Nov 01
19:17:23.803 ▶▶ Permalink
The Whole Earth Blazar Telescope… Blazar?!?

The Whole Earth Blazar Telescope… Blazar?!?

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Oct 11
22:22:00.890 ▶▶ Permalink
A minority of quasars show strong radio emission, which originates from jets of matter moving close to the speed of light. When looked at down the jet, these appear as a blazar and often have regions that appear to move away from the center faster than the speed of light (superluminal expansion.) This is an optical trick due to the properties of special relativity. (via Modern Physics and Astronomy: QUASAR)

A minority of quasars show strong radio emission, which originates from jets of matter moving close to the speed of light. When looked at down the jet, these appear as a blazar and often have regions that appear to move away from the center faster than the speed of light (superluminal expansion.) This is an optical trick due to the properties of special relativity. (via Modern Physics and Astronomy: QUASAR)

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Sep 30
18:59:34.749 ▶▶ Permalink
Quasars have all the same properties as active galaxies, but are more powerful: Their Radiation is ‘nonthermal’ (i.e. not due to a black body), and some (~10%) are observed to also have jets and lobes like those of radio galaxies that also carry significant (but poorly known) amounts of energy in the form of high energy (i.e. rapidly moving, close to the speed of light) particles (either electrons and protons or electrons and positrons). Quasars can be detected over the entire observable electromagnetic spectrum including radio, infrared, optical, ultraviolet, X-ray and even gamma rays. Most quasars are brightest in their rest-frame near-ultraviolet (near the 1216 angstrom (121.6 nm) Lyman-alpha emission line of hydrogen), but due to the tremendous redshifts of these sources, that peak luminosity has been observed as far to the red as 9000 angstroms (900 nm or 0.9 µm), in the near infrared. A minority of quasars show strong radio emission, which originates from jets of matter moving close to the speed of light. When looked at down the jet, these appear as a blazar and often have regions that appear to move away from the center faster than the speed of light (superluminal expansion). This is an optical trick due to the properties of special relativity. (via Science: Quasar)

Quasars have all the same properties as active galaxies, but are more powerful: Their Radiation is ‘nonthermal’ (i.e. not due to a black body), and some (~10%) are observed to also have jets and lobes like those of radio galaxies that also carry significant (but poorly known) amounts of energy in the form of high energy (i.e. rapidly moving, close to the speed of light) particles (either electrons and protons or electrons and positrons). Quasars can be detected over the entire observable electromagnetic spectrum including radio, infrared, optical, ultraviolet, X-ray and even gamma rays. Most quasars are brightest in their rest-frame near-ultraviolet (near the 1216 angstrom (121.6 nm) Lyman-alpha emission line of hydrogen), but due to the tremendous redshifts of these sources, that peak luminosity has been observed as far to the red as 9000 angstroms (900 nm or 0.9 µm), in the near infrared. A minority of quasars show strong radio emission, which originates from jets of matter moving close to the speed of light. When looked at down the jet, these appear as a blazar and often have regions that appear to move away from the center faster than the speed of light (superluminal expansion). This is an optical trick due to the properties of special relativity. (via Science: Quasar)

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Sep 29
20:03:00.793 ▶▶ Permalink
As you might expect, there are also two types of blazars: BL Lacs and Radio Quasars. A lot of work has been done to see which type of radio galaxies produce these blazars. The emerging picture is that BL Lacs are FRI jets pointing at us, and Radio Quasars are FRII jets pointing at us. Furthermore, there are some good reasons that come from physics that this should be the case. (via When do you reject a theory? « Life, the Universe, and Everything.)

As you might expect, there are also two types of blazars: BL Lacs and Radio Quasars. A lot of work has been done to see which type of radio galaxies produce these blazars. The emerging picture is that BL Lacs are FRI jets pointing at us, and Radio Quasars are FRII jets pointing at us. Furthermore, there are some good reasons that come from physics that this should be the case. (via When do you reject a theory? « Life, the Universe, and Everything.)

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Aug 30
16:46:26.657 ▶▶ Permalink
First light from FERMI. Credit: NASA / FERMI (via Tom’s Astronomy Blog » GLAST is Now FERMI) From the NASA press release: […] A fourth bright spot in the LAT image lies some 7.1 billion light-years away, far beyond our galaxy. This is 3C 454.3 in Pegasus, a type of active galaxy called a blazar. It’s now undergoing a flaring episode that makes it especially bright. […]

First light from FERMI. Credit: NASA / FERMI (via Tom’s Astronomy Blog » GLAST is Now FERMI)

From the NASA press release:

[…] A fourth bright spot in the LAT image lies some 7.1 billion light-years away, far beyond our galaxy. This is 3C 454.3 in Pegasus, a type of active galaxy called a blazar. It’s now undergoing a flaring episode that makes it especially bright. […]
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16:39:07.652 ▶▶ Permalink
» Blazars in the Web - A blazar link collection

Blazars are a subset of the Active Galactic Nuclei (AGN or active galaxies). This radio-loud extragalactic objects are optically violent variable quasars, flat-spectrum quasars, high polarized quasars, and BL Lacertae (BL Lac) type objects, which display extremely intense, broad and rapidly varing electromagnetic emission, from radio to gamma-rays in some case. This emission is thought to originate in a relativistic plasma jet which is probably to be powered and accelerated by a billion solar mass black hole in gravitational accretion. Blazars show intense, flat-spectrum radio-loud emission, and their relativistic jet point nearly straight toward us. The Compton Gamma-Ray Observatory-EGRET  found that many blazars are intense gamma-ray sources. This has been one of the most exciting astrophysical discovery of past decade. They are called classic BL Lac type objects if the optical continuum emission dominates compared to any line emission.

Briefly a blazar, is an object thet have the following characteristics:

  1. It appear optically point-like on the sky, i.e. not appear widespread like a galaxy or a nebula. Some blazars have nebulae around them (are fuzzy), but most of the light comes from a point source.

  2. Their spectra appear to be smooth (i.e. no strong absorption lines that a star might have) and flatter than a star. These two properties by themselves would make them a quasar.

  3. Their visible light is often partially polarized.

  4. Their output in all wavelength bands varies more rapidly, and by a larger amount than a classical quasar, with a flare-like behaviour.

  5. Many blazar emits a significant fraction of their radiation at energy above 100 MeV. Their flux is peaked in high bands around 10Mev-1Gev for the LBL (red-blazar) class, around 1GeV-100GeV for the HBL (blue-blazar) class and around 200Gev-1TeV for the few TeV-blazar.

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Aug 13
12:44:00.488 ▶▶ Permalink
Above: Quasar 1317+520; false color: X-ray image from Chandra X-ray Observatory; contours: 5 GHz radio image from the Very Large Array. Click here for more details. (via Blazar Research at Boston University)

Above: Quasar 1317+520; false color: X-ray image from Chandra X-ray Observatory;
contours: 5 GHz radio image from the Very Large Array. Click here for more details. (via Blazar Research at Boston University)

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Aug 06
12:27:11.477 ▶▶ Permalink
“ Utraviolet Telescope for Blazar Emission Lines? UV emission line detection for blazars? Hence able to obtain redshift. Blazars don’t have optical emission lines basically; thus there redshifts might be quite off, if based on associated galaxies.
— zankaon
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Aug 04
15:37:43.609 ▶▶ Permalink
“ The resulting contemporaneous broadband spectral energy distributions of both TeV blazars are discussed in view of implications for intrinsic blazar parameter values, taking into account the gamma-ray absorption in the EBL.
— A Hard X-Ray View of Two Distant VHE Blazars
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Jul 23
0:56:17.997 ▶▶ Permalink
“ [Researchers] believe that large galaxies such as the Milky Way contain supermassive black holes in their cores that drag dust and gas toward them in a disk and fling it back out via jets of ionised gas or plasma moving at up to 99.9 per cent the speed of light. If that jet points toward Earth, researchers call it a blazar, and it is “one of the most impressive high-energy natural laboratories” in the universe […]
— The Statesman
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Jul 22
16:24:01.641 ▶▶ Permalink
“ The GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT) reports on the recent observation of a very bright optical flare from the blazar 3C 454.3. After a moderate flare in June 2008, the source rebrightened from R ~ 15 to ~ 13.4 between the end of June and mid July. Noticeable activity has been also observed in the near-IR (Campo Imperatore), at mm wavelengths (SMA), at 43 GHz (Noto) and 14.5 GHz (UMRAO). [Nevvero?!?]
— The Astronomer’s Telegram
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Jul 19
12:09:42.465 ▶▶ Permalink
“ The team [of Boston University astronomer Alan Marscher] studied a galaxy called BL Lacertae […] about 950 million light years from Earth, with a central black hole containing 200 million times the mass of our Sun. Since this supermassive black hole’s jets are pointing nearly straight at us, it is called a blazar: a quasar is often thought to be the same as a blazar, except its jets are pointed away from us.
— Austin Garrett Ward (slightly adapted)
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Jul 11
14:34:16.565 ▶▶ Permalink
An artist’s conception of the blazar BL Lacertae at it spurts out jets of charged particles accelerated by corkscrew magnetic field lines. (via An Astromical Black Hole, Painting | The News is NowPublic.com)

An artist’s conception of the blazar BL Lacertae at it spurts out jets of charged particles accelerated by corkscrew magnetic field lines. (via An Astromical Black Hole, Painting | The News is NowPublic.com)

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Jul 10
17:49:25.700 ▶▶ Permalink
“ VHE gamma radiation is not an exceptional phenomenon: […] measurements in the VHE gamma radiation region provide astronomers with a unique opportunity to verify the laws of astronomy in new areas of energy. Thus the publication in “Science” was able to disprove the “Blazar Sequence” model, which says that the most energetic objects are also the brightest.
— Universe Is More Transparent To High-energy Radiation Than Previously Assumed
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Jul 04
14:27:01.560 ▶▶ Permalink
“ It has been known for a long time that blazars are variable, both on short (minutes to days) and long (weeks to years) timescales. Various models exist to explain the mechanisms causing variability, and disentangling them has also been particularly hard. A wide variety of tools are used to define and characterize variability, with varying limitations depending on the analysis method and observation uniformity.
— Workshop on Blazar Variability across the Electromagnetic Spectrum, April 2008
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