Frankfurt Quasar Monitoring

MRK 501
Object data

  Cross-Identifications   4C 39.49, B2 1652+39A, 4U 1652+39, 1652+398
  PGC 59214, UGC 10599, MCG +07-35-002, OS+387
  RGB J1653+397, VSOP J1653+3945, PKS 1652+398
  2MASXi J1653522+394536, IRAS Z16522+3950
  RX J1653.8+3945, 1ES 1652+398, H 1652+398
  EUVE J1653+39.7, 0FGL J1653.9+3946, DA 426
ZWG 255.7, B3 1652+398, GB6 J1653+3945
  XSS J16536+3951, SWIFT J1654.0+3946
  Equat. coordinates   RA  16 53 52.2     DE  +39 45 37     (J2000)
  Constellation   Hercules
  Type   BL Lac
  Redshift   z=0.033
  Distance (2) (3)
  137 Mpc
  Total mag range (mv) (4)   13.0 - 14.6
  Catalog Magnitude (1)   13.78
  Absolute Magnitude (1)   -22.4 MB
  Light Travel-Time (2)   0.440 × 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

Comparison stars

star  B V Rc Ic
1 13.55 (0.03) 12.61 (0.02)
12.11 (0.02)
11.65 (0.04)1
2 14.10 (0.03) 13.23 (0.02)
12.79 (0.02) ---
3 15.98 (0.04)
15.24 (0.02)
14.80 (0.02) ---
4 16.05 (0.05)
15.30 (0.02)
14.96 (0.02)
14.56 (0.07)1
5 16.27 (0.04)
15.51 (0.02)
15.08 (0.02)
6 16.82 (0.05)
15.67 (0.04)
14.99 (0.04)
14.34 (0.08)1
comparison stars from Villata et al. 1998, A&AS, 130, 305
(1) comparison stars from Fiorucci et al. 1996, A&AS, 116, 403

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

High resolution images of MRK 501
Credit: SDSS / Size 3´× 3´
The host galaxy shows the typical morphology of an elliptical galaxy
Credit: Nilsson et al. (2003) / Size 123" × 123"
R-band image by the Nordic Optical Telescope (image inverted)

Light curve

Markarian 501 (MRK 501 for short) is a bright and slightly variable object in Hercules, 2.3° ENE of Eta Herculis. The designation MRK 501 refers to the UV-Continuum-Survey run by Markarian et al. (MRK), searching for blue galaxies with excessive UV-emission. This spectroscopic survey was carried out in 1972, using a 1-m Schmidt Telescope, equipped with an objective-prism. In case of MRK 501, a continuous spectrum was found, which led to the classification as a BL Lac object. In 1974/1975, spectral lines were identified that originated from the stellar population of the host galaxy (UGC). Today, the distance is considered as 440 million light-years, so MRK 501 is one of the nearest quasi-stellar objects in the heavens.
MRK 501 was discovered as a radio source in 1965 by the 4th Cambridge Survey of Radio Sources (4C), and was classified as a flat-spectrum radio source. A radio-jet was identified extending at least 55 mas from the core. MRK 501 is also known as a source of infrared (IRAS, 2MASX), X-ray (RX) and even gamma emissions. This unusual object resides in a giant elliptical galaxy with a very bright core, which F. Zwicky (ZWG) described as "extremely compact". The apparent diameter is given as 1.2´× 1.0´.
MRK 501 lies in the "Great Wall" supercluster, but not within any rich cluster, which is very unusual, considering the true size of the host galaxy of approximately 180×150 klyrs.

MRK 501 is a low amplitude variable object with a total range of only about 1.6 magnitudes in the optical. At maximum brightness, visual observers need at least a 6- to 8-inch telescope to glimpse the very bright core as a faint stellar object. Using 10- to 12-inch of aperture and larger reveals a bright star-like nucleus surrounded by a slightly oval and diffuse halo - a clear sign of the host galaxy of MRK 501.

CCD observers, as well as visual observers, shall use the comparison stars given above. Several research groups have published further photometric sequences, which underlines the high astrophysical interest in this very unusual blazar: Véron et al. (1976), Gonzŕlez-Pérez et al. (2001), and Doroshenko et al. (2005).

Visual observers, who point their telescope to Hercules, will of course take a stop for famous M13, the "Great Hercules cluster", the brightest globular cluster in the northern celestial hemisphere. Under dark skies, a 4-inch telescope will resolve this globular. And do not forget about the other two globulars in northern Hercules, M92 and NGC 6229.

Observing MRK 501 offers the joy of taking an interesting visual trip through space and time. The journey begins at Eta Herculis (44 Her), at a distance of only 112 light-years from earth, followed by M13 at a distance of even 25 000 light-years, located some 2.4° south of Eta Her.
Only 28´NE of M13, we meet 12.1-mag galaxy NGC 6207, located at a distance of 46 million light-years. Spiral galaxy NGC 6207 is an easy task for 8-inch telescopes and larger.
Finally, we meet famous blazar MRK 501, at a whopping distance of 440 million
light-years, some 3.6° NE of NGC 6207 - and some 400 million light-years more distant than NGC 6207 !
bservers who like to continue this voyage into the deep space may like to turn to quasar 3C 345, a variable quasi stellar object at a distance of more than 5×109 light-years, 2° W of MRK 501.
Still hungry for more extremely old quasi-stellar photons? No problem!
CCD observers shall turn to z=2.316 quasar FIRST J1651+4002, a 17-mag quasar, some 30´NW of MRK:501. By the way: a redshift of z=2.316 means a light travel time of about 10.8×109 years !
To put an end to this cosmological journey to the edge of the observable universe, CCD observers may finally turn their scope about 1° to the SW to track down an even more distant quasar, HS 1649+3905, an 18-mag high redshift quasar of z=3.166, corresponding to a light travel time of 11.3×109 years !
FIRST J1651+4002:  RA 16 51 37.5,  DE +40 02 18,  z=2.316,  17.66 mag
HS 1649+3905:      RA 16 50 44.7,  DE +39 00 44,  z=3.166,  18.33 mag
Data from Véron-Cetty et al. (2006)

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© Stefan Karge  /  last obs. 2022-12-20