Affiliation
American Association of Variable Star Observers (AAVSO)
Sat, 02/03/2024 - 04:54
The question is about AAVSO 0313+41, well known Perseus A, or NGC 1275, or QSO B0316+413, or... In spite of noted AAVSO number, the object is not presented in VSX, unlike of such QSOs as BL Lac, MRK 421 or QSO B0954+658.
What is the reason? Large diffuse galaxy light obstructs photometry of active nucleus? Low variability? Or something other?
Sorry for the (very) late answer. This is indeed strange, I found some discussions on the Internet where people discussed observing this (among many other AGNs):
http://brucegary.net/blazar/
After checking that this thing is indeed not to be found in VSX (you are definitely right :-) , I remembered I have this on my book shelf: https://www.amazon.de/Aavso-Variable-Atlas-Charles-Scovil/dp/1878174002 and sure enough, on page 199, as the very last entry in the Perseus section, you'll find this:
Designation: AAVSO 0313+41 Name: NGC1275 Type GAL, Range 12.5 -13.0 V AAVSO Chart:P Atlas Charts: 33
Where type "GAL" means Seyfert Galaxy.
I think it was this type that might have caused it to no longer be in VSX. The closest thing you'll find among the VSX variability types is this:
"AGN
Active Galactic Nuclei. Optically variable extragalactic objects only included for historical reasons or observing campaigns.
GCVS type GAL.
"
So if they are not not part of an observing program and have no existing observations that were imported into the AID at some time, AGNs might not qualify for the VSX (well, they are not "stars" I guess...but still...). But I will clarify this with the VSX expert, Sebastian Otero. Stay tuned.
CS
HBE
Thank you for your deep astroarcheological digging! It confirms Perseus A sometime had an AAVSO number. Probably the galaxy is too large for reliable aperture photometry, comparely with BL Lac and AGN objects presented in VSX.
Well...I dunno. If NGC 1275 had a supernova (again...see SN 1968A) we would also try to measure it I guess, despite being embedded in a lot of fluff, so that is no "excuse" I guess.
Anyway, things that are relatively bright and therefore perhaps not so well explored in the optical (the pros probably care more for other wavelengths for this object like radio or X-rays) can sometimes be useful targets for us amateurs. If you want to explore this thing, my understanding is that you could submit this object as a BL Lac QSO to VSX and after that add observations to the AID, potentially after asking for a sequence for it. All I'm saying is that if YOU think this is worthwhile for you, I would not let the absence of it in VSX discourage you. This is actually a very famous QSO and I would think inclusion into VSX should be no problem.
CS
HBE
From one side, NGC 1275 is presented in ASAS-SN database and there are reliable light curves which show slow variability with ranges about 12.6-12.8V and 12.9-13.2g.
But from the other side, the object is not blazar but just AGN, so it can not be included to VSX as BL Lac type. So better to leave decision to Sebastian :)
For some reason I never got a notification on this thread, even when I used to be subscribed to all forums. Maybe the new login system changed that?
Anyway, all your comments regarding this object make sense, but the actual reason it was not in VSX was not very consistent. There is a number of objects that have observations submitted to the AID but didn't get proper classifications and were kept as "Unclassified" objects. Those were not visible publicly but the data could be accessed using the LCG.
Now I have reclassified the object as AGN and made it public so you can see that it has 734 observations in the AID.
Observing this object is challenging, the galaxy is very bright and spreads over several arcseconds (2.2' x 1.7') so your results will depend on the photometric aperture used.
I have included results from several surveys with different apertures in the VSX entry.
As the aperture goes larger, the magnitude becomes brighter and the amplitude smaller.
We can go from V= 12.5, ampl. 0.2 mag. with a 30" radius to V= 14.3 and an amplitude of up to 1 full mag. in radius <1".
I think that if you plan to add it as a HEN target, you need to discuss the aperture you will be using and come to a consensus, otherwise, the results will be incompatible with each other.
Cheers,
Sebastian
Thank you, Sebastian, for returning of NGC 1275 to VSX and especially - for your useful remark regarding aperture. Probably, ASAS-SN radius is a bit of large (for example, R5.5'' was used for MRK 421), but better to use R16'' for the data uniformity. But what to do with comp stars aperture in this case? VPhot uses one aperture for all set, if I understood right...
[Intranight variability of NGC 1275 nucleus in optics: 10'' diaphragm of photometer 5200A and 20" for BVRI photometer-polarimeter.]
`..and your linked study, as well as newer studies, indeed classify this as a BL Lac object.
HBE
There are nice images of NGC 1275 jets, their thin structure was studied with VLBA, and AGN light curves are calm, so I cautiously suppose it is not blazar.
Interesting presentation: Newborn Jets in NGC 1275
> so I cautiously suppose it is not blazar.
I looked it up in this catalog: https://heasarc.gsfc.nasa.gov/db-perl/W3Browse/w3query.pl
and they list it as "Blazar Uncertain type". There are only three possible Blazar sub-types in this catalog:
...but I thought blazar's jet is directed in the eye, however Perseus A hits sideways.
Good question, here's my take on this:
What small angles between the jet axis and the line of sight contributes to the observations, IIRC, is primarily brightness: several relativistic effects boost the brightness with which we can see what is going on in those AGN by a factor of several hundred in the most extreme cases, so we can study those object even for some AGN that are so far away that we no longer see the actual host galaxies. NGC 1275 is obviously so much closer, so we still see blazar-like phenomena from it even tho the jet angle is much greater than for other more distant blazars that we know.
But I guess this is just an example of the old problem of astronomical classifications, which usually start as classifications purely based on "direct" observables like spectra and light curves. With time and increased understanding of the underlying phenomena, those classifications often morph into schemes based on true physical nature of the object deduced by comparing the data to models of the physics at work. This can then start sub-classifications or reclassification of objects and can lead to some confusion and ambiguity.
But that is just my naive take on this, maybe others want to chime in here.
CS
HB
That sounds interesting. Is there a paper that describes the several relativistic effects that boost the brightness. Or would it be quicker to just enumerate them here?
Thanks so much.
Ray
Relativistic Jets in Active Galactic Nuclei
https://arxiv.org/pdf/1812.06025.pdf
Page 5:
SPECIAL RELATIVISTIC EFFECTS
Superluminal Expansion
Doppler Boosting
Nice, thanks for the reference!
For those who'd like just a short enumeration, the English wikipedia article https://en.wikipedia.org/wiki/Blazar gives a good summary as well.
I'm excited to see this discussion. AGN classification is a hard problem. Certain properties make things obviously become classified as blazars, and then certain other things are a bit ambiguous, and that's part of the debate. A lot of the classification schemes are based on optical spectra alone, even though the optical band is usually less than 10% of the emission, and a lot of the mass surveys for optical spectra have a lot of spectra that aren't really deep enough. Often, if you see ambiguous classifications, it's because the data quality isn't good enough.
If folks have some more detailed questions, I'd be happy to try to answer them, and if they are too detailed for me, I'd be happy to try to find a colleague to pop on here.
Doppler Boosting I think is a wavelength shift up. Some mistake the increased energy for more photons. Superluminal is like waves hitting the beach. It is more a phase thing. But I am rusty on that.
My first impression is I don't think either one makes more photons, required for a brighter source and a shorter exposure.
I'll read the paper to see how they apply it.
I'll get back to you.
Ray
I might be full of hooey, but this looks familiar and the notation is much better:
https://www.mso.anu.edu.au/~geoff/HEA/8_Relativistic_Effects.pdf
Superluminal would deliver shorter pulses so you get 1000 photons in 1 millisecond instead of 1000 photons in 10 msec. Both faster than the camera can respond.
The doppler just shifts the wavelength which puts it in another part of the camera response curve.
Then, it looks like the isotropic radiation is directed toward the observer, so you see much of the 4pi steradians is directed, which would make the source appear ~10x brighter.
Then EQ 101 in this citation looks a lot like the one in the paper you site. So I am (naturally) confused about whether the rest frame velocity is the one in the numerator or the one in the denominator.
First, Doppler boosting and superluminal motions are separate phenomena.
First, superluminal motions are caused because the light travel time from a source to Earth is decreasing if the object is moving toward Earth. The apparent speed across the plane of the sky for an object is going to be:
beta sin (theta)/(1-beta cos (theta)), where beta is the speed divided by the speed of light, and theta is the angle between the direction of motion and the line directly from the object to Earth. For really large speeds, almost all angles give apparent superluminal motion.
Second, the Doppler boosting is more than just the Doppler effect on the wavelength. There are three different special relativistic effects that make the object appear brighter. There is the change in wavelength you're talking about. The others are special relativistic factors (getting the Doppler effect right for speeds close to the speed of light also requires special relativity, even though the effect still happens in Newtonian physics)
There is also another factor due to time dilation. This is a multiplication in the number of photons that is the same as the Doppler effect's multiplication of the energy per photon.
Then there are two more powers of the same factor. These are a little harder to understand, but they come from the transformations of velocities in relativity. If the jet is emitting isotropically (i.e. equal power in all directions) in its own reference frame, but it's moving toward us very quickly in our reference frame, it will appear brighter. If you work through the rules of special relativity for how velocities transform, what will happen is that a ray of light going straight up or straight down in the jet's own reference frame will have a large component of its velocity toward us in our reference frame. That will cause most of the light to be emitted in the direction of the motion, in a cone. If we look at these fast jets from the side, they will be much fainter than we would expect from Newtonian physics, and if we look at them pole-on, they are much brighter. Because this happens in two coordinate directions, we get two powers of the factor.
It turns out, then, that we get four powers of something called the Doppler factor due to these three effect.
Some things get a little more complicated than what I've written here, depending on whether the jet is continually supplied with energy or not, but a good rule of thumb is that the Doppler factors for blazars tend to be about 10, and the objects get brighter by a factor of about 10000, and only one factor of 10 is because of the blue shift.
The other thing to remember is that the optical band doesn't include all, or even most, of the power for most blazars, and the blue shift can do different things depending on the shape of the spectrum.
I hope this helps.
I'm replying to the second part of Ray's message, after he signed it.
I want to reiterate that superluminal motions are separate from increases in brightness. There are combinations of the jet speed and angle to the line of sight where there are superluminal motions, but where both the approaching jet and the receeding jet are fainter than they would be to an observer moving at the same speed and direction. If you have a really fast jet speed, the jet will appear superluminal for almost any angle, but the beaming cone will be extremely small.
The wikipedia page for superluminal motions: https://en.wikipedia.org/wiki/Superluminal_motion
is well done.
Time dilation is what can make flares shorter (I'll say flares rather than pulses, because they are not periodic). Whether this matters does, indeed, depend on whether you're making averages over a lot of flares, or measuring single flares (this is the issue I said could make things more complicated than I got into in the first pass through explaining it). The fastest variability timescales for AGN tend to be hours to days.
The doppler factors for blazars are usually about 10, so it's much more than moving things to different parts of a camera's response curve. It's taking light that would be in the infrared and putting it into the optical band. Depending on the spectral shape, this can change what you measure in a particular band by more or less than the doppler factor.
In the equations leading up to equation 101 in that paper, those are the Greek letter nu, not v's.
Thanks a lot for the explanations. If you need to remember just one thing about relativity, it is that it is not intuitive :-). Otherwise it would have emerged earlier in history I guess.
Anyway, Maybe we should focus more on AGNs here. Perhaps have an AGN- (or several)-of-the-month that will get updated photometry? Trying to het useful photometry from our old forgotten pal AAVSO 0313+41 could be a start for March.
HB -- you and I discussed this already once, and just didn't get things organized in time due to my being too busy. BUT I think that what would be a great use of AAVSO resources is to look in red bands at AGN that Swift is observing, to give better nearly simultaneous spectral energy distributions. I think just getting a little bit of photometry isn't that helpful unless the bands are chosen carefully, because things like ASAS-SN do that automatically. But choosing different filters and getting much closer in time to high energy and/or radio observations will provide useful data.
Oh yes I remember...maybe we need to revisit the idea.
Even if we would not be coordinating with Neil Gehrels/SWIFT sat obs, I always thought that maybe a higher cadence (several obs per night up to time series) could add some value compared with the sparser ASASSN et al survey datasets.CS
HB
I think several times per night could be interesting for some AGN, especially in multiple filters. Enough bright AGN have Kepler data that just getting some high cadence AGN light curves may not be a big deal, but picking out the ones with lower mass black holes and higher Eddington fractions, which have the fastest timescales for X-ray data, may be interesting.
Sounds interesting indeed. If you have some specific targets in mind, let us know.
CS
HB
What do you think would be reasonable magnitude limits for such a project?
Depends a bit on the amplitude of the variability that we would hope to be sensitive to in order to be useful.
Would it be more like 0.1 mag or 0.01 mag?
CS
HB
Because the weather report was too uncertain to warrant getting out my 8", I took a quick series of exposures with my new Seestar "smart telescope", which will also optionally annotate all the interesting objects in the field. As you can see, not only is the core of NGC 1275 diffucult to measure because of the fluffy host, this is also a crowded field. Oh well... FOV is ca 1.3 deg x 0.7 deg
/sites/default/files/users/user56707/8529a72d-8b7f-4242-a85c-a101d9726921.jpg
Nice picture
I should really get one of those SeeStar thingies.
Thanks for all the good discussions! It has been 10years since I measured relativistic things in the lab. There I learned that it is easy for experienced physicists to make a mistake in counting these factors. I think we are all thinking along the same lines but I would need to actually crank through the calculations, count photons and get the geometry right to be sure I got all the amplification factors are correct. I should retire from relativistic things too.
A quick check on amplification factors would be to get some data/ count photons.
Ray TRE
As for the Seestar: there was a nice discussion in the ZWO forum about imaging the recently crowned record holder for luminous quasars with this small aperture device: it works! https://bbs.zwoastro.com/d/17829-but-can-we-see-the-j0529-4351-quasar-thats-been-in-the-news-with-the-s50
This is a very…
Gents,
This is a very interesting discussion. Regarding a potential HEN project for AGN, would it make sense to come up with something similar to SNEWS, where some number of candidate objects would be observed and monitored on a continuous basis? I'm not sure what the endgame of such a project would be, but just throwing the idea out there for consideration.
Dave H.
I think it would make sense, but I think ideally this would be done in conjunction with some professional astronomers who might be interested in writing a paper on the data, rather than risking that people make a lot of effort, collect some nice light curves, and then they just sit unused in the archives. I mostly work on stellar mass black holes, so I understand the physics well enough to answer some questions here, but not to pick the right AGN for this work or to write the papers without putting in a lot of effort. I could try to organize a zoom call in a few weeks where we might get some AGN variability people online to discuss what they would be looking for that the public time domain surveys don't already do, and then we might be able to come up with something exciting that will get published.
It's my understanding that a lot of the effort in this area involves figuring out what's going on with the jets. For this the principal observations seem to center on getting polarization measurements of the blazars, which change dramatically when new outbursts happen, and then VLBI observations to try to resolve them The broad international collaboration WEBT seems to act as a coordinating group for this:
https://www.oato.inaf.it/blazars/webt/
Claudia Raiteri and Massimo Villata are the main organizers of this group. People like Svetlana Jorstad at Boston Univ do a lot of the polarization work both in the visible and near-IR.
As Tom notes, probably the sky patrols cover most things on the few-days timescale, so any photometric effort should go to either in the violet or far-red, possibly simply extending the seasonal coverage to low solar elongation, which the surveys don't cover (i.e picking them up first thing in the morning and following them to the bitter end in the evening). Another mode would involve sitting on targets of interest, much as with cv's, to look at the variation on few-minutes timescales, where the lightcurves can indeed look very similar to cv's.
\Brian
"For this the principal observations seem to center on getting polarization measurements of the blazars, which change dramatically when new outbursts happen, and then VLBI observations to try to resolve them "
That's *a* good approach, but it's not the only one. Variability information can come through from spatial scales much smaller than what VLBI measurements can probe, and VLBI also probes only the least energetic electrons in the jet. Big multi-wavelength campaigns are really valuable, too. WEBT does some of that, as well (e.g. note their coordination with MAGIC, which is a very high energy gamma-ray telescope).
"which the surveys don't cover (i.e picking them up first thing in the morning and following them to the bitter end in the evening)."
-- I think the key for AAVSO here is, of course, that with a distributed network of telescopes, it may be possible to observe systems at low airmass by some AAVSO folks that are at too high an airmass for the sky patrols.
" Another mode would involve sitting on targets of interest, much as with cv's, to look at the variation on few-minutes timescales, where the lightcurves can indeed look very similar to cv's."
Yes, although it's then worth thinking about what can be done that Kepler and TESS haven't already done. Color information may be a key here, and there may be parameter space in terms of the types of AGN that have been observed. It's not immediately obvious one way or another what, if anything, is a good use of time there. My guess is that *something* is worth doing, but it really needs the people who focus on this stuff to help advise. Coordinating with campaigns at X-rays may be an excellent application.
So this is why I'd like to coordinate a telecon with some AGN variability experts. There is definitely some stuff worth doing for both blazars and ordinary AGN where the optical emission is coming from the accretion disks, but there is an optimization process that should be done to figure out how to get the potential for the most discovery per amount of observing time. I'm coordinating a faculty search the next few weeks, and then the eclipse comes up shortly after that, but I think April could be a good time for this.
The AAVSOnet is trying something new with the SNEWS project ( https://www.aavso.org/snews-campaign ),
what we are calling a Subscription Project.
We maintain a target list in a google sheet and members can sign up to receive the images from these targets. Their responsibility is to do the photometry and submit it to the AID. The AAVSOnet makes sure the images flow.
The advantage is that more people can participate: you don't need a telescope. And the project provides the structure to make sure all the targets are covered.
The one other thing the project needs is a PI, a Primary Investigator, to monitor and adjust the project over time.
The SNEWS project has some 192 targets and we are still sorting out the infrastructure to monitor, maintain and report on the observations. We are doing this with an eye on being able to generalize and apply the model to other subscription projects.
AGN monitoring could be the next subscription project!
I like the idea of a coherent program where the target list is proposed by the pros based on usefulness of the observations.
The idea to bring together some AGN experts is very interesting indeed. I personally (not an expert!, as an observer) would probably like a shorter list, say 10 or 20 objects that are predicted to do something interesting in the next decades (individually), so that collectively it would be almost guaranteed to have one of them doing something special in the next few years, and we would then have a good dataset about what the object did in the years leading up to the event. Something like that.
Perhaps it also makes sense to include some objects that have regular radio coverage because they are used for precision tracking of the Earth's rotation, because then the dataset would automatically be multi-messenger. Just some random thoughts on this..
CS
HB