Discovery of the Onset of Rapid Accretion by a Dormant Massive Black Hole

Abstract: Massive black holes are believed to reside at the centres of most galaxies. They can be- come detectable by accretion of matter, either continuously from a large gas reservoir or impulsively from the tidal disruption of a passing star, and conversion of the gravitational energy of the infalling matter to light. Continuous accretion drives Active Galactic Nuclei (AGN), which are known to be variable but have never been observed to turn on or off. Tidal disruption of stars by dormant massive black holes has been inferred indirectly but the on- set of a tidal disruption event has never been observed. Here we report the first discovery of the onset of a relativistic accretion-powered jet in the new extragalactic transient, Swift J164449.3+573451. The behaviour of this new source differs from both theoretical models of tidal disruption events and observations of the jet-dominated AGN known as blazars. These differences may stem from transient effects associated with the onset of a powerful jet. Such an event in the massive black hole at the centre of our Milky Way galaxy could strongly ionize the upper atmosphere of the Earth, if beamed towards us.

• The paper reports the first detailed detection of rapid, relativistic accretion in Swift J1644+57, capturing a dormant black hole awakening with coordinated observations.
• The study employs X-ray, radio, and optical instruments to document strong variability and super-Eddington luminosity, supporting a magnetically dominated jet with a bulk Lorentz factor ≤20.
• The paper discusses how these observations challenge current black hole accretion models and suggest implications for future AGN activity and high-energy events in galactic centers.

Discovery of the Onset of Rapid Accretion by a Dormant Massive Black Hole

The paper Discovery of the Onset of Rapid Accretion by a Dormant Massive Black Hole addresses a significant astrophysical event related to massive black holes situated in galactic centers. The research highlights the discovery and observation of a new extragalactic transient, named Swift J164449.3+573451 (Sw J1644+57), indicating the onset of relativistic accretion-powered jet activity from a previously inactive black hole.

Major Observations and Methodology

Sw J1644+57 was initially detected on March 28, 2011, via the Burst Alert Telescope (BAT) aboard the Swift satellite. Coordinated observations followed using the X-Ray Telescope (XRT), optically localizing the source to the center of a galaxy. This transient location was confirmed through multiple instruments, including the EVLA for radio observations and ground-based telescopes for optical and NIR photometry, framing the discovery as a significant accretion event from a dormant black hole located at a redshift of 0.354.

The paper presents a comprehensive study involving multi-wavelength observations. It reports strong variability in X-ray emissions and discusses the lack of pre-outburst detections, confirming the source’s dormancy prior to the event. The X-ray spectra analysis revealed variations with flux and required absorption modeling to fit observed data, involving a host galaxy absorbing column quantified as ${\rm N_H} \sim 2 \times 10^{22}$~cm$^{-2}$.

Numerical Results and Theoretical Implications

Theoretical models proposed to explain the Sw J1644+57 outburst involve either the tidal disruption of a star or the initiation of AGN activity. The central engine’s observed super-Eddington luminosity supports the presence of a relativistic jet aimed toward Earth. The Eddington luminosity calculated for the black hole, estimated to fall within a mass range of $1 < M_6 < 20$ in terms of $10^6 M_\odot$, depicts a super-Eddington accretion scenario, highlighting the need for an anisotropic radiation pattern to explain the observed emissions.

The specific energy distribution suggests a magnetically dominated jet, supported by spectral energy distribution analysis and comparison with blazar jets typically aimed at Earth. Constraining parameters such as the bulk Lorentz factor, needed to remain within observational bounds, posits $\Gamma \lesssim 20$.

Discussion on Academic Contributions and Future Implications

The paper discusses potential future implications of similar relativistic outbursts occurring in galactic centers, including our own Milky Way, where such energetic processes could have pronounced effects on Earth’s atmosphere via ionizing radiation. The findings challenge current models of black hole accretion events and jet dynamics, offering new insights into the physics of AGN onset in dormant systems.

This work also indicates an evolution in understanding the frequency and observational signatures of similar events, challenging theoretical models with its rapid onset and unique energy output profiles. For future research, continuous long-term monitoring of Sw J1644+57 will be crucial to differentiate between the tidal disruption and AGN scenarios for the accretion process.

In summary, this research presents significant evidence of the dynamic nature and energetic processes associated with dormant massive black holes becoming active, providing key observations that will influence astrophysical theories and the understanding of black hole jet mechanics in extragalactic contexts.