Song Liming

Test of pulsar navigation with POLAR on TG-2 spacelab

Pulsar navigation, which utilizes pulsar observations to determine the position or orbit of a spacecraft, has raised interests of many countries. Several projects, such as NICER, have been proposed. POLAR on-board the TG-2 space station of China has worked for about half year and its main task is to measure the polarization of the gamma-ray bursts. POLAR can also detect the photons from pulsars due to its large effective area (about 200 cm2) and wide field of view (more than 2π Sr). In this work we report our first results testing pulsar navigation with POLAR observations. A new navigation algorithm has been used that combines the orbit dynamics and pulsar profile analysis. With 31-day-long observations of the Crab pulsar, the TG-2 orbit was determined successfully. The parameter values of the orbital elements are solved and the errors are estimated by bootstrap method. The errors with 99.7% confidence are: semi-major axis error of 7.0 m, eccentricity error of 0.00026, inclination error of 0.023° Right Ascension of the Ascending Node (RAAN) error of 0.17°, error for argument of perigee of 0.042° and mean anomaly error of 0.042°.

Dense matter with eXTP

In this White Paper we present the potential of the Enhanced X-ray Timing and Polarimetry (eXTP) mission for determining the nature of dense matter; neutron star cores host an extreme density regime which cannot be replicated in a terrestrial laboratory. The tightest statistical constraints on the dense matter equation of state will come from pulse profile modelling of accretion-powered pulsars, burst oscillation sources, and rotation-powered pulsars. Additional constraints will derive from spin measurements, burst spectra, and properties of the accretion flows in the vicinity of the neutron star. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to be launched in the mid 2020s.

Einstein Probe: Exploring the ever-changing X-ray Universe

The Einstein Probe is a small mission dedicated to time-domain astronomy to monitor the sky in the soft X-ray band (0.5–4 keV). It will carry out systematic survey and characterisation of high-energy transients at unprecedented sensitivity, spatial resolution, Grasp and monitoring cadence. Its wide-field imaging capability, as provided by an X-ray monitor with a field of view of 3600 square degrees, is enabled by using established technology of micro-pore lobster-eye focusing optics. Complementary to this wide-field instrument is a follow-up X-ray telescope with a large effective area and a narrow field of view. It is also capable of real time triggering and downlink of transient alerts on the fly, in order to activate multi-wavelength follow-up observations by other astronomical facilities worldwide. Its scientific goals are concerned with discovering new or rare types of transients, particularly tidal disruption events, supernova shock breakouts, high-redshift gamma-ray bursts and, particularly, electromagnetic sources associated with gravitational wave events. The mission is planned for launch around end of 2022, with a lifetime of three years and five years as a goal.

The power spectra of two types of long-duration γ-ray bursts

We have studied the averaged power density spectra (PDSs) of two classes of longduration gamma-ray bursts in the recent classification by Balastegui et al.(2001) based on neural network analysis. Both PDSs follow a power law over a wide frequency range with approximately the same slope, which indicates that a process with a self-similar temporal property may underlie the emission mechanisms of both. The two classes of bursts are divided into groups according to their brightness and spectral hardness respectively and each group’s PDS was calculated; For both classes, the PDS is found to flatten both with increasing burst brightness and with increasing hardness.We have studied the averaged power density spectra (PDSs) of two classes of long-duration gamma-ray bursts in the recent classification by Balastegui et al. (2001) based on neural network analysis. Both PDSs follow a power law over a wide frequency range with approximately the same slope, which indicates that a process with a self-similar temporal property may underlie the emission mechanisms of both. The two classes of bursts are divided into groups according to their brightness and spectral hardness respectively and each groups PDS was calculated. For both classes, the PDS is found.