Exploring the Accretion Disk/Corona Connection in NGC 6814: Insights from UV and X-Ray Spectral-timing Studies
We conducted a comprehensive spectral and timing analysis of NGC 6814 using AstroSat’s 2019 and XMM-Newton’s 2021 observations. A cross-correlation analysis revealed a significant correlation between far-UV (1541 Å)/X-ray and UVW1 (2910 Å)/X-ray variations, with delays of ∼15 ks and 30 ks, respectiv...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ade05c |
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| Summary: | We conducted a comprehensive spectral and timing analysis of NGC 6814 using AstroSat’s 2019 and XMM-Newton’s 2021 observations. A cross-correlation analysis revealed a significant correlation between far-UV (1541 Å)/X-ray and UVW1 (2910 Å)/X-ray variations, with delays of ∼15 ks and 30 ks, respectively. We constructed four broadband spectral energy distributions (SEDs) after applying aperture correction (for the Ultra-Violet Imaging Telescope filter), subtracting host galaxy and emission-line contributions from UV flux, and using mean X-ray spectra alongside selected UV data points. First, we fitted the SEDs with the kynsed model, assuming various combinations of inclination θ , color correction factors f _col , and black hole spins. Best-fit models were achieved for θ = 70° (consistent with past estimates for this source) and for spin ≤0.5, while f _col is not constrained. kynsed provided a satisfactory fit to all SEDs in the case when the corona is powered by the accretion process, with ∼10%–20% of the accretion power transferred to the corona, $\dot{m}/{\dot{m}}_{{\rm{Edd}}}\sim 0.1$ , a corona radius of ∼6–10 r _g , and a height of ∼7.5–35 r _g . Model time lags computed using the SED best-fit results are aligned well with the observed time lags. Although some of the model parameters are not constrained, the important result of our work is that both the broadband X-ray/UV spectra and the X-ray/UV time lags in NGC 6814 are consistent with the hypothesis of X-ray illumination of the disk in a lamp-post geometry framework. Within this model framework, we do not need to assume an outer or inner truncated disk. |
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| ISSN: | 1538-4357 |