J/A+A/577/A36 Sample of weak blazars at mas resolution (Mantovani+, 2015)
A sample of weak blazars at milli-arcsecond resolution.
Mantovani F., Bondi M., Mack K.-H., Alef W., Ros E., Zensus J.A.
<Astron. Astrophys., 577, A36-36 (2015)>
=2015A&A...577A..36M 2015A&A...577A..36M
ADC_Keywords: QSOs ; Active gal. nuclei ; BL Lac objects ; Radio sources
Keywords: galaxies: active - quasars: general - BL Lacertae objects: general
Abstract:
We started a follow-up investigation of the "Deep X-ray Radio Blazar
Survey" objects with declination >-10° to better understand the
blazar phenomenon. We undertook a survey with the European Very Long
Baseline Interferometry Network at 5GHz to make the first images of a
complete sample of weak blazars, aiming at a follow-up comparison
between high- and low-power samples of blazars. We observed 87 sources
with the EVN at 5GHz during the period October 2009 to May 2013. The
observations were correlated at the Max-Planck-Institut fuer
Radioastronomie and at the Joint Institute for VLBI in Europe. The
correlator output was analysed using both the AIPS and DIFMAP software
packages. All of the sources observed were detected. Point-like
sources are found in 39 cases on a milli-arcsecond scale, and 48 show
core-jet structure. The total flux density distribution at 5GHz has a
median value =44+23-10mJy. A total flux density ≤150mJy is
observed in 68 out of 87 sources. Their brightness temperature Tb
ranges between 107K and 1012K. According to the spectral indices
previously obtained with multi-frequency observations, 58 sources show
a flat spectral index, and 29 sources show a steep spectrum or a
spectrum peaking at a frequency around 1-2GHz. Adding to the DXRBS
objects we observed those already observed with ATCA in the Southern
sky, we found that 14 blazars and a Steep Spectrum Radio Quasars, are
associated to γ-ray emitters. We found that 56 sources can be
considered blazars. We also detected 2 flat spectrum narrow line radio
galaxies. About 50% of the blazars associated to a γ-ray object
are BLLacs, confirming that they are more likely detected among
blazars γ-emitters. We confirm the correlation found between the
source core flux density and the γ-ray photon fluxes down to
fainter flux densities. We also found that weak blazars are also
weaker γ-ray emitters compared to bright blazars. Twenty-two
sources are SSRQs or Compact Steep-spectrum Sources, and 7 are GigaHz
Peaked Sources. The available X-ray ROSAT observations allow us to
suggest that CSS and GPS quasars are not obscured by large column of
cold gas surrounding the nuclei. We did not find any significant
difference in X-ray luminosity between CSS and GPS quasars.
Description:
With the EVN (European VLBI Network) we observed all the DXRBS (Deep
X-ray Radio Blazar Survey: Perlman et al. 1998, J/AJ/115/1253; and
Landt et al. 2001, J/MNRAS/323/757) sources with declination
>-10°. The list contains 87 sources selected by applying the
unique criteria of a cut in declination. The pointing positions were
obtained from the FIRST catalogue (Cat. VIII/92) for 63 objects, and
for the remaining sources the coordinates were from the NVSS (Cat.
VIII/65) (Mantovani et al., 2011A&A...533A..79M 2011A&A...533A..79M). This sample of
sources can therefore be considered as a "complete" sample that is
statistically significant.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 84 87 Derived parameters of the observed DXRBS sources
--------------------------------------------------------------------------------
See also:
J/AJ/115/1253 : Deep X-Ray Radio Blazar Survey (DXRBS). I. (Perlman+ 1998)
J/MNRAS/323/757 : Deep X-Ray Radio Blazar Survey (DXRBS). II. (Landt+, 2001)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VIII/92 : The FIRST Survey Catalog, Version 2014Dec17 (Helfand+ 2015)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Name Blazar source name (JHHMM.m+DDMM)
<1WGA JHHMM.m+DDMM> in Simbad
14- 19 A6 --- Code EVN (European VLBI Network) observation code
21- 26 F6.1 mJy Stot [0.5/2378] Total flux density at 5GHz
28- 32 F5.2 mJy rms [0.02/20] Image rms error (in mJy/beam)
34- 37 F4.1 mas aMaj [1.7/21] Beam major axis θmax
39- 41 F3.1 mas aMin [1/6] Beam minor axis θmin
43- 47 F5.1 deg PA [-90/90]? Position angle of beam major axis
49- 51 A3 --- Str [p cj t?] source structure: p=point,
cj=core-jet, t=triple
52- 57 F6.1 mJy Score [0.4/2410] Core flux density obtained by JMFIT
59- 62 F4.1 mas cMaj [0/14] Core major axis θmax
after beam deconvolution
64- 66 F3.1 mas cMin [0/6] Core minor axis θmin
after beam deconvolution
68- 70 I3 deg PAc [0/180]?=- Core major axis position angle
72- 79 F8.4 10+10K Tb [0/108]?=- Brightness temperature (1)
81- 84 F4.2 --- R [0/4]?=- EVN to Effelsberg flux density ratio
--------------------------------------------------------------------------------
Note (1): Tb=4.9*1010Score(1+z)/(θmax*θmin).
Score in Jy and θ in mas; in case of unresolved source,
30% of the beam size is taken; when not available z=0.5 assumed.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 06-Jul-2015