Black Hole Spin Measurements in LMC X-1 and Cyg X-1 Are Highly Model Dependent
The black hole spin parameter, a _* , was measured to be close to its maximum value of 1 in many accreting X-ray binaries. In particular, a _* ≳ 0.9 was found in a number of studies of LMC X-1. These measurements were claimed to take into account both statistical and systematic uncertainties. We per...
| Main Authors: | , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2024-01-01
|
| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ad1b60 |
| _version_ | 1797316447748227072 |
|---|---|
| author | Andrzej A. Zdziarski Srimanta Banerjee Swadesh Chand Gulab Dewangan Ranjeev Misra Michał Szanecki Andrzej Niedźwiecki |
| author_facet | Andrzej A. Zdziarski Srimanta Banerjee Swadesh Chand Gulab Dewangan Ranjeev Misra Michał Szanecki Andrzej Niedźwiecki |
| author_sort | Andrzej A. Zdziarski |
| collection | DOAJ |
| description | The black hole spin parameter, a _* , was measured to be close to its maximum value of 1 in many accreting X-ray binaries. In particular, a _* ≳ 0.9 was found in a number of studies of LMC X-1. These measurements were claimed to take into account both statistical and systematic uncertainties. We perform new measurements using a recent simultaneous observation by NICER and NuSTAR, providing a data set of high quality. We use the disk continuum method together with improved models for coronal Comptonization. With the standard relativistic disk model and optically thin Comptonization, we obtain values of a _* similar to those obtained before. We then consider modifications to the standard model. Using a color correction of 2, we find a _* ≈ 0.64–0.84. We then consider disks with dissipation in surface layers. To account for that, we assume the standard disk is covered by a warm and optically thick Comptonizing layer. Our model with the lowest χ ^2 then yields ${a}_{* }\approx {0.40}_{-0.32}^{+0.41}$ . In order to test the presence of such effects in other sources, we also study an X-ray observation of Cyg X-1 by Suzaku in the soft state. We confirm the previous findings of a _* > 0.99 using the standard model, but then we find a weakly constrained ${a}_{* }\approx {0.82}_{-0.74}^{+0.16}$ when including an optically thick Comptonizing layer. We conclude that determinations of the spin using the continuum method can be highly sensitive to the assumptions about the disk structure. |
| first_indexed | 2024-03-08T03:18:31Z |
| format | Article |
| id | doaj.art-434a11dfb814482db6daebc3008649b9 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-08T03:18:31Z |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-434a11dfb814482db6daebc3008649b92024-02-12T11:21:47ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-01962210110.3847/1538-4357/ad1b60Black Hole Spin Measurements in LMC X-1 and Cyg X-1 Are Highly Model DependentAndrzej A. Zdziarski0https://orcid.org/0000-0002-0333-2452Srimanta Banerjee1https://orcid.org/0000-0002-6051-6928Swadesh Chand2https://orcid.org/0000-0003-3499-9273Gulab Dewangan3https://orcid.org/0000-0003-1589-2075Ranjeev Misra4https://orcid.org/0000-0002-7609-2779Michał Szanecki5https://orcid.org/0000-0001-7606-5925Andrzej Niedźwiecki6https://orcid.org/0000-0002-8541-8849Nicolaus Copernicus Astronomical Center , Polish Academy of Sciences, Bartycka 18, PL-00-716 Warszawa, Poland ; aaz@camk.edu.plInter-University Center for Astronomy and Astrophysics , Pune 411007, IndiaInter-University Center for Astronomy and Astrophysics , Pune 411007, IndiaInter-University Center for Astronomy and Astrophysics , Pune 411007, IndiaInter-University Center for Astronomy and Astrophysics , Pune 411007, IndiaFaculty of Physics and Applied Informatics, Łódź University , Pomorska 149/153, PL-90-236 Łódź, PolandFaculty of Physics and Applied Informatics, Łódź University , Pomorska 149/153, PL-90-236 Łódź, PolandThe black hole spin parameter, a _* , was measured to be close to its maximum value of 1 in many accreting X-ray binaries. In particular, a _* ≳ 0.9 was found in a number of studies of LMC X-1. These measurements were claimed to take into account both statistical and systematic uncertainties. We perform new measurements using a recent simultaneous observation by NICER and NuSTAR, providing a data set of high quality. We use the disk continuum method together with improved models for coronal Comptonization. With the standard relativistic disk model and optically thin Comptonization, we obtain values of a _* similar to those obtained before. We then consider modifications to the standard model. Using a color correction of 2, we find a _* ≈ 0.64–0.84. We then consider disks with dissipation in surface layers. To account for that, we assume the standard disk is covered by a warm and optically thick Comptonizing layer. Our model with the lowest χ ^2 then yields ${a}_{* }\approx {0.40}_{-0.32}^{+0.41}$ . In order to test the presence of such effects in other sources, we also study an X-ray observation of Cyg X-1 by Suzaku in the soft state. We confirm the previous findings of a _* > 0.99 using the standard model, but then we find a weakly constrained ${a}_{* }\approx {0.82}_{-0.74}^{+0.16}$ when including an optically thick Comptonizing layer. We conclude that determinations of the spin using the continuum method can be highly sensitive to the assumptions about the disk structure.https://doi.org/10.3847/1538-4357/ad1b60X-ray binary starsX-ray sourcesAccretionBe starsAstrophysical black holesRotating black holes |
| spellingShingle | Andrzej A. Zdziarski Srimanta Banerjee Swadesh Chand Gulab Dewangan Ranjeev Misra Michał Szanecki Andrzej Niedźwiecki Black Hole Spin Measurements in LMC X-1 and Cyg X-1 Are Highly Model Dependent The Astrophysical Journal X-ray binary stars X-ray sources Accretion Be stars Astrophysical black holes Rotating black holes |
| title | Black Hole Spin Measurements in LMC X-1 and Cyg X-1 Are Highly Model Dependent |
| title_full | Black Hole Spin Measurements in LMC X-1 and Cyg X-1 Are Highly Model Dependent |
| title_fullStr | Black Hole Spin Measurements in LMC X-1 and Cyg X-1 Are Highly Model Dependent |
| title_full_unstemmed | Black Hole Spin Measurements in LMC X-1 and Cyg X-1 Are Highly Model Dependent |
| title_short | Black Hole Spin Measurements in LMC X-1 and Cyg X-1 Are Highly Model Dependent |
| title_sort | black hole spin measurements in lmc x 1 and cyg x 1 are highly model dependent |
| topic | X-ray binary stars X-ray sources Accretion Be stars Astrophysical black holes Rotating black holes |
| url | https://doi.org/10.3847/1538-4357/ad1b60 |
| work_keys_str_mv | AT andrzejazdziarski blackholespinmeasurementsinlmcx1andcygx1arehighlymodeldependent AT srimantabanerjee blackholespinmeasurementsinlmcx1andcygx1arehighlymodeldependent AT swadeshchand blackholespinmeasurementsinlmcx1andcygx1arehighlymodeldependent AT gulabdewangan blackholespinmeasurementsinlmcx1andcygx1arehighlymodeldependent AT ranjeevmisra blackholespinmeasurementsinlmcx1andcygx1arehighlymodeldependent AT michałszanecki blackholespinmeasurementsinlmcx1andcygx1arehighlymodeldependent AT andrzejniedzwiecki blackholespinmeasurementsinlmcx1andcygx1arehighlymodeldependent |