X-ray polarization in the standard band (a few keV) of X-ray astronomy is a window that had not been explored for more than 40 years since the 1970s, mainly due to the lack of high-sensitivity techniques. In 2001, a new technique for high-sensitivity X-ray polarimetry was demonstrated as possible in the INFN-Pisa laboratory and has been developed since then. The technique is based on the photoelectric effect and utilizes the gas pixel detector (GPD) to measure the 2D track of photoelectrons following the absorption of X-rays. As the photoelectric effect is the main interaction mechanism between X-rays and matters in this energy range, high-sensitivity X-ray polarimetry is enabled.

PolarLight is a compact soft X-ray polarimeter onboard a CubeSat, which was launched into a low-Earth orbit on 29 October 2018. The key component of PolarLight is the GPD, which is mounted on a printed circuit board, assisted with a high voltage (HV) board and a data acquisition board. The whole payload has a size of about 10 cm x 10 cm x 10 cm and occupies a standard unit (1U) of a CubeSat. PolarLight is the name of the payload, not the spacecraft. It shares the CubeSat "Tongchuan-1" with other payloads to lower the cost.

This project is a collaboration of Tsinghua, INFN-Pisa, INAF/IAPS-Rome, IHEP, Ningbo University of Technology, North Night Vision, and Spacety.

Papers related to PolarLight


Data archive

As of 2021/03/08

Schematic drawing

Fig. 1 in Feng & Bellazzini 2020, Nature Astronomy, 4, 511

Schematic drawings of the CubeSat, PolarLight and its internal GPD. The right-hand side illustrates how a photoelectron track is measured following the absorption of an X-ray (adopted from Fig. 1 in Feng & Bellazzini 2020, Nature Astronomy, 4, 511).