arXiv subjects

Stamatios I. Stathopoulos

Publications and source records attributed to Stamatios I. Stathopoulos.

4 recordsLinked to original sources

arXiv2026

Time-resolved leptonic modeling of the prompt emission of GRB 211211A

GRB 211211A is a long duration gamma-ray burst with a compact object merger origin. In this work, we model the time-resolved prompt-emission spectra of GRB 211211A within a leptonic radiation framework. Our goal is to infer the physical properties of the emitting region, study the temporal evolution of the radiating particle distribution, and make predictions for prompt emission at TeV energies. We perform Markov Chain Monte Carlo fitting of the time-resolved numerical spectral energy distribution (SED) models computed with the time-dependent non-thermal radiation code LeHaMoC. Our calculations include synchrotron emission and self-absorption, inverse Compton scattering including cooling in the Klein-Nishina regime, and photon-photon pair production. We find that the prompt emission of GRB 211211A between 10 keV and 10 MeV can be successfully reproduced by synchrotron radiation from a population of relativistic electrons. The spectral evolution during the first minute of the burst reflects different physical conditions in the emitting region. Our best-fit models favor fast-cooling solutions for the first 8 s, followed by a transition to slow-cooling solutions at later times. The accompanying synchrotron self-Compton emission extends to TeV energies, with predicted fluxes that would be detectable by CTAO for a burst similar to GRB 211211A, provided a sufficiently rapid response to a Fermi-GBM trigger or if the burst occurs within the CTAO field of view. The observed short variability of this burst requires very high Doppler factors ($\sim1000-2500$) throughout the burst evolution. Such extreme Doppler factors are difficult to reconcile with the jet Lorentz factor inferred from afterglow modeling unless the prompt-emitting regions are themselves moving relativistically with respect to the jet plasma.

astro-ph.HE↗

arXiv2025

A Comprehensive Hadronic Code Comparison for Active Galactic Nuclei

We perform the first dedicated comparison of five hadronic codes (AM$^3$, ATHE$ν$A, B13, LeHa-Paris, and LeHaMoC) that have been extensively used in modeling of the spectral energy distribution (SED) of jetted active galactic nuclei. The purpose of this comparison is to identify the sources of systematic errors (e.g., implementation method of proton-photon interactions) and to quantify the expected dispersion in numerical SED models computed with the five codes. The outputs from the codes are first tested in synchrotron self-Compton scenarios that are the simplest blazar emission models used in the literature. We then compare the injection rates and spectra of secondary particles produced in pure hadronic cases with monoenergetic and power-law protons interacting on black-body and power-law photon fields. We finally compare the photon SEDs and the neutrino spectra for realistic proton-synchrotron and leptohadronic blazar models. We find that the codes are in excellent agreement with respect to the spectral shape of the photons and neutrinos. There is a remaining spread in the overall normalization that we quantify, at its maximum, at the level of $\pm 40\%$. This value should be used as an additional, conservative, systematic uncertainty term when comparing numerical simulations and observations.

astro-ph.HE↗

arXiv2023

Dust-scattering rings of GRB 221009A as seen by the Neil Gehrels Swift satellite: can we count them all?

We present the first results for the dust-scattering rings of GRB 221009A, coined as the GRB of the century, as observed by the Neil Gehrels Swift satellite. We perform analysis of both time resolved observations and stacked data. The former approach enable us to study the expansion of the most prominent rings, associate their origin with the prompt X-ray emission of the GRB and determine the location of the dust layers. The stacked radial profiles increase the signal-to-noise ratio of the data and allows detection of fainter and overlapping peaks in the angular profile. We find a total of 16 dust concentrations (with hints of even more) that span about 15 kpc in depth and could be responsible for the highly structured X-ray angular profiles. By comparing the relative scattered fluxes of the five most prominent rings we show that the layer with the largest amount of dust is located at about 0.44 kpc away from us. We finally compare the location of the dust layers with results from experiments that study the 3D structure of our Galaxy via extinction or CO radio observations, and highlight the complementarity of dust X-ray tomography to these approaches.

astro-ph.HE↗

arXiv2021

Probing Neutrino Emission from X-ray Blazar Flares observed with Swift-XRT

Blazars are the most extreme subclass of active galactic nuclei with relativistic jets emerging from a super-massive black hole and forming a small angle with respect to our line of sight. Blazars are also known to be related to flaring activity as they exhibit large flux variations over a wide range of frequency and on multiple timescales, ranging from a few minutes to several months. 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 naturally strengthened the hypothesis that blazars are cosmic neutrino sources. While neutrino production during gamma-ray flares has been widely discussed, the neutrino yield of X-ray flares has received less attention. Motivated by a theoretical scenario where high energy neutrinos are produced by energetic protons interacting with their own X-ray synchrotron radiation, we make neutrino predictions over a sample of a sample of X-ray blazars. This sample consists of all blazars observed with the X-ray Telescope (XRT) on board Swift more than 50 times from November 2004 to November 2020. The statistical identification of a flaring state is done using the Bayesian Block algorithm to the 1 keV XRT light curves of frequently observed blazars. We categorize flaring states into classes based on their variation from the time-average value of the data points. During each flaring state, we compute the expected muon plus anti-muon neutrino events as well as the total signal for each source using the point-source effective area of Icecube for different operational seasons. We find that the median of the total neutrino number (in logarithm) from flares with duration $<30$ d is $\mathcal{N}^{(\rm tot)}_{ν_μ+\barν_μ} \sim 0.02$.

astro-ph.HE↗