Frankfurt Quasar Monitoring

MRK 421
Object data

  Cross-Identifications   B2 1101+38, OM+303, KUG 1101+384A, 1101+384
  UGC 6132, ZWG 184.50, PGC 33452, 1ES 1101+384
  RX J1104.4+3812, 2EG J1104+3812, 2A 1102+384
  87GB 1101+3828, TXS 1101+384, S4 1101+38
  EUVE J1104+38.1, MASX J11042732+3812320
  SDSS J110427.31+381231.7, GEV J1104+3809
  XSS J11045+3808, SWIFT J1104.4+3812
  Equat. coordinates   RA  11 04 27.2     DE  +38 12 32     (J2000)
  Constellation   Ursa Major
  Type   BL Lac
  Redshift     z=0.031
  Distance (2) (3)
  126 Mpc
  Total mag range (mv) (4)   11.6 - 16.5
  Catalog Magnitude (1)   12.90
  Absolute Magnitude (1)   -22.9 MB
  Light Travel-Time (2)   0.405 × 109 yrs
(1) Véron-Cetty & Véron 2006, A&A 455, 776
(2) NASA/IPAC Extragalactic Database
(3) Co-Moving Radial Distance
(4) Literature

Finding chart

Galaxies in the field above:

UGC 6140 = PGC 33471, 16.1 m, 1.0´× 0.2´, type S
MCG 7-23-21 = PGC 33476, 16.0 m, 0.2´× 0.2´, type E
PGC 33437, 16.0 m, 0.4´× 0.2´, type S
PGC 33453, 15.8 m, 0.3´× 0.2´, type E
PGC 33475, 16.0 m, 0.2´× 0.2´, type C
  PGC 33500, 15.4 m, 0.7´× 0.25´, type S
LEDA 213780, 17.1 m, 0.3´× 0.1´

Comparison stars

star  B V Rc
A 14.501 13.311 ---
B 14.423 13.523 ---
C 15.022 14.362 14.042
D 15.561 14.991 ---
E 16.202 15.572 15.202
F 16.692 15.772 15.242
(1) comparison stars from McGimsey et al. 1976, AJ, 81, 9
(2) comparison stars from Villata et al. 1998, A&AS, 130, 305
(3) comparison star from Véron et al. 1976, A&AS, 25, 287

Colour chart
Credit: SDSS  /  Size 13´× 13´ /  Chart by S. Karge

High resolution images of MRK 421

These two images show the blazar host of MRK 421 (centre), as well as the
interacting galaxy
PGC 33453 = MRK 421-5 (N up, E left)
Credit: Nilsson et al. (1999) / Size 78" × 78"
R-band image by the Nordic Optical Telescope
Credit: Nilsson et al. (2003) / Size 78" × 78"
R-band image by the Nordic Optical Telescope (image inverted)

Light curve

Markarian 421 (MRK 421 for short) is a very bright and violently variable BL Lac object in southern Ursa Major. Its position lies only 2´SW of 6.0-mag star 51 UMa. This unusual object resides in a giant elliptical galaxy which was discovered by F. Zwicky (ZWG), who described the host as "extremely compact". The designation MRK 421 refers to the UV-Continuum-Survey run by B.E. Markarian et al. (MRK), searching for blue galaxies with excessive UV-emission. MRK 421 was later identified with a radio source, which was discovered by the Bologna Radio Survey (B2). Finally, this unusual object was classified as a BL Lacertae-like object based on spectral analysis. In addition, MRK 421 is also a strong X-ray emitter (e.g. ES, RX). Moreover, it is one of the strongest known TeV (gamma) sources in the heavens – and, by the way, the first TeV-emitting Blazar ever discovered.

At a distance of only about 400 million light-years, MRK 421 is one of the nearest quasi-stellar objects known - and therefore one of the best studied objects of its class. Just 14" NE of MRK 421, the charts above show 16-mag spiral PGC 33453 = MRK 421-5, a close companion to MRK 421. The companion galaxy shows clear signs of tital interaction (see high resolution images above). With a true distance of only about 30 000 light-years from the blazar host it is thought to interact with MRK 421, and most probably triggers the strong AGN activity of MRK 421. The AGN activity is produced by a supermassive black hole with an estimatet mass of at least 1×109 solar masses.
A close look at both the finding chart and the color chart reveals a number of faint galaxies.
Together with the host of MRK 421, they are considered to belong to the same galaxy cluster Zw 1057.2+3804.

Blazar MRK 421 is a violently variable object with a total range of 5 magnitudes (!) in the optical. On average, the brightness varies between 12 mag and 14 mag. Due to its remarkable brightness, this blazar is an easy task for visual observers with telescopes of 8- to 10-inch of aperture, at maximum even for 4-inch telescopes. This blazar is one of the showpieces of its class: very bright and very easy to locate!
With 8-inch of aperture, MRK 421 appears as a stellar or star-like object. Through larger telescopes, observers can visually recognize the true nature of the galactic home of MRK 421. The stellar appearance increasingly changes and becomes more extended and diffuse, with a star-like nucleus. With very large telescopes, observers may even recognize both the slightly oval shape of MRK 421´s host galaxy and its slightly bluish hue.
Both visual observers and CCD photometrists may use the comparison stars given above. Other photometric sequences were published by Craine (1977),
Gonzàlez-Pérez et al. (2001), the BAAVSS and the AAVSO.

The position of MRK 421 in southern Ursa Major offers a large number of other bright and interesting quasi-stellar objects around to observe. The violently variable quasar 4C 29.45 lies some 11.5° SE in Coma Berenices. In the same direction, but 19° SE of MRK 421, we find the extragalactic variable W Com. Another bright 14-mag quasar, PG 1116+215, is located some 17° SSE in Leo. And finally, 33° SW in Cancer, another violently variable BL Lac object, OJ 287, might attract the observers interest.

In case observers prefer spotting
galaxies, just sweep the telescope 2.8° to the SE and visit bright edge-on galaxy NGC 3432, an irregular galaxy, also known as Arp 206. NGC 3432 is a member of the NGC 3184-galaxy group. 4° E of MRK 421 we find bright S0 galaxy NGC 3665, together with its 13-mag S0-type companion NGC 3658, only 15´SW.

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Landessternwarte Heidelberg


AAVSO (vsots)

Gary Poyner (light curve)

BAAVSS (light curve)

Sloan Digital Sky Survey

© Stefan Karge  /  last obs. 2022-07-05