arXiv subjects

Timur A. Dzhatdoev

Publications and source records attributed to Timur A. Dzhatdoev.

3 recordsLinked to original sources

arXiv2026

Elemental cosmic ray spectra reveal two populations of Galactic sources and an immediate transition to an extragalactic component after the knee

The energy spectra for individual elements and/or for groups of elements in cosmic rays (CR) in the energy range between 100 $\times$ Z GeV and 10$^{3}$ $\times$ Z PeV (where Z is the charge number of the nucleus) have a number of features, including two steepenings ("knees") with the rigidity-dependent energies $E_{k1} \approx$ 15 $\times$ Z TeV and $E_{k2} \approx$ 3 $\times$ Z PeV and three hardenings ("ankles") at $E_{a1} \approx$ 500 $\times$ Z GeV; for protons $E_{a2-p} \approx$ 150 TeV and $E_{ a3-p} \approx$ 50 PeV. While the values of $E_{a1}$ for different nuclei are rigidity-dependent, the values of $E_{a2}$ (and probably of $E_{a3}$) are not: $E_{a2-He} \approx$ 1 PeV for Helium. The recent advances in precision measurements of the elemental CR spectra in the DAMPE and LHAASO experiments, and, to some extent, in IceTop and other experiments, make it possible, for the first time, to clarify the origin of the aforementioned spectral features. We show that the elemental CR spectra are reasonably well described with a sum of three components: 1) a low-energy Galactic component with a convex spectral shape reflecting the accelerated particle spectrum in the source; this component peters out after the TeV knee, 2) a high-energy Galactic component including the PeV knee, and 3) an extragalactic component. There is no need for any third, additional component of Galactic cosmic rays in the energy range between 10 PeV and 1 EeV.

astro-ph.HE↗

arXiv2026

Multi-TeV $\gamma$-ray candidates from GRB 221009A: a downturn in the intrinsic $\gamma$-ray spectrum, an echo of the prompt emission phase, and intergalactic electromagnetic cascades

The detection of $\gamma$-ray candidates up to the energy of $\approx$13 TeV from the exceptionally bright $\gamma$-ray burst GRB 221009A by the Large High Altitude Air-Shower Observatory (LHAASO) has raised considerable interest in the astrophysical community. The $\gamma$-ray dataset resulting from the LHAASO observations allows one to reconstruct the intrinsic spectrum of GRB 221009A with an unprecedented precision. This intrinsic spectrum reveals a downturn at the energy of several TeV (statistical significance $\gt 5 \sigma$), i.e. the reconstructed intensity is below the intensity expected for a power-law spectrum. We show that a significant TeV $\gamma$-ray component may be produced by neutrons from photohadronic interactions inside the fireball. These neutrons escape the fireball and interact with the surrounding matter, giving rise to a flux of electrons and positrons, eventually resulting in an observable flux of GeV--TeV synchrotron photons -- a high energy "echo" of the GRB prompt emission phase. Finally, we show that at multi-TeV energies the contribution of $\gamma$ rays from intergalactic electromagnetic cascades initiated by primary ultra high energy protons is severely limited during the early afterglow phase for the typical magnetic field strength in the intergalactic filaments above 1 nG.

astro-ph.HE↗

arXiv2023

First constraints on the strength of the extragalactic magnetic field from $γ$-ray observations of GRB 221009A

The extragalactic magnetic field (EGMF) could be probed with $γ$-ray observations of distant sources. Primary very high energy (VHE) $γ$-rays from these sources absorb on extragalactic background light photons, and secondary electrons/positrons from the pair production acts create cascade $γ$-rays. These cascade $γ$-rays could be detected with space $γ$-ray telescopes such as Fermi-LAT. The $γ$-ray burst GRB 221009A was an exceptionally bright transient well suited for intergalactic $γ$-ray propagation studies. Using publicly-available Fermi-LAT data, we obtain upper limits on the spectrum of delayed emission from GRB 221009A during the time windows of 10, 30, and 90 days after the burst, and compare these with model spectra calculated for various EGMF strengths $B$, obtaining constraints on $B$. We show that the values of $B$ between 10^{-20} G and 10^{-18} G are excluded.

astro-ph.HE↗