AGN STORM 2. I. First results: A Change in the Weather of Mrk 817

Abstract

We present the first results from the ongoing, intensive, multiwavelength monitoring program of the luminous Seyfert 1 galaxy Mrk 817. While this active galactic nucleus was, in part, selected for its historically unobscured nature, we discovered that the X-ray spectrum is highly absorbed, and there are new blueshifted, broad, and narrow UV absorption lines, which suggest that a dust-free, ionized obscurer located at the inner broad-line region partially covers the central source. Despite the obscuration, we measure UV and optical continuum reverberation lags consistent with a centrally illuminated Shakura–Sunyaev thin accretion disk, and measure reverberation lags associated with the optical broad-line region, as expected. However, in the first 55 days of the campaign, when the obscuration was becoming most extreme, we observe a de-coupling of the UV continuum and the UV broad emission-line variability. The correlation recovered in the next 42 days of the campaign, as Mrk 817 entered a less obscured state. The short C iv and Lyα lags suggest that the accretion disk extends beyond the UV broad-line region.

CARAMEL-gas: A Step toward Fast Empirical Models of the Broad-line-emitting Gas

“…These modifications lay the groundwork for future model development, such as the implementation of more complex emissivity laws. This is a first step toward simultaneous modeling of multiple emission lines for which data have recently become available (see, for example, the multiline data sets for NGC 5548 and Mrk 817, De Rosa et al 2015;Kara et al 2021).…”

“…By introducing physics to describe the reprocessing of energy, we can ensure that the models are capable of producing the observed flux in the emission lines. Second, as more high-quality data sets come out covering multiple emission lines (e.g., NGC 5548 and Mrk 817;De Rosa et al 2015;Kara et al 2021), we have the opportunity improve BLR parameter measurements by fitting more than one emission line at once.…”

The Lick AGN Monitoring Project 2016: Dynamical Modeling of Velocity-resolved Hβ Lags in Luminous Seyfert Galaxies

“…Modeling data from the AGNSTORM campaign yields the same black hole mass but different geometry of the BLR. This is not surprising, as different aspects of the BLR (luminosity and average size, for example) are known to vary over timescales of a few years (see, e.g., De Rosa et al 2015;Pancoast et al 2018;Kara et al 2021). It is thus interesting to include the results of both campaigns in our analysis.…”

“…With our combined sample, we do not find any significant luminositydependent trends; we do not find higher accretion rates to correlate with BLR outflow behavior and come to the same conclusion as Du et al (2015), that AGNs have diverse BLR geometry and kinematics. A possible interpretation of this diversity is that BLR geometry and kinematics experience weather-like changes and cycle through a range of states on timescales of order a year or less (see, e.g., De Rosa et al 2015;Pancoast et al 2018;Kara et al 2021).…”

Using AGN lightcurves to map accretion disc temperature fluctuations

“…A good next target for our studies is Mrk 817 using data similar to that of NGC 5548 being obtained as part of AGN STORM 2 (Kara et al 2021). While it is not feasible to obtain lightcurves further into the UV than the Lyman limit, near-IR data would significantly extend the coverage to larger radii in future programs.…”