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.

Known IXPE Analysis Issues

2025 June 26: IXPE's Detector Unit 2 (DU2) is operating in an anomalous but stable and functional state since 14 April 2025. The detector response has changed and the data processing is being adjusted. The spectral response has been corrected. The response for polarimetry and background filtering are being recalibrated. The data for observations after 10 May 2025 are being made available with DU2 event data removed. After the processing adjustments are completed and tested, new data sets will be released to HEASARC with DU2 included.

2025 March 31: The IXPE team has identified an issue in the extractor tool in HEASoft v6.35 where in the extraction of polarization data, the normalization of Q and U in resultant spectral files are incorrect. This issue does not appear to be present in extraction of light curves. HEASoft 6.35.1 contains an update to the extractor task to fix this issue, and users are strongly encouraged to dowload and install this patch.

IXPE Data Acknowledgement

It is strongly recommended that publications using IXPE data include the following acknowledgement: "This work reports observations obtained with the Imaging X-ray Polarimetry Explorer (IXPE), a joint US (NASA) and Italian (ASI) mission, led by Marshall Space Flight Center (MSFC). The research uses data products provided by the IXPE Science Operations Center (MSFC), using algorithms developed by the IXPE Collaboration (MSFC, Istituto Nazionale di Astrofisica - INAF, Istituto Nazionale di Fisica Nucleare - INFN, ASI Space Science Data Center - SSDC), and distributed by the High-Energy Astrophysics Science Archive Research Center (HEASARC)."

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.

Users are encouraged to use the latest version of the IXPE software package, which is included with the latest HEAsoft distribution. HEAsoft can be downloaded here.

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 and Meetings

Upcoming Events

• Summer 2025 IXPE Proposers Workshop

Past Events

• July 2024 Joint NICER/IXPE Workshop
• September 2024 International X-ray POlarimetry Symposium
• IXPE splinter session at the HEAD 21 Meeting
• September 2023 IXPE Proposers Workshop

Resolved IXPE Analysis Issues

2023 Aug 31st: The IXPE team 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. The IXPE SOC have updated the processing pipeline so that events with LIVETIME values less than 15 microseconds, where this effect is manifest, are filtered out.

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.