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X-ray detector is a core component for X-ray astronomical observation and pulsar navigation.The on-orbit observation performance of X-ray detector will change gradually,owing to the influences of emission vibration,radiation damage of high-energy particles,and the aging of the components.The on-orbit calibration of X-ray detector facilitates the accurate acquisition and the precise modeling of X-ray radiation of the observation celestial bodies.In this paper a new method of calibrating the performance of X-ray detector is studied by using the radiation spectrum of the pulsar, which can effectively eliminate the influences from detector background and space environment noise.The on-orbit performance of the first focusing X-ray detector in China has been evaluated by analyzing the observations of the X-ray pulsar-based navigation satellite-1(XPNAV-1) for the Crab pulsar.The XPNAV-1 was launched in November 2016, with the aim of conducting the test of the feasibility of applying the regular emission of X-ray signals from pulsars to spacecraft navigation.Now,the first batch of scientific data about the Crab pulsar observations gained by the focusing X-ray detector for almost one month has been released.The pulse profiles of 124 observations and the total observational spectrum of Crab pulsar are achieved from those data.According to the international accurate X-ray radiation parameters of Crab pulsar,which have been determined by other X-ray space satellites,together with the absorption effect of the neutral hydrogen gas in the universe,the effective area of the focusing X-ray detector is estimated.The result shows that the effective area of the focusing X-ray detector on XPNAV-1 in an energy range of 0.6-1.9 keV is better than 2 cm2.The maximum effective area is 3.06 cm2 at an energy of 0.7 keV,which means that its detection efficiency is about 10%.As the observed energy increases,the effective area decreases.The area of the focusing X-ray detector in an energy range of 2-3.5 keV is about 1 cm2,and it is about 0.1 cm2 at energies above 5 keV,and its estimation accuracy is affected seriously by the statistical errors of X-ray photons.At the same time,another method of calibrating the effective area is studied by considering the energy response matrix of detector.The energy response matrix of the focusing X-ray detector is estimated by using the five ground test values of energy resolution.The effective area of the focusing X-ray detector is re-calibrated.However,the result shows that the energy response matrix exerts little effect on the effective area of the focusing X-ray detector.Finally,we suggest that the XPNAV-1 should observe some supernova remnants to monitor the changes of energy resolution and energy linearity and so on.

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The comprehensive positioning navigation timing (PNT) system in China is a multi-source information fusion system with BeiDou navigation satellite system (BDS) as a core. The high-precision millisecond pulsar timing can enhance the long-term stability of the BDS time benchmark and maintain a space-time benchmark for future deep-space users. In this paper, a ground-based pulsar time service system is proposed for detecting and improving the time benchmark of BDS. The preliminary designs and functions of the system are outlined. At the same time, the method of establishing space and ground-based pulsar time is studied. The ground radio timing data from the international pulsar timing array (IPTA), the X-ray timing data from the neutron star interior composition explorer (NICER) in space, and the simulation data from the 500-meter spherical radio telescope (five-hundred-meter aperture spherical radio telescope, FAST) for three millisecond pulsars are used to analyze the stability of ground/space-based pulsar time. The research results are as follows. The annual stability of the PSR J0437-4715 ground-based pulsar time based on IPTA data is 3.30 × 10^–14, and the 10-year stability is 1.23 × 10^–15, respectively. The existence of pulsar red noise can reduce the time stability of the pulsar. The annual stability of the PSR J1939+2134 ground-based pulsar time is 6.51 × 10^–12. We find that the accuracy of the pulse time of Arrival(TOA) is an important factor that restricts the stability of space-based pulsar time. Based on NICER space X-ray timing data, the stability of the pulsar time for PSR J1824-2452A is 1.36 × 10^–13 in one year. Finally, the simulation analysis of the FAST’s data without considering the influence of red noise is completed, and we find that the PSR J1939+2134 ground-based pulsar time based on the FAST has an annual stability of 2.55 × 10^–15, a 10-year stability of 1.39 × 10^–16, and a 20-year stability of 5.08 × 10^–17. It demonstrates that the powerful pulsar observation capability of FAST will help to improve the accuracy of ground-based pulsar time and enhance the long-term stability of the comprehensive PNT system time benchmark in China.

Coordinate transformation parameters between two spatial Cartesian coordinate systems can be solved from the positions of non-colinear corresponding points. Based on the characteristics of translation, rotation and zoom components of the transformation, the complete solution is divided into three steps. Firstly, positional vectors are regulated with respect to the centroid of sets of points in order to separate the translation components. Secondly, the scale coefficient and rotation matrix are derived from the regulated positions independently and correlations among transformation model parameters are analyzed. It is indicated that this method is applicable to other sets of non-position data to separate the respective attributions for transformation parameters.