IXPE Data Analysis

Getting Started with IXPE Data

IXPE Data

On the IXPE archive are released the processed (level 2) event files for each observation. These can be analyzed with the standard multi-mission HEASARC software tools such as ximage and xselect. These can be used to create spectra, images, and light curves for science analysis.

Note that the archive also contains raw (level 1) event files as well as housekeeping data that allows an advanced user to reprocess the data with the IXPE pipeline tools. But this is not needed for most users, since the level 2 events are already highly processed by the IXPE team.

IXPE Software Package

The IXPE software package has been included in HEASoft and first released with HEASoft 6.30 (March 2022) The package includes software routines that process level 1 event data with various corrections and selections to create science-ready level 2 event files. The package also includes several tools to generate related products.

The current version of the IXPE software package is distributed with the latest HEAsoft distribution, which users are encouraged to use.

In addition to the standard HEASoft tools, there is also user-contributed software which has been produced by the community that IXPE users might find helpful.

IXPE Support Documentation

The IXPE team have also provided several documents about the instrument and observatory as well as about using the data and software.

Workshops

Known IXPE Analysis Issues

2023 July 24: The IXPE team have identified an effect in the IXPE detector electronics that produces an artificial hard tail in the energy spectrum of very bright sources but has little or no effect on polarization. This effect is most noticeable in detector unit DU3. It has only been evident in observations of Cyg X-1 taken in May and June 2023. No other observations have been measurably affected. The IXPE SOC plans to apply a filter in the processing pipeline that removes events with very short LIVETIME values where this effect is manifest. This corresponds essentially to an increase of the dead time of at most a few percent in the very brightest sources, so it will be compensated by recalculating the EXPOSURE (the effective area is unchanged).

Resolved IXPE Analysis Issues

2023 Feb 1: The IXPE team have discovered a bug in HEASoft's xselect routine in HEASoft 6.31.1 or before. See the HEASoft known issues for more details and to download a patch.

2022 April 8: The IXPE team have replaced the initial processing of Cas A and Cen X-3 data with corrected versions (see below update from March 18). If you downloaded these data before April 8 2022, you will need to replace them with the current version on the archive. You can also check the DATE keywords in your FITS files; the correct versions have April 4th (Cas A) or 5th (Cen X-3).

2022 March 23: The IXPE team have discovered a bug in HEASoft's barrycor routine in HEASoft 6.30 or before. See the HEASoft known issues for a work-around or update your build to HEASoft 6.30.1 for a fix.

2022 March 18: The IXPE team have discovered an error in the processing of the Q,U data. The significance of any detection measured in a single detector is correct, but the implied angle is effectively meaningless. Further if you add data from all 3 detectors, any true polarization will effectively cancel out. We are working on fixing this problem and will regenerate the level 2 event lists (the only files impacted) and replace the observations on the archive.

Questions?

Questions regarding IXPE data, analysis or calibration can be submitted to the IXPE help desk by using HEASARC's Feedback Form. Please be sure to select "IXPE" as the mailing list so that your question can be routed to the correct help desk promptly.