Black hole spin measurements in LMC X-1 and Cyg X-1 are highly model-dependent
Fuente:
arXiv
Guardado en:
| Autores principales: | , , , , , , |
|---|---|
| Formato: | Preprint |
| Publicado: |
2023
|
| Materias: | |
| Acceso en línea: | |
| Etiquetas: |
Agregar Etiqueta
Sin Etiquetas, Sea el primero en etiquetar este registro!
|
| _version_ | 1866911743817547776 |
|---|---|
| author | Zdziarski, Andrzej A. Banerjee, Srimanta Chand, Swadesh Dewangan, Gulab Misra, Ranjeev Szanecki, Michal Niedzwiecki, Andrzej |
| author_facet | Zdziarski, Andrzej A. Banerjee, Srimanta Chand, Swadesh Dewangan, Gulab Misra, Ranjeev Szanecki, Michal Niedzwiecki, Andrzej |
| contents | 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, $a_*\gtrsim 0.9$ 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 $a_*\approx 0.64$--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 $χ^2$ yields then $a_*\approx 0.40^{+0.41}_{-0.32}$. 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 $a_*\approx 0.82^{+0.16}_{-0.74}$ 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2308_06167 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Black hole spin measurements in LMC X-1 and Cyg X-1 are highly model-dependent Zdziarski, Andrzej A. Banerjee, Srimanta Chand, Swadesh Dewangan, Gulab Misra, Ranjeev Szanecki, Michal Niedzwiecki, Andrzej High Energy Astrophysical Phenomena 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, $a_*\gtrsim 0.9$ 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 $a_*\approx 0.64$--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 $χ^2$ yields then $a_*\approx 0.40^{+0.41}_{-0.32}$. 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 $a_*\approx 0.82^{+0.16}_{-0.74}$ 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. |
| title | Black hole spin measurements in LMC X-1 and Cyg X-1 are highly model-dependent |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2308.06167 |