Results from an extensive simultaneous broadband campaign on the underluminous active nucleus M81*: further evidence for mass-scaling accretion in black holes

TL;DR

This study presents a comprehensive broadband observational campaign on the low-luminosity active galactic nucleus M81*, revealing spectral variability and supporting the idea that accretion physics scales predictably across black hole masses.

Contribution

It provides the first long-term, high-resolution spectral campaign on M81* and demonstrates that accretion models for X-ray binaries also apply to supermassive black holes.

Findings

Spectral variability observed over short and long timescales.

The same accretion model for X-ray binaries applies to M81*.

Spectral data supports mass-scaling of black hole accretion physics.

Abstract

We present the results of a broadband simultaneous campaign on the nearby low-luminosity active galactic nucleus M81*. From February through August 2005, we observed M81* five times using the Chandra X-ray Observatory with the High-Energy Transmission Grating Spectrometer, complemented by ground-based observations with the Giant Meterwave Radio Telescope, the Very Large Array and Very Large Baseline Array, the Plateau de Bure Interferometer at IRAM, the Submillimeter Array and Lick Observatory. We discuss how the resulting spectra vary over short and longer timescales compared to previous results, especially in the X-rays where this is the first ever longer-term campaign at spatial resolution high enough to nearly isolate the nucleus (17pc). We compare the spectrum to our Galactic center weakly active nucleus Sgr A*, which has undergone similar campaigns, as well as to weakly accreting X-ray binaries in the context of outflow-dominated models. In agreement with recent results suggesting that the physics of weakly-accreting black holes scales predictably with mass, we find that the exact same model which successfully describes hard state X-ray binaries applies to M81*, with very similar physical parameters.