On 2022 October 9, an extremely powerful gamma-ray burst, GRB 221009A, was detected by several instruments. Despite being obstructed by the Milky Way galaxy, its afterglow outburst outshone all other GRBs seen before. LHAASO detected several thousand very high energy photons extending up to 18 TeV. Detection of such energetic photons is unexpected due to the large opacity of the universe. It is possible that in the afterglow epoch, the intrinsic very high energy photon flux from the source might have increased manifolds, which could compensate for the attenuation by pair production with the extragalactic background light. We propose such a scenario and show that very high energy photons can be observed on the Earth from the interaction of very high energy protons with the seed synchrotron photons in the external forward shock region of the GRB jet.

Heavy baryons [Formula: see text] and heavy mesons [Formula: see text] for heavy quarks [Formula: see text], [Formula: see text], or [Formula: see text] and light quarks [Formula: see text], [Formula: see text], or [Formula: see text] are considered. Strong interaction coupling-constant sum rules with first-order breaking of SU(3) flavor symmetry are obtained for reaction [Formula: see text] where [Formula: see text] or [Formula: see text], [Formula: see text] or [Formula: see text], and [Formula: see text] is a light meson. Specific results for couplings of doubly charmed baryons and charm and bottom mesons are presented. Also, SU(3) Clebsch-Gordan coefficients for the product of representations [Formula: see text] are explicitly determined.

Baryons [Formula: see text] for heavy quarks [Formula: see text], and light quarks [Formula: see text], are considered. Strong interaction coupling-constant sum rules with first-order breaking of SU(3) flavor symmetry are determined for reactions [Formula: see text] where [Formula: see text], [Formula: see text] and [Formula: see text] is a light meson. Specific applications to couplings of [Formula: see text] charmed and bottom baryons are presented. Also, SU(3) Clebsch–Gordan coefficients for the product of representations [Formula: see text] are explicitly determined.

Extreme high-frequency peaked BL Lacs (EHBLs) are characterized by a synchrotron peak frequency exceeding 1017 Hz and a second peak that can be in the energy range of few GeVs to several TeVs. The MAGIC telescopes detected multi-TeV gamma-rays on April 19, 2018 for the first time from the EHBL PGC 2402248 which was simultaneously observed in multiwavelength by several other instruments. The broad band spectral energy distribution of the source is conventionally modelled using the leptonic and the hadronic models. Due to the success of the photohadronic model in interpreting the enigmatic very high-energy (VHE) flaring events from many high-energy blazars, we extend this model to explain the VHE events from PGC 2402248 observed by MAGIC telescopes and compare our results with other models. We conclude that the photohadronic fits are comparable and even fare better than most other models. Furthermore, we show that the spectrum is not hard and is in a low emission state. The estimated bulk Lorentz factor for this flaring event is found to be ≲ 34.

Observation of several very high energy (VHE) flaring events of the BL Lac object VER J0521+211 were reported by the VERITAS and MAGIC collaborations between 2009 and 2014. The redshift of this source is uncertain and several analysis have derived different limits for it. In the framework of the photohadronic model, and using three different extragalactic background light (EBL) models, we analyze seven independent VHE spectra of VER J0521+211 and determine the limiting values on its redshift. It is observed that the photohadronic scenario provides excellent fits to the reported observations. It is further observed that the photohadronic scenario, along with the EBL model of Domínguez et al., puts the most restrictive limits on the redshift z of VER J0521+211: 0.29 ≤ z ≤ 0.31 from the confidence level (CL) intervals at 2σ, or a more conservative 0.28 ≤ z ≤ 0.33, at 3σ.