高能暂现源 · 每日文献综述

We present the results of our search for and detection of radio emission from the gravitational-wave event GW 190425 at a frequency of 111 MHz with the BSA LPI radio telescope. A new radio source was detected approximately at <inline-formula><tex-math>$2^{\circ}$</tex-math></inline-formula> from the center of the maximally probable localization region of GW 190425; its coordinates (J2000.0) are <inline-formula><tex-math>$\alpha=16^{\textrm{h}}30^{\textrm{m}}\pm 1^{\textrm{m}}$</tex-math></inline-formula> and <inline-formula><tex-math>$\delta=13^{\circ}21^{\prime}\pm 15^{\prime}$</tex-math></inline-formula>. We have constructed the light curve and estimated the peak flux density to be <inline-formula><tex-math>${\approx}2$</tex-math></inline-formula> Jy. The peak of the light curve occurs on day 20--30 after the trigger. We have calculated the false alarm probability for an event of this kind, <inline-formula><tex-math>$P_{fa}=5\times 10^{-7}$</tex-math></inline-formula>.

Gravitational-wave events are interpreted in terms of Bayesian posteriors for their source properties inferred under unphysical reference priors. Though these parameter estimates are important intermediate data products for downstream analyses, we demonstrate that they are generically biased and therefore should not be used for astrophysical interpretation directly, as is common. Hierarchical parameter estimation is the solution, as joint analysis of the entire catalog of observations reduces statistical uncertainties and actually informs the correct prior, with population-informed event parameters now appropriate for astrophysical interpretation. As an example, we show how the most extreme measurements from a catalog can be derived and used to identify exceptional events from previous and ongoing observing runs, pointing out they are more informative about the population than any individual event. Using LIGO-Virgo-KAGRA data, we thus demonstrate that population inference is not optional to interpret gravitational-wave observations.

The photon energy range 0.3--10 MeV is of special interest for studying astrophysical objects of various origins. Gamma-ray spectroscopy of lines from the decay of unstable stellar nucleosynthesis isotopes and studies of nuclear cosmic-ray interactions and electron--positron pair annihilation are based on sensitive observations in this energy range. The MeV energy range accounts for a substantial part of the emission from supernovae, pulsars, gamma-ray burst sources, and accreting black holes. Observations of gamma-ray lines will allow the properties of strongly absorbed compact relativistic stars to be studied. Measuring the spectra and polarization of nonthermal continuum gamma-ray emission is needed to find out the nature of the gamma-ray emission from binary star systems with compact companions and powerful transient sources. At present, the orbital detectors in this energy range are several orders of magnitude less sensitive than both X-ray telescopes and gamma-ray detectors in the GeV and TeV energy ranges. This is related to the peculiarities of the MeV photon detection technology. Compton scattering, which was used in the CGRO/COMPTEL telescope that had operated in its orbit until 2000, offers one of the possibilities for detecting photons of such energies. In this paper we present the concept of an orbital Compton gamma-ray telescope in the energy range 0.3--10 MeV based on the modern technologies of double-sided silicon strip detectors (Si-DSSD), which allow the telescope sensitivity to be improved significantly. We present the results of our simulations of the characteristics of such a gamma-ray telescope in both full-scale and small-sized versions and make a comparison with the characteristics of the instruments in the completed CGRO/COMPTEL (NASA) and planned COSI (NASA) missions.