Long-term X-ray spectral analysis of Cygnus X-1 using AstroSat

Abstract

We performed a spectral analysis of long-term observations (2016-2019) of the black hole binary Cygnus X-1 using AstroSat, covering its hard, intermediate, and soft states. During soft states, we found that a typical spectrum fitted with a single Comptonization, a thermal disc, and an iron line yields poor fits and unphysically small disk radii (R_in < 1 R_g). While adding a relativistic disk component (kerrbb) improved the fit but required high color factors (f_col ~ 3.35-5.08), indicating additional Comptonization. We therefore adopted a dual-Comptonization model with hot (optically thin) and warm (optically thick) coronae. This provided consistent good fits across all soft and hard states of Cygnus X-1. The spectral evolution reveals the critical role of dual Comptonization in shaping the broadband emission of Cygnus X-1.

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BibTeX RIS

BibTeX

@misc{lalthantluanga2026longterm,
  title = {{Long-term X-ray spectral analysis of Cygnus X-1 using AstroSat}},
  author = {H Lalthantluanga and Akash Garg and Ranjeev Misra and Vanzarmawii Chhangte and Lalthakimi Zadeng},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.12072},
  eprint = {2609.12072},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.12072},
}

RIS

TY  - UNPB
TI  - Long-term X-ray spectral analysis of Cygnus X-1 using AstroSat
AU  - H Lalthantluanga
AU  - Akash Garg
AU  - Ranjeev Misra
AU  - Vanzarmawii Chhangte
AU  - Lalthakimi Zadeng
PY  - 2026
DA  - 2026/09/10
PB  - arXiv
DO  - 10.48550/arxiv.2609.12072
UR  - https://arxiv.org/abs/2609.12072
AB  - We performed a spectral analysis of long-term observations (2016-2019) of the black hole binary Cygnus X-1 using AstroSat, covering its hard, intermediate, and soft states. During soft states, we found that a typical spectrum fitted with a single Comptonization, a thermal disc, and an iron line yields poor fits and unphysically small disk radii (R_in < 1 R_g). While adding a relativistic disk component (kerrbb) improved the fit but required high color factors (f_col ~ 3.35-5.08), indicating additional Comptonization. We therefore adopted a dual-Comptonization model with hot (optically thin) and warm (optically thick) coronae. This provided consistent good fits across all soft and hard states of Cygnus X-1. The spectral evolution reveals the critical role of dual Comptonization in shaping the broadband emission of Cygnus X-1.
ER  -

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