An X-ray photometry system I: Chandra ACIS

TL;DR

This paper introduces an X-ray photometry system for the Chandra satellite that estimates fluxes, hardness ratios, and colors with high accuracy, independent of spectral assumptions or instrument variations.

Contribution

It develops a novel X-ray photometry method using effective area and energy-channel conversion to create filters similar to optical photometric filters.

Findings

Reconstructs fluxes within about 20% accuracy for typical spectra

Performs better than 50% accuracy in worst cases

Handles statistical and systematic errors consistently

Abstract

We present a system of X-ray photometry for the Chandra satellite. X-ray photometry can be a powerful tool to obtain flux estimates, hardness ratios, and colors unbiased by assumptions about spectral shape and independent of temporal and spatial changes in instrument characteristics. The system we have developed relies on our knowledge of effective area and the energy-to-channel conversion to construct filters similar to photometric filters in the optical bandpass. We show that the filters are well behaved functions of energy and that this X-ray photometric system is able to reconstruct fluxes to within about 20%, without color corrections, for non-pathological spectra. Even in the worst cases it is better than 50%. Our method also treats errors in a consistent manner, both statistical as well as systematic.