3C 138 is a

quasar A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...

located in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

of Taurus. It has a

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and e ...

of (z) 0.76. The

radio spectrum The radio spectrum is the part of the electromagnetic spectrum with frequencies from 3 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particula ...

of this source appears both compact and steep, making it a compact steep-spectrum radio quasar. It is also one of the few 3C objects showing a defined and turn-over in its

electromagnetic spectrum The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...

at low frequencies. 3C 138 is known to shown linear polarization at high degrees although the source of it remains a mystery. When correcting the Faraday rotation for this object, the

electric field An electric field (sometimes called E-field) is a field (physics), physical field that surrounds electrically charged particles such as electrons. In classical electromagnetism, the electric field of a single charge (or group of charges) descri ...

position angle is ~170°, indicating the

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

direction as ~ 80°. The source of 3C 138 is shown to emit

gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

s with a powerful flare detected in 2012. The radio structure of 3C 138 is unresolved at both 0.151 and 0.408

GHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or Cycle per second, cycle) per second. The hertz is an SI derived unit whose formal expression in ter ...

. However, when detected through higher frequencies, it is revealed to be largely linear. The structure is then further divided into separate components consisting of a bright radio core and a radio jet which is polarized and showing a slight increase from 12 percent at 5 GHz to 14 percent at 15 GHz. There are several extended knots present within the main jet emission region extending 400 milliarcseconds in a 65° position angle. A low surface-brightness counter-jet is located in an opposite direction from the region. Furthermore, 3C 138 has a compact radio lobe located east and a much fainter, diffused radio lobe located west. 3C 138 is one of the four primary calibrators used by the

Very Large Array The Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory in the southwestern United States built in the 1970s. It lies in central New Mexico on the Plains of San Agustin, between the towns of Magdalena, Ne ...

. The other three are 3C 48, 3C 147 and 3C 286. For all visibilities of other sources, they are calibrated via observed visibilities of one of the four calibrators.

References

External links

3C 138 on SIMBAD3C 138 on NASA/IPAC Database
{{Taurus (constellation) Quasars Taurus (constellation) 138 1612 Active galaxies 2817552