Hubble Legacy Archive WFPC2 image of Mark 421 and its companion galaxy 421-5
|Observation data (Epoch J2000)|
|Right ascension||11h 04m 27.314s|
|Declination||+38° 12′ 31.80″|
|Distance||397-434 million light-years
|Apparent magnitude (V)||12.9 (SIMBAD)
11.6-16 (B Band)
|B2 1101+38, UGC 6132, PGC 33452, 2E 2393, QSO B1101+384, Mark 421|
|See also: Quasar, List of quasars|
Markarian 421 (Mrk 421, Mkn 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 (redshift: z=0.0308 eq. 122Mpc) to 434 million light-years (133Mpc) from the Earth. It is one of the closest blazars to Earth, making it one of the brightest quasars in the night sky. It is suspected to have a supermassive black hole (SMBH) at its center due to its active nature, and has a companion galaxy (Markarian 421-5) that is fueling the gas jets observed pointing away from the galaxy.
It was first determined to be a very high energy gamma ray emitter in 1992 by M. Punch at the Whipple Observatory, and an extremely rapid outburst in very high energy gamma rays (15-minute rise-time) was measured in 1996 by J. Gaidos at Whipple Observatory 
Due to its brightness (around 13.3 magnitude, max. 11.6mag. and min. 16mag.) the object can also be viewed by amateurs in smaller telescopes.
- "Mrk 421". SIMBAD Astronomical Database. Retrieved 2010-04-12.
- "NASA/IPAC Extragalactic Database". Results for MRK 0421. Retrieved 2010-04-12.
- "Distance Results for MRK 0421". NASA/IPAC Extragalactic Database. Retrieved 2010-04-13.
- "Variable Star Of The Season AAVSO. Winter 2004: Markarian 421". AAVSO. December 28, 2007. Retrieved 2010-01-10.
- "Detection Of Tev Photons From The Active Galaxy Markarian 421, Nature, Volume 358, Issue 6386, pp 477-478 (Aug. 6, 1992)".
- "Extremely rapid bursts of TeV photons from the active galaxy Markarian 421, Nature, Volume 383, Issue 6598, pp. 319-320 (1996)".
- "Optical monitoring of the blazar Mk421 during the TeV outburst".
- Markarian 421 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
- SEDS Page on Markarian 421
- Focus on Markarian 421
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