HALO I. Photometric continuum reverberation mapping of Fairall 9

Résumé fourni par la source

Context. We investigate the origin of inter-band continuum time delays in active galactic nuclei (AGNs) in order to study the structureand properties of their accretion disks.Aims. We aim to measure the inter-band continuum time delays through photometric monitoring of Seyfert galaxy Fairall 9 to constructthe lag-spectrum. Additionally, we explain the observed features in the Fairall 9 lag-spectrum and discuss the potential drivers behindthem based on our newly collected data from the Obserwatorium Cerro Murphy (OCM) telescope.Methods. We initiated a long-term, continuous AGN photometric monitoring program in 2024 titled Hubble constant constraintsthrough AGN Light curve Observations (HALO) using intermediate and broadband filters. Here, we present the first results fromHALO, focusing on photometric light curves and continuum time-delay measurements for Fairall 9. To complement these observationsand extend the wavelength coverage of the lag-spectrum, we also reanalyzed archival Swift light curves and spectroscopic dataavailable in the literature.Results. Using HALO and Swift light curves, we measured inter-band continuum delays to construct the lag-spectrum of Fairall 9.Excess lags appear in the u and U bands (Balmer continuum contamination) and in the I band (Paschen jump and dust emission fromthe torus). Overall, the lag-spectrum deviates significantly from standard disk model predictions.Conclusions. We find that inter-band delays deviate from the power law, τλ ∝ λβ, due to broad-line region scattering, reprocessing,and dust contributions at longer wavelengths. Power-law fits are therefore not well suited to characterizing the nature of the timedelays. The figure enclosed in the lightcurve obtained from our monitoring. Specifically, Light curves from OCM monitoring and lag analysis. Left: Light curves of Fairall~9 in the $u_s$, $v_s$, $b_s$, $y_s$, and $I_c$ filters, shown from top to bottom, respectively. In each panel, the dashed lines in various colors indicate second-order polynomial detrending, while the solid lines represent the best-fit light curves obtained from {\tt PyROA}. The full light curve is divided into two segments, S1 and S2, separated by an observational gap indicated by the vertical dashed orange line. Right: Distribution of the cross-correlation coefficient relative to the $u_s$ band (solid black line) derived using the ICCF method for the full, non-detrended original light curve. The blue histogram shows the cross-correlation centroid distribution from ICCF, the red histogram represents the lag probability distribution obtained from {\tt PyROA}, {\bf \color{magenta} and the green histogram shows the corresponding distribution from {\tt JAVELIN}.} A vertical dashed gray line marks the reference point at $\tau$ = 0 days. The enclosed table gives the measured time delays under different assumptions. about the part of the data used, and the applied detrending.

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