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john hunter
2006-Oct-23, 03:21 PM
Is there any accurate data about any quasar radii?

By this I mean, not just order of magnitude, but to about 2 sig figs, for any quasars?

Thanks,

J. Hunter.

korjik
2006-Oct-23, 03:24 PM
I am prety sure you arent going to get any more accurate than order of magnitude. I think current thinking is a few ly or less. What exactly are you looking for?

Nereid
2006-Oct-23, 03:35 PM
Is there any accurate data about any quasar radii?

By this I mean, not just order of magnitude, but to about 2 sig figs, for any quasars?

Thanks,

J. Hunter.I guess it depends on what you mean by 'quasar radii'!

Quasars are, in the consensus view of astronomers today, active galaxy (or galactic) nuclei. Even in the 1960s and 1970s, some 'fuzz' was detected around some (low redshift) quasars; with Hubble, the host galaxy (the home in which quasars live) of many has now been resolved and imaged (an example (http://antwrp.gsfc.nasa.gov/apod/ap020309.html)).

The 'quasar' itself remains unresolved, so determining its components has meant a lot of detective work. Fortunately, there are several 'local' AGNs - the nuclei of Seyfert galaxies. A great deal of work has been done on these, because (among other things) if they are 'just the same as' quasars (only much wimpier), then a detailed study of the local objects will tell us a great deal about the quasars.

The unified model of AGNs (http://www.mssl.ucl.ac.uk/www_astro/agn/agn_unified.html) has quasars comprised of four major parts (http://www.mssl.ucl.ac.uk/www_astro/agn/agn_quasartour.html):
*black hole, accretion disk, and jets
*broad line region
*molecular torus
*narrow line region.

The first two have not yet been imaged (AFAIK), even in the nearest Seyfert, a situation unlikely to change in our lifetimes.

The molecular torus and narrow line region have been imaged, for some Seyferts, but not for any quasar.

Is it the radius of the accretion disk that you are interested in?

antoniseb
2006-Oct-23, 10:28 PM
The first two have not yet been imaged (AFAIK), even in the nearest Seyfert, a situation unlikely to change in our lifetimes.

My understanding is that The Einstein's Cross Quasar has had some interesting study done on it. Each of the four images of the quasar have microlening events as stars in the intervening galaxy pass in front of the luminous body. IIRC, the collection of many light curves has shown a luminous disk with a dim center. I do not have a handy reference to the papers about this (there are several), but they might give some of the sizes that Nereid references above.

Nereid
2006-Oct-24, 01:19 AM
My understanding is that The Einstein's Cross Quasar has had some interesting study done on it. Each of the four images of the quasar have microlening events as stars in the intervening galaxy pass in front of the luminous body. IIRC, the collection of many light curves has shown a luminous disk with a dim center. I do not have a handy reference to the papers about this (there are several), but they might give some of the sizes that Nereid references above.When you have a chance, if you could dig those up, I think many folk in BAUT would find them very interesting! :)

john hunter
2006-Oct-24, 10:18 AM
Dear Nereid,


I guess it depends on what you mean by 'quasar radii'!......
Is it the radius of the accretion disk that you are interested in?

It's the size of the part that has the highest luminosity, whether its a black hole and accretion disk, or not, is something that can be investigated... but to do so the radius of this type of region is important.

Apparently, the time variations of variable quasars have shown it might be of the order of 10^13m. Does anyone know of specific quasar examples where, from the time of the variations, the radius of the emitting region has been determined to within 2 sig figs?

Thanks,

John Hunter.

Nereid
2006-Oct-24, 10:42 AM
Dear Nereid,



It's the size of the part that has the highest luminosity, whether its a black hole and accretion disk, or not, is something that can be investigated... but to do so the radius of this type of region is important.

Apparently, the time variations of variable quasars have shown it might be of the order of 10^13m. Does anyone know of specific quasar examples where, from the time of the variations, the radius of the emitting region has been determined to within 2 sig figs?

Thanks,

John Hunter.I'm not sure that your question can be answered ...

Take "the part that has the highest luminosity": for BL Lac objects, which are quasars with their jets pointing directly at us, the jet vastly overwhelms all other parts; for type 2 quasars, which are quasars whose accretion disks are hidden* behind the molecular torus, because of the viewing geometry, the part with the highest luminosity may be the jet(s), or the broad line region.

Similarly with the part which gives rise to the observed variability - the accretion disk, the jets, and broad and narrow line regions all certainly vary in brightness. The regions (or parts) which vary on the shortest timescales are the accretion disk and jets.

Trying to determine a 'radius' for the accretion disk will depend on your definition of 'radius'. Think of a spiral galaxy, or a globular cluster, or the Beta Pictoris circumstellar disk (http://apod.nasa.gov/apod/ap960119.html), ... what are the radii of those objects?

And if you decide "the part that has the highest luminosity" is the jets, how do you decide what its 'radius' is?

*except, of course, in the gamma and hard x-ray bands; the torun is essentially transparent at these wavelengths

john hunter
2006-Oct-25, 09:11 AM
Dear Nereid,

Ok, Let's assume that there is an accretion disk, are there any specific examples of quasars where the radius of the accretion disk is known quite accurately? For definition of radius, let's use the distance for the luminosity to go to half its peak value.

For jets, the definition of radius, is the radius of the thing that is emitting the jet, again from maximum, to half its peak value.

John Hunter.

StupendousMan
2006-Oct-25, 01:13 PM
Ok, Let's assume that there is an accretion disk, are there any specific examples of quasars where the radius of the accretion disk is known quite accurately? For definition of radius, let's use the distance for the luminosity to go to half its peak value.

For jets, the definition of radius, is the radius of the thing that is emitting the jet, again from maximum, to half its peak value.


Go to the Astrophysics Data Service site:

http://adsabs.harvard.edu/abstract_service.html

Into the "Abstract words" box, enter the search words

quasar radius accretion disk

and press "Submit". You will see a list of the first 100
papers which have these words in their abstracts
(out of 135,000 or so papers).

Now, go down the list of papers. Look at the titles.
If the title seems relevant, click on the link for the
article. You will be shown the abstract. Read the
abstract. If it indicates that the paper will indeed
address this question, click on one of the links
to read the entire text of the article (for recent articles,
the link to "arXiv e-print" is often handy).

After you have read 10 or 20 articles, you will
probably know the answer to your question.