Markarian 501

Markarian 501 is a nearby blazar whose relativistic jet points nearly toward Earth. Its emission varies across the electromagnetic spectrum, including at very high gamma-ray energies.

Blazar: An active galactic nucleus whose relativistic jet points close to the line of sight from Earth. Markarian 501 is classified as a blazar because its jet is aimed nearly toward Earth.
1997 Markarian 501 flare: A major 1997 outburst from Markarian 501 that produced exceptionally bright TeV gamma-ray emission. This landmark episode revealed the source’s extreme variability and high-energy output.
Active galactic nucleus: A galaxy’s central region powered by matter accreting onto a supermassive black hole. Markarian 501’s blazar activity is a form of active galactic nucleus activity.
Blazar spectral energy distribution: A plot of a blazar’s emitted energy across frequency, often showing two broad peaks. Markarian 501’s shifting peaks test models of how its jet produces radiation.
Relativistic jet: A narrow outflow of plasma moving at speeds close to the speed of light from an active galactic nucleus. Relativistic beaming from this outflow amplifies Markarian 501’s observed radiation.
TeV gamma-ray astronomy: The study of gamma rays with energies around one teraelectronvolt and above. Markarian 501 became a prominent target as observatories began detecting TeV emission from blazars.
BL Lac object: A type of blazar with weak or absent optical emission lines and strongly variable nonthermal radiation. Markarian 501 belongs to this class, whose spectra lack prominent emission lines.
Hadronic model: A high-energy emission model in which relativistic protons and their products contribute substantially to a source’s radiation. It competes with electron-based explanations for the source’s gamma-ray emission.
Supermassive black hole: A black hole with a mass of millions to billions of times the Sun’s mass, commonly found at galactic centers. The galaxy’s central black hole powers the accretion and jet activity behind its emissions.
High-energy peaked BL Lac object: A BL Lac object whose synchrotron spectral component peaks at X-ray or higher energies. Markarian 501 is a prototype of this blazar subclass.

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