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Hamburger Sternwarte - Research
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The HRX-BL Lac sample - evolution of BL Lac objects
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The unification of X-ray and radio selected BL Lacs has been an outstanding problem in the blazar research in the past years.
Recent investigations have shown that the gap between the two classes can be filled with intermediate objects and that apparently
all differences can be explained by mutual shifts of the peak frequencies of the synchrotron and inverse Compton component of
the emission. We study the consequences of this scheme using a new sample of X-ray selected BL Lac objects comprising 104 objects
with z<0.9 and a mean redshift < z > = 0.34. 77 BL Lacs, of which the redshift could be determined for 64 (83%) objects, form a complete sample.
The new data could not confirm our earlier result, drawn from a subsample, that the negative evolution vanishes below a synchrotron
peak frequency log νpeak = 16.5. The complete sample shows negative evolution at the 2σ level (< Ve/Va > = 0.42 +- 0.04). We conclude
that the observed properties of the HRX BL Lac sample show typical behaviour for X-ray selected BL Lacs. They support an evolutionary model,
in which flat-spectrum radio quasars (FSRQ) with high energetic jets evolve towards low frequency peaked (mostly radio-selected) BL Lac objects
and later on to high frequency peaked (mostly X-ray selected) BL Lacs.
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| Distribution of redshifts in the extended HRX-BL Lac sample. The hatched part refers to the complete sample. |
The plane αox - αro covered by the HRX-BL Lac objects.
The points refer to the complete sample, the triangles mark additional objects found within the course of the work. Objects with
αro < 0.2 are called radio quiet. |
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Optical Spectra:
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Related Publications:
- Beckmann, 2000, Doctoral thesis: "Evolutionary behaviour of AGN:
Investigations on BL Lac objects and Seyfert II galaxies", Hamburg
University
- Beckmann, 2000, "Photometry
of 49 X-ray selected BL Lacs", Blazar Data, Vol. 2, 3
- Beckmann, Bade, Wucknitz, 1999, "The extreme high frequency peaked BL Lac 1517+656", A&A 352, 395
- Beckmann, 1999, "Evolutionary behaviour of BL Lac objects", in: Takalo L. et al. eds., "The BL Lac phenomenon", June 22-26 1998, Turku, Finland, PASPC 159
- Bade, Beckmann, Engels, Cordis, Nass, Voges, 1998,
"On the evolutionary behaviour of BL Lac objects", A&A 334, 459
- Beckmann and Wolter, 2000, "New results from the HRX BL Lac
sample", accepted for publication in Astroph. Lett. and Comm.
- Pursimo, Takalo, Beckmann, et al., 2000, "Intensive
Monitoring of OJ 287", A&AS 146, 141
- Watson, Hanlon, McBreen, Smith, Tashiro,
Foley, Metcalfe, Beckmann, Sanchez, Terasranta,
1999, "Simultaneous
Multifrequency Observations of the BL Lac MS 0205.7+3509", A&A 345,
414
- Nass, Bade, Kollgaard, Laurent-Muehleisen, Reimers,
Voges, 1996, "BL Lacertae objects in the ROSAT All-Sky Survey: new
objects and comparison of different search techniques", A&A 309,
419-430
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Last changed Saturday, 04-March-2006 |
D.Engels
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