Markarian 421

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)^[2] to 434 million light-years (133Mpc)^[3] 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. An early-type high inclination spiral galaxy (Markarian 421-5) is located 14 arc-seconds northeast of Markarian 421.

Markarian 421
Sloan Digital Sky Survey image of Mrk 421
Observation data (Epoch J2000)
Constellation	Ursa Major
Right ascension	11h 04m 27.314s[1]
Declination	+38° 12′ 31.80″[1]
Redshift	0.030021[1][2]
Distance	397-434 million light-years (122[2]-133[3] Mpc)
Type	BL LAC[1][2]
Apparent magnitude (V)	12.9 (SIMBAD)[1] 13.3 (NED)[2] 11.6-16 (B Band)[4]
Other designations
B2 1101+38, UGC 6132, PGC 33452, 2E 2393, QSO B1101+384, Mark 421[1]
See also: Quasar, List of quasars

It was first determined to be a very high energy gamma ray emitter in 1992 by M. Punch at the Whipple Observatory,^[5] 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.^[6]

Markarian 421 also had an outburst in 2001 and is monitored by the Whole Earth Blazar Telescope project.^[7]

Due to its brightness (around 13.3 magnitude, max. 11.6 mag. and min. 16 mag.) the object can also be viewed by amateurs in smaller telescopes.