The background of the gas pixel detector and its impact on imaging X-ray polarimetry

Abstract

The background of the Gas Pixel Detector is expected to be negligible for polarimetry of point sources due to the intrinsic low atomic number and density of the He-DME mixtures and to its imaging properties. Also the background for extended sources is expected to be negligible at least down to the smallest flux for sensitive polarimetry in a reasonable observing time. However in the spatial distribution of the background in a laboratory environment we observed an accumulation on the edges of the sensitive plane due to the presence of the nearby cell walls. We recently developed gas pixel detectors with a new design of the gas cell having a larger distance of the walls from the sensitive plane. In this paper we compare the spatial distribution of the measured background for the two design and their residual systematics. Also the impact of the background in the case of SgrB2 a faint extended source in the galactic center region is evaluated.

Assembly and test of the gas pixel detector for X-ray polarimetry

“…Two versions of sealed test chambers, a small one [11] and a large one [7], were designed by the INFN-Pisa group and assembled by Oxford Instrument Analytical Oy. The major improvement for the large version is that the background induced by the wall of the chamber is reduced and the electric field is more uniform [12].…”

Measurement of the position resolution of the Gas Pixel Detector

“…We report on the first measurement, with a narrow beam at 4.5 keV, of the position resolution of a GPD filled with a mixture of He-DME 80-20 (1 bar) with a large Gas Electron Multiplier (GEM), This proves the capability of the GPD to perform space-resolved measurements, such as those of PulsarWind Nebulae, Supernova Remnants or X-ray jets with a suitable accuracy, and to observe the faintest source accessible to X-ray polarimetry especially in crowded fields [20]. We also compared such measurement with the Monte Carlo simulation relating the characteristics of the image to the modulation factor.…”

The Galactic Center Black Hole Laboratory

“…An improved link between theory and observations will be provided by new and upcoming instrumentation such as the future capability of measuring polarization in the X-ray domain (Soffitta et al 2012(Soffitta et al , 2013, and direct VLBI imaging of the event horizon region for e.g. M87 as a representative of the largest super massive black holes, and SgrA* as a representative for low-mass SMBHs (Dexter et al 2012, Fish et al 2014, Broderick et al 2014.…”