Are there two populations of BL Lac objects?
نویسندگان
چکیده
منابع مشابه
Bl Lac Objects
SUMMARY: We present the radio detection of 18 BL Lac objects from our survey of over 575 deg 2 of sky. These 18 objects are located within 20 ′′ of the X-ray position, of which 11 have a measured red-shift. All candidates are radio emitters above ∼1 mJy and fall within the range of existing samples on the two colour, α ro vs α ox , diagram with a transitional population of three (3) evident. Tw...
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The TeV emission of low power BL Lac objects has been established by the detection of an handful of them. The knowledge of the level of the TeV emission and its spectrum can shed light on the particle acceleration mechanisms, and it is especially important to assess the still uncertain level of the far infrared background radiation, which can absorb the TeV photons through photon–photon interac...
متن کاملOn the Nature of BL Lac Objects
The BL Lacertae objects, or BL Lacs, have multi-wavelength continua dominated by non-thermal emission from a relativistic jet, and are characterised by a lack of optical emission lines. We find, through observations and modelling that the dominant factor in a source being called a BL Lac is the intrinsic lack of flux from the broad-line region – likely connected with a weak accretion disc – rat...
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The HST snapshot imaging survey of 110 BL Lac objects (Urry et al. 2000) has clearly shown that the host galaxies are massive and luminous ellipticals. The dispersion of the absolute magnitudes is sufficiently small, so that the measurement of the galaxy brightness becomes a valuable way of estimating their distance. This is illustrated constructing the Hubble diagram of the 64 resolved objects...
متن کاملRadioband Variability Properties of BL Lac Objects
Centimeter-wavelength total ux density and linear polarization observations have quantiied the high levels of activity in BL Lac objects and identiied variability timescales ranging from < 1 day to several years. Nearly two decades of single-antenna (UMRAO) observations of a ux-limited sample show that the radioband spectra of the total ux are characteristically at even during this activity: th...
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ژورنال
عنوان ژورنال: Monthly Notices of the Royal Astronomical Society
سال: 1993
ISSN: 0035-8711,1365-2966
DOI: 10.1093/mnras/264.4.919