[Paper Review] Discovery of the Onset of Rapid Accretion by a Dormant Massive Black Hole

D. N. Burrows, F. E. Marshall+54 more|Apr 25, 2011

Astrophysics and Cosmic Phenomena45 references246 citations

TL;DR

This paper reports the first detection of the onset of a relativistic jet from a dormant massive black hole, identified in the X-ray transient Swift J1644+57, which likely resulted from the tidal disruption of a star. The event exhibits extreme luminosity, rapid variability, and a magnetically dominated jet with Lorentz factor Γ ≲ 20, providing direct evidence for jet formation during super-Eddington accretion in a previously quiescent black hole system.

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.

Motivation & Objective

• To identify the origin of the extragalactic transient Swift J1644+57, observed as a bright, variable X-ray and gamma-ray source.
• To determine whether the transient arises from tidal disruption of a star or from the onset of active galactic nucleus (AGN) activity in a dormant black hole.
• To constrain the physical properties of the jet, including its Lorentz factor, energy budget, and emission mechanisms.
• To estimate the all-sky rate of such events and compare with theoretical models of tidal disruption and AGN onset.
• To assess the potential impact of such an event on Earth if it occurred in the Milky Way's central black hole Sgr A*.

Proposed method

• Utilized multi-wavelength observations from Swift BAT, XRT, and EVLA to localize and track the X-ray and radio variability of Sw J1644+57.
• Analyzed X-ray spectral energy distributions across flux states, fitting with power laws and more complex models including synchrotron and inverse Compton emission components.
• Applied constraints from Fermi and VERITAS gamma-ray upper limits to infer the bulk Lorentz factor (Γ ≲ 20) via γ-γ absorption in the jet.
• Modeled the jet as magnetically dominated and particle-starved, consistent with minimal optical emission and high efficiency in converting accretion energy to relativistic outflow.
• Estimated the all-sky event rate using redshift-limited volume and galaxy density, comparing observed rate (R₄ₚ ≈ 1 yr⁻¹) with theoretical predictions for tidal disruption (10⁴ yr⁻¹) and AGN onset (3 yr⁻¹).
• Evaluated the probability of such an event being beamed toward Earth, particularly in the context of Sgr A* in the Milky Way.

Experimental results

Research questions

• RQ1 What caused the sudden onset of a relativistic jet in the previously dormant massive black hole in Sw J1644+57?
• RQ2 Is the observed emission consistent with a tidal disruption event or the onset of AGN activity in a quiescent black hole?
• RQ3 What are the physical properties of the jet, including its Lorentz factor, energy budget, and emission mechanism?
• RQ4 How does the observed event rate compare with theoretical predictions for tidal disruption and AGN onset?
• RQ5 What would be the atmospheric and environmental impact on Earth if a similar jet were produced by Sgr A* and beamed toward us?

Key findings

• The transient Sw J1644+57 was first detected by Swift BAT on 25 March 2011, with a peak flux of ~0.09 cts cm⁻² s⁻¹, and triggered on 28 March 2011.
• The X-ray flux decayed from ~5×10⁻⁹ erg cm⁻² s⁻¹ to ~1.5×10⁻¹⁰ erg cm⁻² s⁻¹ over two weeks, with sharp dips to <3×10⁻¹¹ erg cm⁻² s⁻¹.
• The X-ray spectrum evolved from a power law with photon index Γ ≈ 1.3–1.8, indicating a hard spectrum consistent with relativistic jet emission.
• The jet is magnetically dominated and particle-starved, as indicated by the lack of significant optical emission and the requirement for low electron density.
• The bulk Lorentz factor is constrained to Γ ≲ 20 (assumed ≈10) due to γ-γ absorption in the jet, based on Fermi and VERITAS upper limits.
• The all-sky rate of such events is estimated at R₄ₚ ≈ 1 yr⁻¹ (90% CI: 0.08–3.9 yr⁻¹), consistent with theoretical models of jet formation during tidal disruption or AGN onset.