Search

We report the detection of a strong thermal component in the short Gamma-Ray Burst 170206A with three intense pulses in its light curves, throughout which the fluxes of this thermal component exhibit fast temporal variability same as that of the accompanying non-thermal component. The values of the time-resolved low-energy photon index in the non-thermal component are between about -0.79 and -0.16, most of which are harder than -2/3 excepted in the synchrotron emission process. In addition, we found a common evolution between the thermal component and the non-thermal component, $E_{\rm p,CPL} \propto kT_{\rm BB}^{0.95\pm0.28}$, and $F_{\rm CPL} \propto F_{\rm BB}^{0.67\pm0.18}$, where $E_{\rm p,CPL}$ and $F_{\rm CPL}$ are the peak photon energy and corresponding flux of the non-thermal component, and $ kT_{\rm BB}$ and $F_{BB}$ are the temperature and corresponding flux of the thermal component, respectively. Finally, we proposed that the photospheric thermal emission and the Comptonization of thermal photons may be responsible for the observational features of GRB 170206A., Comment: 14 pages, 6 figures, Accepted for publication in ApJ

Combined with the observation of M87*, shadow has gradually became a promising test of the black hole nature. Recently, EHT collaboration gave new constraints on the shadow size at 68\% confidence levels. In this work, we consider the new constrains on the black hole spin and charge for the Kerr and Kerr-Newmann black holes via the local curvature radius. For the Kerr black holes, the cases with high spin and large inclination angle are ruled out. For the Kerr-Newmann black holes, two new characteristic constrained patterns for low and high black hole spins are given. Near extremal black holes are always excluded unless for the high spin and low inclination angle. Moreover, we find that low black hole spin and charge can pass these constraints as expected. These results suggest that this approach of curvature radius is effective on constraining black hole parameters. We expect the local concept of the curvature radius will play a more important role on the study of the black hole shadow in the further., Comment: 11 pages and 7 figures

We searched the possible historical records for the young magnetar Swift J1818.0-1607, and found a guest star in AD 1798 that might be associated with it., Comment: 3 pages, 5 figures. We corrected the name of the object in this version. It should be Swift J1818.0-1607 instead of Swift J1818-5937

The observed time delays between photons with different circular polarizations from an astrophysical object provide a new, interesting way of testing the Einstein Equivalence Principle (EEP). In this paper, we constrain the EEP by considering both Shapiro time delay and Faraday rotation effects. We continue to search for astronomical sources that are suitable for testing the EEP accuracy, and obtain 60 extragalactic radio sources with multi-wavelength polarization angles in three different radio bands (20, 8.6, and 4.8 GHz) and 29 brightest stars within our own Milky Way galaxy with multi-colour linear polarimetric data in five optical bands ($UBVRI$). We apply the Metropolis-Hastings Markov Chain to simulate the fit parameters. The final results show that the values of the parameterized post-Newtonian parameter $\gamma$ discrepancy ($\Delta \gamma_{p}$) are constrained to be in the range of $10^{-26}-10^{-23}$ for 60 radio sources and in the range of $10^{-23}-10^{-20}$ for 29 optical polarization stars. Compared to previous EEP tests that based on the single polarization measurement in the gamma-ray band, our results have profound superiority that nearly a few tens of astrophysical sources with multi-wavelength polarization observations commonly in the optical and radio bands are available. It ensures that these sources can give more significantly robust bounds on the EEP. Although the presented method is straightforward, the resulting constraints on the EEP should be taken as upper limits as other more complex astrophysical effects affecting a polarization rotation are hardly considered., Comment: 9 pages, 3 figures and 4 tables; accepted for publication in MNRAS

Distance measurement is crucial to astronomy. Here we suggest a new conceptual method to measure the distance by using a local instrument. By engaging the double-slit interference and by considering the phase information of the light, the position of the intensity maximum is related to the distance of the source. Consequently, the precise measurement of the position can be used to measure the distance of the remote source., Comment: Accepted for publication in Journal of Astronomical Instrumentation

The association of FRB 200428 with an X-ray burst (XRB) from the Galactic magnetar SGR 1935+2154 offers important implications for the physical processes responsible for the fast radio burst (FRB) phenomena. By assuming that the XRB emission is produced in the magnetosphere, we investigate the possibility that the FRB emission is produced by shock-powered synchrotron maser (SM), which is phenomenologically described with a plenty of free parameters. The observational constraints on the model parameters indicate that the model can in principle be consistent with the FRB 200428 observations, if the ejecta lunched by magnetar activities can have appropriate ingredients and structures and the shock processes occur on the line of sight. To be specific, a complete burst ejecta should consist of an ultra-relativistic and extremely highly collimated $e^{\pm}$ component and a sub-relativistic and wide-spreading baryonic component. The internal shocks producing the FRB emission arise from a collision between the $e^{\pm}$ ejecta and the remnant of a previous baryonic ejecta at the same direction. The parameter constraints are still dependent on the uncertain spectrum and efficiency of the SM emission. While the spectrum is tentatively described by a spectral index of $-2$, we estimate the emission efficiency to be around $10^{-4}$ by requiring that the synchrotron emission of the shocked material cannot be much brighter than the magnetosphere XRB emission., Comment: 7 pages, 1 figure, 1 table

The reverse shock (RS) model is generally introduced to interpret the optical afterglows with the rapid rising and decaying, such as the early optical afterglow of GRB 990123 (which is also called optical flash). In this paper, we collected 11 gamma-ray bursts (GRBs) early optical afterglows, which have such signatures of dominant RS emission. Since the temporal slopes of the optical flashes are determined by both the medium density distribution index $k$ and the electron spectral index $p$, we apply the RS model of the thin shell case to the optical flashes and determine the ambient medium of the progenitors. We find that the $k$ value is in the range of 0 - 1.5. The $k$ value in this paper is consistent with the result in Yi et al. (2013), where the forward shock (FS) model was applied to some onset bumps. However, the method adopted in this paper is only applicable to GRB afterglows with significant sharp rising and decaying RS emission. Our results indicate that the RS model can also be applied to confirm the circumburst medium, further implying that GRBs may have diverse circumburst media., Comment: Accepted for publication in The Astronomical Journal; 10 pages, 4 figures and 2 tables

In this paper, we present a novel method to test the Einstein's Equivalence Principle (EEP) using (simultaneous) multi-wavelength radio observations of polarized blazars. We analyze simultaneous multi-wavelength polarization observations of 3C 279 at 22, 43, and 86 GHz obtained by two antennas of the Korean VLBI Network. We obtained 15 groups of polarization data, and applied the Metropolis-Hastings Markov Chain (MHMC) to simulate the parameters when considering the EEP effect and the simplest form of Faraday rotation (single external Faraday screen). The final results show the constraint of the parameterized post-Newtonian (PPN) parameter $\gamma$ discrepancy as $\Delta \gamma_{p} = (1.91\pm0.34)\times10^{-20}$. However, the single external Faraday screen is an oversimplification for blazars because there are numerous observations show complex Faraday rotation behavior for blazars due to internal/external Faraday dispersion, beam depolarization, etc. The value $\Delta \gamma_{p}$ results of this paper can only be considered as upper limits. Only if all other effects are revealed and considered, should the result be taken as a direct measurement of the violation of the EEP., Comment: 16 pages, 5 figures, 2 tables, accepted for publication in MNRAS

FRB 180916.J0158+65 has been found to repeatedly emit fast radio bursts with the period in roughly 16 days. We propose that such periodicity comes from orbit-induced, spin precession of the emitter, which is possibly a neutron star. Depending on the mass of the companion, the binary period ranges from several hundred to thousands of seconds. Such tight binaries have a relatively short lifetime, which does not likely come from the gravitational decay of a wide binary. We comment on the relation to GW190425 and the possibility in LISA and LIGO detections., Comment: 11 pages, 4 figures