Assembling the pulsed puzzle of X-ray pulsars.
Final Report Abstract
We achieved all planned goals and more in context of the developement and verification of the PCVA method, and were able to apply the PCVA to analysis of Cen X-3 pulse profiles as observed by RXTE. Analysis of a larger sample of pulsars as originally planned was not possible both due to the determined limitations of the method in terms of required counting statistics (which turned to be more stringent than originally anticipated) and due to the incompatibility of the Kraus et al. (1996) results with the observed correlation properties of Cen X-3 discovered as part of the analysis. The latter result is important as it implies that we can not rely on symmetry-based decomposition results, i.e. it is not possible to combine PCVA and Kraus et al. approach to extend analysis to fainter sources or shorter time intervals (PCVA requires much higher count number for reliable reconstruction than Kraus et al. (1996) method) as originally planned. In addition, plans to analyze large sample of pulsars observed by Insight-HXMT and anticipated cooperation with IHEP were hindered by lockdowns in Germany and China. Similarly, the delays in the developement of theoretical models for emission regions of X-ray pulsars which were anticipated to become availabele before IXPE lunch, and thus accessible during the project period, and the unexpected results from IXPE observations of X-ray pulsars (2022) which made theoretical groups to reconsider their assumptions and further delayed theoretical advances in this direction also affected the project. As a result, significant time had to be spent on the developement of the simpler “toy” model describing Cen X-3 beam patterns in terms of simple components to facilitate interpretation of the PCVA results. The apparent inconsistency of the developed “toy” model with pulsar geometry derived by IXPE by Tsygankov et al. (2022) assuming the pulsars inclination estimate by Kraus et al. implies that either interpretation of the polarimetric data needs to be reconsidered, or the model needs to be improved. We emphasize that PCVA results themselves can be interpreted in framework of our toy model, however, the resulting geometry differs with respect to that derived by Kraus or Tsygankov based on symmetry considerations. Most likely the discrepancy can be at least partly attributed to the defficiencies of our “toy” model, which definitively needs to be improved in the future. We discuss some possibilities in this regard, but ultimately better self-consistent theoretical models taking into the account radiative transfer details in strong magnetic field are needed. The need of those is also apparent in light of the IXPE results of Doroshenko et al. (2022) and thus this avenue of research is currently pursued by several groups. Comparison of the results of this modeling together with the PCVA and polarimetric analysises for larger sample of XRPs in wider range of luminositeies are, in our opinion, the way forward to achieve better and more robust understanding of XRP emission mechanism. The code developed during the project has been made public so PCVA can be carried out also by other groups.
Publications
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Introducing a Novel Technique to Decompose X-ray Pulsar Profiles. In 31st Texas Symposium on Relativistic Astrophysics
Inga Saathoff
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Beam Pattern Evolution of Accreting X-Ray Pulsar 1A 0535+262 during Its 2020 Giant Outburst. The Astrophysical Journal, 945(2), 138.
Hu, Y. F.; Ji, L.; Yu, C.; Wang, P. J.; Doroshenko, V.; Santangelo, A.; Saathoff, I.; Zhang, S. N.; Zhang, S. & Kong, L. D.
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Understanding X-ray pulsars: from blind source separation to pulse profile decompositions. PhD thesis, Eberhard Karls Universität Tübingen
Saathoff, Inga
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Blind source separation for decomposing X-ray pulsar profiles. Astronomy & Astrophysics, 683, A52.
Saathoff, I.; Doroshenko, V. & Santangelo, A.
