Rings of fire reveal secrets of a monster black hole
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Astronomers have found a complex pattern of flares in the gamma-ray emission of the blazar 3C 279 that repeated at least three times together with optical polarization rotations, a property of light which is studied extensively at the Institute of Astrophysics and Skinakas Observatory. This discovery has helped to resolve the puzzling nature of the high-energy emission from this source and reveals the internal structure of the releativistic jet. This new work is published in Monthly Notices of the Royal Astronomical Society.
Blazars are a peculiar type of Active Galactic Nuclei where a relativistic jet is pointed almost directly at us. Blazars are dominant sources in the gamma-ray sky, but how they produce this high energy emission is not completely clear.
The scientists analyzed publicly available data from NASA's Fermi gamma-ray space observatory, which observed one of the most active and luminous blazars: 3C 279. They obtained an 8 year long gamma-ray light curve of the blazar and compared it with polarization monitoring data collected with 12 optical telescopes distributed around the world. Typically gamma-ray curves of Acitve Galactic Nuclei behave randomly. In the case of 3C 279 it was found that the gamma-ray emission curve repeats the same pattern composed of multiple flares during or next to time intervals, where the optical polarization plane was rotating. Three such repeating patterns have been identified confidently.
Dr Dmitry Blinov at the Institute of Astrophysics, FORTH who led the new research, explains: "We were intentionally searching exactly for this behaviour, because it was predicted by one of the models explaining how polarization plane rotations occur in blazars."
The chance coincidence of the two triplets of events in the optical and gamma-ray bands is extremely small. Therefore, reasearchers conclude that they must be produced by the same physical mechanism in the jet. The best candidate for such mechanism is a propagation of a plasma blob through a fast spine of the jet surrounded by a cooler and slower sheath as proposed by Marscher et al. in earlier study.
"Enhancements in the photon field of the jet sheath have the potential to create 'rings of fire' through which relativistic electrons in the jet spine pass on their journey down the jet. This 'cosmic collision' of relativistic jet electrons and sheath photons can produce brilliant gamma-ray flares." clarified co-author Nicholas MacDonald from Max Planck Institute for Radio Astronomy.
This new study explains the mechanism behind optical polarization plane rotations exhibited by blazars that was perplexing astronomers for a decade and unabgiously relates high energy flares with such events. .
Scientific publication: Blinov et al. "Repeated pattern of gamma-ray flares in the lightcurve of the blazar 3C 279", 2021, MNRAS (in press)
Dmitry Blinov, Institute of Astrophysics, FORTH, Greece e-mail: firstname.lastname@example.org
Svetlana Jorstad, University of Boston Boston, USA, e-mail: email@example.com
Nicholas MacDonald, Max Planck Institute for Radio Astronomy Bonn, Germany, e-mail: firstname.lastname@example.org
Video illustrating the repeated pattern of gamma-ray flares and the proposed scenario explaining it. The first part shows a large region of the sky in gamma-rays as seen by the Fermi-LAT observatory. Most of the gamma-ray photon emitters away from the Galactic plane are blazars. A few of them along with 3C279 are indicated by annotations. The video then shows the artist's impression of the internal jet structure in 3C 279. The logarithmic length scale is used for demonstration of different AGN components. The transversal jet scale is different from the longitudinal. A helical magnetic field permeating the fast jet spine is surrounded by a set of quasi-stationary rings of cooler plasma within the sheath of the jet. Three plasma blobs with different velocities propagate through the fast jet spine and pass through the set of rings that provide seed photons for the External Compton emission excited in the plasmoid. This emission traces the density profile of the sheath and produces the set of flares that is demonstrated in the inlet graphs. The sound that accompanies the passage of plasmoids is produced using the same parts of the gamma-ray curve with Sonify (by Erin L. Braswell). Since the plasmoids propagate with different velocities, the pattern of flares is observed with different duration in observer's rest frame. The last part of the video demonstrates how after stretching and squeezing the time duration of the second and third flares they are perfectly matched with the first one.
Credit: SokolMedia & Dmitry Blinov
Licence type: Attribution (CC BY 4.0)