arXiv subjects

Hancheng Li

Publications and source records attributed to Hancheng Li.

22 records · Page 2Linked to original sources

arXiv2019

POLAR measurements of the Crab pulsar

POLAR is a Compton polarimeter sensitive in the 50 to 500 keV energy range. The Crab pulsar is a scientific target for POLAR on board the Chinese space laboratory Tiangong-2 (TG-2). With its large Field of View (FoV), POLAR detected significant pulsed signals from the Crab pulsar which is visible by POLAR in about half of observation time. In this work, we present the preliminary results including the pulse profile, timing and polarization measuring method. First, we show the highly significant pulse profile observed by POLAR which is compared to the results of other detectors including Fermi/LAT and INTEGRAL. And the pulse profile as a function of theta incident angle and as a function of channel number, which indicate that POLAR has a good detection performance, have been showed. Second, we find that the timing of the Crab pulses are accurately measured, which provides a unique verification and calibration to the POLAR timing system. Finally, the potential polarization measurement of the Crab pulsar is also discussed.

astro-ph.IM↗

arXiv2018

In-flight energy calibration of the space-borne Compton polarimeter POLAR

POLAR is a compact wide-field space-borne detector for precise measurements of the linear polarisation of hard X-rays emitted by transient sources in the energy range from 50 keV to 500 keV. It consists of a 40$\times$40 array of plastic scintillator bars used as a detection material. The bars are grouped in 25 detector modules. The energy range sensitivity of POLAR is optimized to match with the prompt emission photons from the gamma-ray bursts (GRBs). Polarization measurements of the prompt emission would probe source geometries, emission mechanisms and magnetic structures in GRB jets. The instrument can also detect hard X-rays from solar flares and be used for precise measurement of their polarisation. POLAR was launched into a low Earth orbit on-board the Chinese space-lab TG-2 on September 15th, 2016. To achieve high accuracies in polarisation measurements it is essential to assure both before and during the flight a precise energy calibration. Such calibrations are performed with four low activity $^{22}$Na radioactive sources placed inside the instrument. Energy conversion factors are related to Compton edge positions from the collinear annihilation photons from the sources. This paper presents main principles of the in-flight calibration, describes studies of the method based on Monte Carlo simulations and its laboratory verification and finally provides some observation results based on the in-flight data analysis.

physics.ins-det↗

arXiv2018

In-Orbit Instrument Performance Study and Calibration for POLAR Polarization Measurements

POLAR is a compact space-borne detector designed to perform reliable measurements of the polarization for transient sources like Gamma-Ray Bursts in the energy range 50-500keV. The instrument works based on the Compton Scattering principle with the plastic scintillators as the main detection material along with the multi-anode photomultiplier tube. POLAR has been launched successfully onboard the Chinese space laboratory TG-2 on 15th September, 2016. In order to reliably reconstruct the polarization information a highly detailed understanding of the instrument is required for both data analysis and Monte Carlo studies. For this purpose a full study of the in-orbit performance was performed in order to obtain the instrument calibration parameters such as noise, pedestal, gain nonlinearity of the electronics, threshold, crosstalk and gain, as well as the effect of temperature on the above parameters. Furthermore the relationship between gain and high voltage of the multi-anode photomultiplier tube has been studied and the errors on all measurement values are presented. Finally the typical systematic error on polarization measurements of Gamma-Ray Bursts due to the measurement error of the calibration parameters are estimated using Monte Carlo simulations.

astro-ph.IM↗

arXiv2018

A Low-latency Pipeline for GRB Light Curve and Spectrum using Fermi/GBM Near Real-time Data

Rapid response and short time latency are very important for Time Domain Astronomy, such as the observations of Gamma-ray Bursts (GRBs) and electromagnetic (EM) counterparts of gravitational waves (GWs). Based on the near real-time Fermi/GBM data, we developed a low-latency pipeline to automatically calculate the temporal and spectral properties of GRBs. With this pipeline, some important parameters can be obtained, such as T90 and fluence, within ~20 minutes after the GRB trigger. For ~90% GRBs, T90 and fluence are consistent with the GBM catalog results within 2 sigma errors. This pipeline has been used by the Gamma-ray Bursts Polarimeter (POLAR) and the Insight Hard X-ray Modulation Telescope (Insight-HXMT) to follow up the bursts of interest. For GRB 170817A, the first EM counterpart of GW events detected by Fermi/GBM and INTEGRAL/SPI-ACS, the pipeline gave T90 and spectral information in 21 minutes after the GBM trigger, providing important information for POLAR and Insight-HXMT observations.

astro-ph.IM↗