Wen-g Jin

Revisiting the characteristics of the spectral lags in short gamma-ray bursts

In this paper, we restudy the spectral lag features of short bright gamma-ray bursts (T-90 < 2.6 s) with a BATSE time-tagged event sample including 65 single pulse bursts. The cross-correlation technique is adopted to measure the lags between two different energy channels. Meanwhile, we also make an investigation of the characteristics of the ratios between the spectral lag and the full width at half-maximum of the pulses, called relative spectral lags. We conclude that spectral lags of short gamma-ray bursts (SGRBs) are normally distributed and concentrated around the value of 0.014, with 40 per cent of them having negative lags. With Kolmogorov-Smirnov tests, we find that the lag distribution is identical to a normal one caused by white noises, which indicates that the lags of the vast majority of SGRBs are so small that they are negligible or non-measurable, as Norris & Bonnell have suggested.

Removal of tracking error with image restoration

In this paper, image restoration is presented as a way to remove the influence of tracking error in astrometric CCD images, based on the characteristics of spatially invariant tracking error within a CCD frame. The direct deconvolution method was used in the process of image restoration. The results of reduction using practical data show improved precision in the images of star centers, including those of closely spaced stars. In particular, close binaries can be separated easily after image restoration.

Proper motions of Hipparcos stars in two plate areas

Abstract Using the ACT reference catalogue as preliminary reference we have reduced 31 exposures on 15 plates in two areas taken with the 40-cm refractor of our Observatory. Using the central overlapping technique and an iterative procedure we have derived high-precision positions and proper motions for 54 stars, including 16 Hipparcos stars. For the latter, the mean standard errors, in right ascension and declination, are 0.70 and 0.59 mas/yr in proper motion, and 10.5 and 7.5 mas in position.

Comparison of high frequency variations of the atmosphere and the polar motion

Abstract The inferred excitation function χm derived from EOP(IERS 97C04) polar motion series and the series χp and χpib of the atmospheric angular momentum (AAM) provided by NCEP/NCAR for 1988–1999 are used to assess the contribution of AAM to the polar motion. Power spectra and complex wavelet analysis show that there are high peaks and similar structures in χm and χp, and their cross correlation coefficient is 0.75 (retrograde) and 0.60 (prograde). The peaks in χpib are lower. The phase of χp is about one day ahead of χm. The indications are that atmosphere variation is the main source of excitation of polar motion in the high-frequency range, and particularly so for the retrograde motion, while there may be other sources.

Determination of lunar and solar orbital elements with lunar laser ranging data

Abstract In this paper, the partial derivatives of the range in lunar laser ranging (LLR) with respect to solar and lunar orbital elements and their precision have been deduced. The world LLR data between 1988 and 1992 were then used to derive the corrections to the solar and lunar orbital elements. The results are a little more precise than the previous results.