Frankfurt Quasar Monitoring

S4 1749+70
Object data

  Cross-Identifications  HS 1749+7006, TXS 1749+701, QSO B1749+701
  PKS 1749+701, GB6 B1749+7006, S5 1749+70
  7C 1749+7006, RGB J1748.5+7005, 2E 3964
  2MASS J17483284+7005506, 1E 1749.0+7006
  1RXS J174832.9+700551, WMAP J1748+7006
  1FGL J1748.5+7004, RX J1748.5+7006   
  Equat. coordinates   RA  17 48 33.1     DE  +70 05 50     (J2000)
  Constellation   Draco
  Type   BL Lac
  Redshift (1) (2)   z=0.770
  Distance (2) (3)
  2633 Mpc
  Total mag range (mv) (4) (5)   14.7 - 17.7
  Catalog Magnitude (1)   17.01
  Absolute Magnitude (1)   -26.0 MB
  Light Travel-Time (2)   6.489 × 109 yrs
(1) Véron-Cetty & Véron 2006, A&A 455, 776
(2) NASA/IPAC Extragalactic Database
(3) Co-Moving Radial Distance
(4) Literature
(5) comment in "notes"

Finding chart

Comparison stars

star B V
1 15.340 (0.022) 14.535 (0.039)
2 15.021 (0.025)
14.595 (0.041)
3 15.165 (0.046)
14.617 (0.029)
4 15.748 (0.023)
15.239 (0.084)
5 16.046 (0.049) 15.620 (0.034)
16.416 (0.100) 15.780 (0.084)
comparison stars from APASS (DR6)

Light curve

NGC 6503 and its quasi-stellar neighbour S4 1749+70
Credit: J. Misti (Misti Mountain Observatory)  /  Image cropped  /  Identification marks by S. Karge

S4 1749+70 is a violently variable BL Lac object in north-eastern Draco, only 5´SW of bright galaxy NGC 6503. S4 1749+70 was discovered as a radio source in 1972 during part 4 of the 5-GHz Strong Source Survey (S4). The newly found object was identified with a 17-mag stellar object on POSS plates, and was immediately classified as an unknown quasi stellar object. Independently, S4 1749+70 was also identified as a radio source by the Westerbork 1415 MHz survey in 1974. Soon after, the optical counterpart was found to be variable at optical and radio wavelengths. Just one year later, follow up spectroscopic investigations were carried out with the 5-m Hale reflector at Palomar Observatory, which revealed a featureless continuum. S4 1749+70 was therefore classified as a BL Lac object.
Despite its featureless spectrum, a weak emission line was detected in 1987, leading to a reliable redshift of z=0.770. This corresponds to a light travel time of about 6.5 Gyrs. S4 1749+70 can be best described as a variable, radio loud flat-spectrum radio source, which displays a core-jet structure (detected by radio interferometry).

BL Lac object S4 1749+70 is a violently variable object with a total optical range of about 3 magnitudes (14.7 - 17.7 mag). CCD observers as well as visual observers shall use the comparison stars given above.
Other sequences were published by the AAVSO and the Hamburg Quasar Monitoring project.

The optical maximum of 14.7 mag [*] was detected on March 6, 2011, by Joseph Brimacombe, who observed with a 20-inch reflector and CCD camera from New Mexico. Initially, Brimacombe recognized this object as an unknown variable. The author advised him of the true nature of this object and redetermined the brightness using Brimacombe´s original fits-files, that he kindly provided for photometric reduction. To the knowledge of the author, this was the brightest optical state ever recorded for S4 1749+70.
[* Photometric reduction based on APASS comparison stars]

S4 1749+70 is located only 5´SW of bright galaxy NGC 6503 (see images above). NGC 6503 is some 16 million light-years away from earth. The colour image of NGC 6503 (see above) also shows the BL Lac object S4 1749+70, arbitrarily caught by Jim Misti in his deep and detailed image.
Another interesting deep sky object can be found some 3.6° to the south. There we find the showpiece planetary NGC 6543, also known as the "Cat´s Eye Nebula". NGC 6543 is rich in details and is one of the brightest objects of its class.

A more challenging deep sky object is another
source of quasi-stellar photons: 3C 371. This is a bright 14-mag BL Lac object at a distance of about 0.6×109 light-years, only 1.6° east of S4 1749+70.

Arp, H., Sargent, W.L.W., et al. 1976, ApJ, 207, L13; A BL Lacertae Object near the Spiral Galaxy NGC 6503.
Baath, L.B. 1984, IAUS, 110, 127B; VLBI and Compact Radio Sources. Symposium no. 110 held in Bologna, Italy,
     June 27-July 1, 1983. Edited by R. Fanti, K. Kellermann, and G. Setti.
Nilsson, K., Pursimo, T., et al. 2003, A&A, 400, 95N; R-band imaging of the host galaxies of RGB BL Lacertae objects.
Pauliny-Toth, I.I.K., Witzel, A., et al. 1978, AJ, 83, 451; The 5-GHz Strong Source Surveys. IV. Survey of the area
     between declination 35 and 70 degrees and summary of source counts, spectra and optical identifications.
Pearson, T.J., Readhead, A.C.S. 1988, ApJ, 328, 114P; The milliarcsecond structure of a complete sample of radio
     sources. II - First-epoch maps at 5 GHz.
Pérez-Torres, M.A., Marcaide, J.M., et al. 2004, A&A, 428, 847P; Absolute kinematics of radio source components in
     the complete S5 polar cap sample. II. First and second epoch maps at 15 GHz.
Rector, T.A., Stocke, J.T. 2003, AJ, 125, 2447R; High-Resolution Radio Imaging of Gravitational Lensing Candidates in
     the 1 Jansky BL Lacertae Sample.
Schramm, K.-J., Borgeest, U., et al. 1994, A&AS, 106, 349S; The Hamburg Quasar Monitoring program (HQM) at Calar
     Alto. III. Lightcurves of optically violent variable sources.
Seielstad, G.A., Pearson, T.J., Readhead, A.C.S. 1983, PASP, 95, 842S; 10.8-GHz flux density variations among a
     complete sample of sources from the NRAO-Bonn 84 survey.
Steinicke, W.; Katalog heller Quasare und BL Lacertae Objekte; Umkirch 1998.
Stickel, M., Fried, J.W., Kuehr, H. 1989, A&AS, 80, 103S; Optical spectroscopy of 1 Jy BL Lacertae objects and flat
     spectrum radio sources.
Stickel, M., Fried, J.W., Kuehr, H. 1993, A&AS, 98, 393S; The complete sample of 1 Jy BL Lac objects.
     II - Observational data.
Véron-Cetty, M.-P., Véron, P. 2001, A&A 374, 92; A Catalogue of Quasars and Active Nuclei: 10th edition.
Véron-Cetty, M.-P., Véron, P. 2003, A&A 412, 399; A Catalogue of Quasars and Active Nuclei: 11th edition.
Véron-Cetty, M.-P., Véron, P. 2006, A&A 455, 776; A Catalogue of Quasars and Active Nuclei: 12th edition.
Véron-Cetty, M.-P., Véron, P. 2010, A&A 518, 10; A Catalogue of Quasars and Active Nuclei: 13th edition.


Landessternwarte Heidelberg

Hamburg Quasar Monitoring



Misti Mountain observatory

© Stefan Karge  /  last obs. 2022-12-22