Fast Radio Bursts(FRBs) are intense radio flashes from the sky that are characterized by millisecond durations and Jansky-level flux densities. We carried out a statistical analysis on FRBs that have been discovered. Their mean dispersion measure, after subtracting the contribution from the interstellar medium of our Galaxy, is found to be ~ 660 pc cm^(-3), supporting their being from a cosmological origin. Their energy released in the radio band spans about two orders of magnitude, with a mean value of ~ 10^(39) erg. More interestingly, although the study of FRBs is still in a very early phase, the published collection of FRBs enables us to derive a useful intensity distribution function. For the 16 non-repeating FRBs detected by the Parkes telescope and the Green Bank Telescope, the intensity distribution can be described as d N/d F_(obs) =(4.1 ± 1.3) × 10~3F_(obs)^(-1.1±0.2) sky^(-1)d^(-1), where Fobs is the observed radio fluence in units of Jy ms. Here the power-law index is significantly flatter than the expected value of2.5 for standard candles distributed homogeneously in a flat Euclidean space. Based on this intensity distribution function, the Five-hundred-meter Aperture Spherical radio Telescope(FAST) is predicted to be able to detect about five FRBs for every 1000 h of observation time.
Long-Biao LiYong-Feng HuangZhi-Bin ZhangDi LiBing Li
We analyze the long-term lightcurve of 3C 454.3 observed with Fermi/LAT and investigate its relation to flux in the radio,optical and X-ray bands.By fitting the 1-day binned Ge V lightcurve with multiple Gaussian functions(MGF),we propose that the typical variability timescale in the Ge V band is 1–10 d.The Ge V flux variation is accompanied by the spectral variation characterized as fluxtracking,i.e.,"harder when brighter."The Ge V flux is correlated with the optical and X-ray fluxes,and a weak correlation betweenγ-ray flux and radio flux is also observed.Theγ-ray flux is not correlated with the optical linear polarization degree for the global lightcurves,but they show a correlation for the lightcurves before MJD 56000.The power density spectrum of the global lightcurve shows an obvious turnover at^7.7 d,which may indicate a typical variability timescale of 3C 454.3 in theγ-ray band.This is also consistent with the derived timescales by fitting the global lightcurve with MGF.The spectral evolution and an increase in the optical linear polarization degree along with the increase inγ-ray flux may indicate that the radiation particles are accelerated and the magnetic field is ordered by the shock processes during the outbursts.In addition,the nature of 3C 454.3 may be consistent with a self-organized criticality system,similar to Sagittariusand thus the outbursts could be from plasmoid ejections driven by magnetic reconnection.This may further support the idea that the jet radiation regions are magnetized.
The mono-frequency peak luminosity and the corresponding photon energy of the time-integrated(Ls p,Es p)and peak time(Lt p,Et p)νfνspectra were derived for a sample of 38 redshift-known Fermi GRBs by fitting the spectra with the Band function.It was found that Et pis generally consistent with Es p,and Lt pis averagely three times larger than Ls p.The slope of the Lt p-Et prelation was consistent with that of the Ls p-Es prelation.The photon indices in the peak time spectrum,particularly,the index of the low energy end was,were statistically larger than that in the time-integrated spectrum.These results indicate that Ls pand Es pare dominated by Lt pand Et p,respectively.The difference of the spectral indices between the time-integrated and peak time spectra may be because of the overlap effect of a series of time-resolved spectra within a GRB.Our simulations,which were based on the observed spectral evolution and correlation between the energy flux and the peak energy within individual GRBs support our speculations.The Lt p-Et prelation may be less contaminated by the overlap effect,and it would may be an intrinsic feature of radiation physics.
We present a star catalog extracted from the Lunar-based Ultraviolet Telescope(LUT) survey program. LUT's observable sky area is a circular belt around the Moon's north pole, and the survey program covers a preferred area of about 2400 deg^2 which includes a region of the Galactic plane. The data are processed with an automatic pipeline which copes with stray light contamination, artificial sources, cosmic rays, flat field calibration, photometry and so on. In the first release version, the catalog provides high confidence sources which have been cross-identified with the Tycho-2 catalog. All the sources have signalto-noise ratio larger than 5, and the corresponding magnitude limit is typically 14.4 mag, but can be as deep as ～16 mag if stray light contamination is at the lowest level. A total of 86 467 stars are recorded in the catalog. The full catalog in electronic form is available online.
