Keywords

Polycyclic aromatic hydrocarbons (PAHs), PANHs, and peptoids dust spectral calculations from the interstellar medium (ISM) are important for dust observations and theory. Our goal is to calculate the radiation spectrum of spherical PAHs dust clusters in a vacuum containing ionized and applied in the presence of an electric field. We propose a new simple computational model to calculate the size of three-dimensional spherical dust clusters formed by different initial dust structures. By the Vienna Ab-initio Simulation Package code, the density functional theory with the generalized approximation was used to calculate the electron density gradient and obtain the radiation spectrum of dust. When the radius of spherical dust clusters is ∼[0.009–0.042] μm, the dust radiation spectrum agrees well with the Z = 0.02 mMMP stellar spectra, and the PAHs radiation spectrum of NGC 4676 at wavelengths of (0–5] μm and (5–10] μm, respectively. In the ionized state, the N-PAH, C₁₀H₉N, 2(C₄H ₄)¹⁺, and peptoids 4(CHON), (C₈H₁₀N₂O₅)¹⁺ dust clusters at 3.3 μm, while the 2(C₂₂H₂₁N₃O ₂)¹⁺, 4(CHON) dust clusters at 5.2 μm have obvious peaks. There is a characteristic of part of PAHs and peptoids clusters radiation at the near-infrared wavelength of 2 μm. However, especially after applying an electric field to the dust, the emission spectrum of the dust increases significantly in the radiation wavelength range [3–10] μm. Consequently, the dust clusters of PAHs, PANHs, and peptoids of the radius size ∼[0.009–0.042] μm are likely to exist in the ISM.

Gamma-ray bursts (GRBs) exhibit powerful radiation and relativistic jets similar to blazars. However, the central engine of GRBs remains unknown. In this paper, we use the fundamental plane to analyze a sample of GRBs with measured mass. We extend, over ∼12 orders of magnitude, the correlation analysis and fundamental plane with a sample of X-ray binaries, active galactic nuclei (AGNs) including blazars, and brightest cluster galaxies. The fundamental plane of our de-beamed sample, with a measured mass ($\mathrm{log}{L}_{{\rm{R}}}$ = (0.60 ± 0.03)$\mathrm{log}{L}_{{\rm{X}}}$+(0.78 ± 0.02)$\mathrm{log}M$+7.23 ± 0.95), closely aligns with the findings of previous work on AGNs. This finding suggests that GRBs adhere to the fundamental plane of AGNs and supports the theory proposed in previous work that the central engine of GRBs may be black holes. This observation provides a plausible explanation for the striking similarities between GRBs and AGNs.

We present a new total intensity image of M31 at 1.248 GHz, observed with the Five-hundred-meter Aperture Spherical radio telescope (FAST) with an angular resolution of $4^{\prime}$ and a sensitivity of about 16 mK. The new FAST image clearly reveals weak emission outside the ring due to its high sensitivity on large-scale structures. We derive a scale length of 2.7 kpc for the cosmic ray electrons and find that the cosmic ray electrons propagate mainly through diffusion by comparing the scale length at 4.8 GHz. The spectral index of the total intensity varies along the ring, which can be attributed to the variation of the spectra of synchrotron emission. This variation is likely caused by the change of star formation rates along the ring. We find that the azimuthal profile of the non-thermal emission can be interpreted by an axisymmetric large-scale magnetic field with varying pitch angle along the ring, indicating a complicated magnetic field configuration in M31.

Fast radio bursts (FRBs) are extragalactic radio transients with millisecond duration and brightness temperature. An FRB-associated X-ray burst (XRB) was recently found to arise from the Galactic magnetar SGR J1935+2154. Following the model of Dai, in which an FRB may originate from a magnetar encountering an asteroid, we focus on explaining the spectrum of the XRB associated with FRB 200428 from SGR J1935+2154. Collisions between asteroidal fragments and the magnetar surface produce a fireball, which further expands relativistically. Due to the velocity difference among some shells in the fireball, internal shocks would form far away from the magnetar, and further emit X-ray emission. We propose that the FRB-associated XRB can be produced by synchrotron emission from the internal shocks, and then constrain the physical parameters by the observed XRB spectrum.

On 2020 April 27, the soft gamma-ray repeater SGR J1935+2154 entered its intense outburst episode again. Insight-HXMT carried out about one month observation of the source. A total number of 75 bursts were detected during this activity episode by Insight-HXMT, and persistent emission data were also accumulated. We report on the spin period search result and the phase distribution of burst start times and burst photon arrival times of the Insight-HXMT high energy detectors and Fermi/Gamma-ray Burst Monitor (GBM). We find that the distribution of burst start times is uniform within its spin phase for both Insight-HXMT and Fermi/GBM observations, whereas the phase distribution of burst photons is related to the type of a burst's energy spectrum. The bursts with the same spectrum have different distribution characteristics in the initial and decay episodes for the activity of magnetar SGR J1935+2154.

Results of long time observations of the pulsar B0950+08 are given. These observations were carried out at the LPA radio telescope at the frequency of 111 MHz from January of 2016 to May of 2019 (450 days). A strong variability in emission of this pulsar has been detected with changes in signal to noise ratios hundreds of times. Part of the long-time flux density variability can be explained by refractive scintillations in the interstellar medium. The existence of radiation between the interpulse (IP) and main pulse (MP) was confirmed. It was more powerful than at high frequencies. We detected the unusual IP and precursor (Pr) radiation on 2017 August 1. On the basis of 65 strong IPs we found the correlations between energies of IP and Pr and between the phase of IP and the distance Pr–IP. It is shown that the observed peculiarities of this pulsar can be explained in the frame of the aligned rotator model. We estimated distances of radiation levels from the center of the neutron star. The calculated value of the initial period of 0.2 s means that not all pulsars are born with millisecond periods. The large age of the pulsar (6.8 million years) and the small angle between its magnetic moment and the rotation axis (less than 20°) confirm the suggestion related to pulsar evolution with respect to alignment.

X-ray data for quasar 4C 74.26 have previously been modeled with a broad Fe Kα emission line and reflection continuum originating in the inner part of the accretion disk around the central supermassive black hole (SMBH), i.e., the strong-gravity regime. We modeled broadband X-ray spectra from Suzaku and NuSTAR with mytorus, self-consistently accounting for Fe Kα line emission, as well as direct and reflected continuum emission, from matter with a finite column density. A narrow Fe Kα emission line originating in an X-ray reprocessor with solar Fe abundance far from the central SMBH is sufficient to produce excellent fits for all spectra. For the first time, we are able to measure the global column density, out of the line of sight, to be in the range ∼1.5 to ∼$2.9\,\times {10}^{24}$ ${\mathrm{cm}}^{-2}$, i.e., in the Compton-thick regime, while the line-of-sight column density is Compton-thin in all observations. The Fe Kα emission line is unresolved in all observations but one. The Compton-scattered continuum from distant matter removes the need for relativistic broadening of the Fe Kα emission line, which is required for SMBH spin measurements. The resolved line observation can alternatively be modeled with a relativistic model but we do not find evidence for a truncated accretion disk model. We conclude that the X-ray emission in these 4C 74.26 data is unlikely to originate in the inner accretion disk region and thus cannot be used to measure SMBH spin.

After the identification of a candidate γ-ray transient in the error region of the binary black hole (BBH) merger GW150914 by the Fermi satellite, the question of whether BBH mergers can be associated with electromagnetic counterparts remains highly debated. Here, we present radio follow-up observations of GW170608, a BBH merger that occurred during the second observing run (O2) of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). Our radio follow-up focused on a specific field contained in the GW170608 sky localization area, where a candidate high-energy transient was detected by the Fermi Large Area Telescope (LAT). We make use of data collected at 1.4 GHz with the Karl G. Jansky Very Large Array (VLA), as well as with the VLA Low-band Ionosphere and Transient Experiment (VLITE). Our analysis is sensitive to potential radio afterglows with luminosity densities L_1.4GHz ≳ 6 × 10²⁸ erg s⁻¹ Hz⁻¹. In the most optimistic theoretical models, ≈20% of BBH events occurring in massive hosts could be associated with outflows as radio luminous as this. Although we find no evidence for the presence of a radio counterpart associated with the LAT candidate in the GW170608 error region, our analysis demonstrates the feasibility of future radio follow-up observations of well-localized BBHs. Comparing our radio upper limits with theoretical expectations for the radio afterglows potentially associated with jets launched in BBH mergers, we find that for jets of energy ≈10⁴⁹ erg seen on-axis, only jet angles θ_jet ≳ 40° are compatible with the observations.

We have revisited the spectral width in the EF_E spectrum of gamma-ray bursts with the BEST peak flux P and time-integrated F spectral data provided by the Fermi GBM Burst Catalog. We first compute the BEST spectral widths to compare with some typical physics models. Our analysis results consist with the previous results: blackbody emission alone cannot explain the observed spectrum and most of the observed spectra cannot be interpreted by the synchrotron radiation. We then check the correlations between the spectral width and the observable model-independent burst properties of duration, fluence, and peak flux and find that positive correlations exist between them for both the P and F spectra. Moreover, the short burst appears to extend the correlation found for the long burst. We further demonstrate that these positive correlations also exist in the cosmological rest frame; that is, the spectral width correlates with the isotropic-equivalent energy E_iso as well as the isotropic-equivalent peak luminosity L_iso for different energy bands and timescales. Our results show that the wider bursts have larger energy and luminosity. Moreover, short bursts would appear to extend this trend qualitatively. Taking the Amati relation into account, we tend to believe that the spectral shape is related to energy and luminosity.

FRB 181228 was detected by the Molonglo Synthesis Radio Telescope (MOST) at a position and time coincident with Transiting Exoplanet Survey Satellite (TESS) observations, representing the first simultaneous multiwavelength data collection for a fast radio burst (FRB). The large imaged field of view of TESS allows a search over the uncertainty region produced by MOST. However, the TESS pixel scale of 21'' and the full-frame image (FFI) cadence of 30 minutes is not optimal for the detection of a fast optical burst (FOB) with a possible millisecond duration. We search the TESS FFIs and find no events with a limiting TESS magnitude of 16, assuming a 30 minute event duration, corresponding to an optical flux density upper limit of approximately 2000 Jy for a ∼1 ms signal duration, assuming no signal loss. In addition, the cosmic-ray mitigation method for TESS significantly reduces its sensitivity to short-timescale transients, which we quantify. We compare our results to the predictions of Yang et al. and find that the upper limit is a factor of 2000 higher than the predicted maximum optical flux density. However, we find that if FRB 181228 had occurred in the galaxy thought to host the nearest FRB detection to date (37 Mpc), an FOB may have been detectable by TESS. In the near future, when the Canadian Hydrogen Intensity Mapping Experiment and Australian SKA Pathfinder will detect hundreds to thousands of FRBs, TESS may be able to detect FOBs from those rare bright and nearby FRBs within this large population (if more sophisticated cosmic-ray excision can be implemented).