A high-density relativistic reflection origin for the soft and hard X-ray excess emission from Mrk 1044

Abstract

We present the first results from a detailed spectral-timing analysis of a long (∼130 ks) XMM-Newton observation and quasi-simultaneous NuSTAR and Swift observations of the highly accreting narrow-line Seyfert 1 galaxy Mrk 1044. The broad-band (0.3-50 keV) spectrum reveals the presence of a strong soft X-ray excess emission below ∼1.5 keV, iron K_α emission complex at ∼6-7 keV and a `Compton hump' at ∼15-30 keV. We find that the relativistic reflection from a high-density accretion disc with a broken power-law emissivity profile can simultaneously explain the soft X-ray excess, highly ionized broad iron line and the Compton hump. At low frequencies ([2 - 6] × 10^-5 Hz), the power-law continuum-dominated 1.5-5 keV band lags behind the reflection-dominated 0.3-1 keV band, which is explained with a combination of propagation fluctuation and Comptonization processes, while at higher frequencies ([1 - 2] × 10^-4Hz), we detect a soft lag which is interpreted as a signature of X-ray reverberation from the accretion disc. The fractional root-mean-squared variability of the source decreases with energy and is well described by two variable components: a less variable relativistic disc reflection and a more variable direct coronal emission. Our combined spectral-timing analyses suggest that the observed broad-band X-ray variability of Mrk 1044 is mainly driven by variations in the location or geometry of the optically thin, hot corona.