Compton hump reverberation lag in the bright Seyfert 1 galaxy IC 4329A with NuSTAR

TL;DR

This study detects relativistic reverberation of the Compton reflection hump in IC 4329A using NuSTAR data, measuring black hole mass, coronal height, and temperature through timing and spectral analysis.

Contribution

It presents the first detection of the Compton hump reverberation lag in IC 4329A and combines timing and spectral modeling for comprehensive black hole and corona characterization.

Findings

Measured lag time of ~1825 s at low frequencies.

Estimated black hole mass of ~1.37×10^8 solar masses.

Constrained coronal temperature to ~50 keV.

Abstract

Recent reverberation delay measurements have moved beyond the 10 keV X-ray range, providing evidence for the Compton hump (a.k.a. reflection hump) in the lag spectra. We report the relativistic reverberation of the reflection hump in the bright Seyfert\,1 galaxy IC\,4329A based on a long {\it NuSTAR} observation. We find a delayed response of the 20--30 keV X-ray band, with a lag time of $\sim1825$ s at frequencies $0.5-1.5 \times 10^{-4}$ Hz. The lag amplitude drops to $\sim195$ s as the frequencies increase to $(1.5-10)\times10^{-4}$ Hz. Including IC\,4329A, so far five sources have been explored for reflection hump reverberation. We perform reverberation modelling of the 3--50 keV lag-energy spectra using the general relativistic transfer function code, which provides independent timing-based measurements of the black hole mass $M_{\rm BH}=1.37_{-0.36}^{+0.33}\times10^8~M_{\odot}$ and the coronal height $h=2.45_{-2.36}^{+1.92}~R_{\rm g}$ (with uncertainties at 90\% confidence). Within the uncertainties, the measured mass is found to be consistent with the previous finding. Furthermore, we undertake reflection spectroscopy to account for the hump feature and the associated relativistic effect using the time-averaged flux spectrum. Further sampling of the {\it NuSTAR} data (with a bin width of 0.2/0.4 keV below and above 10 keV) that reshapes the spectral resolution allows us to constrain the coronal temperature at $50.26_{-4.03}^{+5.58}$ keV -- consistent with the previous result from the combined {\it Suzaku} and {\it NuSTAR} data.