207 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
Discovery of a Radio-loud/Radio-quiet Binary Quasar
We report the discovery of a small separation quasar pair (z=0.586, O=18.4,
19.2, sep. = 2.3 arcsec) associated with the radio source FIRST
J164311.3+315618 (S_1400 = 120 mJy). The spectrum of the brighter quasar (A)
has a much stronger narrow emission-line spectrum than the other (B), and also
stronger Balmer lines relative to the continuum. The continuum ratio of the
spectra is flat in the blue at about 2.1, but falls to 1.5 at longer
wavelengths. A K' image shows two unresolved sources with a flux ratio of 1.3.
The different colors appear to result from the contribution of the host galaxy
of B, which is evident from Ca II and high-order Balmer absorption lines
indicative of a substantial young stellar population. New 3.6 cm VLA
observations show that the compact radio source is coincident with quasar A (B
is only marginally detected). We rule out the lensing hypothesis because the
optical flux ratio is A/B = 1.2 to 2, while the radio flux ratio is A/B > 40,
and conclude that this system is a binary. Moreover, the radio-loud quasar is a
compact steep spectrum source. FIRST J164311.3+315618A, B is the lowest
redshift and smallest separation binary quasar yet identified.Comment: 8 pages, 3 figures, to appear in Astrophysical Journal Letter
Discovery of a Classic FR-II Broad Absorption Line Quasar from the FIRST Survey
We have discovered a remarkable quasar, FIRST J101614.3+520916, whose optical
spectrum shows unambiguous broad absorption features while its double-lobed
radio morphology and luminosity clearly indicate a classic Fanaroff-Riley Type
II radio source. Its radio luminosity places it at the extreme of the recently
established class of radio-loud broad absorption line quasars (Becker et al.
1997, 2000; Brotherton et al. 1998). Because of its hybrid nature, we speculate
that FIRST J101614.3+520916 is a typical FR-II quasar which has been
rejuvenated as a broad absorption line (BAL) quasar with a Compact Steep
Spectrum core. The direction of the jet axis of FIRST J101614.3+520916 can be
estimated from its radio structure and optical brightness, indicating that we
are viewing the system at a viewing angle of > 40 degrees. The position angles
of the radio jet and optical polarization are not well-aligned, differing by 20
to 30 degrees. When combined with the evidence presented by Becker et al.
(2000) for a sample of 29 BAL quasars showing that at least some BAL quasars
are viewed along the jet axis, the implication is that no preferred viewing
orientation is necessary to observe BAL systems in a quasar's spectrum. This,
and the probable young nature of compact steep spectrum sources, leads
naturally to the alternate hypothesis that BALs are an early stage in the lives
of quasars.Comment: 14 pages, 6 postscript figures; accepted for publication in the
Astrophysical Journa
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