Scientists have tested the hypothesis of blazars as sources of high-energy neutrinos

Researchers from St Petersburg University, the Institute of Astrophysics (FORTH) and the University of Crete analyzed
data from the Fermi space gamma-ray observatory and the IceCube neutrino
observatory and confirmed the theoretically predicted possibility that the radial jet
structure of blazars contributes to the formation of neutrinos in them.

Massive black holes, whose mass exceeds millions of solar masses, are located at the
center of galaxies. Surrounding the black hole is a large amount of stars, gas, and
dust, which begin to «fall» into the black hole as they get closer to it. However, the
black hole cannot engulf all of this substance and ejects a portion of it in the form of
superluminal streams of plasma known as relativistic jets.

Blazars are a class of active galactic nuclei (AGN) where the jets are directed towards
Earth at an angle of no more than 15 degrees. These objects are the primary sources
of gamma-ray radiation in the Universe.

Gamma-ray light curves of blazars are well described by noise processes of different
types, but some objects exhibit periodic or quasi-periodic variations in their emissions. In this study, we investigated an another type of a regular behaviour called
«repeated patterns,» where the same pattern of multiple flares is repeated.

Previously, such behavior was observed in two objects: 3c454.3 and 3c279. Two
models have been proposed to explain this. In the first model, individual flares of the
pattern are caused by a moving emission feature passing through a system of conical
recollimation shocks. In the second model, it is assumed that the jet has a structure: a
fast spine and a slower sheath (see figure). In this case, a plasma blob, while moving
along the jet’s spine, passes through a system of ring-like condensations in the sheath
and scatters its low-energy photons, causing gamma-ray flares.

By systematically searching through data from the Fermi Large Area Telescope (LAT) for 15 years, scientists have found 10 objects with reprated patterns of gamma-ray emission among the hundred brightest objects. They concluded that a spine-sheath jet structure scenario applies to many of them.

Previously, theorists put forward a hypothesis according to which exactly such jets,
with a fast spine and a slow sheath, can produce cosmic particles with very low mass
– neutrinos. Repeated patterns of 5 blazars coincided in time and direction with the
registration of high-energy neutrinos detected at IceCube and Baikal-GVD. Using the
ICECAT-1 catalog of the IceCube neutrino observatory, it was possible to prove this
hypothesis with a significance level of 2.8σ.

The figure shows patterns in PKS 1424-41 (the arrow indicates the arrival time of the
«Big Bird» neutrino with an energy of 2 PeV, detected by IceCube):

The animation demonstrates how these patterns can be generated in the jet:

B2 1420+32 is in high optical and polarization state

Astronomer’s Telegram #14819

S. S. Savchenko, M. I. Chazov, A. E. Nazarova, E. V. Shishkina, E. G. Larionova

We perform optical photometric and polarimetric monitoring of a sample of gamma-bright blazars using 0.7-m AZT-8 telescope (Crimean Astrophysical Observatory), within the frames of GASP/WEBT project. We report that the blazar B21420+32 (z=0.681) is active in optical, reaching R=15.156 at JD=2459425.3107 with the degree of linear polarization of 33.5% (the previous night measurement was R=15.50 and polarization degree 27.5%). We plan to continue the monitoring of this object. The nightly updated light curve for this object can be found on our website.

The blazar PKS 1510-089 is in high optical state

Astronomer’s Telegram #14797

S. S. Savchenko, E. N. Kopatskaya, E. G. Larionova

We perform optical photometric and polarimetric monitoring of a sample of gamma-bright blazars using 0.7-m AZT-8 telescope (Crimean Astrophysical Observatory), within the frames of GASP/WEBT project. We report that the blazar PKS 1510-089 (z=0.36) is active in optical, reaching R=14.15 at JD=2459413.2689 with the degree of linear polarization of 25.0%. According to our data, this is the brightest state of this source since the middle of 2015. We plan to continue the monitoring of this object. The nightly updated light curve for this object can be found on our website.

Презентация о тени черной дыры в галактике M87

Старший научный сотрудник лаборатории наблюдательной астрофизики Светлана Георгиевна Эрштадт,участвующая в проекте EHT (Телескоп Горизонта Событий), 2 мая выступила с докладом на семинаре кафедры астрофизики СПбГУ. В докладе были представлены результаты первого в истории астрономии наблюдения тени от черной дыры в галактике M87.

Презентацию можно скачать здесь (230 Мб).

Ученые СПбГУ стали участниками международного проекта по получению первого изображения черной дыры

В середине апреля международная команда астрономов впервые обнародовала изображение черной дыры. Старший научный сотрудник лаборатории наблюдательной астрофизики СПбГУ Светлана Эрштадт, которая участвовала в этом проекте и непосредственно занималась получением изображения, рассказала о том, как ученым удалось добиться такого результата.