91 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
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
A VLA Survey of Radio-Selected SDSS Broad Absorption Line Quasars
We have built a sample of 74 radio-selected broad absorption line quasars
from the Sloan Digital Sky Survey Data Release 5 (SDSS DR5) and Faint Images of
the Radio Sky at Twenty Centimeters (FIRST), along with a well matched sample
of 74 unabsorbed "normal" quasars. The sources have been observed with the NRAO
Very Large Array/Expanded Very Large Array at 8.4 GHz (3.5 cm) and 4.9 GHz (6
cm). All sources have additional archival 1.4 GHz (21 cm) data. Here we present
the measured radio fluxes, spectral indices, and our initial findings. The
percentage of BAL quasars with extended structure (on the order of 10%) in our
sample is similar to previous studies at similar resolutions, suggesting that
BAL quasars are indeed generally compact, at least at arsecond resolutions. The
majority of sources do not appear to be significantly variable at 1.4 GHz, but
we find two previously unidentified BAL quasars that may fit into the "polar"
BAL category. We also identify a significant favoring of steeper radio spectral
index for BAL compared to non-BAL quasars. This difference is apparent for
several different measures of the spectral index, and persists even when
restricting the samples to only include compact objects. Because radio spectral
index is a statistical indicator of viewing angle for large samples, these
results suggest that BAL quasars do have a range of orientations but are more
often observed farther from the jet axis compared to normal quasars.Comment: Accepted for publication in the Astrophysical Journa
Four New BL Lac Surveys: Sampling New Populations
The advent of large area deep radio and X-ray surveys is leading to the
creation of many new BL Lac samples. In particular, the ROSAT All-Sky, Green
Bank and FIRST surveys are proving to be rich sources of new BL Lacs. We will
discuss the methods used in four independent BL Lac searches based on these
surveys. Comparison of the broadband spectral energy distributions of these BL
Lacs with those of previously known objects clearly points to the existence of
a large previously unrecognized population of objects with characteristics
intermediate between those exhibited by Low and High energy peaked BL Lacs.Comment: 4 pages, 3 postscript figures, To be published in the Proceedings of
the conference "BL Lac Phenomenon" held in Turku, Finland, June 22-26, 199
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