Disk-Corona Energy Balance Evolves with Flux State in the Quasar PDS 456
Abstract
We investigate the long-term X-ray spectral evolution of the highly luminous, radio-quiet quasar PDS 456 using AstroSat observations obtained in 2019 and 2021 together with archival XMM-Newton, NuSTAR and Suzaku observations spanning 2001-2024. The AstroSat observations provide valuable coverage following the bright flaring state observed in 2018, revealing that the source underwent a relatively quiescent phase in 2019 before re-brightening in 2021. During the AstroSat epochs, PDS 456 exhibits a harder-when-brighter spectral trend, whereas the long-term XMM-Newton, NuSTAR, and Suzaku observations confirm the overall softer-when-fainter behavior. This behavior is consistent with the presence of a very cool corona (~15 keV), possibly driven by a strong incident photon field for upscattering, as suggested by a prominent big blue bump. Broadband spectral modeling of simultaneous XMM-Newton and NuSTAR observations, complemented by the 2021 AstroSat flaring epoch and interpreted within the self-consistent physical framework reXcor, indicates that the disk-corona energy balance evolves with flux. In low-flux states, the spectrum is reflection-dominated, implying efficient illumination of the inner accretion disk by a compact corona. In contrast, high-flux states show an enhanced contribution from the warm Comptonizing region at larger coronal heights. The Fe Kα emission line displays a positive correlation with the 2-10 keV continuum flux at low to intermediate flux levels, while deviations at the highest flux states suggest a reduced relative reflection contribution as the warm corona becomes energetically dominant.
Related
- MAXI J1820+070: A rapidly rotating black hole with a mildly truncated disk and warm corona layers in the soft state
- Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. VII. Testing Disk–Corona Diagnostics with eROSITA
- Mapping the Contracting Corona in GS 1354-64 with Insight-HXMT and XRISM: Evolving X-ray Lags and Quenched Reflection across a Complete State Transition
- Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. VII. Testing Disk-Corona Diagnostics with eROSITA
- Gen-EBM: An energy balance model for terrestrial planets. Climate multistability from snowball to post-runaway greenhouse climates
BibTeX
@misc{s2026diskcorona,
title = {{Disk-Corona Energy Balance Evolves with Flux State in the Quasar PDS 456}},
author = {Fida Fathima S S and Arijit Sar and Tathagata Saha and Ritaban Chatterjee},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.41509},
eprint = {2610.41509},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.41509},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Disk-Corona Energy Balance Evolves with Flux State in the Quasar PDS 456
AU - Fida Fathima S S
AU - Arijit Sar
AU - Tathagata Saha
AU - Ritaban Chatterjee
PY - 2026
DA - 2026/10/30
PB - arXiv
DO - 10.48550/arxiv.2610.41509
UR - https://arxiv.org/abs/2610.41509
AB - We investigate the long-term X-ray spectral evolution of the highly luminous, radio-quiet quasar PDS 456 using AstroSat observations obtained in 2019 and 2021 together with archival XMM-Newton, NuSTAR and Suzaku observations spanning 2001-2024. The AstroSat observations provide valuable coverage following the bright flaring state observed in 2018, revealing that the source underwent a relatively quiescent phase in 2019 before re-brightening in 2021. During the AstroSat epochs, PDS 456 exhibits a harder-when-brighter spectral trend, whereas the long-term XMM-Newton, NuSTAR, and Suzaku observations confirm the overall softer-when-fainter behavior. This behavior is consistent with the presence of a very cool corona (~15 keV), possibly driven by a strong incident photon field for upscattering, as suggested by a prominent big blue bump. Broadband spectral modeling of simultaneous XMM-Newton and NuSTAR observations, complemented by the 2021 AstroSat flaring epoch and interpreted within the self-consistent physical framework reXcor, indicates that the disk-corona energy balance evolves with flux. In low-flux states, the spectrum is reflection-dominated, implying efficient illumination of the inner accretion disk by a compact corona. In contrast, high-flux states show an enhanced contribution from the warm Comptonizing region at larger coronal heights. The Fe Kα emission line displays a positive correlation with the 2-10 keV continuum flux at low to intermediate flux levels, while deviations at the highest flux states suggest a reduced relative reflection contribution as the warm corona becomes energetically dominant.
ER -