# Data reproduction package for “X-ray polarization detection of Cassiopeia A with IXPE” (Vink, Prokhorov, Ferrazzoli et al. 2022) published by the Astrophysical Journal

## Summary
This package contains processed data of observation of Cassiopeia A obtained by the NASA/ASI Imaging X-ray Polarimetry Explorer (IXPE) as well as data products
based on Chandra X-ray Observatory. The products consists of FITS-files used for generating the figures in the paper, including the corrected event list of the NASA IXPE observations (including WCS and background corrections), the full model files and results for the Chandra X-ray spectral model, which was used to assess how much of the radiation was due to synchrotron radiation. The Chandra model data consist of xcm files from which X-ray spectral models can be generated in using the `xspec12` software package. The spectral models were used to generate in FITS-format maps of plasma parameters as a function of position using a 20” grid.

The paper itself can be found here: https://ui.adsabs.harvard.edu/abs/2022arXiv220606713V/abstract


## Contents of the package

This package contains 5 gzipped *.tar archive files, which when unpacked contain provide 5 directories (folders), in some cases with subdirectories, with data products.

The 5 archives are:

1. *IXPE_events.tar.gz*
2. *IXPE_maps.tar.gz*
3. *Chandra_spectral_models.tar.gz*
4. *other.tar.gz*
5. *ds9_backupfiles.tar.gz*

Here is a short description of their contents:
1) The IXPE event files are publically available at https://heasarc.gsfc.nasa.gov/docs/ixpe/archive/. However, the first data release of the Cassiopeia A observations had wrong sky coordinate information and the the three detector units were not properly aligned. The event lists in this archive have corrected WCS keywords, based on a cross correlation with Chandra observations (see paper for details). In addition, events were removed that are likely particles rather than photons, based on the event tracks.


2) The event lists were processed with `ixpeobsim` package (https://ui.adsabs.harvard.edu/abs/2022arXiv220306384B/abstract), which resulted in 3-6 keV maps of the Stokes parameters contained in a data cube. The data cube used for the final figures is included here. Seperate code was used to provide chi-square maps and rebinned data products. These are included in this directory as FITS-files (img.gz extension).

3) In order to assess the best strategy for analyzing data simulations were performed with `ixpeobsim`. The input for `ixpeobsim` consisted of a detailed spectral model based on the analysis of an observation of Cas A with Chandra (ObsID 4638). The input data can be obtained from a public archive: https://cda.harvard.edu/chaser.
This directory contains several subdirectories: *Spectra* and *Masks*.
*Masks* contains masks in FITS formats, used for extracting the spectra.
*Spectra* contains the spectral files as well as the best-fit spectral models as obtained by automated fitting. In a number of cases we intervened if the automated fit was inadequate and a manual one is provided. The *Spectra* directory contains subdirectories:
1. *Logs* contains log files from `xspec12` which provides information about the fluxes in several bands.
2. *PS* contains the postscript and pdf files of the spectra and models
3. *Maps* contains maps of the best-fit plasma parameters as well as fluxes.

4) The other.tar.gz file contains a few maps used in the paper based on Chandra X-ray data.

5) Contains `DS9` readable backup files. Loading them in `DS9` provide the figures as shown in the paper. The material in the subdirecories contain the same fits files as under 2)