Assessing the Power-Law Emissivity Assumption in X-ray Reflection Spectroscopy: A Simulation-Based Evaluation of Different Coronal Geometries
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| Main Authors: | , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866918147897950208 |
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| author | Li, Songcheng Nosirov, Abdurakhmon Bambi, Cosimo Liu, Honghui Zhang, Zuobin Riaz, Shafqat |
| author_facet | Li, Songcheng Nosirov, Abdurakhmon Bambi, Cosimo Liu, Honghui Zhang, Zuobin Riaz, Shafqat |
| contents | The emissivity profile assumed in X-ray reflection spectroscopy significantly impacts black hole spin measurements. Using simulated NuSTAR spectra generated for lamppost and disk-like coronae with the relxill model suite, we evaluate systematic biases introduced when fitting with power-law or broken power-law emissivity profiles. We find that a simple power-law can accurately recover spins for low-height lamppost coronae with long exposures and low inclination angle, while broken power-laws introduce degeneracies when the simple power-law already performs adequately. However, for extended or high-height coronae, especially at high inclinations, both models produce large systematic biases unresolved by longer exposure times. Our results demonstrate that power-law approximations are reliable for compact coronae, highlighting the need for geometry-specific models in complex cases. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_20752 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Assessing the Power-Law Emissivity Assumption in X-ray Reflection Spectroscopy: A Simulation-Based Evaluation of Different Coronal Geometries Li, Songcheng Nosirov, Abdurakhmon Bambi, Cosimo Liu, Honghui Zhang, Zuobin Riaz, Shafqat High Energy Astrophysical Phenomena The emissivity profile assumed in X-ray reflection spectroscopy significantly impacts black hole spin measurements. Using simulated NuSTAR spectra generated for lamppost and disk-like coronae with the relxill model suite, we evaluate systematic biases introduced when fitting with power-law or broken power-law emissivity profiles. We find that a simple power-law can accurately recover spins for low-height lamppost coronae with long exposures and low inclination angle, while broken power-laws introduce degeneracies when the simple power-law already performs adequately. However, for extended or high-height coronae, especially at high inclinations, both models produce large systematic biases unresolved by longer exposure times. Our results demonstrate that power-law approximations are reliable for compact coronae, highlighting the need for geometry-specific models in complex cases. |
| title | Assessing the Power-Law Emissivity Assumption in X-ray Reflection Spectroscopy: A Simulation-Based Evaluation of Different Coronal Geometries |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2509.20752 |