Modulation of X-Ray Flux by Obscuration of Neutron Star Boundary Layer
The quasiperiodic oscillations (QPOs) observed in the X-ray variability of both black hole (BH) and neutron star (NS) systems provide a tool for probing strong gravity and dense matter equations of state. Nevertheless, the mechanism of QPO modulation in NS systems, where the amplitudes of QPOs with...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/adad71 |
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| author | G. Török K. Klimovičová D. Lančová M. Matuszková E. Šrámková M. Urbanec M. Čemeljić R. Šprňa V. Karas |
| author_facet | G. Török K. Klimovičová D. Lančová M. Matuszková E. Šrámková M. Urbanec M. Čemeljić R. Šprňa V. Karas |
| author_sort | G. Török |
| collection | DOAJ |
| description | The quasiperiodic oscillations (QPOs) observed in the X-ray variability of both black hole (BH) and neutron star (NS) systems provide a tool for probing strong gravity and dense matter equations of state. Nevertheless, the mechanism of QPO modulation in NS systems, where the amplitudes of QPOs with frequencies approaching the kHz range are very high in comparison to BH high-frequency QPOs, remains an unsolved puzzle. Relativistic ray tracing of photons emitted from the immediate vicinity of compact objects has, to date, been used to investigate various mechanisms that explain the observed weak BH QPOs. However, it has not been applied to model the NS QPO signal, which requires incorporating the NS surface and a bright boundary layer (BL) on it. Here, we explore the QPO modulation mechanisms based on the BL obscuration. Using simplified models of axisymmetric oscillations of thick accretion disks (tori), we demonstrate that the disk oscillations drive the high NS QPO amplitudes through BL obscuration, which is relevant, especially for vertical oscillations. We also demonstrate that obscuration effects enable the observability of the Keplerian frequency in the case of disks that decay due to instabilities. |
| format | Article |
| id | doaj-art-0534cce4835d4e249ae335b9305b0e70 |
| institution | DOAJ |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-0534cce4835d4e249ae335b9305b0e702025-08-20T03:01:15ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-0198111010.3847/1538-4357/adad71Modulation of X-Ray Flux by Obscuration of Neutron Star Boundary LayerG. Török0https://orcid.org/0000-0003-3958-9441K. Klimovičová1https://orcid.org/0000-0002-0930-0961D. Lančová2https://orcid.org/0000-0003-0826-9787M. Matuszková3https://orcid.org/0000-0002-4193-653XE. Šrámková4https://orcid.org/0000-0002-0733-5052M. Urbanec5https://orcid.org/0000-0001-9635-5495M. Čemeljić6https://orcid.org/0000-0002-3434-3621R. Šprňa7https://orcid.org/0000-0002-5085-9740V. Karas8https://orcid.org/0000-0002-5760-0459Research Center for Computational Physics and Data Processing, Institute of Physics, Silesian University in Opava , Bezručovo nám. 13, CZ-746-01 Opava, Czech RepublicResearch Center for Computational Physics and Data Processing, Institute of Physics, Silesian University in Opava , Bezručovo nám. 13, CZ-746-01 Opava, Czech RepublicResearch Center for Computational Physics and Data Processing, Institute of Physics, Silesian University in Opava , Bezručovo nám. 13, CZ-746-01 Opava, Czech Republic; Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences , Bartycka 18, 00-716 Warsaw, PolandResearch Center for Computational Physics and Data Processing, Institute of Physics, Silesian University in Opava , Bezručovo nám. 13, CZ-746-01 Opava, Czech RepublicResearch Center for Computational Physics and Data Processing, Institute of Physics, Silesian University in Opava , Bezručovo nám. 13, CZ-746-01 Opava, Czech RepublicResearch Center for Computational Physics and Data Processing, Institute of Physics, Silesian University in Opava , Bezručovo nám. 13, CZ-746-01 Opava, Czech RepublicResearch Center for Computational Physics and Data Processing, Institute of Physics, Silesian University in Opava , Bezručovo nám. 13, CZ-746-01 Opava, Czech Republic; Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences , Bartycka 18, 00-716 Warsaw, Poland; Nicolaus Copernicus Superior School, College of Astronomy and Natural Sciences , Gregorkiewicza 3, 87-100, Toruń, Poland; Academia Sinica, Institute of Astronomy and Astrophysics , P. O. Box 23-141, Taipei 106, TaiwanResearch Center for Computational Physics and Data Processing, Institute of Physics, Silesian University in Opava , Bezručovo nám. 13, CZ-746-01 Opava, Czech RepublicAstronomical Institute of the Czech Academy of Sciences , Boční II 1401, CZ-14100, Prague, Czech RepublicThe quasiperiodic oscillations (QPOs) observed in the X-ray variability of both black hole (BH) and neutron star (NS) systems provide a tool for probing strong gravity and dense matter equations of state. Nevertheless, the mechanism of QPO modulation in NS systems, where the amplitudes of QPOs with frequencies approaching the kHz range are very high in comparison to BH high-frequency QPOs, remains an unsolved puzzle. Relativistic ray tracing of photons emitted from the immediate vicinity of compact objects has, to date, been used to investigate various mechanisms that explain the observed weak BH QPOs. However, it has not been applied to model the NS QPO signal, which requires incorporating the NS surface and a bright boundary layer (BL) on it. Here, we explore the QPO modulation mechanisms based on the BL obscuration. Using simplified models of axisymmetric oscillations of thick accretion disks (tori), we demonstrate that the disk oscillations drive the high NS QPO amplitudes through BL obscuration, which is relevant, especially for vertical oscillations. We also demonstrate that obscuration effects enable the observability of the Keplerian frequency in the case of disks that decay due to instabilities.https://doi.org/10.3847/1538-4357/adad71Black holesNeutron starsX-ray binary stars |
| spellingShingle | G. Török K. Klimovičová D. Lančová M. Matuszková E. Šrámková M. Urbanec M. Čemeljić R. Šprňa V. Karas Modulation of X-Ray Flux by Obscuration of Neutron Star Boundary Layer The Astrophysical Journal Black holes Neutron stars X-ray binary stars |
| title | Modulation of X-Ray Flux by Obscuration of Neutron Star Boundary Layer |
| title_full | Modulation of X-Ray Flux by Obscuration of Neutron Star Boundary Layer |
| title_fullStr | Modulation of X-Ray Flux by Obscuration of Neutron Star Boundary Layer |
| title_full_unstemmed | Modulation of X-Ray Flux by Obscuration of Neutron Star Boundary Layer |
| title_short | Modulation of X-Ray Flux by Obscuration of Neutron Star Boundary Layer |
| title_sort | modulation of x ray flux by obscuration of neutron star boundary layer |
| topic | Black holes Neutron stars X-ray binary stars |
| url | https://doi.org/10.3847/1538-4357/adad71 |
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