[en] The jet properties of Mrk 501 and 3C 279 are derived by fitting broadband spectral energy distributions (SEDs) with lepton models. The derived γ_b (the break Lorenz factor of the electron distribution) is 10⁴-10⁶ for Mrk 501 and 200 ∼ 600 for 3C 279. The magnetic field strength (B) of Mrk 501 is usually one order of magnitude lower than that of 3C 279, but their Doppler factors (δ) are comparable. A spectral variation feature where the peak luminosity is correlated with the peak frequency, which is opposite from the blazar sequence, is observed in the two sources. We find that (1) the peak luminosities of the two bumps in the SEDs for Mrk 501 depend on γ_b in both the observer and co-moving frames, but they are not correlated with B and δ and (2) the luminosity variation of 3C 279 is dominated by the external Compton (EC) peak and its peak luminosity is correlated with γ_b and δ, but anti-correlated with B. These results suggest that γ_b may govern the spectral variation of Mrk 501 and δ and B would be responsible for the spectral variation of 3C 279. The narrow distribution of γ_b and the correlation of γ_b and B in 3C 279 would be due to the cooling from the EC process and the strong magnetic field. Based on our brief discussion, we propose that this spectral variation feature may originate from the instability of the corona but not from the variation of the accretion rate as does the blazar sequence.

[en] The optical properties of a thin-shell wormhole (TSW) with a Hayward profile is investigated. Adopting the ray-tracing method, we demonstrate that the TSW's contralateral spacetime is capable of reflecting a significant portion of light back to the observer spacetime. We analyze the effective potential, light deflection, and azimuthal angle of the TSW and find that these quantities are affected by the mass ratio of the black holes (BHs). Specifically, if the mass of the contralateral spacetime BH is greater than that of the original spacetime BH, and the impact parameter satisfies the condition Hb${}_{c2}$< b${}_1$< b${}_{c1}$, the trajectory of the photon exhibits round-trip characteristics. Assuming the presence of a thin accretion disk surrounding the observing spacetime BH, our results indicate that the image formed by the TSW exhibits additional photon rings and a lensing band compared to an image produced by a BH alone.

[en] The regular (Bardeen)–anti-de Sitter (AdS) (BAdS) black hole (BH) in the extended phase space is taken as an example for investigating the BH phase transition grade from both macroscopic and microscopic points of view. The equation of state and thermodynamic quantities of this BH are obtained. It is found that the BAdS BH phase space in the extended phase space should be a second-order phase transition near the critical point by verifying the Ehrenfest’s equation, and the possibility of its first-order phase transition can be ruled out by the entropy continuity and the heat capacity mutation. The critical exponents from the microscopic structure are analytically and numerically presented with the Landau continuous phase transition theory by introducing a microscopic order-parameter. (paper)

[en] In this paper, we investigate the early-time optical–near-infrared (NIR) spectral energy distributions (SEDs) of four Type Ibn supernovae (SNe). We find that the SEDs of SN 2010al, LSQ13ddu, and SN 2015G can be well explained by the single-component blackbody model, while the SEDs of OGLE-2012-SN-006 cannot. We invoke the double-component model assuming that the SEDs were produced by the SN photosphere and the heated dust to fit the optical−NIR SEDs of the four SNe Ibn, finding that the derived temperatures of the dust associated with OGLE-2012-SN-006 favor the scenario that the dust consists of the graphite grains, and the mass and temperature of dust are ∼0.5–2.0 × 10⁻³ M _⊙ and ∼1200–1300 K, respectively. Moreover, our fits for SN 2010al, LSQ13ddu, and SN 2015G show that the upper limits of the masses of the dust associated with the three SNe Ibn are respectively 1.45 × 10⁻⁵ M _⊙, 5.9 × 10⁻⁷ M _⊙, and 2.4 × 10⁻⁷ M _⊙. A further analysis demonstrates that the inferred radius of the dust shell surrounding OGLE-2012-SN-006 is significantly larger than that of the SN ejecta at early epochs, indicating that the NIR excesses of the SEDs of OGLE-2012-SN-006 were produced by a preexisting dust shell. Our study for the early-time SEDs of four SNe Ibn, together with the previous studies and the fact that some SNe showed evidence of dust formation at the late-time SEDs, indicates that at least ∼1/3 of SNe Ibn show evidence for dust formation.

[en] The observed delay of GRB 170817A relative to GW170817 provides significant information about gamma-ray burst (GRB) physics, and is subject to intense debate. In this Letter, we present an approach for discussing the major source of this time delay. First, we use the structured jet model to fit the X-ray/optical/radio afterglows of GRB 170817A together with superluminal motion measured using Very Long Baseline Interferometry. Our structured jet is modeled with angle-dependent energy and baryon loading. It is found that our model well fits the afterglows of GRB 170817A. Then, the baryon loading in the jet is inferred based on our fitting results. By comparing the baryon loading to the mass outflow in different stages, we infer that the time lag of the jet launch relative to the merger is less than hundreds or tens of milliseconds. It suggests that the time delay of GRB 170817A relative to GW170817 is defined mostly by the spreading time of the jet propagating to its dissipation radius.

[en] Although the physical origin of prompt emission in gamma-ray bursts (GRBs) remains inconclusive, previous studies have considered the synchrotron radiation of relativistic electrons as a promising mechanism. These works usually adopted an invariable injection rate of electrons (Q) which may be discordant with that in a Poynting-flux-dominated jet. In a Poynting-flux-dominated jet (e.g., internal-collision-induced magnetic reconnection and turbulence model), the number of magnetic reconnections occurring simultaneously may grow rapidly with time and result in an increase of Q with time. This paper is dedicated to studying the synchrotron radiation spectrum in this scenario. It is found that the radiation spectrum would obviously get harder if an increasing Q is adopted and a Band-like radiation spectrum can be obtained if the increase of Q is fast enough. The latter is related to the fact that a bump shape rather than a power-law spectrum appears in the low-energy regime of the obtained electron spectrum. This effect can strongly harden the low-energy radiation spectrum. It indicates that an increasing Q can help to alleviate the “fast-cooling problem” of synchrotron radiation for GRBs. Our studies also reveal that a Poynting-flux dominated jet with a large emission radius, a short magnetic reconnection region length, or an injected electron with low minimum energy would prefer to form a Band-like radiation spectrum. We suggest that the Band spectrum found in GRBs may be the synchrotron emission of the electrons with a bump-shape distribution in its low-energy regime.

[en] Growing evidence indicates that the synchrotron radiation mechanism may be responsible for the prompt emission of gamma-ray bursts (GRBs). In the synchrotron radiation scenario, the electron energy spectrum of the prompt emission is diverse in theoretical works and has not been estimated from observations in a general way (i.e., without specifying a certain physical model for the electron spectrum). In this paper, we creatively propose a method to directly estimate the electron spectrum for the prompt emission, without specifying a certain physical model for the electron spectrum in the synchrotron radiation scenario. In this method, an empirical function (i.e., a four-order Bézier curve jointed with a linear function at high energy) is applied to describe the electron spectrum in log–log coordinates. It is found that our empirical function can well mimic the electron spectra obtained in many numerical calculations or simulations. Then, our method can figure out the electron spectrum for the prompt emission without specifying a model. By employing our method on observations, taking GRB 180720B and GRB 160509A as examples, it is found that the obtained electron spectra are generally different from that in the standard fast-cooling scenario and even a broken power law. Moreover, the morphology of electron spectra in its low-energy regime varies with time in a burst and even in a pulse. Our proposed method provides a valuable way to confront the synchrotron radiation mechanism with observations.

[en] High energy photon radiations of gamma-ray bursts (GRBs) and active galactic nuclei (AGNs) are dominated by their jet radiations. We examine whether the synchrotron radiations of jets in BL Lacs, flat spectrum radio quasars (FSRQs), and Narrow Line Seyfert 1 galaxies (NLS1s) follow the relation between the prompt gamma-ray emission and the initial Lorentz factor (Γ₀) of GRBs. It is shown that the AGN sample does not agree with the L _p − E _p,z − Γ₀ relation of GRBs. In addition, we obtain a tight relation of $L_{\mathrm{s}\mathrm{y}\mathrm{n}}\propto <!--\; ???\; -->E_{\mathrm{s}\mathrm{y}\mathrm{n},\mathrm{p}}^{0.45\pm <!--\; ??\; -->0.15}{\mathrm{\delta <!--\; ??\; -->}}^{3.50\pm <!--\; ??\; -->0.25}$ for FSRQs and NLS1 galaxies, where L _syn is the luminosity at peak photon energy E _{syn, p} of the synchrotron radiations. This relation is different from the L _p − E _p,z − Γ₀ relation of GRBs. The dependence of L _syn to δ is consistent with the expectation of the Doppler boosting effect for the FSRQs and NLS1 galaxies, but it is not for GRBs. We argue that Γ₀ may be a representative of the kinetic power of the radiating region and the tight L _p − E _{p, z} − Γ₀ relation is shaped by the radiation physics and the jet power together. (paper)

[en] Early shallow-decaying X-ray afterglows of gamma-ray bursts (GRBs) may be attributed to the dipole radiations of newly born magnetars. Assuming that the GRB jets powered by magnetars are quasi-universal, we find that the jet structure can be parameterized as a uniform jet with a luminosity of $\mathrm{l}\mathrm{o}\mathrm{g}{L}_{\mathrm{j}}/\mathrm{e}\mathrm{r}\mathrm{g}{\mathrm{s}}^{-<!--\; ???\; -->1}={52.68}_{-<!--\; ???\; -->0.33}^{+0.76}$ (1σ) and an opening angle ${\mathrm{\theta <!--\; ??\; -->}}_{\mathrm{j}}={2.10}_{-<!--\; ???\; -->1.28}^{+1.90}$ (50% confidence level), surrounding by a power-law decay component with an index of $-<!--\; ???\; -->{4.00}_{-<!--\; ???\; -->0.37}^{+0.27}$ (1σ). The inferred local GRB rate is ρ = 9.6 Gpc⁻³ yr⁻¹ by including both the typical GRBs and LL-GRBs as the same population. The typical viewing angle is 3.3°, and may be 20° ∼ 30° for LL-GRBs. The X-ray luminosity function of the dipole radiation wind can be empirically described by a broken power-law function with indices ${\mathrm{\beta <!--\; ??\; -->}}_1={0.78}_{-<!--\; ???\; -->0.15}^{+0.16}$ and ${\mathrm{\beta <!--\; ??\; -->}}_2><!--\; >\; -->1.6$ broken at $\mathrm{l}\mathrm{o}\mathrm{g}{L}_{\mathrm{b},\mathrm{w}}/\mathrm{e}\mathrm{r}\mathrm{g}{\mathrm{s}}^{-<!--\; ???\; -->1}={48.51}_{-<!--\; ???\; -->0.65}^{+0.53}$. In the case where the wind outflow is collimated and coaxial with the GRB jet, we find that the wind structure is similar to the GRB jet, i.e., $\mathrm{l}\mathrm{o}\mathrm{g}{L}_{\mathrm{c},\mathrm{w}}/\mathrm{e}\mathrm{r}\mathrm{g}{\mathrm{s}}^{-<!--\; ???\; -->1}={48.38}_{-<!--\; ???\; -->0.48}^{+0.30}$, ${\mathrm{\theta <!--\; ??\; -->}}_{\mathrm{c},\mathrm{w}}={{2.65}^o}_{-<!--\; ???\; -->{1.19}^o}^{+1.{73}^o}$, and $k_{\mathrm{w}}={4.57}_{-<!--\; ???\; -->0.75}^{+1.21}$. The observed correlation between the prompt gamma-ray luminosity and X-ray luminosity of the wind may result from the viewing angle effect in such a jet–wind system. A discussion on surveys using the X-ray instruments on board the Einstein Probe mission in the soft X-ray band for the jet and wind emission is also presented.

[en] In this work, we re-analyze the Fermi-LAT observation of NGC 1275 to search for axion-like particle (ALP) effects and constrain ALP parameters. Instead of fitting the observed spectrum with ALP models, we adopt an alternative method for the analysis of this source which calculates the irregularity of the spectrum. With the newly used method, we find no spectral oscillation for the NGC 1275 and rule out couplings $g_{a\gamma }>3\times {10}^{-12}{\text{GeV}}^{-1}$ around ALP mass of $m_a\sim 1$ neV at 95% confidence level, which is more stringent than the previous results. We also show that the constraints can be further improved by combining the observation of PKS 2155-304. We suggest that with more sources taken into account, we could obtain a much wider exclusion region.