Evidence for variability timescale dependent UV/X-ray delay in Seyfert 1 AGN NGC 7469

Using a month-long X-ray lightcurve from ${it RXTE}$/PCA and 1.5 month long UV continuum lightcurves from ${it IUE}$ spectra in 1220$-$1970 $r{A}$, we performed a detailed time-lag study of the Seyfert 1 galaxy NGC 7469. Our cross-correlation analysis confirms previous results showing that the X-rays are delayed relative to the UV continuum at 1315 $r{A}$ by 3.49 $pm$ 0.22 days which is possibly caused by either propagating fluctuation or variable comptonisation. However, if variations slower than 5 days are removed from the X-ray lightcurve, the UV variations then lag behind the X-rays variations by 0.37$pm$0.14 day, consistent with reprocessing of the X-rays by a surrounding accretion disc. A very similar reverberation delay is observed between ${it Swift}$/XRT X-ray and ${it Swift}$/UVOT UVW2, U lightcurves. Continuum lightcurves extracted from the ${it Swift}$/GRISM spectra show delays with respect to X-rays consistent with reverberation. Separating the UV continuum variations faster and slower than 5 days, the slow variations at 1825 $r{A}$ lag those at 1315 $r{A}$ by $0.29pm0.06$ day, while the fast variations are coincident ($0.04pm0.12$ day). The UV/optical continuum reverberation lag from ${it IUE}$, ${it Swift}$ and other optical telescopes at different wavelengths are consistent with the relationship: $tau propto lambda^{4/3}$, predicted for the standard accretion disc theory while the best-fit X-ray delay from ${it RXTE}$ and ${it Swift}$/XRT shows a negative X-ray offset of $sim$0.38 days from the standard disc delay prediction.

AstroSat and Chandra view of the high soft state of 4U 1630-47 (4U 1630-472): evidence of the disk wind and a rapidly spinning black hole

We present the X-ray spectral and timing analysis of the transient black hole X-ray binary 4U 1630-47, observed with the AstroSat, Chandra and MAXI space missions during its soft X-ray outburst in 2016. The outburst, from the rising phase until the peak, is neither detected in hard X-rays (15-50 keV) by the Swift/BAT nor in radio. Such non-detection along with the source behavior in the hardness-intensity and color-color diagrams obtained using MAXI data confirm that both Chandra and AstroSat observations were performed during the high soft spectral state. The High Energy Grating (HEG) spectrum from the Chandra high-energy transmission grating spectrometer (HETGS) shows two strong, moderately blueshifted absorption lines at 6.705$_{-0.002}^{+0.002}$ keV and 6.974$_{-0.003}^{+0.004}$ keV, which are produced by Fe XXV and Fe XXVI in a low-velocity ionized disk wind. The corresponding outflow velocity is determined to be 366$pm$56 km/s. Separate spectral fits of Chandra/HEG, AstroSat/SXT+LAXPC and Chandra/HEG + AstroSat/SXT+LAXPC data show that the broadband continuum can be well described with a relativistic disk-blackbody model, with the disk flux fraction of $sim 0.97$. Based on the best-fit continuum spectral modeling of Chandra, AstroSat and Chandra+AstroSat joint spectra and using the Markov Chain Monte Carlo simulations, we constrain the spectral hardening factor at 1.56$^{+0.14}_{-0.06}$ and the dimensionless black hole spin parameter at 0.92 $pm$ 0.04 within the 99.7% confidence interval. Our conclusion of a rapidly-spinning black hole in 4U 1630-47 using the continuum spectrum method is in agreement with a previous finding applying the reflection spectral fitting method.