Frankfurt Quasar Monitoring

1ES 0647+250
Object data

  Cross-Identifications   QSO B0647+250, MG2 J065043+2503, 0647+250
  2MASS J06504649+2502596, RX J0650.7+2502
  2XMM J065046.5+250259, 1FGL J0650.7+250
  1RXS J065046.7+250257, GB6 J0650+2503
  87GB 064743.0+250645, RGB J0650+250

  Equat. coordinates   RA  06 50 46.5     DE  +25 03 00     (J2000)
  Constellation   Gemini
  Type   BL Lac
  Redshift (2)   z=0.203
  Distance (2) (3)
  799 Mpc
  Total mag range (mv) (4)   15.24 - 16.84   
  Catalog Magnitude   15.3 (1)  /  15.7 (2)
  Absolute Magnitude (1)   ---
  Light Travel-Time (2)   2.377 × 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
A 13.593 (0.015) 13.089 (0.008) 12.768 (0.013) 12.459 (0.016)
B 14.125 (0.021) 13.446 (0.015) 13.057 (0.017) 12.699 (0.021)
C 14.405 (0.028) 13.782 (0.023) 13.394 (0.028) 13.033 (0.031)
D 14.870 (0.025) 14.094 (0.013) 13.651 (0.022) 13.264 (0.024)
E 15.648 (0.018) 14.725 (0.011) 14.190 (0.019) 13.703 (0.023)
F 15.892 (0.038) 15.073 (0.028) 14.580 (0.036) 14.089 (0.039)
G 16.085 (0.044) 15.477 (0.026) 15.111 (0.057) 14.743 (0.062)
H 16.695 (0.051) 15.878 (0.026) 15.399 (0.060) 14.929 (0.069)
comparison stars from the AAVSO

Light curve

1ES 0647+250 is a violently variable BL Lac object in Gemini. Its position lies about 1.5° E of 3-mag star Epsilon (27) Gem. 1ES 0647+250 was discovered as a radio source in 1987 during the Second MIT-Green Bank 5 GHz Survey (MG2), which was carried out with the 91-m NRAO radio telescope in Green Bank, West Virginia. The designation 1ES 0647+250 refers to the Einstein Slew Survey, where this object was detected as an X-ray source in the early 1990s. The radio and X-ray position of the new source were matched with a stellar optical counterpart of about mag 15.3 on POSS blue plates. In 1991, spectral analysis revealed a featureless continuum, which led to the classification as a BL Lacertae type object.

The new blazar was found to be violently variable from radio to X-ray wavelengths. Besides the radio and X-ray, 1ES 0647+250 has been detected also as a source of infrared, ultra-violet and even gamma emissions.
The redshift of z=0.203, as given above, is not based on direct spectroscopy but results from the BL Lac luminosity, which is hosted by a typical elliptical galaxy. Other investigations conclude a larger redshift of z=0.41 (Kotilainen 2011). New spectroscopic investigations with large 8-m/10-m class telescopes are needed to fix the true distance of this blazar.

Blazar 1ES 0647+250 is a violently variable object with a total optical range of about 1.6 magnitudes.
According to the literature, the brightness level varies between 15.24 mag and 16.84 mag in the optical, so visual observers need large aperture telescopes to glimpse this stellar object. Both CCD observers and visual observers shall use the comparison stars given above. Another photometric sequence was published by Nilsson et al. (2007).

The finding chart above also shows a circular object, 8.4 arcmin E of the blazar. At first glance its photographic appearance resembles that of a planetary nebula. But in fact, this is a faint face-on disk galaxy with the designation 2MASX J06511477+2503237, denoted as 2MASX (Data from NASA/IPAC Extragalactic database).


The position of blazar 1ES 0647+250 lies about 1.5° E of 3-mag star Epsilon (27) Gem. At a distance of at least 800 Mpc, this blazar is located far behind the eastern outskirts of the Milky Way in Gemini. Therefore, observers find some galactic deep sky showpieces around the blazar:
Open clusters M 35 and NGC 2158 lie some 10° W, supernova remnant IC 443 lies about 8° WSW, and finally sweep your scope 10° to the ESE from the blazar position to meet planetary NGC 2392, the famous  "Eskimo-Nebula". 
Far beyond our Milky Way, two other blazars, both located in Cancer, may attract the observers interest:
OJ 287 (29° east), and PKS 0754+100 (22° to the south-east). Both extragalactic variables lie at a distance of about 3×109 light-years.

Elvis, M., et al. 1992, ApJS 80, 257; The Einstein Slew Survey.
Falomo, R., Kotilainen, J.K., 1999, A&A 352, 85; Optical imaging of the host galaxies of X-ray selected BL Lacertae
Kapanadze, B.Z. 2009, MNRAS, 398, 832; Optical R-band variability of seven X-ray-selected BL Lacertae objects.
Kotilainen, J.K., et al. 2011, A&A 534, L2; The host galaxy of the BL Lacertae object 1ES 0647+250 and its imaging
Langston, G.I., et al. 1990, ApJS 72, 621; The Second MIT-Green Bank 5 GHz Survey.
Linford, J.D., et al. 2012, ApJ 744, 177; Contemporaneous VLBA 5 GHz Observations of Large Area Telescope
     Detected Blazars.
Nilsson, K., et al. 2007, A&A 475, 199; Host galaxy subtraction of TeV candidate BL Lacertae objects.
Sbarufatti, B., Treves, A., Falomo, R. 2005, ApJ 635, 173; Imaging Redshifts of BL Lacertae Objects.
Schachter, J.F., et al. 1993; Ten new BL Lacertae Objects discovered by an efficient X-ray/Radio/Optical Technique.
Urry, C.M., Scarpa, R., et al. 2000, ApJ 532, 816; The Hubble Space Telescope Survey of BL Lacertae Objects.
     II. Host Galaxies.
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

ATel #6726: Optical flare of the TeV blazar 1ES 0647+250


© Stefan Karge  /  last obs. 2023-01-27