Whole Earth Blazar Telescope
Encyclopedia
The Whole Earth Blazar Telescope (WEBT) is an international consortium of astronomers created in 1997, with the aim to study a particular category of Active Galactic Nuclei (AGN) called blazars, which are characterized by strong and fast brightness variability, on time scales down to hours or less.
This collaboration involves many telescopes observing at optical, near-infrared, and radio (millimetric and centimetric) wavelengths. Thanks to their different geographic location all around the world, the emission variations of the pointed source can be monitored 24 hours a day, with the observing task moving from east to west as the Earth rotates.
WEBT observations are often carried out in conjunction with observations at higher frequencies, from ultraviolet to gamma rays, performed by both space and ground-based telescopes. In this way, information on blazar emission over almost the whole electromagnetic spectrum
can be obtained.
The multi-wavelength studies performed by the WEBT have the purpose of understanding the physical mechanisms that rule the variable emission of these celestial objects. This emission mainly comes from a plasma jet pointing closely to the line of sight, and originating from a supermassive black hole located in the core of the host galaxy.
, as a collaboration among optical observers.
Three years after, in 2000, the leadership was committed to Massimo Villata, from the Osservatorio Astronomico di Torino.
A constitution was issued, defining purposes and management of the organization. Soon after, also radio and near-infrared observers joined the consortium.
This is the list of the blazars that have been targets of WEBT campaigns:
), and AGILE (Astro-rivelatore Gamma a Immagini LEggero).
The GASP strategy is a long-term monitoring of selected targets, with periodic data gathering and analysis.
The list of the GASP monitored blazars includes 28 bright objects:
3C 66A
, AO 0235+16, PKS 0420−01, PKS 0528+134, S5 0716+71, PKS 0735+17, OJ 248, OJ 49, 4C 71.07, OJ 287
, S4 0954+65, Markarian 421
, 4C 29.45, ON 231, 3C 273, 3C 279, PKS 1510−08, DA 406, 4C 38.41, 3C 345, Markarian 501, 4C 51.37, 3C 371
, PKS 2155−304, BL Lacertae
, CTA 102, 3C 454.3
and 1ES 2344+514.
This collaboration involves many telescopes observing at optical, near-infrared, and radio (millimetric and centimetric) wavelengths. Thanks to their different geographic location all around the world, the emission variations of the pointed source can be monitored 24 hours a day, with the observing task moving from east to west as the Earth rotates.
WEBT observations are often carried out in conjunction with observations at higher frequencies, from ultraviolet to gamma rays, performed by both space and ground-based telescopes. In this way, information on blazar emission over almost the whole electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
can be obtained.
The multi-wavelength studies performed by the WEBT have the purpose of understanding the physical mechanisms that rule the variable emission of these celestial objects. This emission mainly comes from a plasma jet pointing closely to the line of sight, and originating from a supermassive black hole located in the core of the host galaxy.
Foundation
The WEBT was founded in autumn 1997 by John Mattox, from the Institute of Astrophysical Research at the Boston UniversityBoston University
Boston University is a private research university located in Boston, Massachusetts. With more than 4,000 faculty members and more than 31,000 students, Boston University is one of the largest private universities in the United States and one of Boston's largest employers...
, as a collaboration among optical observers.
Three years after, in 2000, the leadership was committed to Massimo Villata, from the Osservatorio Astronomico di Torino.
A constitution was issued, defining purposes and management of the organization. Soon after, also radio and near-infrared observers joined the consortium.
Observing campaigns
Until February 2009, the WEBT has organised 24 observing campaigns, with the participation of more than one hundred telescopes. Each campaign is devoted to a specific source, and is led by a Campaign Manager appointed by the President. The Campaign Manager is responsible for the observing strategy, data collection, analysis and interpretation, and finally takes care of the publication of the results.This is the list of the blazars that have been targets of WEBT campaigns:
- AO 0235+16
- Markarian 421Markarian 421Markarian 421 is a blazar located in the constellation Ursa Major. The object is an active galaxy and a BL Lacertae object, and is a strong source of gamma rays. It is about 397 million light-years to 434 million light-years from the Earth...
- S5 0716+71
- BL LacertaeBL LacertaeBL Lacertae or BL Lac is a highly variable, extragalactic AGN . It was first discovered by Cuno Hoffmeister in 1929, but was originally thought to be an irregular variable star in the Milky Way galaxy and so was given a variable star designation...
- Markarian 501
- 3C 66A3C 66A3C 66A is a Blazar located in the constellation Andromeda.The "distance" of a far away galaxy depends on what distance measurement you use. With a redshift of 0.444, light from this active galaxy is estimated to have taken around 4.5 billion years to reach us...
- OJ 287OJ 287OJ 287 is a BL Lac object located 3.5 billion light years away that has produced quasi-periodic optical outbursts going back approximately 120 years, as first apparent on photographic plates from 1891...
- 3C 454.33C 454.33C 454.3 is a quasar/blazar located off the galactic plane. It lies some 7.1 billion light-years away in Pegasus and is currently undergoing a flaring episode that makes it especially bright, especially in the gamma-ray part of the spectrum.- History :...
- 3C 279
Papers
After twelve years of operations, more than ninety scientific publications have been released .The GASP
On September 4, 2007, the WEBT started a new project: the GLAST-AGILE Support Program (GASP). Its aim is to provide observing support at longer wavelengths to the observations by the gamma-ray satellites GLAST (Gamma-ray Large Area Space Telescope, later renamed Fermi Gamma-ray Space Telescope in honor of the famous italian physicist Enrico FermiEnrico Fermi
Enrico Fermi was an Italian-born, naturalized American physicist particularly known for his work on the development of the first nuclear reactor, Chicago Pile-1, and for his contributions to the development of quantum theory, nuclear and particle physics, and statistical mechanics...
), and AGILE (Astro-rivelatore Gamma a Immagini LEggero).
The GASP strategy is a long-term monitoring of selected targets, with periodic data gathering and analysis.
The list of the GASP monitored blazars includes 28 bright objects:
3C 66A
3C 66A
3C 66A is a Blazar located in the constellation Andromeda.The "distance" of a far away galaxy depends on what distance measurement you use. With a redshift of 0.444, light from this active galaxy is estimated to have taken around 4.5 billion years to reach us...
, AO 0235+16, PKS 0420−01, PKS 0528+134, S5 0716+71, PKS 0735+17, OJ 248, OJ 49, 4C 71.07, OJ 287
OJ 287
OJ 287 is a BL Lac object located 3.5 billion light years away that has produced quasi-periodic optical outbursts going back approximately 120 years, as first apparent on photographic plates from 1891...
, S4 0954+65, Markarian 421
Markarian 421
Markarian 421 is a blazar located in the constellation Ursa Major. The object is an active galaxy and a BL Lacertae object, and is a strong source of gamma rays. It is about 397 million light-years to 434 million light-years from the Earth...
, 4C 29.45, ON 231, 3C 273, 3C 279, PKS 1510−08, DA 406, 4C 38.41, 3C 345, Markarian 501, 4C 51.37, 3C 371
3C 371
3C 371 is a BL Lac object located in the constellation Draco. With a redshift of 0.051, this active galaxy is about 730 million light-years away....
, PKS 2155−304, BL Lacertae
BL Lacertae
BL Lacertae or BL Lac is a highly variable, extragalactic AGN . It was first discovered by Cuno Hoffmeister in 1929, but was originally thought to be an irregular variable star in the Milky Way galaxy and so was given a variable star designation...
, CTA 102, 3C 454.3
3C 454.3
3C 454.3 is a quasar/blazar located off the galactic plane. It lies some 7.1 billion light-years away in Pegasus and is currently undergoing a flaring episode that makes it especially bright, especially in the gamma-ray part of the spectrum.- History :...
and 1ES 2344+514.