Mrk 421 (UGC 6132, CGCG 184-050, PGC 33452)
Ursa Major
11 04 27
+38 12 32
MAG: 12.9v
Redshift: 0.03
Distance: ~ 400 mly
Type: BL Lac (blazar)
Do you know a simple 13mag fuzzy which listed 133 cross-ID's in NED and over 1400 references? Here we go with the well known Mrk 421.
This "AGN galaxy", or even better "BL Lac blazar" was first mentioned by Fritz Zwicky in the Catalogue of Galaxies and of Clusters of Galaxies (CGCG) between 1961-1968. Its first real attention was given in a paper from 1972 [1972Afz.....8..155M] by Benjamin Markarian. The Armenian astronomer uses a 40-inch Schmidt telescope (102 cm correcting plate) with a full aperture objective prism - until then the largest and most powerful equipment, located in the Byurakan Observatory. Between 1967 and 1981 he listed 1500 objects in 15 paper, all with an ultraviolet excess. As late as 1973 it became a member of the more famous UGC catalogue.
But what is this object about and why did I choose it as the current OOTW?
Summarising, Mrk 421 has an extremely active central region and it is suspected to have a supermassive black hole (SMBH) at its centre. It can be seen across the entire spectrum of wavelengths, from radio to gamma rays - that's why the huge number of references and scientific studies. Combining with its relative small distance of around 400 million light-years, our object presents one of the brightest quasars in the sky. In addition to this unique combination, the 6mag star "51 UMa" is located only 2' north of the galaxy.
Somewhat more detailed, Mrk 421 is not fixed to the give 12.9vmag above. It varies between 12th and 14th magnitude, past decade brightness variations ranged from 11.6 to 16bmag. This variation gives us amateur astronomer a possibility to help science. The AAVSO is collecting magnitude estimations.
As an interesting fact, one of the jets appears to be oriented exactly in the direction of earth, a typically feature of a blazar, first mentioned by, you suspected right - Benjamin Markarian. Another interesting feature was observed in May 1996 - the largest flux of gamma rays that had been recorded for an astronomical object. The culprit is of course monitored.
But what else is still to be said? Looking deeper, a much fainter galaxy is located only 14" east-northeast of Mrk 421, known as Mrk 421-5 or PGC 33453. This companion is gravitational bound to Mrk 421 and may be sweeping through its stellar halo. The given magnitude are not really sure, but after my own observation a brightness of around 17bmag might be fitting and makes it possible to detect it in the 20-inch class.
Observing in the near of 51 UMa, lots of other galaxies are found in the field, for example UGC 6140, 3' east of Mrk 421 or 1.6' south of the other bight star in the field, the 7.5mag 95976.
Under good transparency but soft seeing, Mrk 421 appears as a bright, stellar spot with a faint halo in the 27-inch telescope. Mrk 421 was visible a very faint glow with averted vision. Sometimes it shows a slightly elongation towards Mrk 421. But now it is your turn to try this unique object. What is the smallest aperture to detect Mrk 421 and/or Mrk 421-5? Can you see the elongation of Mrk 421-5?
DSS (b), 15'x15'
Mrk421_DSSb15.jpg
PanSTARRS (g), 2'x2'
Mrk421_Pg2.jpg
sketch: 27", 293x-419x, NELM 7m0+, Seeing IV (bad)
UGC6132_UGC6140.jpg
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As always, give it a go and let us know!
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