On the discrepancy between Chandra and XMM temperature profiles for A1835

TL;DR

This paper investigates discrepancies in galaxy cluster temperature profiles derived from Chandra and XMM data, attributing differences to background flares and PSF scattering effects, which impact temperature measurements and gradients.

Contribution

It identifies the causes of temperature profile discrepancies between Chandra and XMM for A1835, highlighting the importance of background flare correction and PSF effects.

Findings

Background flare biased temperatures upwards in Chandra data.

XMM PSF scattering causes underestimation of temperature gradients.

Discrepancies can be mitigated by accounting for these effects.

Abstract

This short technical note addresses a large discrepancy between the temperature profiles for the galaxy cluster A1835 derived by Schmidt et al. (2001) using Chandra and by Majerowicz et al. (2002) using XMM. The causes of this discrepancy may be instructive for the Chandra and XMM cluster analyses in general. The observation used by Schmidt et al. was affected by a mild background flare that could not be identified by the usual technique. This flare biased upwards the measured temperatures at large radii. The remaining discrepancy appears to be due to the XMM PSF scattering that was not taken into account in the published analyses. While the XMM PSF is narrow, the surface brightness of a typical cluster also declines very steeply with radius. For the moderately distant, cooling flow cluster A1835, about 1/3 of the observed XMM brightness at any radius is due to the PSF scattering from the smaller radii. As a result, the contamination from the bright cool cluster center biases low the measured temperatures near the core, and in general, any temperature gradients are underestimated.