The design and flight performance of the PoGOLite Pathfinder balloon-borne hard X-ray polarimeter

摘要

In the 50 years since the advent of X-ray astronomy there have been manyscientific advances due to the development of new experimental techniques fordetecting and characterising X-rays. Observations of X-ray polarisation have,however, not undergone a similar development. This is a shortcoming since aplethora of open questions related to the nature of X-ray sources could beresolved through measurements of the linear polarisation of emitted X-rays. ThePoGOLite Pathfinder is a balloon-borne hard X-ray polarimeter operating in the25 - 240 keV energy band from a stabilised observation platform. Polarisationis determined using coincident energy deposits in a segmented array of plasticscintillators surrounded by a BGO anticoincidence system and a polyethyleneneutron shield. The PoGOLite Pathfinder was launched from the SSC Esrange SpaceCentre in July 2013. A near-circumpolar flight was achieved with a duration ofapproximately two weeks. The flight performance of the Pathfinder design isdiscussed for the three Crab observations conducted. The signal-to-backgroundratio for the observations is shown to be 0.25$\pm$0.03 and the MinimumDetectable Polarisation (99% C.L.) is (28.4$\pm$2.2)%. A strategy for thecontinuation of the PoGOLite programme is outlined based on experience gainedduring the 2013 maiden flight.