Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.sao.ru/hq/marat/publ/articles/aah2533.ps Äàòà èçìåíåíèÿ: Wed Feb 24 17:32:50 2010 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 07:37:19 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: m 80

A&A 370, 78--86 (2001)
DOI: 10.1051/0004­6361:20010215
c
# ESO 2001
Astronomy
&
Astrophysics
Observations of the bright radio sources in the North Celestial
Pole region at the RATAN­600 radio telescope
M. G. Mingaliev 1 , V. A. Stolyarov 1,2 , R. D. Davies 3 , S. J. Melhuish 4 , N. A. Bursov 1 , and G. V. Zhekanis 1
1 Special Astrophysical Observatory of Russian Academy of Sciences, Nizhnij Arkhyz,
Karachaevo­Cherkessia Republic 357147, Russia
e­mail: marat@sao.ru; vlad@sao.ru; nnb@ratan.sao.ru; gvz@ratan.sao.ru
2 University of Cambridge, Institute of Astronomy, Madingley Rd., Cambridge CB3 OHA, UK
e­mail: vlad@ast.cam.ac.uk
3 University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, UK
e­mail: rdd@jb.man.ac.uk
4 University of Wales, Cardi#, Department of Physics and Astronomy, 5, The Parade, Cardi# CF24 3YB, UK
e­mail: Simon.Melhuish@astro.cf.ac.uk
Received 3 November 2000 / Accepted 2 February 2001
Abstract. A survey of the North Celestial Pole region using the RATAN­600 radio telescope at five frequencies
in the range 2.3 to 21.7 GHz is described. Sources were chosen from the NVSS catalogue. The flux densities of
171 sources in the Declination range +75 # to +88 # are presented; typical flux density errors are 5--10 percent
including calibration errors. About 20 percent of the sources have flat spectra or a flat component.
Key words. radio astronomy -- radio continuum -- galaxies
1. Introduction
In the current paper we present the results of observa­
tions of bright radio sources in the North Celestial Pole
(NCP) region within the declination range of +75 # # # #
+88 # taken with the RATAN­600 radio telescope of the
Russian Academy of Sciences (Korolkov & Pariiskii 1979;
Parijskij 1993). This NCP survey was initiated as a com­
pliment to the 5 GHz interferometric study of Galactic
foreground emission in the NCP made at Jodrell Bank in
1998--1999 (Melhuish et al. 2001). In order to obtain infor­
mation about Galactic synchrotron and free­free emission
in the survey area it was necessary to determine the 5 GHz
flux densities of the point sources in the area and remove
their contribution from the map.
Up to the present time, there has been no sensitive
survey of the NCP region at frequencies higher than the
1.4 GHz NRAO VLA Sky Survey (NVSS), (Condon et al.
1998). The 5 GHz Greenbank survey (Gregory et al. 1996)
only extends northwards as far as # = +75 # . There is
limited data available at 5 GHz from the early survey
at +88 # # # # +90 # of Pauliny­Toth et al. (1978) and
Send o#print requests to: V. Stolyarov,
e­mail: vlad@ast.cam.ac.uk
from the Kuehr et al. (1981) catalogue of bright sources.
Furthermore, since a sizable fraction (perhaps as many
as 20%) of 5 GHz sources may have flat spectra and are
variable, a contemporary survey covering 5 GHz was re­
quired for the NCP project. The upper Declination limit
of the present RATAN­600 survey was set at +88 # since
the telescope is used in transit mode and data cannot be
collected close to the NCP in this mode.
2. Selection criteria for the survey
The aim of this NCP survey was to obtain information
about bright point sources which might make a signifi­
cant contribution to the 5 GHz degree­scale interferom­
eter survey of foreground Galactic emission in the NCP
(Melhuish et al. 2001). The interferometer has a resolution
of 2 # and a temperature/flux density sensitivity of 60 µK
in antenna temperature per Jansky. In order to achieve
a survey sensitivity approaching 10 µK it was decided to
measure directly with RATAN­600 all those sources giv­
ing 10 µK or more with the interferometer, corresponding
to a flux density S # 150 mJy. At this flux density there
is one source per interferometer beam area of 2 # â 2 # .

M. G. Mingaliev et al.: Observations in the NCP region 79
Table 1. Parameters of the receivers used in the survey. See
text for meaning of the symbols
#c , GHz ##, GHz #T , mK Tphys , K Tampl , K T sys , K
21.7 2.5 3.5 15 23 77
11.2 1.4 3.0 15 18 70
7.7 1.0 3.0 15 14 62
3.9 0.6 2.5 15 8 37
2.3 0.4 8.0 310 35 95
The sources chosen for measurement were taken from
the 1.4 GHz NVSS catalogue, the catalogue covering the
NCP region which is nearest in frequency to 5 GHz.
A 150 mJy flux density limit at 5 GHz corresponds to
350--400 mJy at 1.4 GHz assuming an average spectral in­
dex of 0.7 (S # # -# ) for the sources. Accordingly, the
adopted ``complete sample'' criteria for the sources se­
lected from the NVSS catalogue were:
1. Flux density S # # 400 mJy at the NVSS frequency of
1.4 GHz;
2. 00 h
# # # 24 h ;
3. +75 # # # # +88 # .
In total we have selected for observation 182 objects which
satisfy these criteria.
3. The observations
The observations were made in February­March 1999
using the South sector of the RATAN­600 reflector
-- type radio telescope at 2.3, 3.9, 7.7, 11.2 and
21.7 GHz (Parijskij 1993; Berlin et al. 1997; Berlin &
Friedman 1996). The parameters of the receivers are listed
in Table 1, where # c is the central frequency, ## is the
bandwidth, #T is the sensitivity of the radiometer over
1 s integration, T phys is the physical temperature of the
radiometer amplifier, T ampl is the noise temperature of the
amplifier and T sys is the noise temperature of the whole
system at the given frequency. All of the radiometers have
HEMT first­stage amplifiers.
Information about FWHM can be found in the article
by Kovalev et al. (1999). For example at 11.2 GHz the
FWHM is about 17 ## â 2 # at the elevations of the NCP
observations.
Usually each source was observed 5--8 times per set.
Scans of all of the sources were corrected for baseline slope
when fitted to a Gaussian response using data reduction
software developed by Verkhodanov (1997). The accuracy
of the antenna temperature of each source was determined
as the standard error of the mean from the N observations
of the set.
4. Calibration and data reduction
The calibration of our observations is a challenging task.
There are no radio astronomical calibrators listed in this
area of the sky. The only place where we have some in­
formation about source fluxes in a wide frequency range
(0.325--42 GHz) in the NCP region is the VLA Calibrator
List (Perley & Taylor 1999). However, the fluxes listed
there are approximate because most of the sources from
the VLA List are compact and, hence, variable. To address
this problem we selected for our purpose only sources with
steep spectra that are not likely to be variable and, if possi­
ble, with minimal expected VLA amplitude closure errors
(about 3%). The fluxes of the calibrators from the VLA
Calibrator List are listed at 90, 20, 6, 3.7, 2 and 0.7 cm
wavelength bands (0.325, 1.5, 5, 8.1, 15 and 42.9 GHz
respectively). In order to get fluxes at the RATAN­600
frequency bands the spectra of the calibrators were in­
terpolated to the desired frequencies by second order
polynomial.
4.1. The calibration errors, # c
The flux density measurement procedure at the RATAN­
600 is described by Aliakberov et al. (1985). The response
of the antenna to a source with known flux density at
a given frequency # is a function of antenna elevation
(Mingaliev et al. 1998), which may be expressed as:
T ant,# = F # (S # , e) = S # f # (e) S # = T ant,# g # (e), (1)
where
g # (e) = 1/f # (e) ­ elevation calibration function;
T ant,# ­ antenna temperature;
F # , f # ­ arbitrary functions;
e = 90 - # + # ­ antenna elevation;
# = 43. # 65333 ­ latitude of the telescope site.
In order to get the flux density from T ant,# we have to mul­
tiply it by the elevation calibration function g # (e), which is
believed to be a second order polynomial (Trushkin 1985).
To get an estimate of this function we observe the calibra­
tion sources of known flux density spanning a wide range
of declination, #. Having the list of values
g # (e i ) = S #,i /T ant,#,i
for di#erent sources we can approximate the functions
g # (e) by a second order polynomial with the help of min­
imization of the mean square value of the estimated error
(least square estimator).
The names of calibration sources we used and their
adopted flux densities are listed in the Table 2. The as­
sumed flux density errors are 3% as given in the VLA
Calibrator List.
The calibration curves g # (e) for 2.3, 3.9, 7.7 and
11.2 GHz are given in Fig. 1. A second order polynomial
fit was made to the observational data at each frequency.
We found the errors in the calibration curves were 11,
10.3, 2.4, 5.6 and 7.4% at 21.7, 11.2, 7.7, 3.9 and 2.3 GHz
respectively. The total calibration error is the quadratic
addition of the 3% VLA Calibration List error and the
error from the g # (e) calibration curve.

80 M. G. Mingaliev et al.: Observations in the NCP region
n c = 3.9 GHz
25 30 35 40 45 50 55 60
0
1
2
3
4
5
6
n c
= 7.7 GHz
g
n
(e),
Jy/K
Elevation e, deg.
0
1
2
3
4
5
6 n c = 2.3 GHz
g
n
(e),
Jy/K
25 30 35 40 45 50 55 60
n c
= 11.2 GHz
Elevation e, deg.
Fig. 1. Calibration curves for 2.3, 3.9, 7.7 and 11.2 GHz bands
Table 2. Adopted calibrator source flux densities. Sources are from the VSA Calibrator List; errors are assumed to be 3%
Name S(#c = 21.7 GHz), S(#c = 11.2 GHz), S(#c = 7.7 GHz), S(#c = 3.9 GHz), S(#c = 2.3 GHz),
of the source Jy Jy Jy Jy Jy
J0017+815 0.48 0.78 0.94 1.00 0.9
J0229+777 -- -- 0.41 1.05 1.8
J0410+769 1.14 1.77 2.23 3.35 4.49
J0626+820 0.31 0.56 0.74 1.01 0.95
J1435+760 -- 0.31 0.44 0.74 1.03
J1459+716 1.00 1.72 2.27 3.69 5.33
J2022+761 0.42 0.41 0.43 0.44 0.46
4.2. The errors of T ant measurements, #m
The specifics of the RATAN­600 observations lead to the
fact that the errors of the antenna temperature measure­
ments depend not only on the receiver noise, but also
on the atmospheric fluctuations on the scale of the main
beam, on the accuracy of antenna surface setting for the
actual source observation and on the accuracy of the feed
cabin positioning (the cabin with secondary mirror and
receivers).
Generally speaking, the part of these errors due to the
receiver noise can be estimated according to the formula
#T rec = #T/(#tNk) 1/2 (2)
where #T is the sensitivity of the receiver over 1 s (listed
in Table 1); #t is an integration time, the time that the
source takes to cross the main beam of the antenna during
the drift scan; N is the number of the drift scans; k is equal
to 1 for single horn receivers (2.3 and 3.9 GHz) and 2 for
beam­switching receivers (7.7, 11.2, 21.7 GHz), where we
can take into account both positive and negative beams.
The variable parameter is #t, because it depends on the
width of the main beam which is di#erent for di#erent
frequencies, and varies with declination. In the case of the
NCP declination range and the frequency range 21.7 to
2.3 GHz, #t lies in the range 1--15 s. As an example for
3.9 GHz, # = +75 # , #t = 4 s and N = 5, #T rec is equal
to 0.56 mK.
Unfortunately the contribution of atmospheric fluctu­
ations increases as #t increases corresponding to larger
angular scales thereby partially reducing the growth of
sensitivity expected from longer integration times. The er­
rors related to the accuracy of antenna surface setting and
feed cabin positioning are more complicated to account
for. The feed cabin position errors are most important for
high frequency observations; as an example it is necessary
to position the cabin with an accuracy of 0.1#, which is
1.4 mm in the case of 21.7 GHz.
However, estimating of the antenna temperature of the
source for every drift scan (e.g by Gaussian fitting) and
then calculating the variance of the T ant for the N obser­
vations of the data set can give us the measurement error,
#m , including all of the components listed above.
4.3. The total errors, # t
The total fractional error in the flux densities listed in this
survey is the quadratic sum of the total calibration error

M. G. Mingaliev et al.: Observations in the NCP region 81
and the error in the antenna temperature measurement,
namely,
# # t
S #
# 2
= # # c
g # (e) # 2
+ # #m
T ant,#
# 2
(3)
where
# t ­ total standard error;
# c ­ standard error of calibration;
#m ­ standard error of T ant,# measurement;
S # ­ flux density;
g # (e) = 1/f # (e) ­ elevation calibration function;
T ant,# ­ antenna temperature.
The values of the standard error of T ant,# measurement,
#m , are 2--3% for 11.2, 7.7 and 3.9 GHz, 3--5% for 2.3 GHz
and 7--11% for 21.7 GHz. For the brighter sources #m is
typically half these values, indicating highly consistent
observations. Thus at the frequencies of 21.7, 11.2 and
3.9 GHz the calibration errors dominate.
4.4. Comparison with the other catalogues
The RATAN­600 results described in this paper are in
good accordance with the flux densities given by NVSS at
1.4 GHz, the Westerbork Northern Sky Survey (WENSS;
Rengelink et al. 1997) at 0.325 GHz and the earlier data
of the Kuehr (1981) Catalogue. Four sample spectra are
shown in Fig. 2 which compare the RATAN­600 data with
those from the three above catalogues. The sources illus­
trated all have steep spectra and as a consequence are not
likely to be variable. The few discrepancies in the plotted
spectra are all in the older Kuehr data.
5. Results
The spectra for 171 sources in the present RATAN­600
NCP survey are given in Table 4. Data from WENSS
and NVSS are included. Nearly all the sources have com­
plete data at 2.3, 3.9, 7.7 and 11.2 GHz; 40 sources have
21.7 GHz flux densities. Only a few of these sources have
been observed previously over this wide frequency range.
The columns in the table are:
Column 1 : The source name (NVSS notation), cor­
responding to epoch J2000 coordinates;
Columns 2-3 : The flux density in Jy and standard er­
ror at 0.325 GHz (WENSS catalogue,
Rengelink et al. 1997);
Columns 4-5 : The flux density in Jy and standard error
at 1.4 GHz (NVSS catalogue, Condon
et al. 1998);
Columns 6-15 : The flux density in Jy and total stan­
dard error, # t , at 2.3, 3.9, 7.6, 11.2 and
21.7 GHz respectively;
Column 16 : The spectral index # = - log(S(# 1 )/
S(# 2 ))/ log(# 1 /# 2 ), computed between
fluxes at 0.325 and 11.2 GHz (or the
nearest available frequencies).
A number of the sources in the NVSS target list were
not fully resolved in the RATAN­600 observations, largely
as a result of the more extended beam in the declination
direction. These closely adjacent sources are listed as a
single entry in Table 4 and are designated as RAXXX
and DecXXX. The listed flux densities of these complexes
are the sum of the flux densities of the individual sources.
The NVSS sources contributing to each of the 7 complexes
are given in Table 3.
6. Discussion
Some preliminary comments are worthwhile on the multi­
frequency data for this NCP survey in which 171 individ­
ual sources were identified.
6.1. The contribution to 5 GHz interferometry
The first aim of these observations was to obtain a list of
those sources which would contribute at a significant level
to our 5 GHz survey (Melhuish et al. 2001) of the NCP.
The chosen limit to the flux density at 5 GHz was 150 mJy
which corresponds to a signal amplitude of 10 µK in the
interferometer. The majority of sources (80 percent) were
stronger than this limit and would make a significant con­
tribution to the CMB foreground and should be removed
from the interferometer survey.
The question then arises as to the further contribu­
tion from flat spectrum and rising spectrum sources not
included in our survey which would have a 5 GHz flux den­
sity of #150 mJy. Remembering that our source selection
criterion was 400 mJy at 1.4 GHz, a spectral index of 0.7
gives a flux density of 150 mJy at 5 GHz. A source spectral
index of 0.2 will give twice this limit; only 10 percent of
our sources chosen at 1.4 GHz have spectral indices flatter
than this value. Accordingly there will be a further con­
tribution from such sources with flux densities at 1.4 GHz
of 200--400 mJy. Assuming the fraction of flat spectrum
sources stays constant with decreasing frequency, we may
expect #5 sources in this category. Yet another contri­
bution will come from Gigahertz Peaked Spectrum (GPS)
sources; likewise there will be #5 extra sources with a flux
density above 150 mJy at 5 GHz.
6.2. Statistics of sources spectra
Although this is a modest sample of GHz spectra, it
provides an indication of the spectral properties of the
brightest radio sources in the NCP region (+75 # # # #
+88 # ). We would expect them to follow the trends in
the general field. One particular advantage of the present
catalogue is that all the sources were observed simul­
taneously at all frequencies to provide an instantaneous
spectrum una#ected by source variability. The histograms
of spectral index values estimated over the frequency
ranges 0.325/1.4 GHz, 0.325/3.9 GHz, 3.9/11.2 GHz and
0.325/11.2 GHz are presented in Figs. 3--6 respectively.

82 M. G. Mingaliev et al.: Observations in the NCP region
0,1
1
10
100
Flux,
Jy
J001631+791651 Kuehr
RATAN­600
WENSS and NVSS
1
10
J041045+765645 Kuehr
RATAN­600
WENSS and NVSS
0,1 1 10
0,1
1
10
Frequency, GHz
Flux,
Jy
J144709+765621 Kuehr
RATAN­600
WENSS and NVSS
0,1 1 10
1
10
Frequency, GHz
J234403+862640 Kuehr
RATAN­600
WENSS and NVSS
Fig. 2. Four sample source spectra from Kuehr catalogue compared with RATAN­600, NVSS and WENSS data
Table 3. Complex sources
Name in NVSS Name in the Table 4 Name in NVSS Name in the Table 4
J022235+861727 J0222XX+861XXX J184142+794752 J184XXX+794XXX
J022248+861851 J184151+794727
J022249+862027 J184214+794613
J184226+794517
J074246+802741 J074XXX+802XXX
J074305+802544 J204257+750428 J20425X+750XXX
J204259+750306
J101330+855411 J101XXX+855XXX
J101412+855349 J211814+751203 J2118XX+751XXX
J211817+751112
J235521+795552 J2355XX+795XXX
J235525+795442
The majority of the sources have spectral indices in
the range 0.6 to 1.5 at GHz frequencies. The canonical
steepening of synchrotron spectra at higher frequencies
is evident in the data. The median spectral index in the
range 0.325/1.4 GHz is 0.78. This value rises to 0.82 for
1.4/2.3 GHz, to 0.95 for 2.3/3.9 GHz and to 1.15 for
3.9/11.2 GHz. At the higher part of this frequency range
there is an increasing spread in the range of spectral in­
dices which indicates that the turn­over of the spectrum
occurs at a range of GHz frequencies. This broadening of
the histogram is readily seen in Fig. 5 where a significant
number (#30 percent) have a spectral index greater than
1.2 in the frequency range 3.9/11.2 GHz; a small fraction
(#10 percent) of these higher spectral indices are a re­
sult of the significant total error, # t , on weaker sources
at 11.2 GHz.
The fraction of flatter spectrum sources in our GHz
NCP survey, as illustrated in Figs. 4--6, is 20--25 percent.
This family of flattish spectrum sources is of particular
concern as a foreground in the measurement of fluctua­
tions in the cosmic microwave background.
6.3. Individual sources with compact components
The spectral signature of compact radio sources is a flat
component arising from synchrotron self­absorption. Such
a component may be seen as a flat spectrum over a wide
frequency range, a flat spectrum component at a high
frequency emerging from a steep spectrum low­frequency
source or a GHz Peaked Spectrum source. Such spectra are
found in some 20 percent of the 171 sources of the present
survey. 14 sources show a relatively flat spectrum over the

M. G. Mingaliev et al.: Observations in the NCP region 83
Table 4. Fluxes of the sources in the NCP region
Name, S 0.325 # t S 1.4 # t S 2.3 # t S 3.9 # t S 7.7 # t S 11.2 # t S 21.7 # t Sp. index
NVSS Jy, WENSS Jy, NVSS Jy Jy Jy Jy Jy # 0.325/11.2
J000943+772440 2.059 0.082 0.628 0.021 0.447 0.04 0.267 0.017 0.161 0.007 0.14 0.016 -- -- 0.76
J001236+854313 1.605 0.064 0.691 0.023 0.539 0.048 0.246 0.018 0.148 0.005 0.099 0.011 -- -- 0.79
J001311+774846 4.517 0.181 2.101 0.071 1.578 0.141 0.981 0.056 0.467 0.012 0.314 0.034 0.202 0.03 0.75
J001631+791651 9.959 0.398 3.651 0.123 2.46 0.183 1.422 0.087 0.643 0.017 0.422 0.044 0.145 0.022 0.89
J001708+813508 0.688 0.028 0.693 0.023 0.853 0.067 1.022 0.058 0.919 0.023 0.788 0.082 0.441 0.065 --0.04
J001816+782743 2.16 0.086 0.707 0.024 0.428 0.038 0.252 0.015 0.109 0.005 0.054 0.006 -- -- 1.04
J003812+844727 0.972 0.039 0.406 0.014 0.332 0.03 0.223 0.017 0.108 0.005 0.084 0.01 -- -- 0.69
J004617+751752 1.371 0.055 0.444 0.015 0.273 0.025 0.163 0.012 0.074 0.004 0.04 0.005 -- -- 1
J011045+873822 2.215 0.089 0.686 0.023 0.467 0.042 0.206 0.015 0.118 0.005 0.081 0.009 -- -- 0.93
J013156+844612 2.072 0.083 0.777 0.026 0.603 0.054 0.361 0.027 0.186 0.005 0.136 0.016 -- -- 0.77
J015207+755035 2.823 0.113 0.839 0.028 0.526 0.047 0.285 0.016 0.095 0.005 0.054 0.006 -- -- 1.12
J020537+752207 0.86 0.035 1.151 0.039 0.873 0.078 0.611 0.036 0.309 0.009 0.202 0.021 0.097 0.015 0.41
J020723+795602 3.89 0.156 1.363 0.046 0.932 0.072 0.582 0.033 0.252 0.008 0.18 0.021 -- -- 0.87
J0222XX+861XXX 20.538 0.822 6.478 0.217 4.006 0.422 3.006 0.261 1.137 0.133 0.813 0.095 -- -- 0.91
J022454+765554 5.949 0.238 1.927 0.065 1.271 0.095 0.744 0.042 0.334 0.009 0.21 0.023 0.085 0.013 0.94
J022914+774316 8.067 0.323 2.683 0.09 1.663 0.124 0.95 0.054 0.401 0.011 0.259 0.028 0.111 0.016 0.97
J023010+814129 2.285 0.091 1.048 0.035 0.783 0.07 0.544 0.031 0.284 0.008 0.213 0.023 0.212 0.031 0.67
J025100+791359 2.475 0.099 0.713 0.024 0.475 0.043 0.226 0.013 0.089 0.003 0.036 0.004 -- -- 1.2
J025417+791147 2.186 0.088 0.643 0.022 0.463 0.041 0.212 0.013 0.105 0.006 0.067 0.008 -- -- 0.98
J030011+820238 2.415 0.097 1.379 0.046 1.078 0.102 0.586 0.034 0.265 0.008 0.177 0.022 -- -- 0.74
J030454+772731 0.164 0.008 0.977 0.033 0.926 0.07 0.634 0.036 0.344 0.009 0.262 0.028 0.157 0.024 --0.13
J035150+800437 1.534 0.061 0.546 0.018 0.368 0.033 0.211 0.012 0.078 0.004 0.041 0.005 -- -- 1.02
J035446+800929 1.243 0.05 0.644 0.022 0.499 0.045 0.371 0.023 0.279 0.008 0.259 0.028 0.211 0.031 0.44
J035629+763742 1.969 0.079 0.629 0.021 0.397 0.036 0.252 0.016 0.127 0.007 0.098 0.011 -- -- 0.85
J035817+783719 1.334 0.053 0.508 0.017 0.367 0.033 0.226 0.016 0.102 0.003 0.065 0.007 -- -- 0.85
J040652+763354 1.592 0.064 0.527 0.018 0.384 0.034 0.195 0.012 0.095 0.004 0.068 0.008 -- -- 0.89
J041045+765645 9.406 0.376 5.62 0.189 4.538 0.336 3.512 0.197 2.215 0.054 1.769 0.182 1.279 0.142 0.47
J041426+761243 1.359 0.054 0.405 0.014 0.259 0.023 0.147 0.011 0.061 0.003 0.04 0.005 -- -- 1
J041531+842457 1.965 0.079 0.578 0.019 0.453 0.041 0.235 0.015 0.128 0.004 0.09 0.01 -- -- 0.87
J041946+755915 1.491 0.06 0.427 0.014 0.273 0.025 0.166 0.01 0.076 0.004 0.045 0.005 -- -- 0.99
J042205+762708 3.75 0.15 1.043 0.035 0.598 0.053 0.309 0.018 0.1 0.006 0.05 0.006 -- -- 1.22
J042408+765341 1.614 0.065 0.408 0.014 0.223 0.02 0.146 0.011 0.035 0.002 0.019 0.002 -- -- 1.25
J042918+770911 4.702 0.188 0.945 0.032 0.517 0.044 0.266 0.015 0.085 0.004 0.026 0.003 -- -- 1.47
J044545+783856 1.807 0.072 0.65 0.022 0.46 0.041 0.292 0.022 0.156 0.004 0.113 0.013 0.068 0.01 0.78
J050731+791257 1.859 0.074 0.629 0.021 0.496 0.044 0.307 0.019 0.155 0.004 0.122 0.014 0.066 0.01 0.77
J050842+843204 0.149 0.007 0.295 0.01 0.302 0.031 0.242 0.019 0.246 0.008 0.25 0.027 0.169 0.025 --0.15
J061837+782123 2.511 0.101 1.075 0.036 0.733 0.066 0.501 0.038 0.227 0.012 0.119 0.014 -- -- 0.86
J062205+871948 2.105 0.084 0.645 0.022 0.534 0.048 0.251 0.019 0.1 0.006 0.072 0.008 -- -- 0.95
J062602+820225 0.199 0.009 0.681 0.023 0.962 0.086 0.947 0.054 0.763 0.019 0.717 0.074 0.521 0.06 --0.36
J063012+763245 2.187 0.088 0.783 0.026 0.7 0.063 0.339 0.025 0.152 0.009 0.092 0.011 -- -- 0.9
J063012+763245 1.512 0.061 0.481 0.016 -- -- 0.193 0.015 0.085 0.004 0.053 0.006 -- -- 0.95
J063825+841106 3.834 0.153 1.1 0.037 0.737 0.066 0.426 0.029 0.197 0.005 0.155 0.018 -- -- 0.91
J064045+781327 1.605 0.064 0.688 0.023 0.403 0.036 0.249 0.018 0.092 0.004 0.048 0.005 -- -- 0.99
J064558+775502 2.054 0.082 0.608 0.02 0.458 0.041 -- -- 0.098 0.006 0.067 0.008 -- -- 0.97
J071452+815153 1.704 0.068 0.551 0.018 0.419 0.037 0.255 0.016 0.141 0.004 0.127 0.014 -- -- 0.73
J072611+791130 0.092 0.005 0.501 0.017 0.75 0.057 0.904 0.051 0.818 0.02 0.742 0.077 0.48 0.054 --0.59
J073433+765813 1.361 0.055 0.475 0.016 0.282 0.025 0.217 0.013 0.098 0.006 0.074 0.009 -- -- 0.82
J074XXX+802XXX 9.574 0.383 3.322 0.112 2.408 0.185 1.699 0.124 0.954 0.05 0.681 0.076 -- -- 0.75
J075058+824158 3.741 0.15 1.845 0.062 1.579 0.119 1.421 0.08 0.959 0.024 0.881 0.091 0.643 0.095 0.41
J080626+812620 1.506 0.06 0.406 0.014 0.251 0.023 0.127 0.008 0.045 0.002 0.033 0.004 -- -- 1.08
J080734+784610 1.574 0.063 0.525 0.018 0.39 0.035 0.218 0.013 0.106 0.003 0.084 0.01 -- -- 0.83
J082550+765313 1.903 0.076 0.689 0.023 0.491 0.044 0.303 0.018 0.159 0.004 0.121 0.014 0.028 0.004 0.78
J083236+800601 2.019 0.081 0.867 0.029 0.638 0.057 0.392 0.023 0.184 0.005 0.132 0.015 0.051 0.008 0.77
J084833+783003 5.369 0.215 1.509 0.051 0.86 0.077 0.508 0.029 0.203 0.006 0.127 0.014 0.038 0.006 1.06
J085834+750121 0.239 0.01 0.948 0.032 0.578 0.052 0.302 0.017 0.097 0.006 0.048 0.005 -- -- 0.45
J090112+780930 1.422 0.057 0.447 0.015 0.252 0.023 0.165 0.012 0.069 0.003 0.059 0.007 -- -- 0.9
J090842+834543 1.039 0.042 0.448 0.015 0.325 0.029 0.221 0.013 0.118 0.003 0.099 0.011 -- -- 0.66
J092016+862845 2.122 0.085 0.519 0.017 0.345 0.031 0.173 0.013 0.065 0.003 0.036 0.004 -- -- 1.15
J093239+790629 9.234 0.369 2.241 0.075 1.333 0.119 0.667 0.038 0.235 0.006 0.127 0.014 -- -- 1.21
J093817+781528 2.062 0.083 0.699 0.023 0.426 0.038 0.272 0.016 0.125 0.004 0.075 0.009 -- -- 0.94
J093923+831526 11.592 0.464 2.953 0.099 1.802 0.134 0.917 0.052 0.304 0.009 0.171 0.02 -- -- 1.19
J094440+825408 1.904 0.076 0.735 0.025 0.54 0.048 0.358 0.023 0.173 0.006 0.129 0.015 -- -- 0.76
J095559+791134 1.295 0.052 0.415 0.014 0.254 0.023 0.152 0.009 0.061 0.003 0.047 0.005 -- -- 0.94
J100005+812702 2.541 0.102 0.864 0.029 0.561 0.05 0.304 0.017 0.122 0.007 0.069 0.008 -- -- 1.02
J100741+813150 3.632 0.145 0.855 0.029 0.496 0.044 0.257 0.015 0.096 0.003 0.05 0.006 -- -- 1.21
J100949+810719 1.5 0.06 0.455 0.015 0.328 0.029 0.195 0.012 0.081 0.004 0.062 0.007 -- -- 0.9
J101015+825014 0.741 0.03 0.504 0.017 0.507 0.045 0.622 0.035 0.607 0.015 0.628 0.066 0.548 0.064 0.05
J101037+765052 3.076 0.123 0.806 0.027 0.522 0.047 0.235 0.02 0.071 0.004 0.033 0.004 -- -- 1.28
J101XXX+855XXX 1.973 0.079 0.81 0.027 0.537 0.045 0.303 0.034 0.109 0.007 0.066 0.008 -- -- 0.96
J101734+810517 2.894 0.116 1.172 0.039 0.838 0.075 0.512 0.03 0.194 0.006 0.12 0.014 -- -- 0.9
J102326+803255 6.905 0.276 1.807 0.061 1.144 0.102 0.627 0.036 0.185 0.005 0.093 0.011 -- -- 1.22
J102926+785241 2.559 0.102 1.111 0.037 0.741 0.066 0.525 0.03 0.25 0.006 0.164 0.019 -- -- 0.78
J104423+805439 0.643 0.026 0.828 0.028 0.829 0.074 0.961 0.054 1.212 0.029 1.362 0.14 1.206 0.134 --0.21

84 M. G. Mingaliev et al.: Observations in the NCP region
Table 4. continued
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
J105150+791341 1.894 0.076 0.525 0.018 0.314 0.028 0.179 0.01 0.078 0.004 0.06 0.007 -- -- 0.98
J110405+793253 0.338 0.014 0.514 0.017 0.491 0.044 0.377 0.021 0.237 0.006 0.172 0.018 0.11 0.016 0.19
J110412+765859 7.554 0.302 2.341 0.079 1.518 0.113 0.887 0.05 0.395 0.01 0.224 0.023 -- -- 0.99
J111342+765449 1.534 0.061 0.471 0.016 0.29 0.026 0.183 0.011 0.095 0.005 0.066 0.007 -- -- 0.89
J112342+773123 1.516 0.061 0.407 0.014 0.228 0.02 0.151 0.009 0.055 0.003 0.036 0.004 -- -- 1.06
J114829+782721 0.97 0.039 0.42 0.014 0.3 0.027 0.206 0.012 0.088 0.005 0.074 0.009 -- -- 0.73
J115312+805829 1.39 0.056 1.343 0.045 1.887 0.146 1.922 0.108 1.715 0.042 1.696 0.175 1.251 0.138 --0.06
J115504+753439 1.822 0.073 0.817 0.027 0.594 0.053 0.407 0.025 0.201 0.006 0.137 0.016 -- -- 0.73
J115522+815709 2.017 0.081 0.671 0.023 0.428 0.038 0.227 0.019 0.1 0.004 0.065 0.007 -- -- 0.97
J115608+823505 1.4 0.056 0.404 0.014 0.25 0.023 0.175 0.02 0.065 0.003 0.056 0.007 -- -- 0.91
J115713+811824 1.269 0.051 0.981 0.033 0.766 0.06 0.556 0.033 0.301 0.009 0.222 0.023 -- -- 0.49
J122015+792732 1.409 0.056 0.517 0.017 0.334 0.03 0.214 0.012 0.084 0.004 0.043 0.005 -- -- 0.99
J122340+804004 1.204 0.048 0.705 0.024 0.701 0.063 0.752 0.043 0.767 0.019 0.808 0.083 0.775 0.087 0.11
J122518+860839 1.532 0.061 0.453 0.015 0.294 0.026 0.164 0.016 0.082 0.004 0.041 0.005 -- -- 1.02
J123708+835704 1.909 0.076 0.778 0.026 0.667 0.051 0.333 0.02 0.186 0.005 0.122 0.014 -- -- 0.78
J125736+834231 1.145 0.046 0.475 0.016 0.375 0.034 0.27 0.019 0.176 0.005 0.164 0.019 -- -- 0.55
J130035+805438 4.837 0.194 1.251 0.042 0.777 0.069 0.386 0.022 0.166 0.004 0.107 0.012 -- -- 1.08
J130538+815626 1.734 0.069 0.49 0.016 0.32 0.029 0.17 0.01 0.077 0.004 0.054 0.006 -- -- 0.98
J130609+800825 2.218 0.089 0.785 0.026 0.597 0.053 0.365 0.022 0.18 0.007 0.142 0.016 -- -- 0.78
J130705+764918 1.178 0.047 0.754 0.025 0.531 0.048 0.359 0.021 0.18 0.006 0.124 0.014 -- -- 0.64
J130811+854424 1.711 0.069 0.593 0.02 0.418 0.037 0.236 0.015 0.156 0.009 0.108 0.012 -- -- 0.78
J131723+821916 3.126 0.125 0.869 0.029 0.46 0.041 0.29 0.017 0.114 0.007 0.08 0.009 -- -- 1.04
J132053+845011 0.702 0.028 0.436 0.015 0.484 0.044 0.28 0.021 0.211 0.007 0.189 0.022 -- -- 0.37
J132145+831613 0.829 0.033 0.565 0.019 0.485 0.043 0.333 0.025 0.275 0.015 0.262 0.03 -- -- 0.33
J132331+780947 1.192 0.048 0.482 0.016 0.346 0.031 0.23 0.014 0.106 0.003 0.072 0.008 -- -- 0.79
J132351+794251 0.574 0.023 0.599 0.02 0.642 0.057 0.575 0.033 0.476 0.012 0.435 0.046 0.331 0.042 0.08
J135639+794340 2.121 0.085 0.579 0.019 0.349 0.031 0.189 0.011 0.072 0.004 0.036 0.004 -- -- 1.15
J135755+764320 0.419 0.017 0.647 0.022 0.575 0.051 0.7 0.04 0.769 0.02 0.819 0.085 0.761 0.085 --0.19
J141419+790547 1.445 0.058 0.424 0.014 0.251 0.023 0.153 0.01 0.082 0.004 0.056 0.007 -- -- 0.92
J141718+805939 1.519 0.061 0.541 0.018 0.356 0.032 0.217 0.016 0.115 0.005 0.077 0.009 -- -- 0.84
J141947+760033 3.216 0.129 0.981 0.033 0.635 0.057 0.388 0.022 0.192 0.007 0.137 0.016 0.058 0.009 0.89
J142248+770416 1.094 0.044 0.541 0.018 0.329 0.029 0.173 0.01 0.063 0.003 0.029 0.003 -- -- 1.03
J142613+794607 1.257 0.05 0.407 0.014 0.266 0.024 0.168 0.012 0.067 0.003 0.036 0.004 -- -- 1
J143547+760526 2.644 0.106 1.304 0.044 0.979 0.087 0.724 0.041 0.428 0.011 0.323 0.034 0.191 0.028 0.59
J144314+770726 6.648 0.266 1.882 0.063 1.069 0.095 0.552 0.034 0.225 0.006 0.131 0.015 -- -- 1.11
J144709+765621 6.168 0.247 1.667 0.056 0.997 0.089 0.559 0.032 0.226 0.006 0.144 0.016 -- -- 1.06
J150008+751851 3.858 0.154 0.784 0.026 0.395 0.035 0.19 0.011 0.076 0.004 0.044 0.005 -- -- 1.26
J150207+860811 0.863 0.035 0.416 0.014 0.379 0.034 0.229 0.014 0.108 0.003 0.087 0.01 -- -- 0.65
J151304+814326 2.144 0.086 0.782 0.026 0.554 0.05 0.302 0.022 0.134 0.004 0.088 0.01 -- -- 0.9
J153112+770604 1.446 0.058 0.566 0.019 0.346 0.031 0.18 0.01 0.056 0.003 0.021 0.002 -- -- 1.2
J153700+815431 0.2 0.009 0.433 0.015 0.39 0.035 0.314 0.018 0.2 0.005 0.163 0.019 0.095 0.014 0.06
J160222+801558 4.507 0.18 1.016 0.034 0.515 0.046 0.255 0.015 -- -- 0.049 0.005 -- -- 1.28
J160929+793954 2.806 0.112 1.239 0.042 0.965 0.086 0.711 0.04 0.431 0.012 0.333 0.035 0.193 0.028 0.6
J161940+854921 3.965 0.159 1.643 0.055 1.322 0.098 0.801 0.046 0.433 0.011 0.319 0.034 -- -- 0.71
J163051+823345 -- -- 0.875 0.029 0.378 0.034 0.259 0.019 0.086 0.005 0.052 0.006 -- -- 1.36
J163226+823220 -- -- 0.802 0.027 0.777 0.064 0.644 0.037 0.555 0.014 0.615 0.065 0.647 0.096 0.13
J163925+863153 2.234 0.089 0.852 0.029 0.633 0.057 0.418 0.026 0.233 0.006 0.173 0.019 -- -- 0.72
J164843+754628 5.799 0.232 1.942 0.065 1.246 0.111 0.746 0.042 0.365 0.01 0.245 0.026 0.109 0.016 0.89
J165752+792808 2.458 0.098 0.872 0.029 0.599 0.054 0.399 0.024 0.179 0.006 0.123 0.014 -- -- 0.85
J171416+761245 1.916 0.077 0.459 0.015 0.268 0.024 0.139 0.008 0.056 0.003 0.031 0.004 -- -- 1.17
J172359+765312 0.216 0.009 0.424 0.014 0.342 0.03 0.358 0.02 0.343 0.011 0.315 0.033 0.279 0.042 --0.11
J172529+770805 0.979 0.039 0.565 0.019 0.425 0.038 0.262 0.016 0.134 0.005 0.096 0.011 -- -- 0.66
J172550+772624 3.077 0.123 1.163 0.039 0.795 0.071 0.499 0.028 0.27 0.007 0.206 0.023 0.132 0.019 0.76
J173021+794916 4.444 0.178 1.02 0.034 0.648 0.058 0.309 0.033 0.126 0.004 0.064 0.007 -- -- 1.2
J173734+844543 1.971 0.079 0.444 0.015 0.258 0.023 0.128 0.009 0.054 0.003 0.029 0.003 -- -- 1.19
J175056+814736 1.139 0.046 0.44 0.015 0.269 0.024 0.161 0.011 0.054 0.003 0.033 0.004 -- -- 1
J180045+782804 1.918 0.077 2.224 0.075 2.679 0.205 2.883 0.162 2.674 0.067 2.69 0.278 2.427 0.272 --0.1
J183712+851449 1.852 0.074 0.69 0.023 0.526 0.047 0.246 0.016 0.113 0.004 0.057 0.007 -- -- 0.98
J184XXX+794XXX 30.187 1.207 12.944 0.435 9.44 0.859 5.94 0.416 3.63 0.37 -- -- -- -- 0.85
J184502+765230 1.517 0.061 0.536 0.018 0.347 0.031 0.251 0.016 0.101 0.006 0.061 0.007 -- -- 0.91
J185750+774636 1.636 0.066 0.474 0.016 0.291 0.026 0.166 0.01 0.074 0.004 0.042 0.005 -- -- 1.03
J190350+853647 2.533 0.101 0.905 0.03 0.63 0.056 0.411 0.03 0.192 0.005 0.147 0.017 -- -- 0.8
J190919+781330 0.823 0.033 0.465 0.016 0.33 0.03 0.202 0.012 0.094 0.003 0.057 0.007 -- -- 0.75
J193419+795606 2.721 0.109 0.765 0.026 0.518 0.046 0.231 0.016 0.101 0.006 0.049 0.005 -- -- 1.13
J193739+835629 0.844 0.034 0.43 0.014 0.392 0.035 0.239 0.015 0.22 0.008 0.265 0.028 -- -- 0.33
J194136+850138 2.477 0.099 0.662 0.022 0.596 0.053 0.29 0.02 0.129 0.007 0.094 0.011 -- -- 0.92
J194340+785829 1.107 0.044 0.499 0.017 0.444 0.04 0.205 0.014 0.111 0.004 0.078 0.009 -- -- 0.75
J194420+781602 1.631 0.065 0.503 0.017 0.322 0.029 0.147 0.009 0.044 0.002 -- -- -- -- 1.45
J194958+765413 1.827 0.073 0.51 0.017 0.312 0.028 0.164 0.009 0.074 0.004 0.051 0.006 -- -- 1.01
J200531+775243 0.806 0.032 1.061 0.036 1.343 0.102 1.463 0.083 1.453 0.035 1.428 0.147 1.324 0.146 --0.16
J202235+761126 0.567 0.023 0.429 0.014 0.5 0.045 0.449 0.025 0.414 0.01 0.393 0.041 0.369 0.055 0.1
J2042XX+750XXX -- -- 1.144 0.038 1.172 0.1 0.842 0.062 0.555 0.028 -- -- -- -- 0.71

M. G. Mingaliev et al.: Observations in the NCP region 85
Table 4. continued
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
J204541+762510 3.238 0.13 0.953 0.032 0.603 0.054 0.474 0.027 0.257 0.008 0.201 0.023 -- -- 0.79
J205033+752622 2.107 0.084 0.556 0.019 0.365 0.032 0.182 0.012 0.082 0.004 0.046 0.005 -- -- 1.08
J210407+763307 15.52 0.621 3.891 0.131 2.27 0.169 1.314 0.074 0.486 0.012 0.259 0.027 -- -- 1.16
J2118XX+751XXX 4.717 0.189 1.261 0.042 0.66 0.059 0.419 0.027 0.135 0.004 0.078 0.009 -- -- 1.16
J211956+765734 1.188 0.048 0.432 0.015 0.307 0.027 0.15 0.011 0.082 0.004 0.05 0.006 -- -- 0.89
J212926+845326 3.514 0.141 1.274 0.043 0.809 0.072 0.482 0.035 0.168 0.007 0.072 0.008 -- -- 1.1
J213008+835730 5.098 0.204 1.798 0.06 1.332 0.119 0.846 0.048 0.382 0.01 0.279 0.032 -- -- 0.82
J213139+843011 0.445 0.018 0.677 0.023 0.647 0.058 0.422 0.032 0.241 0.007 0.185 0.021 -- -- 0.25
J213334+823905 1.93 0.077 0.915 0.031 0.809 0.072 0.617 0.035 0.433 0.01 0.39 0.045 0.192 0.028 0.45
J213929+833953 1.418 0.057 0.48 0.016 0.306 0.027 0.217 0.012 0.107 0.006 0.081 0.009 -- -- 0.81
J214928+754045 1.735 0.069 0.524 0.018 0.329 0.029 0.202 0.012 0.104 0.006 0.073 0.009 -- -- 0.9
J215657+833714 0.474 0.019 0.474 0.016 0.442 0.039 0.285 0.022 0.214 0.009 0.184 0.021 -- -- 0.27
J215712+764642 2.283 0.091 0.777 0.026 0.56 0.05 0.309 0.018 0.149 0.006 0.091 0.011 -- -- 0.91
J220955+835356 1.787 0.072 0.578 0.019 0.4 0.036 0.191 0.018 0.09 0.005 0.069 0.008 -- -- 0.92
J222800+753219 2.039 0.082 0.651 0.022 0.429 0.038 0.289 0.018 0.142 0.005 0.111 0.013 -- -- 0.82
J224714+855542 1.432 0.057 0.516 0.017 0.356 0.032 0.205 0.013 0.098 0.006 0.076 0.009 -- -- 0.83
J230122+795406 1.447 0.058 0.431 0.014 0.291 0.026 0.154 0.01 0.077 0.004 0.044 0.005 -- -- 0.99
J230138+820015 1.518 0.061 0.45 0.015 0.378 0.034 0.196 0.016 0.085 0.004 0.046 0.005 -- -- 0.99
J232503+791715 0.705 0.028 1.136 0.038 0.912 0.082 0.578 0.037 0.285 0.007 0.189 0.021 -- -- 0.37
J232640+823158 2.964 0.119 1.001 0.034 0.728 0.065 0.35 0.022 0.16 0.009 0.066 0.007 -- -- 1.07
J232803+761738 1.466 0.059 0.459 0.015 0.26 0.023 0.172 0.01 0.072 0.004 0.053 0.006 -- -- 0.94
J234403+822640 5.667 0.227 3.777 0.127 2.904 0.259 1.787 0.102 0.896 0.022 0.65 0.067 0.292 0.043 0.61
J234914+751744 1.428 0.057 0.43 0.014 0.322 0.029 0.2 0.013 0.117 0.007 0.096 0.011 -- -- 0.76
J235413+804753 1.634 0.065 0.482 0.016 0.307 0.027 0.178 0.01 0.075 0.004 0.058 0.007 -- -- 0.94
J2355XX+795XXX 6.463 0.259 1.706 0.057 0.967 0.073 0.603 0.034 0.196 0.007 0.094 0.011 -- -- 1.2
J235622+815252 0.569 0.023 0.521 0.017 0.454 0.041 0.5 0.032 0.586 0.016 0.667 0.071 0.713 0.08 --0.04
­1,2 ­0,8 ­0,4 0,0 0,4 0,8 1,2
0
20
40
60
Number
of
sources,
N
Spectral index, a 0.325/1.4 GHz
Fig. 3. Spectral index distribution between 0.325 and 1.4 GHz
whole frequency range measured; of these, 4 show weak
GPS behavior (see below) and 3 show weakly rising spec­
tra up to the highest frequency observed and may also be
GPS sources. 4 sources show evidence for a flat spectrum
component at the higher frequencies of the survey.
There is a potential 10 percent of this survey which
are GPS sources. These are believed to be compact
objects with a peak in their spectra at GHz frequen­
cies in the redshift frame of emission. They are char­
acterized by a di#erence of spectral index (``curvature'')
on either side of the peak of more than 0.6 (de Vries
et al. 1997). The observed peak frequency may be
as low as 0.5 GHz (Marecki et al. 1999). There are
9 sources in our list which satisfy these spectral char­
acteristics. It is possible that several may be giant
radio galaxies with low frequency absorption (for
­0,8 ­0,4 0,0 0,4 0,8 1,2
0
20
40
60
Spectral index, a 0.325/3.9 GHz
Number
of
sources,
N
Fig. 4. Spectral index distribution between 0.325 and 3.9 GHz
­0,4 0,0 0,4 0,8 1,2 1,6 2,0 2,4
0
10
20
30
40
Spectral index, a 3.9/11.2 GHz
Number
of
sources,
N
Fig. 5. Spectral index distribution between 3.9 and 11.2 GHz

86 M. G. Mingaliev et al.: Observations in the NCP region
­0,4 0,0 0,4 0,8 1,2 1,6
0
20
40
Number
of
sources,
N
Spectral index, a 0.325/11.2 GHz
Fig. 6. Spectral index distribution between 0.325 and 11.2 GHz
example 085834+750121); mapping will be required to es­
tablish their compactness. Four sources (132351+794251;
172359+765312; 180045+782804; 200531+775243) have a
curvature of 0.4 to 0.6, just below the canonical limit of
de Vries et al.; they are compact as indicated by their
spectra and are potential GPS sources. Three sources
(104423+805439; 135755+764320; 235622+815252) have
spectra which are weakly rising with # = 0.2 to 0.3 at the
highest frequencies of observation. These are also likely
GPS sources with peak frequencies #10 to 20 GHz.
Acknowledgements. This research is partially supported by
the Russian Foundation for Basis Research Project No. 98­
02­16428 and Russian Federal Program ``Astronomy'' Project
No. 1.2.5.1. VS acknowledges the receipt of NATO/Royal
Society Postdoctoral Fellowship.
The authors used extensively the database CATS
(http://cats.sao.ru, Verkhodanov et al. 1997) of the Special
Astrophysical Observatory (Russia) in the search for counter­
parts in the radio catalogues.
References
Aliakberov, K., Mingaliev, M., Naugol'naya, M., et al. 1985,
Astrophys. Issled. (Izvestiya SAO), 19, 60
Berlin, A., & Friedman, P. 1996, Real Time Radiometric
Data Processing Against Electromagnetic Pollution, in
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