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arxiv: 2604.03366 · v1 · submitted 2026-04-03 · 🌌 astro-ph.HE · astro-ph.IM

The hitchhiker's guide to the IXPE data analysis

Alessandro Di Marco This is my paper

Pith reviewed 2026-05-13 18:18 UTC · model grok-4.3

classification 🌌 astro-ph.HE astro-ph.IM
keywords IXPEX-ray polarimetrydata analysispolarimetric informationsystematic errorsinstrument response functionsmodel-independent analysismodel-dependent analysis
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The pith

This guide compiles the data formats, processing steps, and analysis strategies needed to extract reliable polarization measurements from IXPE observations.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The chapter serves as a handbook for IXPE data analysis. It introduces the spacecraft and instrument before detailing strategies for extracting polarimetric information and optimizing responses. Data formats and processing steps are provided to avoid systematic errors and achieve optimal results. Both model-independent and model-dependent analyses are covered along with instrument response functions. The purpose is to answer common user questions and help maximize the scientific value of IXPE observations.

Core claim

The author presents an almost comprehensive guide that collects suggestions and answers to typical questions raised by users of IXPE data, with the aim of enabling researchers to maximize the scientific return from the observations through proper extraction of polarimetric information and avoidance of systematic errors.

What carries the argument

The central mechanism is the set of data processing steps and analysis strategies, including model-independent and model-dependent methods, that allow for accurate polarimetry while using the instrument response functions in their available forms.

If this is right

  • Applying the described strategies enables extraction of polarimetric information from IXPE observations.
  • Optimizing the response leads to the best possible results from the data.
  • Using the correct data formats and processing avoids potential systematic errors.
  • Both model-independent and model-dependent analyses can be performed effectively with the available response functions.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Similar guides could improve data analysis for other space-based X-ray instruments.
  • Adopting these methods uniformly might lead to more consistent polarization measurements across different research groups.
  • Extensions to handle new data types from future missions could build directly on this framework.

Load-bearing premise

The assumption that the outlined strategies, data formats, and processing steps are complete enough to eliminate all potential systematic errors in actual IXPE observations.

What would settle it

Comparing polarization results obtained using the guide's recommended procedures against independent measurements or simulations for a standard candle source with well-known polarization properties.

Figures

Figures reproduced from arXiv: 2604.03366 by Alessandro Di Marco.

Figure 1.1
Figure 1.1. Figure 1.1: Examples of simulated ionization tracks resulting from the absorption of [PITH_FULL_IMAGE:figures/full_fig_p003_1_1.png] view at source ↗
Figure 1.2
Figure 1.2. Figure 1.2: Example of a modulation curve observed with an ideal detector for unpo [PITH_FULL_IMAGE:figures/full_fig_p004_1_2.png] view at source ↗
Figure 1.3
Figure 1.3. Figure 1.3: (Top) Difference between the reconstructed and the true direction angle [PITH_FULL_IMAGE:figures/full_fig_p007_1_3.png] view at source ↗
Figure 1.4
Figure 1.4. Figure 1.4: Example of the content from one of the IXPE observations. It is possible [PITH_FULL_IMAGE:figures/full_fig_p009_1_4.png] view at source ↗
Figure 1.5
Figure 1.5. Figure 1.5: (a) On-axis effective area as a function of the energy. The solid lines rep [PITH_FULL_IMAGE:figures/full_fig_p011_1_5.png] view at source ↗
Figure 1.6
Figure 1.6. Figure 1.6: Overall IXPE response: blue lines report the [PITH_FULL_IMAGE:figures/full_fig_p012_1_6.png] view at source ↗
Figure 1.7
Figure 1.7. Figure 1.7: Example of a good (left) and a bad (right) alignment of two segments of [PITH_FULL_IMAGE:figures/full_fig_p013_1_7.png] view at source ↗
Figure 1.8
Figure 1.8. Figure 1.8: IXPE imaging selections radii for source (light blue) and background [PITH_FULL_IMAGE:figures/full_fig_p015_1_8.png] view at source ↗
Figure 1.9
Figure 1.9. Figure 1.9: IXPE light curve in time bins of 300 s when the background region is [PITH_FULL_IMAGE:figures/full_fig_p016_1_9.png] view at source ↗
Figure 1.10
Figure 1.10. Figure 1.10: Left: example of a protractor plot provided by the [PITH_FULL_IMAGE:figures/full_fig_p019_1_10.png] view at source ↗
Figure 1.11
Figure 1.11. Figure 1.11: Comparison for the Q (black) and U (red) spectra in case of no rebinning (left) and after a constant rebin (right) for the IXPE observationID 01002501. this, a constant binning of 3 or 5 bins (120 or 200 eV, respectively) to reduce the uncertainties should be used: grppha ixpe det3 src NEF U.pha ixpe det3 src NEF U rb.pha comm="group 1 375 3 & chkey ANCRFILE ixpe det3 NEF.mrf & chkey RESPFILE ixpe d3 20… view at source ↗
Figure 1.12
Figure 1.12. Figure 1.12: Results for two-component spectro-polarimetric analysis as obtained by [PITH_FULL_IMAGE:figures/full_fig_p025_1_12.png] view at source ↗
Figure 1.13
Figure 1.13. Figure 1.13: Left: a scatter plot showing the number of pixels as a function of the [PITH_FULL_IMAGE:figures/full_fig_p027_1_13.png] view at source ↗
Figure 1.14
Figure 1.14. Figure 1.14: Left: threshold on the energy fraction as a function of energy for which [PITH_FULL_IMAGE:figures/full_fig_p028_1_14.png] view at source ↗
read the original abstract

This chapter provides an almost comprehensive guide to the Imaging X-ray Polarimetry Explorer (IXPE) data analysis. The chapter briefly introduces the IXPE spacecraft and the instrument onboard; subsequently, the strategies adopted to extract polarimetric information and to optimize the response are given. Moreover, the data formats and processing steps to avoid potential systematic errors and to achieve the best results from the IXPE data are reported. Both the model-independent and the model-dependent analyses are summarized, as the instrument response functions and their different available flavors. The idea behind this chapter is to collect suggestions and answers to questions that are typically raised by users, aiming to enable researchers to maximize the scientific return from IXPE observations.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 2 minor

Summary. The manuscript presents a guide to IXPE data analysis. It introduces the spacecraft and onboard instrument, describes strategies for extracting polarimetric information and optimizing the response, details data formats and processing steps to avoid systematic errors, and summarizes model-independent and model-dependent analysis paths together with the available flavors of the instrument response functions. The central aim is to compile answers to common user questions so that researchers can maximize the scientific return from IXPE observations.

Significance. If the compiled advice is followed, the chapter provides a practical, centralized resource that draws directly from established mission documentation. It should reduce the incidence of common analysis errors and thereby improve the reliability of polarimetric results in high-energy astrophysics, particularly for users new to the mission.

minor comments (2)
  1. The abstract states that the guide is 'almost comprehensive'; the introduction would benefit from an explicit statement of the topics deliberately omitted (e.g., advanced time-resolved polarimetry or specific calibration updates post-launch).
  2. Section describing data formats would be clearer if it included a short table or schematic showing the relationship between the primary event list, the response matrix, and the ancillary response files.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive summary of the manuscript, recognition of its utility as a centralized resource for IXPE users, and recommendation to accept. The referee's description accurately reflects the chapter's goals of compiling practical guidance on data formats, analysis strategies, and best practices to maximize scientific return from IXPE observations.

Circularity Check

0 steps flagged

No significant circularity; handbook-style guide with no derivations

full rationale

This manuscript is an explanatory handbook compiling strategies, data formats, processing steps, instrument response functions, and both model-independent and model-dependent analysis paths for IXPE observations. It draws from prior mission documentation and standard practices without presenting any new mathematical derivations, predictions, fitted parameters, or first-principles results. No equations, self-referential definitions, or load-bearing self-citations reduce any claimed result to its own inputs by construction. The central claim is practical guidance to maximize scientific return, which remains self-contained against external benchmarks and does not invoke uniqueness theorems or ansatzes from the authors' prior work.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper introduces no new free parameters, axioms beyond standard instrument knowledge, or invented entities; it synthesizes established mission information.

axioms (1)
  • domain assumption Standard assumptions about IXPE instrument response functions and data formats as provided by the mission team.
    The guide relies on the established properties of the IXPE spacecraft and detectors.

pith-pipeline@v0.9.0 · 5402 in / 1073 out tokens · 33585 ms · 2026-05-13T18:18:58.338208+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

38 extracted references · 38 canonical work pages

  1. [1]

    The Instrument of the Imaging X-Ray Polarimetry Explorer,

    P. Soffitta, L. Baldini,et al., “The Instrument of the Imaging X-Ray Polarimetry Explorer,” AJ162no. 5, (Nov., 2021) 208,arXiv:2108.00284 [astro-ph.IM]

    work page arXiv 2021

  2. [2]

    The Imaging X-Ray Polarimetry Explorer (IXPE): Pre-Launch,

    M. C. Weisskopf, P. Soffitta,et al., “The Imaging X-Ray Polarimetry Explorer (IXPE): Pre-Launch,”JATIS8no. 2, (Apr., 2022) 026002,arXiv:2112.01269 [astro-ph.IM]

    work page arXiv 2022

  3. [3]

    Design, construction, and test of the Gas Pixel Detectors for the IXPE mission,

    L. Baldini, M. Barbanera,et al., “Design, construction, and test of the Gas Pixel Detectors for the IXPE mission,”Astroparticle Physics133(Dec., 2021) 102628, arXiv:2107.05496 [astro-ph.IM]

    work page arXiv 2021

  4. [4]

    Heitler,Quantum theory of radiation

    W. Heitler,Quantum theory of radiation. International Series of Monographs on Physics, Oxford: Clarendon, 1954

    work page 1954

  5. [5]

    Calibration of the IXPE Focal Plane X-Ray Polarimeters to Polarized Radiation,

    A. Di Marco, S. Fabiani,et al., “Calibration of the IXPE Focal Plane X-Ray Polarimeters to Polarized Radiation,” AJ164no. 3, (Sept., 2022) 103,arXiv:2206.07582 [astro-ph.IM]

    work page arXiv 2022

  6. [6]

    Evidence for a shock-compressed magnetic field in the northwestern rim of Vela Jr. from X-ray polarimetry,

    D. A. Prokhorov, Y .-J. Yang,et al., “Evidence for a shock-compressed magnetic field in the northwestern rim of Vela Jr. from X-ray polarimetry,” A&A692(Dec., 2024) A59, arXiv:2410.20582 [astro-ph.HE]

    work page arXiv 2024

  7. [7]

    Vela pulsar wind nebula X-rays are polarized to near the synchrotron limit,

    F. Xie, A. Di Marco,et al., “Vela pulsar wind nebula X-rays are polarized to near the synchrotron limit,” Nature612no. 7941, (Dec., 2022) 658–660,arXiv:2303.12437 [astro-ph.HE]

    work page arXiv 2022

  8. [8]

    Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1,

    H. Krawczynski, F. Muleri,et al., “Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1,”Science378no. 6620, (Nov., 2022) 650–654, arXiv:2206.09972 [astro-ph.HE]

    work page arXiv 2022

  9. [9]

    Weakly Magnetized Accreting Neutron Stars as Seen by IXPE,

    A. Di Marco, “Weakly Magnetized Accreting Neutron Stars as Seen by IXPE,” Astronomische Nachrichten346no. 1, (Jan., 2025) e20240126

    work page 2025

  10. [10]

    Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1,

    F. La Monaca, A. Di Marco,et al., “Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1,” ApJ960no. 2, (Jan., 2024) L11, arXiv:2311.06359 [astro-ph.HE]

    work page arXiv 2024

  11. [11]

    Polarized Multiwavelength Emission from Pulsar Wind—Accretion Disk Interaction in a Transitional Millisecond Pulsar,

    M. C. Baglio, F. Coti Zelati,et al., “Polarized Multiwavelength Emission from Pulsar Wind—Accretion Disk Interaction in a Transitional Millisecond Pulsar,” ApJ987no. 1, (July, 2025) L19,arXiv:2412.13260 [astro-ph.HE]

    work page arXiv 2025

  12. [12]

    Determination of X-ray pulsar geometry with IXPE polarimetry,

    V . Doroshenko, J. Poutanen,et al., “Determination of X-ray pulsar geometry with IXPE polarimetry,”Nature Astronomy6(Dec., 2022) 1433–1443,arXiv:2206.07138 [astro-ph.HE]

    work page arXiv 2022

  13. [13]

    X-Ray Dips and Polarization Angle Swings in GX 13+1,

    A. Di Marco, F. La Monaca,et al., “X-Ray Dips and Polarization Angle Swings in GX 13+1,” ApJ979no. 2, (Feb., 2025) L47,arXiv:2501.05511 [astro-ph.HE]

    work page arXiv 2025

  14. [14]

    Discovery of polarized X-ray emission from the accreting millisecond pulsar SRGA J144459.2–604207,

    A. Papitto, A. Di Marco,et al., “Discovery of polarized X-ray emission from the accreting millisecond pulsar SRGA J144459.2–604207,” A&A694(Feb., 2025) A37, arXiv:2408.00608 [astro-ph.HE]

    work page arXiv 2025

  15. [15]

    Magnetic field properties inside the jet of Mrk 421. Multiwavelength polarimetry, including the Imaging X-ray Polarimetry Explorer,

    D. E. Kim, L. Di Gesu,et al., “Magnetic field properties inside the jet of Mrk 421. Multiwavelength polarimetry, including the Imaging X-ray Polarimetry Explorer,” A&A681 (Jan., 2024) A12,arXiv:2310.06097 [astro-ph.HE]

    work page arXiv 2024

  16. [16]

    Ingram et al

    A. Ingram, M. Ewing,et al., “The X-ray polarization of the Seyfert 1 galaxy IC 4329A,” MNRAS525no. 4, (Nov., 2023) 5437–5449,arXiv:2305.13028 [astro-ph.HE]

    work page arXiv 2023

  17. [17]

    , keywords =

    A. Di Marco, E. Costa,et al., “A weighted analysis to improve the x-ray polarization sensitivity of the imaging x-ray polarimetry explorer,” AJ163no. 4, (Mar, 2022) 170. https://dx.doi.org/10.3847/1538-3881/ac51c9

    work page doi:10.3847/1538-3881/ac51c9 2022

  18. [18]

    Handling the Background in IXPE Polarimetric Data,

    A. Di Marco, P. Soffitta,et al., “Handling the Background in IXPE Polarimetric Data,” AJ 165no. 4, (Apr., 2023) 143,arXiv:2302.02927 [astro-ph.IM]

    work page arXiv 2023

  19. [19]

    Novel gaseus X-ray polarimeter: data analysis and simulation,

    R. Bellazzini, F. Angelini,et al., “Novel gaseus X-ray polarimeter: data analysis and simulation,” inPolarimetry in Astronomy, S. Fineschi, ed., vol. 4843 ofSociety of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, pp. 383–393. Feb., 2003. 30 Alessandro Di Marco

    work page 2003

  20. [20]

    On the statistical analysis of x-ray polarization measurements,

    T. E. Strohmayer and T. R. Kallman, “On the statistical analysis of x-ray polarization measurements,”The Astrophysical Journal773no. 2, (Jul, 2013) 103. https://doi.org/10.1088/0004-637X/773/2/103

    work page doi:10.1088/0004-637x/773/2/103 2013

  21. [21]

    Analyzing the data from x-ray polarimeters with stokes parameters,

    F. Kislat, B. Clark, M. Beilicke, and H. Krawczynski, “Analyzing the data from x-ray polarimeters with stokes parameters,”Astroparticle Physics68(2015) 45–51.https: //www.sciencedirect.com/science/article/pii/S092765051500033X

    work page 2015

  22. [22]

    An Algorithm to Calibrate and Correct the Response to Unpolarized Radiation of the X-Ray Polarimeter Onboard IXPE,

    J. Rankin, F. Muleri,et al., “An Algorithm to Calibrate and Correct the Response to Unpolarized Radiation of the X-Ray Polarimeter Onboard IXPE,” AJ163no. 2, (Feb., 2022) 39,arXiv:2111.14867 [astro-ph.IM]

    work page arXiv 2022

  23. [23]

    X-Ray Spectro-polarimetry with Photoelectric Polarimeters,

    T. E. Strohmayer, “X-Ray Spectro-polarimetry with Photoelectric Polarimeters,” ApJ838 no. 1, (Mar., 2017) 72,arXiv:1703.00949 [astro-ph.IM]

    work page arXiv 2017

  24. [24]

    On understanding the figures of merit for detection and measurement of x-ray polarization

    M. C. Weisskopf, R. F. Elsner, and S. L. O’Dell, “On understanding the figures of merit for detection and measurement of x-ray polarization,” inSpace Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray, M. Arnaud, S. S. Murray, and T. Takahashi, eds., vol. 7732 ofSociety of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, p. 773...

    work page Pith review arXiv 2010

  25. [25]

    Polarisation leakage due to errors in track reconstruction in gas pixel detectors,

    N. Bucciantini, N. Di Lalla, R. W. R. Romani, S. Silvestri, M. Negro, L. Baldini, A. F. Tennant, and A. Manfreda, “Polarisation leakage due to errors in track reconstruction in gas pixel detectors,” A&A672(Apr., 2023) A66,arXiv:2302.00346 [astro-ph.IM]

    work page arXiv 2023

  26. [26]

    A study of background for IXPE,

    F. Xie, R. Ferrazzoli, P. Soffitta, S. Fabiani, E. Costa, F. Muleri, and D. Marco, “A study of background for IXPE,”Astroparticle Physics128(Mar., 2021) 102566, arXiv:2102.06475 [astro-ph.IM]

    work page arXiv 2021

  27. [27]

    The future of X-ray polarimetry towards the 3-dimensional photoelectron track reconstruction,

    D. E. Kim, A. Di Marco,et al., “The future of X-ray polarimetry towards the 3-dimensional photoelectron track reconstruction,”Journal of Instrumentation19no. 2, (Feb., 2024) C02028,arXiv:2309.17206 [astro-ph.IM]

    work page arXiv 2024

  28. [28]

    In-flight calibration system of imaging x-ray polarimetry explorer,

    R. Ferrazzoli, F. Muleri,et al., “In-flight calibration system of imaging x-ray polarimetry explorer,”JATIS6(Oct., 2020) 048002,arXiv:2010.14185 [astro-ph.IM]

    work page arXiv 2020

  29. [29]

    ixpeobssim: A simulation and analysis framework for the imaging X-ray polarimetry explorer,

    L. Baldini, N. Bucciantini, N. D. Lalla, S. Ehlert, A. Manfreda, M. Negro, N. Omodei, M. Pesce-Rollins, C. Sgr`o, and S. Silvestri, “ixpeobssim: A simulation and analysis framework for the imaging X-ray polarimetry explorer,”SoftwareX19(July, 2022) 101194, arXiv:2203.06384 [astro-ph.IM]

    work page arXiv 2022

  30. [30]

    Optics for the imaging x-ray polarimetry explorer,

    B. D. Ramsey, S. D. Bongiorno,et al., “Optics for the imaging x-ray polarimetry explorer,” Journal of Astronomical Telescopes, Instruments, and Systems8(Apr., 2022) 024003

    work page 2022

  31. [31]

    IXPE DU-FM ions-UV filters characterization,

    F. La Monaca, S. Fabiani,et al., “IXPE DU-FM ions-UV filters characterization,” inSociety of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, J.-W. A. den Herder, S. Nikzad, and K. Nakazawa, eds., vol. 11444 ofSociety of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, p. 1144463. Jan., 2021

    work page 2021

  32. [32]

    In-orbit monitoring of the imaging x-ray polarimeters on-board IXPE,

    A. Di Marco, F. Muleri,et al., “In-orbit monitoring of the imaging x-ray polarimeters on-board IXPE,” inSpace Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, J.-W. A. den Herder, S. Nikzad, and K. Nakazawa, eds., vol. 12181 ofSociety of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, p. 121811C. Aug., 2022

    work page 2022

  33. [33]

    Simultaneous space and phase resolved X-ray polarimetry of the Crab pulsar and nebula,

    N. Bucciantini, R. Ferrazzoli,et al., “Simultaneous space and phase resolved X-ray polarimetry of the Crab pulsar and nebula,”Nature Astronomy7(May, 2023) 602–610, arXiv:2207.05573 [astro-ph.HE]

    work page arXiv 2023

  34. [34]

    IXPE Observations of the Quintessential Wind-accreting X-Ray Pulsar Vela X-1,

    S. V . Forsblom, J. Poutanen,et al., “IXPE Observations of the Quintessential Wind-accreting X-Ray Pulsar Vela X-1,” ApJ947no. 2, (Apr., 2023) L20,arXiv:2303.01800 [astro-ph.HE]

    work page arXiv 2023

  35. [35]

    A polarized view of the young pulsar wind nebula 3C 58 with IXPE,

    N. Bucciantini, J. Wong,et al., “A polarized view of the young pulsar wind nebula 3C 58 with IXPE,” A&A699(June, 2025) A33,arXiv:2504.20534 [astro-ph.HE]

    work page arXiv 2025

  36. [36]

    First X-Ray Polarimetric View of a Low-luminosity Active Galactic Nucleus: The Case of NGC 2110,

    S. Chakraborty, A. Ratheesh,et al., “First X-Ray Polarimetric View of a Low-luminosity Active Galactic Nucleus: The Case of NGC 2110,” ApJ990no. 1, (Sept., 2025) 89, arXiv:2503.01071 [astro-ph.HE]. 1 The hitchhiker’s guide to the IXPE data analysis 31

    work page arXiv 2025

  37. [37]

    Magnetic-field Order in the Southwestern Rim of RCW 86 Constrained Using X-Ray Polarimetry,

    S. Silvestri, D. Prokhorov,et al., “Magnetic-field Order in the Southwestern Rim of RCW 86 Constrained Using X-Ray Polarimetry,” ApJ998no. 1, (Feb., 2026) 172, arXiv:2602.19200 [astro-ph.HE]

    work page arXiv 2026

  38. [38]

    XSPEC: The First Ten Years,

    K. A. Arnaud, “XSPEC: The First Ten Years,” inAstronomical Data Analysis Software and Systems V, G. H. Jacoby and J. Barnes, eds., vol. 101 ofASP Conf. Ser ., pp. 17–20. Astron. Soc. Pac., San Francisco, 1996

    work page 1996