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REVIEW 4 major objections 4 minor 64 references

X-ray polarization of Cygnus X-1 stays put during accretion dips, pointing to a large-scale corona as the source of the polarized emission.

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2026-08-01 00:38 UTC pith:SM45THER

load-bearing objection First dedicated dip spectro-polarimetric analysis of Cyg X-1; the null result is real but too weak to carry the extended-oblate-corona conclusion the abstract hangs on it. the 4 major comments →

arxiv 2607.26144 v1 pith:SM45THER submitted 2026-07-28 astro-ph.HE

Unchanged X-Ray Polarization During Accretion Dips in the Low Hard State of Cygnus X-1

Yu-shan Ling , Fei Xie , Alessandro Di Marco , Fabio La Monaca , Ming-Yu Ge This is my paper
classification astro-ph.HE
keywords X-ray polarimetryCygnus X-1accretion dipslow hard stateaccretion-disk coronapartial covering absorptionblack hole X-ray binariesIXPE
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

The paper asks where the polarized X-rays of the black hole binary Cygnus X-1 come from in its low hard state. It uses short, sharp flux drops ('dips') caused by dense clumps of gas crossing the line of sight as a natural experiment: if the dips remove the soft thermal disk emission while leaving the harder Comptonized emission, then any change in polarization during a dip would reveal the disk's polarized contribution. The paper finds that the 2-8 keV polarization degree and angle are statistically unchanged between dip and off-dip intervals across two 2022 observations. It concludes that the thermal disk contributes negligibly to the observed polarization and that the polarization is instead produced by an extended, likely oblate, accretion-disk corona whose large scale is not perturbed by localized absorbing clumps. This matters because it provides direct geometric evidence about the corona in a stellar-mass black hole, something timing and spectroscopy alone cannot pin down.

Core claim

The central claim is that during accretion dips in Cygnus X-1's low hard state, the polarization signature is stable: in joint IXPE/NICER/NuSTAR spectro-polarimetric fits, the 2-8 keV polarization degree (roughly 3-4%) and polarization angle (about -20 to -30 degrees, aligned with the radio jet) are consistent between dip and off-dip intervals, within the larger dip uncertainties. The spectral model requires a partial-covering absorber (TBpcf) whose covering fraction rises to about 0.72 in the dip, absorbing the DISKBB thermal component to an upper limit that corresponds to zero disk flux in the 2-8 keV band. Since removing the disk's photons does not change the polarization, the disk emissi

What carries the argument

The central mechanism is the accretion dip as a natural spectro-polarimetric lever: dense, cold clumps from the companion wind or outer disk partially cover the X-ray source, modeled with the TBpcf partial-covering absorption model, which heavily suppresses the soft DISKBB thermal component while leaving the NTHCOMP Comptonized emission and reflection largely intact. By comparing IXPE polarization in dip and off-dip intervals selected from hardness-ratio light curves, and by fitting Stokes I, Q, U spectra with the same broadband spectral model, the paper isolates whether the removed disk component carries polarization. The constancy of polarization degree and angle across the dip is the evid

Load-bearing premise

The conclusion rests on the assumption that the flux dips are pure absorption events—cold, partial-covering absorption of an otherwise unchanged intrinsic spectrum—so that the dip genuinely removes the disk's photons rather than changing the corona's own emission; if the dips include intrinsic coronal variability or a different absorber geometry, the unchanged polarization would not isolate the disk contribution.

What would settle it

A future Cygnus X-1 dip observation with enough counts to measure the 2-3.5 keV polarization to better than 1% precision would settle it: if the polarization degree or angle changes during the dip while the disk component is firmly suppressed, the extended-corona claim fails; if polarization remains constant while DISKBB is undetected, it holds. Alternatively, finding a dip where the partial-covering fraction reaches above 0.9 and the DISKBB component remains measurable with non-zero polarization would directly contradict the assumption of a negligible disk contribution.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • If the disk contributes negligibly to the 2-8 keV polarization, then measuring polarization in Cygnus X-1's hard state is effectively measuring the corona alone, simplifying the interpretation of IXPE data.
  • The unchanged polarization angle during dips supports a coronal geometry extended parallel to the disk plane (oblate), rather than a compact lamp-post along the jet axis, because a small emission region would be more easily affected by passing clumps.
  • The stability of polarization across dips distinguishes black hole X-ray binaries from dipping neutron-star low-mass X-ray binaries, where polarization degree and angle changes have been reported; this points to a different Comptonizing structure in the inner region.
  • The alignment of the polarization angle with the radio jet across states and dips ties the polarized X-ray emission to the jet-launching region, suggesting the corona and jet share a common vertical axis.
  • Future observations with higher sensitivity could use short dips as probes of outer-disk and corona geometry without needing long exposures for each orbital phase.

Where Pith is reading between the lines

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

  • If the corona is truly the sole polarized component, then in the soft state, where the disk dominates the flux, the polarization should drop or change in a way that tracks the disk's geometric orientation; comparing soft-state and hard-state polarization with the same instruments would test whether the disk is intrinsically unpolarized or simply diluted.
  • The constancy of the polarization angle during dips implies the absorbing clumps cover the line of sight in a way that is symmetric with respect to the polarization plane; a future dip with better statistics showing a temporary angle rotation would set a quantitative upper limit on the corona's size relative to the clumps.
  • The contrast with the dipping neutron-star source GX 13+1 suggests that the presence or absence of a solid surface and boundary layer changes the corona's geometry; this could be tested by polarimetric monitoring of a larger sample of dipping neutron-star and black hole binaries with simultaneous broadband coverage.
  • A stronger test of the large-corona claim would be to model how a clump of given size and optical depth partially covers an extended slab corona and predict the expected polarization variation as a function of covering fraction; the current non-detection of variation could then be translated into a lower limit on the coronal scale.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

4 major / 4 minor

Summary. The paper presents a joint IXPE/NICER/NuSTAR spectro-polarimetric analysis of Cygnus X-1 during flux dips in the 2022 low hard state. The authors identify dip and off-dip intervals from hardness-ratio selections, measure the 2–8 keV polarization with the model-independent PCUBE algorithm, and fit a broadband spectral model with partial-covering absorption (TBpcf). They find that the dip and off-dip polarization degree and angle are consistent, while the spectral fit drives the DISKBB normalization to zero in the dip. They conclude that the obscured thermal disk does not contribute significantly to the X-ray polarization and that the polarization originates from an extended, oblate accretion-disk corona whose geometry is unaffected by localized clumping.

Significance. The paper combines three observatories and performs a rare dip-state polarimetric measurement; the model-independent PCUBE results and the detailed appendices are strengths. If the conclusion were robust, it would provide direct evidence against significant disk-polarized emission in the Cyg X-1 hard state and support an extended-slab coronal geometry. However, the dip-state polarization is often a non-detection, and the central interpretation rests on a single absorption model that is not tested against intrinsic-variability alternatives. The manuscript is valuable as a measurement and a tentative constraint, but the stated conclusion is not supported at the claimed strength; a major revision with a reframing and additional model competition is needed.

major comments (4)
  1. [§3.2, Table 1, Abstract/Conclusions] The dip-state polarization is not a significant detection: for June 2022, the 2–8 keV dip PD is 2.6±1.3% with MDP99=3.8%, and the 2–3.5 keV dip PD is 1.2±1.7% with MDP99=5.3%. The paper's own text states in §3.2 that 'the dip state is not significant enough to support any claim.' Yet the Abstract and §4 conclude that the obscured disk does not contribute to the polarization and that the corona is extended/oblate. This is internally inconsistent. The conclusions must be reframed as tentative or upper-limit statements, or the combined May+June analysis must demonstrate a significant dip/off-dip comparison.
  2. [§2.2, Table 2, Appendix E] The central inference assumes that dips are partial-covering absorption (TBpcf) of an otherwise unchanged intrinsic spectrum. No competing intrinsic-variability model (e.g., the DISKBB component fading, or the NTHCOMP seed/normalization changing without an absorber) is tested. Appendix E re-fits NICER data with the same TBpcf model; this checks internal consistency of the MBPO treatment but does not test model uniqueness. Moreover, off-dip DISKBB contributes only 0.19/7.11 ≈ 2.7% of the 2–8 keV flux, so the total polarization would be nearly unchanged if this weak component vanished for any reason. The paper needs a quantitative diagnostic or a direct comparison with an intrinsic-variability model to support the absorption interpretation.
  3. [§2.3, Table 3] The component-resolved polarization constraints are degenerate and assumption-dependent. In the dip, Table 3 gives only an upper limit for NTHCOMP (PD<30%) and a very broad range for reflection (PD>20%), while the 'unphysical' disk polarization values (72–89%) are obtained only after freezing other components at chosen values. Thus the assertion that the disk's polarized contribution is negligible is an inference from total PD/PA stability plus the spectral model, not a measured bound. The authors should derive and quote an upper limit on the disk polarized flux, or explicitly state that the data only weakly constrain it.
  4. [§2.2, MBPO parameters, Table 2] The MBPO cross-calibration parameters change significantly between off-dip and dip (e.g., IXPE dΓ2 from −0.098±0.010 to −0.48±0.13; IXPE norm from 0.865±0.004 to 1.13±0.05). Because the spectro-polarimetric analysis fixes these parameters, a cross-calibration mismatch could affect the modeled IXPE polarization. Appendix E validates the TBpcf fit only with NICER data (which use no MBPO), so it does not fully address this concern for IXPE. Please show that the dip/off-dip polarization conclusions are stable under reasonable variations of the IXPE MBPO parameters.
minor comments (4)
  1. [Table 2] The column header 'Overlap dip' is unclear. If it refers simply to the dip interval used in the joint fit, rename it 'Dip' for consistency with Table 1.
  2. [Figure 2 and Appendix B] The dip-selection criterion is described as HR > 2σ_HR + HR_average in Appendix B, while Figure 2's caption says '2.0 standard deviations above the mean.' Please specify the exact statistic and make the caption consistent with the text.
  3. [Eq. (1)] The definition MBPO(E1)=N(E1/Ebr)^{dΓ1} and MBPO(E2)=... reads like a step function. It would help to state explicitly that the formula is evaluated at a representative energy E in each band, with E1<Ebr<E2.
  4. [References] The reference list contains two separate entries for Arnaud 1996. Please remove the duplicate.

Circularity Check

0 steps flagged

No significant circularity: the polarization comparison is model-independent, and the absorption interpretation is an assumption rather than a derived prediction.

full rationale

The central measured result—PD/PA consistency between dip and off-dip states—is obtained with the model-independent PCUBE algorithm (Appendix A.1, Table 1), not from a model that assumes the conclusion. The spectral decomposition attributing the dip flux reduction to TBpcf absorption is a fitted interpretation, and the inference that the disk contributes negligibly to polarization follows from the small fitted disk flux (Table 2: off-dip disk flux 0.19 vs total 7.11; dip disk flux 0.00) combined with the independent polarization comparison. This is a standard observational inference, not an equation-level reduction of a prediction to its inputs. The paper itself concedes in §3.2 that 'the dip state is not significant enough to support any claim,' so the abstract's stronger wording is an overstatement but not a circularity. Self-citations (e.g., Di Marco et al. 2025; Di Marco 2026 for pollin; La Monaca et al.) provide context, tools, and comparisons on other sources; none functions as a load-bearing uniqueness theorem or ansatz that forces the result. No step in the derivation chain is equivalent by construction to its own inputs, so no significant circularity is found.

Axiom & Free-Parameter Ledger

8 free parameters · 6 axioms · 0 invented entities

The central claim is not a derivation; it is an interpretation of a spectral+polarimetric fit. It rests on ~8 fitted spectral parameters, several fixed literature values, and the TBpcf model. No new physical entities are introduced; the dense clumps and extended corona are already established scenarios.

free parameters (8)
  • TBPCF column density (dip) = 5.2 ± 0.2 × 10^22 cm^-2
    Free absorber column in the dip spectral fit; drives soft-band suppression (Table 2).
  • TBPCF covering fraction = 0.715 (+0.012, -0.011) dip; <0.068 off-dip
    Partial-covering fraction; its increase during dip is the main spectral change.
  • DISKBB normalization = 10.4 (+3.7,-1.1) ×10^2 off-dip; <3.8 dip
    Disk flux normalization; the dip upper limit underpins the claim that the disk is absorbed away.
  • NTHCOMP photon index = 1.620 (+0.010,-0.006) off-dip; 1.54±0.03 dip
    Coronal Comptonization slope from the same joint fit.
  • RELXILLCP normalization = 4.1 (+0.2,-0.3) ×10^-2 off-dip; 4.9 (+2.0,-1.7) ×10^-2 dip
    Relativistic reflection normalization; poorly constrained in dip.
  • XILLVERCP normalization = 2.5 (+0.5,-0.3) ×10^-3 off-dip; <6.0 ×10^-3 dip
    Distant reflection component; weakly constrained.
  • MBPO cross-calibration parameters = dΓ ≈ -0.09 to -0.22; Ebr 2.6–4.0 keV; norm 0.87–1.17
    Free gain/cross-calibration adjustments per detector that could absorb spectral shape; robustness checked only with NICER-only fit.
  • DISKBB temperature = 0.503 (+0.013,-0.017) keV off-dip
    Disk temperature fitted off-dip and fixed in dip; affects soft-band model.
axioms (6)
  • domain assumption The 2022 May/June observations are in the same low hard state; flux dips are due to variable absorption, not a spectral state change.
    Invoked to justify comparing dip/off-dip polarization and fixing spectral state; based on Krawczynski et al. 2022 (§2).
  • ad hoc to paper The dip flux reduction is produced by cold partial-covering absorption (TBpcf), with the same intrinsic continuum outside the absorber.
    Chosen because it best fits the broadband spectra (§2.2, Table 2); conclusion that DISKBB is absent in dips follows from this model.
  • domain assumption The reflection component is dominated by the Fe line and is unpolarized.
    Used to reduce degeneracies in component polarizations (§2.3), citing Churazov et al. 2002 and Veledina et al. 2024.
  • domain assumption Black hole spin = 0.998, inclination = 27.5°, kTe(NTHCOMP) = 94.2 keV, abundances = wilm.
    Fixed parameters taken from Miller-Jones et al. 2021 and Krawczynski et al. 2022 (§2.2, Table 2).
  • domain assumption MBPO cross-calibration adjustments do not mimic or suppress the intrinsic absorption signal.
    The model includes free gain indices per detector; tested only against NICER without MBPO in Appendix E.
  • domain assumption IXPE Stokes parameters add linearly across spectral components in the spectro-polarimetric decomposition.
    Required for the component-resolved polconst fits in §2.3 and Table 3.

pith-pipeline@v1.3.0-alltime-deepseek · 20806 in / 19048 out tokens · 169671 ms · 2026-08-01T00:38:59.190065+00:00 · methodology

0 comments
read the original abstract

Cygnus X-1 serves as a foundational benchmark for studying accretion mechanisms in stellar-mass black hole X-ray binaries. While traditional X-ray timing and spectroscopy have mapped its bimodal state transitions, constraining the exact geometric configuration of its accreting plasma requires additional tools. In this letter, we present a joint spectro-polarimetric analysis of Cygnus X-1 during flux-decrease events, or ``dips'', observed in its low hard state using simultaneous data from IXPE, NICER, and NuSTAR. The broadband spectral model reveals that the energy-dependent flux reduction during these dips is best described by a partial-covering absorption model, heavily impacting the softer energy bands. This absorption is consistent with obscuration by dense, cold clumps originating from the companion's stellar wind or the outer accretion disk during superior conjunction. Notably, our polarimetric analysis demonstrates that despite significant flux drops, the polarization degree and polarization angle in the 2-8 keV band remain largely consistent between dip and off-dip intervals. The stability of the polarization signature during these highly absorbed periods indicates that the obscured thermal disk emission does not significantly contribute to the total polarization. Ultimately, these results strongly support a scenario where the X-ray polarization originates from an extended, likely oblate, accretion-disk corona whose large scale renders its overall geometry unaffected by localized clumping.

Figures

Figures reproduced from arXiv: 2607.26144 by Alessandro Di Marco, Fabio La Monaca, Fei Xie, Ming-Yu Ge, Yu-shan Ling.

Figure 1
Figure 1. Figure 1: Hardness-intensity diagram reporting the average intensity and hardness for each IXPE observation of Cyg X-1 performed. Hardness is defined as the ratio of photon counts in the 3.5–8 keV range to those in 2–3.5 keV. Circular, trian￾gular, and square markers indicate observations in the soft, intermediate, and hard states, respectively. be used to investigate X-ray emission from the outer region of the disk… view at source ↗
Figure 2
Figure 2. Figure 2: Light curves and hardness ratio of Cyg X-1 from observations in May (left) and June (right) 2022. Panels (a), (b), and (c) report the light curves from IXPE, NuSTAR and NICER observations, respectively; panel (d) is the hardness ratio of IXPE. The time binning is 75 seconds for all of them. The shaded time intervals highlight periods when the IXPE hardness ratio was persistently elevated, identified via a … view at source ↗
Figure 3
Figure 3. Figure 3: Stokes parameters for each IXPE observation in 2–8 keV (left), 2–3.5 keV (center) and 3.5–8 keV (right), with error bars at 68%. The epoch numbers refer to [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 5
Figure 5. Figure 5: A comparison of the polarization in the dip and off-dip states across different energy bands, employing all IXPE datasets in which dips are detected, with a 68% CL. The polarization angles of dip and off-dip across different energies align closely with the radio jet direction, which has a position angle of -27◦±8 ◦ (J. C. A. Miller-Jones et al. 2021). TBabs model, while TBpcf was included to account for ab… view at source ↗
Figure 6
Figure 6. Figure 6: Spectra for off-dip (left) and dip (right) time intervals. that the spectral state of Cyg X-1 continued to soften during the observation period (V. Kravtsov et al. 2025). Summarizing, the PD is lower in the soft state (∼1.7 %), higher in the hard state (∼3.6 %), and around 2.2% in the intermediate state. This PD–hardness depen￾dence, reported in [PITH_FULL_IMAGE:figures/full_fig_p008_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: shows the HID where “dip” (darker points) and “off-dip” (lighter points) intervals for the considered IXPE observations are reported [PITH_FULL_IMAGE:figures/full_fig_p014_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Light curves and hardness ratios of Cyg X-1 from IXPE observations in 2023, 2024 and 2026, showing dips [PITH_FULL_IMAGE:figures/full_fig_p015_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Polarization comparison between dip and off-dip states. The data used in each panel are as follows: (a) combines observations 01002901 and 01250101; (b) combines observations 02008201 and 02008301; (c) incorporates 03003101, 03010001, and 03010101; (d) is based on observation 05250601. The gray shaded region denotes the radio jet direction of -27◦±8 ◦ (J. C. A. Miller-Jones et al. 2021). Allowed regions ar… view at source ↗
Figure 10
Figure 10. Figure 10: The spectra of the off-dip (left) and dip (right) time intervals using only NICER datasets [PITH_FULL_IMAGE:figures/full_fig_p020_10.png] view at source ↗

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Reference graph

Works this paper leans on

64 extracted references · 6 canonical work pages · 1 internal anchor

  1. [1]

    , keywords =

    New results from long-term observations of Cygnus X-1. , keywords =. doi:10.1086/182020 , adsurl =

    work page doi:10.1086/182020

  2. [2]

    , keywords =

    Bimodal behavior of accretion disks: theory and application to Cygnus X-1 transitions. , keywords =. doi:10.1086/155314 , adsurl =

    doi:10.1086/155314

  3. [3]

    , keywords =

    Correlated X-Ray Spectral and Timing Behavior of the Black Hole Candidate XTE J1550-564: A New Interpretation of Black Hole States. , keywords =. doi:10.1086/318954 , archivePrefix =. astro-ph/0001163 , primaryClass =

    Pith/arXiv arXiv

  4. [5]

    , keywords =

    The evolution of the timing properties of the black-hole transient GX 339-4 during its 2002/2003 outburst. , keywords =. doi:10.1051/0004-6361:20042457 , archivePrefix =. astro-ph/0504577 , primaryClass =

    Pith/arXiv arXiv 2002

  5. [6]

    Astrophysics of Black Holes: From Fundamental Aspects to Latest Developments , year = 2016, editor =

    Transient Black Hole Binaries. Astrophysics of Black Holes: From Fundamental Aspects to Latest Developments , year = 2016, editor =. doi:10.1007/978-3-662-52859-4_2 , archivePrefix =. 1603.07872 , primaryClass =

    Pith/arXiv arXiv 2016

  6. [7]

    Progress of Theoretical Physics Supplement , keywords =

    Radiative Processes, Spectral States and Variability of Black-Hole Binaries. Progress of Theoretical Physics Supplement , keywords =. doi:10.1143/PTPS.155.99 , archivePrefix =. astro-ph/0403683 , primaryClass =

    Pith/arXiv arXiv

  7. [8]

    X- and Gamma-Ray Astronomy , year = 1973, editor =

    Black Holes in Binary Systems: Observational Appearances. X- and Gamma-Ray Astronomy , year = 1973, editor =

    1973

  8. [9]

    , keywords =

    Comptonization of X-Rays in Plasma Clouds - Typical Radiation Spectra. , keywords =

  9. [10]

    , keywords =

    Simultaneous X-ray and gamma-ray observations of CYG X-1 in the hard state by GINGA and OSSE. , keywords =. doi:10.1093/mnras/288.4.958 , archivePrefix =. astro-ph/9610156 , primaryClass =

    Pith/arXiv arXiv

  10. [11]

    Galaxies , keywords =

    Fifty Years After the Discovery of the First Stellar-Mass Black Hole: A Review of Cyg X-1. Galaxies , keywords =. doi:10.3390/galaxies12060080 , archivePrefix =. 2411.12507 , primaryClass =

    Pith/arXiv arXiv

  11. [12]

    Science , year = 1965, month = jan, volume =

    Cosmic X-ray Sources. Science , year = 1965, month = jan, volume =. doi:10.1126/science.147.3656.394 , adsurl =

    doi:10.1126/science.147.3656.394 1965

  12. [13]

    , year = 1972, month = oct, volume =

    Observation of a Correlated X-Ray Transition in Cygnus X-1. , year = 1972, month = oct, volume =. doi:10.1086/181042 , adsurl =

    work page doi:10.1086/181042 1972

  13. [14]

    Everything you always wanted to know about accretion but were afraid to ask

    Modelling the behaviour of accretion flows in X-ray binaries. Everything you always wanted to know about accretion but were afraid to ask. , keywords =. doi:10.1007/s00159-007-0006-1 , archivePrefix =. 0708.0148 , primaryClass =

    Pith/arXiv arXiv

  14. [15]

    Long term variability of Cygnus X-1. IV. Spectral evolution 1999-2004. , keywords =. doi:10.1051/0004-6361:20053938 , archivePrefix =. astro-ph/0510193 , primaryClass =

    Pith/arXiv arXiv 1999

  15. [16]

    Long term variability of Cygnus X-1. V. State definitions with all sky monitors. , keywords =. doi:10.1051/0004-6361/201321128 , archivePrefix =. 1303.1198 , primaryClass =

    Pith/arXiv arXiv

  16. [17]

    , keywords =

    X-ray emitting region of Cygnus X-1 constrained by short absorption dips. , keywords =. doi:10.1093/pasj/psaf107 , adsurl =

    work page doi:10.1093/pasj/psaf107

  17. [18]

    , keywords =

    Identification of the soft X-ray excess in Cygnus X-1 with disc emission. , keywords =. doi:10.48550/arXiv.astro-ph/9509020 , archivePrefix =. astro-ph/9509020 , primaryClass =

    Pith/arXiv arXiv doi:10.48550/arxiv.astro-ph/9509020

  18. [19]

    Dependence of the orbital modulation and spectral hardness on the superorbital phase

    Superorbital variability of X-ray and radio emission of Cyg X-1 - II. Dependence of the orbital modulation and spectral hardness on the superorbital phase. , keywords =. doi:10.1111/j.1365-2966.2008.13666.x , archivePrefix =. 0802.1391 , primaryClass =

    arXiv 2008

  19. [20]

    , keywords =

    2D wind clumping in hot, massive stars from hydrodynamical line-driven instability simulations using a pseudo-planar approach. , keywords =. doi:10.1051/0004-6361/201731718 , archivePrefix =. 1710.07780 , primaryClass =

    Pith/arXiv arXiv

  20. [21]

    Journal of Astronomical Telescopes, Instruments, and Systems , keywords =

    The Imaging X-Ray Polarimetry Explorer (IXPE): Pre-Launch. Journal of Astronomical Telescopes, Instruments, and Systems , keywords =. doi:10.1117/1.JATIS.8.2.026002 , archivePrefix =. 2112.01269 , primaryClass =

    Pith/arXiv arXiv

  21. [22]

    , keywords =

    The Two-Phase Pair Corona Model for Active Galactic Nuclei and X-Ray Binaries: How to Obtain Exact Solutions. , keywords =. doi:10.1086/177865 , archivePrefix =. astro-ph/9605073 , primaryClass =

    Pith/arXiv arXiv

  22. [23]

    , keywords =

    The Instrument of the Imaging X-Ray Polarimetry Explorer. , keywords =. doi:10.3847/1538-3881/ac19b0 , archivePrefix =. 2108.00284 , primaryClass =

    Pith/arXiv arXiv

  23. [24]

    , keywords =

    Doughnut strikes sandwich: the geometry of hot medium in accreting black hole X-ray binaries. , keywords =. doi:10.1051/0004-6361/201732345 , archivePrefix =. 1711.08509 , primaryClass =

    Pith/arXiv arXiv

  24. [25]

    , keywords =

    Polarization signatures of strong gravity in active galactic nuclei accretion discs. , keywords =. doi:10.1111/j.1365-2966.2004.08396.x , archivePrefix =. astro-ph/0409356 , primaryClass =

    arXiv 2004

  25. [26]

    , keywords =

    New Constraints on the Spin of the Black Hole Cygnus X-1 and the Physical Properties of its Accretion Disk Corona. , keywords =. doi:10.3847/1538-4357/ac7725 , archivePrefix =. 2201.07360 , primaryClass =

    Pith/arXiv arXiv

  26. [27]

    Science , keywords =

    Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1. Science , keywords =. doi:10.1126/science.add5399 , archivePrefix =. 2206.09972 , primaryClass =

    Pith/arXiv arXiv

  27. [28]

    , keywords =

    X-Ray Dips and Polarization Angle Swings in GX 13+1. , keywords =. doi:10.3847/2041-8213/ada7f8 , archivePrefix =. 2501.05511 , primaryClass =

    Pith/arXiv arXiv 2041

  28. [29]

    , keywords =

    Variability of X-ray polarization of Cyg X-1. , keywords =. doi:10.1051/0004-6361/202555411 , archivePrefix =. 2505.03942 , primaryClass =

    Pith/arXiv arXiv

  29. [30]

    , keywords =

    An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing. , keywords =. doi:10.3847/2041-8213/ad58e4 , archivePrefix =. 2406.12014 , primaryClass =

    Pith/arXiv arXiv 2041

  30. [31]

    Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray , year = 2014, editor =

    The neutron star interior composition explorer (NICER): mission definition. Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray , year = 2014, editor =. doi:10.1117/12.2056811 , adsurl =

    doi:10.1117/12.2056811 2014

  31. [32]

    Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray , year = 2016, editor =

    The Neutron star Interior Composition Explorer (NICER): design and development. Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray , year = 2016, editor =. doi:10.1117/12.2231304 , adsurl =

    doi:10.1117/12.2231304 2016

  32. [33]

    Astroparticle Physics , keywords =

    Design, construction, and test of the Gas Pixel Detectors for the IXPE mission. Astroparticle Physics , keywords =. doi:10.1016/j.astropartphys.2021.102628 , archivePrefix =. 2107.05496 , primaryClass =

    arXiv 2021

  33. [34]

    Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray , year = 2022, editor =

    In-orbit monitoring of the imaging x-ray polarimeters on-board IXPE. Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray , year = 2022, editor =. doi:10.1117/12.2629413 , adsurl =

    work page doi:10.1117/12.2629413 2022

  34. [35]

    Astronomical Data Analysis Software and Systems V, A.S.P

    XSPEC: The First Ten Years , author=. Astronomical Data Analysis Software and Systems V, A.S.P. Conference Series , year=

  35. [36]

    , keywords =

    On the Absorption of X-Rays in the Interstellar Medium. , keywords =. doi:10.1086/317016 , archivePrefix =. astro-ph/0008425 , primaryClass =

    Pith/arXiv arXiv

  36. [37]

    , keywords =

    The role of the reflection fraction in constraining black hole spin. , keywords =. doi:10.1093/mnrasl/slu125 , archivePrefix =. 1408.2347 , primaryClass =

    Pith/arXiv arXiv

  37. [38]

    Definition of the reflection fraction and its implementation in relxill

    Normalizing a relativistic model of X-ray reflection. Definition of the reflection fraction and its implementation in relxill. , keywords =. doi:10.1051/0004-6361/201628135 , archivePrefix =. 1601.03771 , primaryClass =

    Pith/arXiv arXiv

  38. [39]

    , keywords =

    Improved Reflection Models of Black Hole Accretion Disks: Treating the Angular Distribution of X-Rays. , keywords =. doi:10.1088/0004-637X/782/2/76 , archivePrefix =. 1312.3231 , primaryClass =

    Pith/arXiv arXiv

  39. [40]

    Science , keywords =

    Cygnus X-1 contains a 21-solar mass black hole Implications for massive star winds. Science , keywords =. doi:10.1126/science.abb3363 , archivePrefix =. 2102.09091 , primaryClass =

    arXiv

  40. [41]

    The hitchhiker's guide to the IXPE data analysis

    The hitchhiker's guide to the IXPE data analysis. arXiv e-prints , keywords =. doi:10.48550/arXiv.2604.03366 , archivePrefix =. 2604.03366 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.48550/arxiv.2604.03366

  41. [42]

    , year = 2026, month = jun, doi =

    High Polarization and Complex Accretion Wind Structure in 4U 1700-37. , year = 2026, month = jun, doi =

    2026

  42. [43]

    , keywords =

    Calibration of the IXPE Focal Plane X-Ray Polarimeters to Polarized Radiation. , keywords =. doi:10.3847/1538-3881/ac7719 , archivePrefix =. 2206.07582 , primaryClass =

    Pith/arXiv arXiv

  43. [44]

    , keywords =

    Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1. , keywords =. doi:10.3847/2041-8213/ad132d , archivePrefix =. 2311.06359 , primaryClass =

    Pith/arXiv arXiv 2041

  44. [45]

    Astronomische Nachrichten , keywords =

    Weakly Magnetized Accreting Neutron Stars as Seen by IXPE. Astronomische Nachrichten , keywords =. doi:10.1002/asna.20240126 , adsurl =

    doi:10.1002/asna.20240126

  45. [46]

    , keywords =

    The very high X-ray polarization of accreting black hole IGR J17091‑3624 in the hard state. , keywords =. doi:10.1093/mnras/staf859 , archivePrefix =. 2503.22665 , primaryClass =

    Pith/arXiv arXiv

  46. [47]

    , keywords =

    Detection of X-Ray Polarization in the Hard State of IGR J17091-3624: Spectropolarimetric Study with IXPE and NuSTAR Data. , keywords =. doi:10.3847/1538-4357/adf1e6 , archivePrefix =. 2504.16402 , primaryClass =

    Pith/arXiv arXiv

  47. [48]

    , keywords =

    The effect of returning radiation on relativistic reflection. , keywords =. doi:10.1093/mnras/stac1593 , archivePrefix =. 2206.07973 , primaryClass =

    Pith/arXiv arXiv

  48. [49]

    , keywords =

    Handling the Background in IXPE Polarimetric Data. , keywords =. doi:10.3847/1538-3881/acba0f , archivePrefix =. 2302.02927 , primaryClass =

    Pith/arXiv arXiv

  49. [50]

    , keywords =

    The Nuclear Spectroscopic Telescope Array (NuSTAR) High-energy X-Ray Mission. , keywords =. doi:10.1088/0004-637X/770/2/103 , archivePrefix =. 1301.7307 , primaryClass =

    Pith/arXiv arXiv

  50. [51]

    Astronomical Data Analysis Software and Systems XII , year = 2003, editor =

    New Features of SAOImage DS9. Astronomical Data Analysis Software and Systems XII , year = 2003, editor =

    2003

  51. [52]

    SoftwareX , keywords =

    ixpeobssim: A simulation and analysis framework for the imaging X-ray polarimetry explorer. SoftwareX , keywords =. doi:10.1016/j.softx.2022.101194 , archivePrefix =. 2203.06384 , primaryClass =

    arXiv 2022

  52. [53]

    , keywords =

    Optimal binning of X-ray spectra and response matrix design. , keywords =. doi:10.1051/0004-6361/201527395 , archivePrefix =. 1601.05309 , primaryClass =

    Pith/arXiv arXiv

  53. [54]

    , keywords =

    X-ray polarization changes with the state transition in Cygnus X-1. , keywords =. doi:10.1093/mnras/stad3961 , archivePrefix =. 2307.14604 , primaryClass =

    Pith/arXiv arXiv

  54. [55]

    , keywords =

    A Weighted Analysis to Improve the X-Ray Polarization Sensitivity of the Imaging X-ray Polarimetry Explorer. , keywords =. doi:10.3847/1538-3881/ac51c9 , archivePrefix =. 2202.01093 , primaryClass =

    Pith/arXiv arXiv

  55. [56]

    Astronomical Data Analysis Software and Systems V , year = 1996, editor =

    XSPEC: The First Ten Years. Astronomical Data Analysis Software and Systems V , year = 1996, editor =

    1996

  56. [57]

    , keywords =

    The orbital period of HDE 226868/Cyg X-1. , keywords =. doi:10.1046/j.1365-8711.1998.02064.x , archivePrefix =. astro-ph/9812101 , primaryClass =

    arXiv 1998

  57. [58]

    , keywords =

    X-ray spectropolarimetric characterization of GX 340+0 in the horizontal branch: A highly inclined source?. , keywords =. doi:10.1051/0004-6361/202451966 , archivePrefix =. 2410.00972 , primaryClass =

    Pith/arXiv arXiv

  58. [59]

    \ in press , keywords =

    X-ray spectropolarimetric characterization of the Z-source GX 340+0 in the normal branch. \ in press , keywords =. doi:https://doi.org/10.1051/0004-6361/202555134 , archivePrefix =. 2508.13278 , primaryClass =

    arXiv

  59. [60]

    , keywords =

    IXPE view of the Sco-like source GX 349+2 in the normal branch. , keywords =. doi:10.1051/0004-6361/202555647 , archivePrefix =. 2507.07163 , primaryClass =

    arXiv

  60. [61]

    , keywords =

    Polarization of X-ray emission from the Sgr B2 cloud. , keywords =. doi:10.1046/j.1365-8711.2002.05113.x , archivePrefix =. astro-ph/0111065 , primaryClass =

    arXiv 2002

  61. [62]

    Nature Astronomy , keywords =

    Cygnus X-3 revealed as a Galactic ultraluminous X-ray source by IXPE. Nature Astronomy , keywords =. doi:10.1038/s41550-024-02294-9 , archivePrefix =. 2303.01174 , primaryClass =

    Pith/arXiv arXiv

  62. [63]

    , keywords =

    Comptonization of low-frequency radiation in accretion disks Angular distribution and polarization of hard radiation. , keywords =

  63. [64]

    , keywords =

    X-Ray Polarized View of the Accretion Geometry in the X-Ray Binary Circinus X-1. , keywords =. doi:10.3847/2041-8213/ad1832 , archivePrefix =. 2311.04632 , primaryClass =

    Pith/arXiv arXiv 2041

  64. [65]

    Galaxies , keywords =

    IXPE View of BH XRBs during the First 2.5 Years of the Mission. Galaxies , keywords =. doi:10.3390/galaxies12050054 , adsurl =

    work page doi:10.3390/galaxies12050054