Discovery of soft and hard X-ray time lags in low-mass AGNs

Abstract

The scaling relations between the black hole (BH) mass and soft lag properties for both active galactic nuclei (AGNs) and BH X-ray binaries (BHXRBs) suggest the same underlying physical mechanism at work in accreting BH systems spanning a broad range of mass. However, the low-mass end of AGNs has never been explored in detail. In this work, we extend the existing scaling relations to lower-mass AGNs, which serve as anchors between the normal-mass AGNs and BHXRBs. For this purpose, we construct a sample of low-mass AGNs ($M_{\mathrm{BH}}<3\times 10^6{M}_{\odot }$) from the XMM-Newton archive and measure frequency-resolved time delays between the soft (0.3-1 keV) and hard (1-4 keV) X-ray emissions. We report that the soft band lags behind the hard band emission at high frequencies $\sim [1.3-2.6]\times 10^{-3}$ Hz, which is interpreted as a sign of reverberation from the inner accretion disc in response to the direct coronal emission. At low frequencies ($\sim [3-8]\times 10^{-4}$ Hz), the hard band lags behind the soft band variations, which we explain in the context of the inward propagation of luminosity fluctuations through the corona. Assuming a lamppost geometry for the corona, we find that the X-ray source of the sample extends at an average height and radius of $\sim 10r_{\mathrm{g}}$ and $\sim 6r_{\mathrm{g}}$, respectively. Our results confirm that the scaling relations between the BH mass and soft lag amplitude/frequency derived for higher-mass AGNs can safely extrapolate to lower-mass AGNs, and the accretion process is indeed independent of the BH mass.

11 pages, 5 figures, 4 tables, Published in MNRAS

References in corpus (9)

• Some Aspects of Measurement Error in Linear Regression of Astronomical Data
• X-ray reverberation around accreting black holes
• The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements
• A New Sample of Low-mass Black Holes in Active Galaxies
• The Comptonisation of accretion disc X-ray emission: Consequences for X-ray reflection and the geometry of AGN coronae
• Revealing structure and evolution within the corona of the Seyfert galaxy I Zw 1
• Examining the Physical Conditions of a Warm Corona in Active Galactic Nuclei Accretion Discs
• A Physical Model for the X-ray Time Lags of Narrow Line Seyfert Type 1 Active Galactic Nuclei
• The long term X-ray time-lags of NGC 4051

Cited by in corpus (3)

• High-density disc reflection spectroscopy of low-mass active galactic nuclei
• Wavelet spectral timing: X-ray reverberation from a dynamic black hole corona hidden beneath ultrafast outflows
• An Analytical Fourier-Transformation Model for the Production of Hard and Soft X-Ray Time Lags in AGNs: Application to 1H 0707-495