164 research outputs found
Recent X-ray observations of intermediate BL Lac objects
We present recent ROSAT, ASCA and SAX observations of intermediate BL Lac
objects (IBLs), i.e. BL Lacs which are located between high-energy and
low-energy peaked BL Lac objects with respect to alpha_rx. Both the statistical
properties of IBLs from the RGB sample and a detailed broad band X-ray spectral
analysis of two objects (1424+2401, 1055+5644) point towards a continuous
distribution of synchrotron emission peak frequencies among BL Lac objects.Comment: 4 pages, 4 figures; to appear in the proceedings of the conference
"BL Lac Phenomenon" held in Turku, Finland, June 22-26, 199
EVN observations of low-luminosity flat-spectrum AGNs
We present and discuss the results of VLBI (EVN) observations of three
low-luminosity (P(5 GHz)<10^25 W/Hz) Broad Emission Line AGNs carefully
selected from a sample of flat spectrum radio sources (CLASS). Based on the
total and the extended radio power at 5 GHz and at 1.4 GHz respectively, these
objects should be technically classified as radio-quiet AGN and thus the origin
of their radio emission is not clearly understood. The VLBI observations
presented in this paper have revealed compact radio cores which imply a lower
limit on the brightness temperature of about 3X10^8 K. This result rules out a
thermal origin for the radio emission and strongly suggests an emission
mechanism similar to that observed in more powerful radio-loud AGNs. Since, by
definition, the three objects show a flat (or inverted) radio spectrum between
1.4 GHz and 8.4 GHz, the observed radio emission could be relativistically
beamed. Multi-epoch VLBI observations can confirm this possibility in two years
time.Comment: Accepted for publication in MNRA
BZBJ1058+5628: a new quasi-periodic BL Lac
We present the historic photographic light curves of three little known
Blazars (two BL Lacs and one FSRQ), BZB J1058+5628, BZQ J1148+5254 and BZB
J1209+4119 spanning a time interval of about 50 years, mostly built using the
Asiago plate archive. All objects show evident long-term variability, over
which short-term variations are superposed. One source, BZB J1058+5628, showed
a marked quasi-periodic variability of 1 mag on time scale of about 6.3 years,
making it one of the few BL Lac objects with a quasi-periodic behavior.Comment: Accepted by The Astronomical Journal; 7 figures; 7 table
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