Inflight Calibration of the Hitomi Soft X-ray Spectrometer (2) Point Spread Function

TL;DR

This paper reports on the inflight calibration of the Hitomi Soft X-ray Spectrometer's point spread function, comparing observed images of the Crab nebula to raytracing models, and analyzing pixel-to-pixel variations.

Contribution

It provides the first inflight calibration results of the PSF for the Hitomi SXS, validating raytracing models against observed data with detailed pixel analysis.

Findings

Raytracing model with 1'.2 HPD matches observed images.

Pixel-to-pixel ratio scatter is within 40%.

Central pixels show less variation with 15% ratio and 6% error.

Abstract

We present results of inflight calibration of the point spread function (PSF) of the Soft X-ray Telescope (SXT-S) that focuses X-ray onto the pixel array of the Soft X-ray Spectrometer system (SXS). We make a full array image of a point-like source by extracting a pulsed component of the Crab nebula emission. Within the limited statistics afforded by an exposure time of only 6.9~ksec and the limited knowledge of the systematic uncetainties, we find that the raytracing model of 1'.2 half-power-diameter (HPD) is consistent with an image of the observed event distributions across pixels. The ratio between the Crab pulsar image and the raytracing shows scatter from pixel to pixel that is 40% or less in all except one pixel. The pixel-to-pixel ratio has a spread of 20%, on average, for the 15 edge pixels, with an averaged statistical error of 17% (1 sigma). In the central 16 pixels, the corresponding ratio is 15% with an error of 6%.