Doppler disc tomography applied to low mass AGN spin

TL;DR

This paper demonstrates the application of Doppler tomography to measure the spin of a low mass AGN, RX J1301.9+2747, revealing a very low spin and providing insights into SMBH growth mechanisms.

Contribution

It introduces a novel application of Doppler tomography for spin measurement in low mass AGN, using phase-resolved spectra during flares.

Findings

Measured very low spin for RX J1301.9+2747

First spin measurement of a low mass AGN using this technique

Supports chaotic accretion model for SMBH growth

Abstract

Doppler tomography can provide a powerful means of determining black hole spin when our view to the central regions are revealed and obscured by optically thick orbiting material, and can provide an independent estimate that does not suffer as many degeneracies as traditional methods. For low mass AGN, time-dependent obscuration is expected to leave a signature in the changing spectrum of the disc emission which extends into the soft X-ray bandpass. We create a spectral model incorporating Doppler tomography and apply it to the case of the low mass (8 $\times$ 10$^{5}$ M$_{\odot}$) AGN, RX J1301.9+2747 which shows unusual timing properties in the form of short-lived flares that we argue are best explained by the orbit of a window through an optically thick wind. Modelling the phase-resolved spectrum over the course of the highest data quality flare indicates a very low spin even when we relax our constraints. This is the lowest mass AGN for which a spin has been measured and the first via this technique. We note that, as the mass and spin are very low, this appears to favour supermassive black hole (SMBH) growth by chaotic rather than constant accretion.