Detection of X-ray/UV delay in NGC 4051 using AstroSat observations

Abstract

We study the connection between the variations in the far ultra-violet (FUV), near ultra-violet (NUV) and X-ray band emission from NGC 4051 using 4-days long AstroSat observations performed during 5-9 June 2016. NGC 4051 showed rapid variability in all three bands with the strongest variability amplitude in the X-ray band ($F_{var}\sim 37\%$) and much weaker variability in the UV bands ($F_{var}\sim 3-5\%$). Cross-correlation analysis performed using Interpolated cross-correlation Functions (ICCF) and Discrete cross-correlation Functions (DCF) revealed a robust correlation ($\sim 0.75$) between the UV and X-ray light curves. The variations in the X-ray band are found to lead those in the FUV and NUV bands by $\sim 7.4\mathrm{ks}$ and $\sim 24.2\mathrm{ks}$, respectively. The UV lags favour the thermal disc reprocessing model. The FUV and NUV bands are strongly correlated ($\sim 0.9$) and the variations in the FUV band lead those in the NUV band by $\sim 13\mathrm{ks}$. Comparison of the UV lags found using the AstroSat observations with those reported earlier and the theoretical model for thermal reverberation time-lag suggests a possible change in either the geometry of the accretion disc/corona or the height of the corona.

8 pages, 5 figures, Accepted for publication in MNRAS

References in corpus (15)

• The AGN Black Hole Mass Database
• Testing thermal reprocessing in AGN accretion discs
• Modeling the UV/optical continuum time-lags in AGN
• UV/optical disk thermal reverberation in AGN: an in-depth study with an analytic prescription for the time-lag spectra
• Evidence for variability timescale dependent UV/X-ray delay in Seyfert 1 AGN NGC 7469
• A hard look at thermal reverberation and optical/UV lags in NGC 5548
• X-ray and optical variability of Seyfert 1 galaxies as observed with XMM-Newton
• A combined timing/spectral study of IRAS 13224-3809 using XMM-Newton data
• Explaining the moderate UV/X-ray correlation in AGN
• Acceleration and cooling of the corona during X-ray flares from the Seyfert galaxy I Zw 1
• Contrasting X-ray/UV time-lags in Seyfert 1 galaxies NGC 4593 and NGC 7469 using AstroSat observations
• UV to X-ray Comptonization delay in Mrk 493
• Investigation of a small X-ray flaring event in NLS1 galaxy NGC 4051
• Revealing the intrinsic X-ray reverberation lags in IRAS 13224-3809 through the Granger causality test
• Coronal height constraint in IRAS 13224-3809 and 1H 0707-495 by the random forest regressor

Cited by in corpus (4)

• Broadband X-ray/UV/optical time-resolved spectroscopy of NGC 5548: The origin of the UV/optical variability in active galactic nuclei
• Continuum optical-UV and X-ray variability of AGN: current results and future challenges
• X-ray reverberation modelling of the continuum, optical/UV time-lags in quasars
• Extracting the X-ray reverberation response functions from the AGN light curves using an autoencoder