Astronomy Journal Article Extract, Edited Version
Here wWe use apply, for the first time, the Cappellari & Copin (2003; hereafter CC03) Voronoi tesselation algorithm (hereafter VT) to build the XMM EPIC temperature map of A3266.
This is the first time that this algorithm has been applied to XMM data We first extract ed source and
background images in the 0.5-7.5 keV energy band, . The chosen energy range optimizing ses the contrast between cluster signal and over the particle background inover the temperature range of the cluster. These two images are were then used to estimate the Signal-to-Noise (S/N) of each pixel.
We were unable to use the CC03 algorithm in a single step,
sinceAs X-ray events are distributed
follow ing a Poisson
distribution statistics and, many of the pixels have a low S/N and it is therefore inappropriate to apply the CC03 algorithm
directly to our data. Our implementation of the algorithm thus involves two steps.
We first select ed only those all the pixels with
a sufficiently high S/N (i.e. (S–N)/N ≥ 1.05) and use d the CC03 algorithm to bin
them se pixels into meta-pixel
groups with a
S/N ~ 130 (our final goal for the temperature map). Since these meta-pixels
weare obtained from
athe high S/N subset, they are not generated from a continuous set of pixelsregion.
In t The second step, we consists of assign ing alleach of the so-far unbinned pixels to
theirits closest meta-pixel.
Obviously, the addition of theseWhile including the lower S/N pixels clearly increases the adds
to the S/N of the final distribution of
the meta-pixel s. S/N distribution, However, the resulting
distributionset of convex meta-pixel
s (cells) covers the whole image without significantly degrading the overall S/N.
Application of this technique to the A3266 mosaic event list,
of A3266 results inwe obtain a total of 138 cells. We fit ted the spectrum of each cell with
an absorbed mekal model to the spectrum of each cell using XSPEC v11.2. Note: you fit a model to the data, not the other way around.
The absorption is was fixed
to the Galactic value (NH = 1.6×1020 cm-2; Dickey & Lockman 1990), and the abundances are were fixed
to 0.2 Z/Zsol=0.2. This abundance value
wasis obtained by fitting a a two-temperature mekal model with a single abundance to the
global spectrum, extracted within a circle of 10 arcmin and excluding point sources , with a two-temperature mekal model with abundances tied together. Our best fitting global abundance is
in reasonable agreement with the value found by Henriksen & Tittley (2002) in the central region mapped by Chandra
(see also De Grandi & Molendi, 1999).
We note that a single temperature model iprovides
an acceptable fit to alleach of the
138 cell s spectra.