the MOJAVE sub-selection corresponds to a slightly smaller time lag. Delayed radio flares or extended radio emission appear to be notable features within the general blazar population.

astro-ph.HE↗

arXiv2025

A Seyfert galaxy as a hidden counterpart to a neutrino-associated blazar

The origin and production mechanisms of high-energy astrophysical neutrinos remain open questions in multimessenger astronomy. Previous studies have hinted at a possible linear correlation between the hard X-ray and high-energy neutrino emission in active galactic nuclei. New \textit{NuSTAR} observations, first presented here, reveal that blazar PKS 1424+240, located within a prominent IceCube neutrino hotspot, is far fainter in hard X-rays than expected from this trend. Motivated by this apparent ambiguity, we identify the nearby Seyfert galaxy NGC 5610, also coincident with the hotspot, whose unabsorbed hard X-ray flux exceeds that of PKS 1424+240 by about an order of magnitude. When the local IceCube neutrino flux is apportioned between the two AGN in proportion to their hard X-ray emission, both align with the previously suggested X-ray-neutrino correlation. This suggests that certain IceCube hotspots may be unresolved blends of multiple AGN, and supports a multimessenger scenario in which high-energy neutrinos and hard X-rays originate from the same hadronic interactions, with the X-ray emission produced through cascade reprocessing.

astro-ph.HE↗

arXiv2025

Galactic forcing increases origination of marine microplankton

The continuous flux of Galactic cosmic rays that bombard Earth's atmosphere creates ionizing radiation that can damage the DNA of living organisms. While this radiation on Earth is relatively constant in the short term, large and long-scale fluctuations are expected with a period of $\sim 63.5$ million years. As the Solar System moves above or below the Galactic plane during its oscillatory motion about the Galactic center, the Galactic magnetic shielding weakens, allowing more cosmic rays to reach Earth and trigger mutations in organisms. We identify a significant correlation (weighted global p-value: $1.25\times 10^{-4}$, or $3.72\sigma$) between the Solar System's Galactic oscillations and the origination of marine zoo- and phyto-microplankton genera over the Phanerozoic. When we restrict the analysis to time intervals during which all four groups coexisted, a post-trial significance of $4.52\sigma$ emerges. Our findings suggest that changes in biodiversity have been significantly influenced by long-term Galactic forcing.

astro-ph.HE↗

arXiv2024

Possible correlation between unabsorbed hard X-rays and neutrinos in radio-loud and radio-quiet AGN

The first high-energy neutrino source identified by IceCube was a blazar -- an active galactic nucleus driving a relativistic jet towards Earth. Jets driven by accreting black holes are commonly assumed to be needed for high-energy neutrino production. Recently, IceCube discovered neutrinos from Seyfert galaxies, which appears unrelated to jet activity. Here, we show that the observed luminosity ratios of neutrinos and hard X-rays from blazars TXS 0506+056 and GB6 J1542+6129 are consistent with neutrino production in a $\gamma$-obscured region near a central supermassive black hole, with the X-ray flux corresponding to reprocessed $\gamma$-ray emission with flux comparable to that of neutrinos. Similar neutrino - hard X-ray flux ratios are found for four Seyfert galaxies, NGC 1068, NGC 4151, CGCG 420-015 and NGC 3079, raising the possibility of a common neutrino production mechanism that may not involve a strong jet.

astro-ph.HE↗

arXiv2024

European VLBI Network observations of the peculiar radio source 4C 35.06 overlapping with a compact group of nine galaxies

Context. According to the hierarchical structure formation model, brightest cluster galaxies (BCGs) evolve into the most luminous and massive galaxies in the Universe through multiple merger events. The peculiar radio source 4C 35.06 is located at the core of the galaxy cluster Abell 407, overlapping with a compact group of nine galaxies. Low-frequency radio observations have revealed a helical, steep-spectrum, kiloparsec-scale jet structure and inner lobes with less steep spectra, compatible with a recurring active galactic nucleus (AGN) activity scenario. However, the host galaxy of the AGN responsible for the detected radio emission remained unclear. Aims. We aim to identify the host of 4C 35.06 by studying the object at high angular resolution and thereby confirm the recurrent AGN activity scenario. Methods. To reveal the host of the radio source, we carried out very long baseline interferometry (VLBI) observations with the European VLBI Network of the nine galaxies in the group at 1.7 and 4.9 GHz. Results. We detected compact radio emission from an AGN located between the two inner lobes at both observing frequencies. In addition, we detected another galaxy at 1.7 GHz, whose position appears more consistent with the principal jet axis and is located closer to the low-frequency radio peak of 4C 35.06. The presence of another radio-loud AGN in the nonet sheds new light on the BCG formation and provides an alternative scenario in which not just one but two AGNs are responsible for the complex large-scale radio structure

astro-ph.GA↗

arXiv2024

Cosmic radiation drives quasi-periodic changes in the diversity of siliceous marine microplankton

Radiolarians are significant contributors to the oceanic primary productivity and the global silica cycle in the last 500 Myr. Their diversity throughout the Phanerozoic shows periodic fluctuations. We identify a possible abiotic candidate for driving these patterns which seems to potentially influence radiolarian diversity changes during this period at a significance level of $\sim 2.2 \sigma$. Our finding suggests a significant correlation between the origination of new radiolaria species and maximum excursions of the Solar system from the Galactic plane, where the magnetic shielding of cosmic rays is expected to be weaker. We connect the particularly strong radiolaria blooming during the Middle Triassic to the so-called Mesozoic dipole-low of the geomagnetic field, which was in its deepest state when radiolarias were blooming. According to the scenario, high-energy cosmic rays presumably implied particular damage to the DNA during the maximum excursions which may trigger large chromosomal abnormalities leading to the appearance of a large number of new genera and species during these periods.

q-bio.PE↗

arXiv2024

VLBI Analysis of a Potential High-Energy Neutrino Emitter Blazar

Recent studies suggest that high-energy neutrinos can be produced in the jets of blazars, radio-loud active galactic nuclei (AGN) with jets pointing close to the line of sight. Due to the relatively poor angular resolution of current neutrino detectors, several sources can be regarded as the possible counterpart of a given neutrino event. Therefore, follow-up observations of counterpart candidates in the electromagnetic regime are essential. Since the Very Long Baseline Interferometry (VLBI) technique provides the highest angular resolution to study the radio jets of blazars, a growing number of investigations are being conducted to connect individual blazars to given high-energy neutrino events. We analyzed more than 20 years of available archival VLBI data of the blazar CTD 74, which has been listed as a possible counterpart of a neutrino event. Using cm-wavelength data, we investigated the jet structure, determined the apparent speed of jet components, and the core flux density before and after the neutrino event. Our results indicate stationary jet features and a significant brightening of the core after the neutrino event.

astro-ph.HE↗

arXiv2023

Follow-up on the Supermassive Black Hole Binary Candidate J1048+7143: Successful Prediction of the Next Gamma-ray Flare and Refined Binary Parameters in the Framework of Jet Precession Model

Analyzing single-dish and VLBI radio, as well as \textit{Fermi}-LAT $\gamma$-ray observations, we explained the three major flares in the $\gamma$-ray light curve of FSRQ J1048+7143 with the spin--orbit precession of the dominant mass black hole in a supermassive black hole binary system. Here, we report on the detection of a fourth $\gamma$-ray flare from J1048+7143, appearing in the time interval which was predicted in our previous work. Including this new flare, we constrained the mass ratio into a narrow range of $0.062<q<0.088$, and consequently we were able to further constrain the parameters of the hypothetical supermassive binary black hole at the heart of J1048+7143. We predict the occurrence of the fifth major $\gamma$-ray flare that would appear only if the jet will still lay close to our line sight. The fourth major $\gamma$-ray flare also shows the two-subflare structure, further strengthening our scenario in which the occurrence of the subflares is the signature of the precession of a spine--sheath jet structure that quasi-periodically interacts with a proton target, e.g. clouds in the broad-line region.

astro-ph.HE↗

arXiv2023

Neutrino Emissions of TXS 0506+056 caused by a Supermassive Binary Black Hole Inspiral?

The IceCube neutrino observatory detected two distinct flares of high-energy neutrinos from the direction of the blazar TXS 0506+056: a $\sim 300$ TeV single neutrino on September 22, 2017 and a $3.5\sigma$ signature of a dozen TeV neutrinos in 2014/2015. In a previous work, it was shown that these two episodes of neutrino emission could be due to an inspiral of a supermassive binary black hole (SMBBH) close to its merger at the core of TXS 0506+056. Such an inspiral can lead to quasi-periodic particle emission due to jet precession close to the final coalescence. This model made predictions on when the next neutrino emission episode must occur. On September 18, 2022, IceCube detected an additional, $\sim 170$ TeV neutrino in directional coincidence with the blazar TXS 0506+056, being consistent with the model prediction. Additionally, in April 2021, the Baikal Collaboration reported the detection of a $224\pm 75$ TeV neutrino, with TXS 0506+056 being in the uncertainty range of the event direction. We show that these four distinct flares of neutrino emission from TXS 0506+056 are consistent with a precessing jet scenario, driven by an inspiraling SMBBH. Using improved modeling, we are now able to constrain the total mass together with the mass ratio for the binary. We predict when the next neutrino flares from TXS 0506+056 should be happening. Finally, we estimate the detection potential of the Laser-interferometer Space Antenna (LISA) for the merger in the future.

astro-ph.HE↗

arXiv2023

Precession-induced Variability in AGN Jets and OJ 287

The combined study of the flaring of Active Galactic Nuclei (AGN) at radio wavelengths and pc-scale jet kinematics with Very Long Baseline Interferometry (VLBI) has led to the view that i) the observed flares are associated with ejections of synchrotron blobs from the core, and ii) most of the flaring would follow a one-to-one correlation with the component ejection. Recent results have provided mounting evidence that the quasi-regular component injections into the relativistic jet may not be the only cause of the flux variability. We propose that AGN flux variability and jet morphology changes can both be of deterministic nature, i.e. having a geometric/kinetic origin linked to the time-variable Doppler beaming of the jet emission as its direction changes due to precession (and nutation). The physics of the underlying jet leads to shocks, instabilities, or to ejections of plasmoids. The appearance (morphology, flux, etc.) of the jet can, however, be strongly affected and modulated by precession. We demonstrate this modulating power of precession for OJ 287. For the first time, we show that the spectral state of the Spectral Energy Distribution (SED) can be directly related to the jet's precession phase. We model the SED evolution and reproduce the precession parameters. Further, we apply our precession model to eleven prominent AGN. We show that for OJ 287 precession seems to dominate the long-term variability ($\gtrsim 1\,{\rm yr}$) of the AGN flux, SED spectral state, and jet morphology, while stochastic processes affect the variability on short timescales ($\lesssim 0.2\,{\rm yr}$).

astro-ph.HE↗

arXiv2023

Searching for temporary gamma-ray dark blazars associated with IceCube neutrinos

Tensions between the diffuse gamma-ray sky observed by the Fermi Large Area Telescope (LAT) and the diffuse high-energy neutrino sky detected by the IceCube South Pole Neutrino Observatory question our knowledge about high-energy neutrino sources in the gamma-ray regime. While blazars are among the most energetic persistent particle accelerators in the Universe, studies suggest that they could account for up to for 10-30% of the neutrino flux measured by IceCube. Our recent results highlighted that the associated IceCube neutrinos arrived in a local gamma-ray minimum (dip) of three strong neutrino point-source candidates. We increase the sample of neutrino-source candidates to study their gamma-ray light curves. We generate the one-year Fermi-LAT light curve for 8 neutrino source candidate blazars (RBS 0958, GB6 J1040+0617, PKS 1313-333, TXS 0506+056, PKS 1454-354, NVSS J042025-374443, PKS 0426-380 and PKS 1502+106), centered on the detection time of the associated IceCube neutrinos. We apply the Bayesian block algorithm on the light curves to characterize their variability. Our results indicate that GB6 J1040+0617 was in the phase of high gamma-ray activity, while none of the other 7 neutrino source candidates were statistically bright during the detection of the corresponding neutrinos and that indeed even most of the times neutrinos arrived in a faint gamma-ray phase of the light curves. This suggests that the 8 source-candidate blazars (associated with 7 neutrino events) in our reduced sample are either not the sources of the corresponding IceCube neutrinos, or that an in-source effect (e.g. suppression of gamma rays due to high gamma-gamma opacity) complicates the multimessenger scenario of neutrino emission for these blazars.

astro-ph.HE↗

arXiv2022

Multimessenger Picture of J1048+7143

We draw the multimessenger picture of J1048+7143, a flat-spectrum radio quasar known to show quasi-periodic oscillations in the $\gamma$-ray regime. We generate the adaptively-binned Fermi Large Area Telescope light curve of this source above 168 MeV to find three major $\gamma$-ray flares of the source, such that all three flares consist of two-two sharp sub-flares. Based on radio interferometric imaging data taken with the Very Large Array, we find that the kpc-scale jet is directed towards west, while our analysis of $8.6$-GHz very long baseline interferometry data, mostly taken with the Very Long Baseline Array, revealed signatures of two pc-scale jets, one pointing towards east, one pointing towards south. We suggest that the misalignment of the kpc- and pc-scale jets is a revealing signature of jet precession. We also analyze the $5$-GHz total flux density curve of J1048+7143 taken with the Nanshan(Ur) and RATAN-600 single dish radio telescopes and find two complete radio flares, slightly lagging behind the $\gamma$-ray flares. We model the timing of $\gamma$-ray flares as signature of the spin-orbit precession in a supermassive black hole binary, and find that the binary could merge in the next $\sim 60-80$ years. We show that both the Pulsar Timing Arrays and the planned Laser Interferometer Space Antenna lack sensitivity and frequency coverage to detect the hypothetical supermassive black hole binary in J1048$+$7143. We argue that the identification of sources similar to J1048+7143 plays a key role to reveal periodic high-energy sources in the distant Universe.

astro-ph.HE↗

arXiv2022

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, 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 ($2.1\sigma$, $1.2\sigma$, $2\sigma$ at $4.8~\mathrm{GHz}$, $2.1\sigma$ at $8.4~\mathrm{GHz}$, respectively, assuming 50% astrophysical signalness). After collecting redshifts and deriving sub-samples of the CRATES catalog complete in the redshift--luminosity plane, we find that the 4.8 GHz ($8.4$~GHz) sub-sample can explain between 4% and 53% ($3$% and $42$%) of the neutrinos (90% C.L.), when the probability to detect 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 $5\sigma$ level. Our selection serves as a starting point to further select the correct sources.

astro-ph.HE↗

arXiv2022

Searching for the Origin of Double-peaked Broad Emission Lines in a Merging Galaxy with EVN

The current cosmological structure formation models predict that galaxies evolve through frequent mergers. During these events, the supermassive black holes (SMBHs) residing in the centres of the galaxies shrink to the central region, while losing energy via dynamical friction. Detection of SMBHs in these galaxy mergers is straightforward if they are actively accreting matter from their surroundings as active galactic nuclei (AGN). Currently, only a few dual AGN are known. One way to identify dual AGN candidates is by detecting double-peaked emission lines in their spectra. If these are broad spectral lines, it may indicate the existence of two broad line regions associated with two AGN. 2MASS J165939.7+183436 is a merging system, where the detected double-peaked broad emission lines can be explained by a dual AGN with an estimated separation of $0.085"$. Radio emission from this object was detected in the Faint Images of the Radio Sky at Twenty-centimeters survey with a flux density of 2.6 mJy. We used the European Very Long Baseline Interferometer Network and the enhanced Multi-Element Remotely Linked Interferometer Network to image 2MASS J165939.7+183436 at 1.7 GHz. We did not detect compact radio emission from the source.

astro-ph.GA↗

arXiv2021

European VLBI Network Observations of the Proposed Dual AGN SDSS J101022.95+141300.9

During galaxy merger events, the supermassive black holes in the center of the galaxies may form a pair of active galactic nuclei (AGN) with kpc-scale or even pc-scale separation. Recently, optical observations revealed a promising dual AGN candidate at the center of the galaxy SDSS J101022.95$+$141300.9 (hereafter J1010$+$1413). The presence of two distinct [O III]-emitting point sources with a projected separation of $\sim 430$ pc indicates a dual AGN system. To search for AGN-dominated radio emission originating from the Hubble Space Telescope (HST) point sources, we carried out very long baseline interferometry observations. We resolved the radio structure of J1010$+$1413 and detected a single feature offset from the HST point sources and also from the Gaia optical position of the object. Our multi-wavelength analysis of J1010$+$1413 inferred two possible interpretations of the observed properties challenging its proposed dual AGN classification.

astro-ph.GA↗

arXiv2020

Cosmic neutrinos from temporarily gamma-suppressed blazars

Despite the uncovered association of a high-energy neutrino with the apparent flaring state of blazar TXS 0506+056 in 2017, the mechanisms leading to astrophysical particle acceleration and neutrino production are still uncertain. Recent studies found that when transparent to $\gamma$-rays, $\gamma$-flaring blazars do not have the opacity for protons to produce neutrinos. Here we present observational evidence for an alternative explanation, in which $\gamma$-ray emission is suppressed during efficient neutrino production. A large proton and target photon density help produce neutrinos while temporarily suppress the observable $\gamma$-emission due to a large $\gamma \gamma$ opacity. We show that the Fermi-LAT $\gamma$-flux of blazar PKS 1502+106 was at a local minimum when IceCube recorded the coincident high-energy neutrino IC-190730A. Using data from the OVRO 40-meter Telescope, we find that radio emission from PKS 1502+106 at the time period of the coincident neutrino IC-190730A was in a high state, in contrast to earlier time periods when radio and $\gamma$ fluxes are correlated for both low and high states. This points to an active outflow that is $\gamma$-suppressed at the time of neutrino production. We find similar local $\gamma$-suppression in other blazars, including in MAGIC's TeV flux of TXS\,0506+056 and Fermi-LAT's flux of blazar PKS B1424-418 at the time of coincident IceCube neutrino detections. Using temporary $\gamma$-suppression, neutrino-blazar coincidence searches could be substantially more sensitive than previously assumed, enabling the identification of the origin of IceCube's diffuse neutrino flux possibly with already existing data.

astro-ph.HE↗