Astronomers investigate extreme variability of the 'Big Dipper' active galactic nucleus

February 26, 2019 by Tomasz Nowakowski, Phys.org report
The multiwavelength spectral energy distribution of SDSS J2232−0806. Modelled data are shown in pink: the XMM-Newton OM and EPIC-pn data of 2013 December 14; WHT spectrum of 2013 September 9 and WISE W1 and W2 IR photometry. Additionally, other archival data in white: WISE W3 and W4 IR photometry from 2010; 2MASS IR photometry from 1998; SDSS photometry from 2000 and two epochs of GALEX UV photometry from 2003 (faint) and 2004 (bright). Credit: Kynoch et al., 2019.

Astronomers have carried out an observational campaign to study the extreme variability of the active galactic nucleus (AGN) SDSS J2232−0806, nicknamed the Big Dipper. Results of these observations, described in a paper published February 18 on the arXiv pre-print server, shed some new light on the nature of this variability.

AGNs are compact regions at the center of galaxies, more luminous than surrounding galaxy light. They are very energetic due either to the presence of a black hole or star formation activity at the core of the galaxy.

Significant multi-frequency on many timescales is one of the characteristic features of AGNs. However, mechanisms behind this variability are still a subject of debate. Among the proposed explanations are changes in the dust extinction, changes in the emission from the accretion disc or its associated Comptonisation regions, stellar tidal disruption, supernovae in the nuclear regions, and even gravitational microlensing.

In order to resolve these uncertainties, more studies of the properties of AGN variability are required. One such study was conducted by a team of astronomers led by Daniel Kynoch of Durham University, U.K., using various ground-based telescopes. The researchers performed an optical photometric and spectroscopic monitoring campaign of SDSS J2232−0806 to investigate its variability. The Big Dipper is an AGN at a redshift of 0.276 and was initially classified as a "slow-blue nuclear hypervariable" object.

"Here, we report an analysis of the eleven optical spectra obtained to date, and we assemble a multiwavelength dataset including infrared, ultra-violet and X-ray observations," the astronomers wrote in the paper.

Observations conducted by Kynoch's team recorded one major dimming event and subsequent rise over a period of around four years. Moreover, archival photometry data indicate similar events taking place in the past.

The researchers noted that SDSS J2232−0806 appears to have been in a relatively bright state when observed in late 1980s, but was in a deep minimum in the data from observations conducted in 2000. Furthermore, lightcurve from the Catalina Sky Survey (CSS) suggests that another dip occurred between 2005 and 2007.

Analysis of the collected data allowed the team to exclude the extrinsic cause of the observed variability of SDSS J2232−0806. They concluded that the object's variability is most likely due to an intrinsic change in the luminosity of the accreting matter. It could be a result of an intrinsic variation in the continuum emission from the nuclear region, primarily powered by processes occurring within the accretion disc.

Although the researchers were unable to determine the exact origin of variability of SDSS J2232−0806, they hope that future observations could answer this question. "SDSS J2232−0806 is one of a growing number of objects which challenge our models of viscous accretion discs. Whilst we are unable to determine the cause of the intrinsic luminosity change, X-ray and UV monitoring of future episodes should greatly improve our understanding of the processes at work," the scientists concluded.

Explore further: Astronomers discover 21 changing-look active galactic nuclei

More information: Daniel Kynoch et al. The 'Big Dipper': The nature of the extreme variability of the AGN SDSS J2232-0806 arXiv:1902.06753 [astro-ph.GA]. arxiv.org/abs/1902.06753

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Tuxford
2.3 / 5 (3) Feb 26, 2019
They concluded that the object's variability is most likely due to an intrinsic change in the luminosity of the accreting matter. It could be a result of an intrinsic variation in the continuum emission from the nuclear region, primarily powered by processes occurring within the accretion disc.

And what causes short-timescale changes in the nuclear region? It really can only be from rapid changes in the core star itself. So then, what can cause such rapid variations in the core star? Could it be from heretofore unknown internal processes generating new matter and energy entering our observable subset of the pre-existing whole universe? Heresy!
rrwillsj
1 / 5 (1) Feb 26, 2019
Oh tux my boy, you wouldn't qualify as a hershey bar.
I admit, you almost had an original thought. Too bad you couldn't control your impulses to utter woolunacy gibberish.

& There you are. Again.

"... Could it be from heretofore unknown internal processes generating new matter and energy entering our observable subset of the pre-existing whole universe? ..."
Uhh, no.

Only happens in the Faerie Universe. Go ahead, I'll give you a moment to mourn lost opportunities.
Yes, I agree you'd have looked very cute with butterfly wings.
RME

Correct to: Could it be from heretofore unknown internal processing of energy to generate transmuted elements from the material that already exists in that vicinity?
As are being observed to occur all across the visible universe.

There, all better now?
No, no.You keep that hanky.
I have plenty more were that came from.
No, sorry. Not from another universe.
jeebus, I need a drink after that!
Satire, Art applied to Science!
observicist
not rated yet Feb 26, 2019
@Tuxford,

They concluded that the object's variability is most likely due to an intrinsic change in the luminosity of the accreting matter.

And what causes short-timescale changes in the nuclear region? It really can only be from rapid changes in the core star itself. So then, what can cause such rapid variations in the core star?


What core star?

The article is about an AGN -- otherwise known as an "active galactic nucleus," or an accretion disk surrounding a supermassive black hole; that is, a quasar. There is no core star.
Tuxford
5 / 5 (1) Feb 27, 2019
What core star?

The article is about an AGN -- otherwise known as an "active galactic nucleus," or an accretion disk surrounding a supermassive black hole; that is, a quasar. There is no core star.

You must be new here. Since black holes only exist in the minds of merger maniacs, the core star is the object they call a black hole. It is more likely only dim and therefore grey. It reaches a finite density and forms and periodically ejects newly formed matter and energy therefrom. It is often supermassive.

So the massive question is how such new matter and energy could be generated over time. However, recent observations support that such a condition actually exists. No matter, merger maniacs are lost in fantasy, committed to the Huge Bang Fantasy no matter the evidence to the contrary.
rrwillsj
1 / 5 (1) Feb 27, 2019
so tux "... the core star is the object they call a black hole. It is more likely only dim and therefore grey. ..."

So, you do not know as a confirmed fact?
You are admitting that you are guessing?
& 'grey". really?
Wouldn't "invisible" be more plausible for your argument?
Since all the sane observers with good eyesight, fail to detect such a marvelously fabulist crypto-critter.

Then you woo on with contradicting yourself.
:... It reaches a finite density and forms and periodically ejects newly formed matter and energy therefrom. It is often supermassive. ..."

You are tiptoeing around the reality of Gravity as a Constant of Mass.
If your intent is to deny G?
What are you replacing it with that is Attractant?
Never runs out of energy, turns off or fails to correctly scale with Mass?
That is as relentless or Infinite?
"finite density" is pretty small pohtahtohs & does not qualify as "Supermassive"

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