Updating the Chandra HETGS Efficiencies using In-Orbit Observations

TL;DR

This paper describes how in-orbit observations of bright sources were used to update and verify the efficiency calibrations of the Chandra HETGS gratings, improving spectral accuracy.

Contribution

The authors developed a method to update HETGS efficiencies using in-flight data, ensuring better calibration between different grating orders and energy ranges.

Findings

Fluxes from +1 and -1 orders match, confirming calibration consistency.

Efficiency adjustments improve spectral fits to blazar data.

Polynomial fits effectively model efficiency ratios across energies.

Abstract

The efficiencies of the gratings in the High Energy Transmission Grating Spectrometer (HETGS) were updated using in-flight observations of bright continuum sources. The procedure first involved verifying that fluxes obtained from the +1 and -1 orders match, which checks that the contaminant model and the CCD quantum efficiencies agree. Then the fluxes derived using the high energy gratings (HEGs) were compared to those derived from the medium energy gratings (MEGs). The flux ratio was fit to a low order polynomial, which was allocated to the MEGs above 1 keV or the HEGs below 1 keV. The resultant efficiencies were tested by examining fits to blazar spectra.