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As has now been corrected, BBC has misunderstood term "Seyfert flare", instead calling it a "Sifter flare". A "Seyfert flare", is not really a common term, but the authors refer to an energetic outburst from the type of active galaxies called Seyfert galaxies (after Carl Seyfert). Like a quasar, a Seyfert galaxy is powered by gas accretion onto a central, ...


10

Neutrinos are typically produced in AGN jets through what we refer to as hadronic processes. Protons are accelerated to relativistic speeds and interact with nearby photons. Depending on the particular type of AGN, there are a number of possible sources of these photons: Ambient light within the jet Emission from the accretion disk Photons from the broad ...


3

A few sources come to mind to add to MAST and Sloan. Data releases from the SAMI Galaxy survey, which contain (or will eventually contain) emission line spectra for about 3500 galaxies. The papers for the first two releases can be found [here] and [here]. Another (smaller and older) dataset can be found at the Penn State Center for Astrophysics. It contains ...


3

Seyfert galaxies differ from other active galaxies (most notably quasars) in that their galactic nuclei are lower in luminosity compared to the rest of the galaxy. Quasars have nuclei that easily outshine the rest of the galaxy. Seyfert galaxies, on the other hand, host active nuclei that do not outshine the rest of the galaxy by the same amount. ...


3

Yes of course, there are other forms apart from the four stated above. Basically you have just two kinds: the radio-quiet, and the radio-loud. But then again, there are two Seyferts Seyfert I, and Seyfert II Apart from Quasar, Blazar and Radio galaxy, we also have presently, BL Lac (Named after its prototype BL Lacarte (original member of Blazar type)),...


2

The frequency is related to the redshift by $$\frac{\nu_{\rm obs}}{\nu_{\rm emit}} = \frac{1}{1+z}$$ Another useful relation is the fact that, for any redshift, $$\frac{I_{\nu}}{\nu^3} = {\rm constant}$$ where $I_{\nu}$ is the specific radiative intensity. The specific count rate (counts per area per time per energy interval) is proportional to $I_{\nu}/\...


2

Addressing (2) and (3) first: In a case like this, your best option is to go straight to the source. In this case, that would be Blandford & Znajek (1977), the originators of the proposed mechanism. they have several figures regarding different magnetospheric structures depending on different magnetic fields. However, the most important one is Figure 1, ...


2

Only a few percent of galaxies in the local universe have active galactic nuclei (e.g., Mishra & Dai 2020). The fraction with optically visible AGN (e.g., Seyfert nuclei) is lower than this, since in some galaxies only the X-ray or radio emission gets through the dust in the nuclear region of the galaxy. Even when the AGN is directly visible in optical ...


1

Active Galactic Nuclei (AGNs) are very luminous galactic nuclei. In Quasars, a type of an AGN, the nucleus outshines the host galaxy. Therefore the main source of radiation is the nucleus, not the stars and the host.


1

As Pela said in the comment, it is highly redshift dependent so there is no straight answer. "Some" is the safest option.


1

Answering the who is part of the question. Carl Seyfert (1911-1960) was a US astronomer. He is best known for his 1943 research paper on high-excitation line emission from the centers of some spiral galaxies, which are named Seyfert galaxies after him. Seyfert's Sextet, a group of galaxies, is also named after him.


1

pc is the abbreviation for parsec, a common unit of distance objects outside the Solar system. In order to compress the scales, they have also taken the logarithm (to base 10) of the distances in parsecs. So the scale in the figure on the x-axis in the radial (r) direction from the central black hole spans from 1e-5 to 100 parsecs. The z-axis, which is ...


1

There is total confusion in the answers you refer to. Quasars were first defined because of their star-like appearance - quasi-stellar objects or QSOs. The fact that they are Galaxy-sized objects with point-like appearances means they are very luminous, dominated by central nuclear emission and far away (as confirmd by their high redshifts). It was later ...


1

Blazar sequence Let's first look at which kind of sources are studied. Blazars are special type of radio-loud AGN. One of their special properties is that their spectral energy distributions (SED) form the so-called Blazar sequence. They all have a characteristic double peak SED and the position of the peaks mainly depend on their luminosity. The higher the ...


1

Metallicity and abundance Metallicity Without specifying a given metal, the term "metallicity" — abbreviated $Z$ — usually refers to the total metallicity of all elements, i.e. the mass fraction of all metals to the total mass of some ensemble of elements, e.g. a star, a cloud of gas, a galaxy, etc. (as usual, the term "metal" refers to all elements that ...


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