arXiv subjects

A. Mikhno

Publications and source records attributed to A. Mikhno.

3 recordsLinked to original sources

arXiv2026

Study of blazar variability through their flux distribution for CTAO long-term monitoring

The CTAO Key Science Project on Active Galactic Nuclei (AGN) includes a long-term monitoring (LTM) program of blazars. The probability distribution function (PDF) of the flux extracted from unbiased blazar lightcurves can provide important insight into the physical processes taking place in relativistic jets and their connection to observed variability. The aim of this work is to define an optimal observational strategy for the CTAO LTM program using the flux distributions as a quantitative metric. To achieve this goal, we develop a simulation-based analysis framework that enables a systematic comparison of different observational strategies. Light curves were simulated as would be observed with the future CTAO for a representative set of AGN sources, following four different observational strategies within a fixed time budget. For each simulated light curve, different PDF models were fitted and their goodness of fit was evaluated. Based on the best-fit parameters, Monte Carlo simulations were generated to assess the ability of the method to recover the underlying PDF model. Since the true model used to generate the simulated light curves is known, this procedure allows us to quantify the discriminatory power of the algorithm and to identify which observational strategy maximizes model discrimination. Additionally, the algorithm has the potential of discrimination against different models for the flux distributions, such as Gaussian and lognormal. Once validated on simulations, the method is applied to archival lightcurves from existing gamma-ray instruments to extract flux PDFs and study the physical processes driving blazar variability. The analysis framework has been developed and tested on simulated CTAO-like data, showing good stability and robustness. A study to optimize the observing strategy for the CTAO LTM is presented.

astro-ph.HE↗

arXiv2026

Synergy between the Cherenkov Telescope Array Observatory and the Vera C. Rubin Observatory

The Cherenkov Telescope Array Observatory (CTAO) and the Vera C. Rubin Observatory are set to transform our understanding of the universe over the next decade. These two observatories have multiple areas of complementarity in their scientific applications, ranging from constraints on cosmological parameters to studies of asteroid occultations. The most opportune area of synergy probably lies in the field of time-domain astronomy. Due to their sensitivity and saturation limits, it will be difficult for the two observatories to conduct joint studies of variable and transient sources in the Milky Way. However, they could offer a fresh and rich perspective on non-thermal extragalactic sources, in particular gamma-ray bursts, active galactic nuclei and jetted tidal disruption events. Among these sources lie the best candidates for multi-messenger research into the origin of TeV-PeV neutrinos and multi-EeV cosmic rays. Thus, combined with multi-wavelength observations by X-ray satellites and wide-field gamma-ray instruments, the synergy between Rubin and the CTAO could provide answers to some of the most important questions in astroparticle physics. This scientific potential comes with a challenge: selecting a few alerts from the ten million issued by Rubin each night to repoint the CTAO telescopes. We use the variability of blazars over timescales ranging from a few days to several years as a case study to demonstrate how to address this challenge using the Fink broker of Rubin.

astro-ph.HE↗

arXiv2026

The second H.E.S.S. gamma-ray burst catalogue: 15 years of observations with the H.E.S.S. telescopes

Recent observational efforts using imaging atmospheric Cherenkov telescopes (IACTs) have led to firm detections of very-high-energy (VHE) signals from bright gamma-ray bursts (GRBs), often at moderate redshifts. This work presents 15 years of H.E.S.S. GRB observations and examines their implications through population comparisons and selected modelling cases. GRBs are a key science target of the High Energy Stereoscopic System (H.E.S.S.). With a low-energy threshold ($\lesssim$100 GeV) and rapid repointing capabilities, H.E.S.S. can begin follow-up observations within tens of seconds after a GRB trigger, covering the late prompt or early afterglow phases. We report GRB follow-up observations with H.E.S.S. from 2004 to 2019, which resulted in no significant VHE signals (aside from the detections of GRB~180720B and GRB~190829A). The resulting upper limits comprise the largest set available for GRBs at VHE. A subset of bursts with favourable conditions were selected for X-ray analysis and emission modelling. Population studies were performed to compare detected and non-detected GRBs. The results indicate that VHE-detected GRBs are not a distinct population, but tend to feature luminous X-ray emission and favourable redshift and observing conditions. This highlights the potential of next-generation IACTs such as the Cherenkov Telescope Array Observatory (CTAO), whose lower energy threshold will enhance the detection of fainter and more distant GRBs.

astro-ph.HE↗