[en] One of the cornerstones of modern physics is Einstein's special relativity, with its constant speed of light and zero photon mass assumptions. Constraint on the rest mass $m_{\gamma }$ of photons is a fundamental way to test Einstein's theory, as well as other essential electromagnetic and particle theories. Since non-zero photon mass can give rise to frequency- (or energy-) dependent dispersions, measuring the time delay of photons with different frequencies emitted from explosive astrophysical events is an important and model-independent method to put such a constraint. The cosmological gamma-ray bursts (GRBs), with short time scales, high redshifts as well as broadband prompt and afterglow emissions, provide an ideal testbed for $m_{\gamma }$ constraints. In this paper we calculate the upper limits of the photon mass with GRB early time radio afterglow observations as well as multi-band radio peaks, thus improve the results of Schaefer (1999) by nearly half an order of magnitude.

[en] The Hard X-ray Modulation Telescope (HXMT) named Insight is China's first X-ray astronomical satellite, with the Low Energy X-ray Telescope (LE) as one of its main payloads onboard. The detectors of LE adopt swept charge device CCD236 using L-shaped transfer electrodes. To measure the time response distribution resulted from the continuous readout of charges in detection area along specific paths, a long exposure readout mode has been designed. In this mode, CCD236 firstly performs exposure without readout, then all charges generated in preceding exposure phase are read out completely. And an analysis of the photons readout time in this mode is carried out, to obtain the time response distribution.

[en] With the arrival of future neutrino detectors, a new window is opening to study high-energy astrophysical sources with the help of neutrinos. This work focuses on those neutrinos produced by thermal processes within the progenitors of short gamma-ray bursts (sGRBs), a black hole-neutron star (BH-NS), or a neutron star-neutron star (NS-NS) configuration. Several numerical simulations show that whereas the remnant of the BH-NS merger preserves the magnetic field of the single neutron star ($\sim {10}^{12}\mathrm{G}$), the magnetic field strength of the post-merger central remnant of NS-NS binary system could be amplified by several orders of magnitude, reaching values of $\sim ({10}^{15}-{10}^{16})$ G. Considering the strength of the magnetic field and the opacity created by the baryon-loaded winds ejected in each case, we study the neutrino oscillation and propagation in both scenarios to discriminate between the sGRBs progenitors. We found that it is more feasible to detect neutrinos from BH-NS mergers than those originated from NS-NS since in the second case, the neutrinos cannot go through the medium highly opaque and leave the source freely. In particular, 20 MeV-neutrinos created during an NS-NS merger can hardly leave the progenitor when they propagate with half-opening angles greater than $\sim {62}^{\circ }$. Finally, we estimate the number of events expected on the future Hyper-Kamiokande detector, finding that it is indeed possible to detect around 20 neutrinos from a burst with a typical photon luminosity of $\sim 8\times {10}^{51}$ erg s⁻¹ located at 40 Mpc.

[en] The study of space-time variations of dimensionless physical constants is a necessary approach to search for mysterious phenomena beyond the Standard Model (SM) and General Relativity (GR) motivated by Grand Unification Theories (GUTs). Potentially, the variations of these constants at any location and region of the universe could be tested by using white dwarf spectra with high gravitational fields. Based on the white dwarf star spectra of G191-B2B, our study yields an estimate for the possible cosmological deviations of the proton-to-electron mass ratio, $\mathrm{\Delta }\mu /\mu =(-0.360\pm 0.864)\times {10}^{-8}$ with a gravitational redshift $z=\mathrm{\Delta }\varphi \approx 5\times {10}^{-5}$. This limit serves as an essential tool for examining the framework of the GUTs.

[en] Comparing the parameterized post-Newtonian parameter γ values for different types of particles, or the same type of particles with different energies is an important method to test the Einstein Equivalence Principle (EEP). Assuming that the observed time delays are dominated by the gravitational potential of the Laniakea supercluster of galaxies, better results of EEP constraints can be obtained. In this paper, we apply photons from three kinds of cosmic transients, including TeV blazars, gamma-ray bursts as well as fast radio bursts to constrain EEP. With a gravitational field far more stronger than a single galaxy, we obtain 4–5 orders of magnitude more stringent than the previous results.

[en] e-ASTROGAM (‘enhanced ASTROGAM’) is a breakthrough Observatory space mission, with a detector composed by a Silicon tracker, a calorimeter, and an anticoincidence system, dedicated to the study of the non-thermal Universe in the photon energy range from 0.3 MeV to 3 GeV – the lower energy limit can be pushed to energies as low as 150 keV for the tracker, and to 30 keV for calorimetric detection. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. Thanks to its performance in the MeV–GeV domain, substantially improving its predecessors, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on the surroundings. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous generation instruments, e-ASTROGAM will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LIGO-Virgo-GEO600-KAGRA, SKA, ALMA, E-ELT, TMT, LSST, JWST, Athena, CTA, IceCube, KM3NeT, and LISA.

[en] We present the observational results from a detailed timing analysis of the black hole candidate Swift J1658.2–4242 during its 2018 outburst with the observations of Hard X-ray Modulation Telescope (Insight-HXMT), Neutron Star Interior Composition Explorer (NICER) and AstroSat in 0.1–250 keV. The evolution of intensity, hardness and integrated fractional root mean square (rms) observed by Insight-HXMT and NICER are presented in this paper. Type-C quasi-periodic oscillations (QPOs) observed by NICER (0.8–3.5 Hz) and Insight-HXMT (1–1.6 Hz) are also reported in this work. The features of the QPOs are analyzed with an energy range of 0.5–50 keV. The relations between QPO frequency and other characteristics such as intensity, hardness and QPO rms are carefully studied. The timing and spectral properties indicate that Swift J1658.2–4242 is a black hole binary system. Besides, the rms spectra of the source calculated from the simultaneous observation of Insight-HXMT, NICER and AstroSat support the Lense-Thirring origin of the QPOs. The relation between QPO phase lag and the centroid frequency of Swift J1658.2–4242 reveals a near zero constant when $<4\text{Hz}$ and a soft phase lag at 6.68 Hz. This independence follows the same trend as the high inclination galactic black hole binaries such as MAXI J1659–152.

[en] Super-massive black holes (SMBHs) hosted in active galactic nuclei (AGNs) can be characterized by multi-accreting periods as the attractors interact with the environment during their life-time. These multi-accretion episodes should leave traces in the matter orbiting the attractor. Counterrotating and even misaligned structures orbiting around the SMBHs would be consequences of these episodes. Our task in this work is to consider situations where such accretions occur and to trace their remnants represented by several toroidal accreting fluids, corotating or counterrotating relative to the central Kerr attractor, and created in various regimes during the evolution of matter configurations around SMBHs. We focus particularly on the emergence of matter instabilities, i.e., tori collisions, accretion onto the central Kerr black hole, or creation of jet-like structures (proto-jets). Each orbiting configuration is governed by the general relativistic hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluid. We prove that sequences of configurations and hot points, where an instability occurs, characterize the Kerr SMBHs, depending mainly on their spin–mass ratios. The occurrence of tori accretion or collision are strongly constrained by the fluid rotation with respect to the central black hole and the relative rotation with respect to each other. Our investigation provides characteristic of attractors where traces of multi-accreting episodes can be found and observed.

[en] Blazars, a class of highly variable active galactic nuclei, sometimes exhibit Orphan γ-ray flares. These flares having high flux only in γ-ray energies do not show significant variations in flux at lower energies. We study the temporal and spectral profile of these Orphan γ-ray flares in detail from three $\gamma -ray$ bright blazars, 3C 273, PKS 1510-089 and 3C 279 and also their simultaneous broadband emissions. We find that the variability timescales of the Orphan γ-ray flares were ($0.96\pm 0.28$) days, ($3.12\pm 2.40$) hr and ($2.16\pm 0.72$) hr, for 3C 273, PKS 1510-089 and 3C 279, respectively. The broadband spectral energy distributions (SEDs) during these flares have been modelled with a leptonic model from two emission regions. This model suggests that Orphan γ-ray flares might have originated from inverse Compton scattering of relativistic electrons by the seed photons from the broad-line region or dusty torus, which is the first region. While the second broader region, lying further down the jet, could be responsible for X-ray and radio emissions. The possible locations of these emission regions in the jets of the three sources have been estimated from SED modelling.

[en] The multi-band observation, from radio to gamma-ray, plays a crucial role in constraining the emission physics and geometrical magnetospheric models of the pulsars. In this paper, We use three-dimensional magnetospheric model, with the joint of the annular gap (AG) and core gap (CG) model, to simulate the radio and gamma-ray light curves for two representative pulsars, a millisecond pulsar J2302+4442 and a young pulsar J0659+1414. It is found that for PSR J2302 + 4442, the simulated magnetic inclination angle α and viewing angle ζ are ${34}^{\circ }$ and ${46}^{\circ }$, and for PSR J0659 + 1414 are ${45}^{\circ }$ and ${33}^{\circ }$. This implies that the radio and gamma-ray pulse emission originates from different magnetospheric regions and the radiation geometry for millisecond and young pulsar is different. The studies show that the joint of the AG and CG model can describe the light curves not only for millisecond pulsars but also for young pulsars, and hence it can be used to explain the multi-wavelength observations of pulsars.