arXiv subjects

Ievgen Vovk

Publications and source records attributed to Ievgen Vovk.

At least 19 recordsLinked to original sources

arXiv2026

AI's Capability in Assisting Scientific Research in Physics, Astrophysics, and Cosmology I: Literature Review

We investigate how well large language models (LLMs) can assist with literature reviews for scientific research. We perform a controlled study of eight expert-conceived research projects across the areas of physics, astrophysics, and cosmology. Each project has a defined background and goal, and human experts and AI prompters are asked to perform identical literature review tasks in parallel. We compare the relevant literature selected by humans with that selected by mid-2025 LLMs (ChatGPT-4o, ChatGPT Deep Research, and Gemini). We find the overlap between human- and AI-selected references to be small ($<$6\%), indicating that AI models do not yet reproduce a competent expert search on their own, though they have the potential to complement literature searches by humans. We then assess the reliability and completeness of AI-generated candidate references, distinguishing two types of hallucination: fabrications (references to nonexistent papers) and metadata mismatches (real papers with one or more incorrect fields). We find that while fabricated references make up 3\% of the AI-generated references, 64\% are real papers with at least one incorrect field (title, author, year, journal, DOI, or link), indicating that the mid-2025 models require systematic verification. However, the performance is significantly improved for the 2026 model ChatGPT Pro 5.5, with a single-project test showing zero fabrication or metadata mismatches.

astro-ph.IM↗

arXiv2026

AI's Capability in Assisting Scientific Research in Physics, Astrophysics, and Cosmology II: Project Planning and Proposal Evaluation

We investigate how well large language models (LLMs) can assist scientific project planning and proposal evaluation. One-page project plans were independently generated for eight expert-conceived research projects in physics, astrophysics, and cosmology by human researchers and three contemporary LLMs (ChatGPT, Claude, and DeepSeek; mid-2025 models, used with their default tool access). The resulting 32 proposals were blindly evaluated by four human reviewers and two newer frontier LLMs (Claude Opus 4.8 and ChatGPT Pro 5.5) using a four-aspect evaluation rubric. Reviewers were also asked to identify whether each proposal was written by a human or an AI. Human reviewers rated human- and AI-written proposals similarly overall, whereas both AI reviewers scored AI-written proposals about one point higher (on a five-point scale) than human-written proposals. Human reviewers correctly identified human- and AI-written proposals 72% and 79% of the time, respectively, while both AI reviewers correctly classified all 32 proposals (100%). These results suggest that current LLMs can produce project plans comparable to human-written ones in the eyes of human reviewers, but that AI reviewers show a systematic preference for AI-generated proposals. Our results suggest caution when deploying LLMs widely in proposal preparation and evaluation.

cs.CL↗

arXiv2025

Intergalactic magnetic field lower limits up to the redshift $z\approx3$

Large-scale intergalactic magnetic fields may contain a mixture of galactic and cosmogenic contributions, that can be probed via observations of $\gamma$-ray "echo" - a delayed emission from electromagnetic cascades initiated by the highest energy photons from the sources at cosmological distances. While these fields contributions may be disentangled based on the difference in their redshift evolution, thus far indications of non-negligible magnetic field have been found only at low redshifts. This work aims at extending the intergalactic magnetic field constraints to redshifts $z\gtrsim 1$ using 17-year long all-sky observations of high-redshift active galactic nuclei with Fermi/LAT $\gamma$-ray telescope. Combing the Fermi/LAT measurements in the 0.1 GeV - 1 TeV energy range with the Monte Carlo simulations of the $\gamma$-ray "echo", it is shown that the zero field strength hypothesis at $z = [0.5; 3]$ is disfavoured at the $\approx 8.6\sigma$ significance level, yielding the lower limit of $B \gtrsim 1\times10^{-18}$ cG for the magnetic field correlation length above 1 Mpc. It is further shown that the same data put a lower limit on the volume-filling fraction of this field of $f\gtrsim 90\%$ in the redshift range considered. It is also demonstrated that the derived limits are not substantially affected by either source flux variability or the assumed $\gamma$-ray emission attenuation model. Implications of these limits for intergalactic magnetic field origin are discussed.

astro-ph.HE↗

arXiv2025

The very high energy view of gamma-ray bursts with the MAGIC telescopes

Gamma-ray bursts (GRBs) are one of the main targets for the observations of the MAGIC telescopes. As a result of the effort in improving the sensitivity of the instrument and the automatic follow-up strategy, MAGIC detected two GRBs in the very-high-energy (VHE, $E>100$ GeV) range, namely GRB 190114C and GRB 201216C. In GRB 190114C ($z=0.42$), the data collected by MAGIC revealed a new emission component at sub-TeV energies in the afterglow of the GRB. The very rich multi-wavelength dataset, spanning 17 orders of magnitude in energy, allowed to perform a detailed modelling of the broadband emission. The multi-wavelength data could be modelled within a one-zone synchrotron-self Compton scenario with internal $\gamma-\gamma$ absorption, where the model parameters are compatible with those found in previous GRB afterglow studies below GeV energies. Similarly, GRB 201216C broadband emission could be explained using the same model, although the amount of simultaneous multi-wavelength data is reduced with respect to GRB 190114C. In particular, GRB 201216C challenged the current MAGIC detection potential, as its redshift was determined to be $z=1.1$, strongly reducing the observed gamma-ray flux but making it the most distant source detected at VHE. These two detections, accompanied by evidence of VHE emission from a few more GRBs, opened up new questions such as the presence of sub-TeV emission in different classes and phases of GRBs. In this contribution we will present the status of the MAGIC GRB follow-up program, with an highlight on its detected GRBs. Moreover we will show the results on the GRBs observed by MAGIC from 2013 to 2019 with no evidence of VHE emission, in particular for those with simultaneous X-ray observations and redshift $z<2$. We will discuss the implications of these results for GRB physics and the challenges and prospects for future GRB observations with MAGIC.

astro-ph.HE↗

arXiv2024

Marginal Role of the Electrostatic Instability in the GeV-scale Cascade Flux from 1ES 0229+200

Relativistic pair beams produced in the intergalactic medium (IGM) by TeV gamma rays from blazars are expected to generate a detectable GeV-scale electromagnetic cascade, yet this cascade is absent in the observed spectra of hard-spectrum TeV emitting blazars. This suppression is often attributed to weak intergalactic magnetic fields (IGMF) deflecting electron-positron pairs out of the line of sight. Alternatively, it has been proposed that beam-plasma instabilities could drain the energy of the beam before they produce the secondary cascades. Recent studies suggest that the modification of beam distribution due to these instabilities is primarily driven by particle scattering, rather than energy loss. In this paper, we quantitatively assess, for the blazar 1ES 0229+200, the arrival time of secondary gamma rays at Earth from the beam scattering by the electrostatic instability. We first computed the production rates of electron-positron pairs at various distances using the Monte Carlo simulation CRPropa. We then simulated the feedback of the plasma instability on the beam, incorporating production rates and inverse-Compton cooling, to determine the steady-state distribution function. Our findings reveal that the time delay of the GeV secondary cascade arrival due to instability broadening is on the order of a few months. This delay is insufficient to account for the missing cascade emission in blazar spectra, suggesting that plasma instabilities do not significantly affect IGMF constraints.

astro-ph.HE↗

arXiv2024

Probing intergalactic intergalactic magnetic fields with LOFAR LoTSS DR2 data

We use Faraday rotation measurements from the latest catalog LoTSS DR2 from LOFAR to probe intergalactic magnetic fields. To identify the extragalactic component of the observed rotation measure (RM) we use two different techniques: residual rotation measure (RRM) and close radio pairs. For the RRM approach, we conclude that, despite smaller measurement errors in the LOFAR data, robust and conservative treatment of the systematic uncertainties in the Galactic contribution to RM results in the constraint on a homogeneous volume-filling magnetic field at the level 2.4 nG, slightly weaker than previous constraints from NVSS data, and does not allow to probe the presence of over-magnetized bubbles predicted by the AGN feedback model of the IllustrisTNG. Analyzing close radio pairs we found that in only 0.5% of our mock realizations of observed data, the expected contribution from the over-magnetized bubbles does not exceed LoTSS DR2 data.

astro-ph.CO↗

arXiv2023

Search of the pair echo signatures in the high-energy light curve of GRB190114C

A model of the time delayed electromagnetic cascade "echo" is applied to the bright gamma-ray burst GRB190114C - the first gamma-ray burst to be contemporaneously detected in high and very high energy gamma-ray bands. It is shown that the internal spread of the cascade in the absence of the intervening magnetic fields dilutes the "echo" emission over $10^3-10^5$ seconds depending on the energy. Accounting for the measured source flux in the $0.3-1$ TeV gamma-ray band, the prediction of the "echo" model is shown to match the detected lower-energy gamma-ray emission $10^4$ seconds after the burst. However, the "echo" emission remains indistinguishable from the intrinsic GRB190114C flux within the measurement uncertainties. Implications of this in the context of the intergalactic magnetic field measurement are discussed.

astro-ph.HE↗

arXiv2021

CTA sensitivity for probing cosmology and fundamental physics with gamma rays

The Cherenkov Telescopic Array (CTA), the next-generation ground-based gamma-ray observatory, will have unprecedented sensitivity, providing answers to open questions in gamma-ray cosmology and fundamental physics. Using simulations of active galactic nuclei observations foreseen in the CTA Key Science Program, we find that CTA will measure gamma-ray absorption on the extragalactic background light with a statistical error below 15% up to the redshift of 2 and detect or establish limits on gamma halos induced by the intergalactic magnetic field of at least 0.3 pG. Extragalactic observations using CTA also demonstrate the potential for testing physics beyond the Standard Model. The best state-of-the-art constraints on the Lorentz invariance violation from astronomical gamma-ray observations will be improved at least two- to threefold. CTA will also probe the parameter space where axion-like particles can represent a significant proportion - if not all - of dark matter. Joint multiwavelength and multimessenger observations, carried out together with other future observatories, will further foster the growth of gamma-ray cosmology.

astro-ph.IM↗

arXiv2019

MAGIC observations of Dragonfly Nebula at TeV Energies using the Very Large Zenith Angle Technique

One of the brightest regions of diffuse gamma-ray emission in the northern sky is the Cygnus star-forming region, where one can assume the most energetic processes are taking place. The Dragonfly Nebula (MGRO J2019+37) is one of the brightest sources in the Cygnus region. First discovered by MILAGRO, it was later resolved into two sources by VERITAS: the faint point-like source VER J2016+371 and the bright extended source VER J2019+368. The latter accounts for the bulk of the MGRO J2019+37 emission, with the spectrum among the hardest in the TeV range. We report the results of a dedicated MAGIC observational campaign of VER J2019+368. The data obtained with the Very Large Zenith Angle observational technique provides an effective collection area of about one square kilometer. We used $\sim$45 hours of data collected under Very Large Zenith Angles for exploring the flux of the source at TeV energies.

astro-ph.HE↗

arXiv2019

Searching for Variability of the Crab Nebula Flux at TeV Energies using MAGIC Very Large Zenith Angle Observations

The Crab nebula was once considered to be a stable source until strong flares, up to 30 times increase in flux, were observed in the MeV and GeV energy range by the AGILE and Fermi Gamma-ray Observatories. Existing nebula models often assume that the electron population emitting synchrotron radiation at lower energies is responsible for the VHE emission via Inverse Compton (IC) scattering. This suggests that the variability of the synchrotron $γ$-ray emission may also become observable in the multi-TeV energy range. Until now, no variability in the Crab Nebula flux has been found in the VHE regime. In 2015, MAGIC started an observational campaign which improved the collection efficiency of $γ$-rays above several tens of TeV. These observations are performed under Very Large Zenith Angles (VLZA) and lead to a large increase in the collection area. This allows us to observe the low fluxes at TeV energies in a shorter time compared to standard observations, and to significantly increase the observable energy towards higher energies. We have studied the Crab Nebula light curve obtained from the VLZA data since 2015 in search for the flux variability at the highest TeV energies. The results of this study will be presented.

astro-ph.HE↗

arXiv2019

The Crab Nebula Spectrum at ~100 TeV Measured with MAGIC under Very Large Zenith Angles

The Crab Nebula was discovered as the first very-high-energy gamma-ray source by the Whipple Observatory in 1989. Thirty years after its discovery it is still the reference source and the standard candle for Imaging Atmospheric Cherenkov Telescopes (IACTs). Its spectrum has been measured from the cm radio band to energies up to tens of TeV. Some studies reported a possible but still debated cut-off in its spectrum at few tens of TeV. The MAGIC collaboration is currently investigating the spectrum of the Crab Nebula by using the Very Large Zenith Angle observation technique. The latter provides a significantly increased collection area for energies above 10 TeV. The details of these MAGIC observations will be presented.

astro-ph.IM↗

arXiv2019

Extending the observation limits of Imaging Air Cherenkov Telescopes toward horizon

Usually the Imaging Atmospheric Cherenkov Telescopes, used for the ground-based gamma-ray astronomy in the very high energy range 50 GeV - 50 TeV, perform air shower observations till the zenith angle of ~60 deg. Beyond that limit the column density of air increases rapidly and the Cherenkov light absorption starts playing a major role. Absence of a proper calibration method of light transmission restrained researchers performing regular measurements under zenith angles >>60 deg. We extend the observation of air showers in Cherenkov light till almost the horizon. We use an aperture photometry technique for calibrating the Cherenkov light transmission in atmosphere during observations under very large zenith angles. Along with longer in time observations of a given source, this observation technique allows one to strongly increase the collection area and the event statistics of Cherenkov telescopes for the very high energy part of the spectrum. Study of the spectra of the highest energy gamma rays from a handful of candidate sources can provide a clue for the origin of the galactic cosmic rays. We show that MAGIC very large zenith angle observations yield a collection area in excess of a square kilometer. For selected sources this is becoming comparable with the target collection area anticipated with the Cherenkov Telescope Array.

astro-ph.IM↗

arXiv2017

Studying cosmological $γ$-ray propagation with the Cherenkov Telescope Array

The measurement of $γ$-rays originating from active galactic nuclei offers the unique opportunity to study the propagation of very-high-energy photons over cosmological distances. Most prominently, $γ$-rays interact with the extragalactic background light (EBL) to produce $e^+e^-$ pairs, imprinting an attenuation signature on $γ$-ray spectra. The $e^+e^-$ pairs can also induce electromagnetic cascades whose detectability in $γ$-rays depends on the intergalactic magnetic field (IGMF). Furthermore, physics beyond the Standard Model such as Lorentz invariance violation (LIV) or oscillations between photons and weakly interacting sub-eV particles (WISPs) could affect the propagation of $γ$-rays. The future Cherenkov Telescope Array (CTA), with its unprecedented $γ$-ray source sensitivity, as well as enhanced energy and spatial resolution at very high energies, is perfectly suited to study cosmological effects on $γ$-ray propagation. Here, we present first results of a study designed to realistically assess the capabilities of CTA to probe the EBL, IGMF, LIV, and WISPs.

astro-ph.HE↗

arXiv2017

White paper on EUSO-SPB2

EUSO-SPB2 is a second generation Extreme Universe Space Observatory (EUSO) on a Super-Pressure Balloon (SPB). This document describes the physics capabilities, the proposed technical design of the instruments, and the simulation and analysis software.

astro-ph.HE↗

arXiv2015

Detection of very-high-energy gamma rays from the most distant and gravitationally lensed blazar QSO B0218+357 using the MAGIC telescope system

QSO B0218+357 is a blazar located at a cosmological redshift of z=0.944. It is gravitationally lensed by a spiral galaxy at a redshift of z=0.68. The blazar and its lens are well studied in the radio through X-ray bands, and several blazar outbursts were detected by Fermi-LAT at energies above 100 MeV. Strong gravitational lensing was invoked to explain the two components appar- ent in the radio and GeV light curves, separated by 10-12 days. In July 2014 another outburst was observed by Fermi-LAT, triggering follow-up observations with the MAGIC telescopes at energies above 100 GeV. The observations were scheduled at the expected time of arrival of the component delayed by the strong gravitational field of the lens, resulting in a firm detection of QSO B0218+357. Using the combined Fermi-LAT and MAGIC data sets, we report on variability of this unique blazar, the most distant among all currently known very high energy sources.

astro-ph.HE↗

arXiv2015

Microlensing constraint on the size of the gamma-ray emission region in blazar B0218+357

Context. Observations of the effect of microlensing in gravitationally lensed quasars could potentially be used to study the structure of the source on distance scales down to the size of the supermassive black hole powering the quasar activity. Aims. We search for the microlensing effect in the gamma-ray band using the signal from a gravitationally lensed blazar B0218+357. Methonds. We develop a method of deconvolution of contributions of two images of the source into the gamma-ray band flaring lightcurve. We use this method to study the evolution of the magnification factor ratio between the two images throughout the flaring episodes. We interpret the time variability of the ratio as a signature of the microlensing effect and derive constraints on the physical parameters of the gamma-ray source by comparing the observed variability properties of the magnification factor ratio with those derived from numerical simulations of the microlensing caustics networks. Results. We find that the magnification factor ratio has experienced a change characteristic for a microlensing caustic crossing event during a 100 d flaring period in 2012. It has further changed between 2012 and a recent flaring episode in 2014. We use the measurement of the maximal magnification and duration of the caustic crossing event to derive an estimate of the projected size of the gamma-ray emission region in B0218+357, $R_γ\sim 10^{14}$ cm. This estimate is compatible with a complementary estimate found from the minimal variability time scale. The microlensing / minimal variability time scale measurements of the source size suggest that the gamma-ray emission is produced at the base of the blazar jet, in the direct vicinity of the central supermassive black hole.

astro-ph.HE↗

arXiv2013

Variability of gamma-ray emission from blazars on the black hole timescales

We investigate the variability properties of blazars in the GeV band using the data of the Fermi/LAT telescope. We find that blazars exhibit variability on the scales down to the minimal timescale resolvable by Fermi, which is a function of the peak photon count rate in the LAT. This implies that the real minimal variability timescales for the majority of blazars are typically shorter than those resolvable by the LAT. We find that for several blazars these minimal variability timescales reach those associated to the blazar central engine, the supermassive black hole. At the same time, none of the blazars exhibits variability on the timescale shorter than the black hole horizon light crossing time and/or the period of rotation around the last stable circular orbit. Based on this fact, we argue that the timing properties of the gamma-ray signal could be determined by the processes in the direct vicinity of the supermassive black hole.

astro-ph.HE↗

arXiv2012

Fermi/LAT observations of 1ES 0229+200: implications for extragalactic magnetic fields and background light

We report the observation in the GeV band of the blazar 1ES 0229+200, which over recent years has become one the primary sources used to put constraints on the Extragalactic Background Light (EBL) and Extragalactic Magnetic Field (EGMF). We derive constraints on both the EBL and EGMF from the combined Fermi-HESS data set taking into account the direct and cascade components of the source spectrum. We show that the limit on the EBL depends on the EGMF strength and vice versa. In particular, an EBL density twice as high as that derived by Franceschini et al. (2008) is allowed if the EGMF is strong enough. On the other hand, an EGMF strength as low as 6x10^-18 G is allowed if the EBL density is at the level of the lower bound from the direct source counts. We present the combined EBL and EGMF limits on as an exclusion plot in two dimensional parameter space: EGMF strength vs. EBL density.

astro-ph.CO↗