Investigating the Anti-Correlation between Photon Index and Flux of the Crab using RXTE and NuSTAR

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Autori principali: Chatterjee, Debjit, Chang, Hsiang-Kuang, Debnath, Dipak, Augustine, Koothodil Abhijith, Lin, Tzu-Hsuan
Natura: Preprint
Pubblicazione: 2025
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author Chatterjee, Debjit
Chang, Hsiang-Kuang
Debnath, Dipak
Augustine, Koothodil Abhijith
Lin, Tzu-Hsuan
author_facet Chatterjee, Debjit
Chang, Hsiang-Kuang
Debnath, Dipak
Augustine, Koothodil Abhijith
Lin, Tzu-Hsuan
contents We present a systematic study of the recently reported anti-correlation between X-ray flux and photon index ($Γ$) in the Crab Nebula, using archival RXTE/PCA (3 - 50 keV), RXTE/HEXTE (20 - 100 keV), and NuSTAR (3 - 78 keV) observations. Spectra were extracted in soft (3 - 10 keV) and hard bands (10 - 50 keV, 10 - 78 keV, 20 - 100 keV) and fitted with an absorbed power-law model. Across all instruments and energy ranges, we confirm the existence of a persistent negative correlation -- harder spectra at higher flux levels. The correlation is stronger in the hard bands compared to the soft bands. This is consistent with synchrotron emission modulated by magnetic field variations in the pulsar wind nebula.
format Preprint
id arxiv_https___arxiv_org_abs_2506_17899
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Investigating the Anti-Correlation between Photon Index and Flux of the Crab using RXTE and NuSTAR
Chatterjee, Debjit
Chang, Hsiang-Kuang
Debnath, Dipak
Augustine, Koothodil Abhijith
Lin, Tzu-Hsuan
High Energy Astrophysical Phenomena
Astrophysics of Galaxies
We present a systematic study of the recently reported anti-correlation between X-ray flux and photon index ($Γ$) in the Crab Nebula, using archival RXTE/PCA (3 - 50 keV), RXTE/HEXTE (20 - 100 keV), and NuSTAR (3 - 78 keV) observations. Spectra were extracted in soft (3 - 10 keV) and hard bands (10 - 50 keV, 10 - 78 keV, 20 - 100 keV) and fitted with an absorbed power-law model. Across all instruments and energy ranges, we confirm the existence of a persistent negative correlation -- harder spectra at higher flux levels. The correlation is stronger in the hard bands compared to the soft bands. This is consistent with synchrotron emission modulated by magnetic field variations in the pulsar wind nebula.
title Investigating the Anti-Correlation between Photon Index and Flux of the Crab using RXTE and NuSTAR
topic High Energy Astrophysical Phenomena
Astrophysics of Galaxies
url https://arxiv.org/abs/2506.17899