Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://jet.sao.ru/hq/marat/publ/articles/aah2533.pdf Äàòà èçìåíåíèÿ: Wed Feb 24 17:32:53 2010 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 05:35:14 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: south pole

A&A 370, 78­86 (2001) DOI: 10.1051/0004-6361:20010215
c ESO 2001

Astronomy & Astrophysics

Observations of the bright radio sources in the North Celestial Pole region at the RATAN-600 radio telescope
M. G. Mingaliev1 , V. A. Stolyarov1,2 , R. D. Davies3 , S. J. Melhuish4 , N. A. Bursov1 , and G. V. Zhekanis1
1

2

3

4

Special Astrophysical Observatory of Russian Academy of Sciences, Nizhnij Arkhyz, Karachaevo-Cherkessia Republic 357147, Russia e-mail: marat@sao.ru; vlad@sao.ru; nnb@ratan.sao.ru; gvz@ratan.sao.ru University of Cambridge, Institute of Astronomy, Madingley Rd., Cambridge CB3 OHA, UK e-mail: vlad@ast.cam.ac.uk University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, UK e-mail: rdd@jb.man.ac.uk University of Wales, Cardiff, Department of Physics and Astronomy, 5, The Parade, Cardiff CF24 3YB, UK e-mail: 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 RATAN-600 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 5­10 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. Intro duction
In the current paper we present the results of observations of bright radio sources in the North Celestial Pole (NCP) region within the declination range of +75 +88 taken with the RATAN-600 radio telescope of the Russian Academy of Sciences (Korolkov & Pariiskii 1979; Parijskij 1993). This NCP survey was initiated as a compliment to the 5 GHz interferometric study of Galactic foreground emission in the NCP made at Jodrell Bank in 1998­1999 (Melhuish et al. 2001). In order to obtain information about Galactic synchrotron and free-free 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 Pauliny-Toth et al. (1978) and
Send offprint requests to : V. Stolyarov, e-mail: 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 required for the NCP pro ject. The upper Declination limit of the present RATAN-600 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 significant contribution to the 5 GHz degree-scale interferometer 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 RATAN-600 all those sources giving 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 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 Tsys , K 21.7 2.5 3.5 15 23 77 1.4 3.0 15 18 70 11.2 7.7 1.0 3.0 15 14 62 3.9 0.6 2.5 15 8 37 0.4 8.0 310 35 95 2.3

79

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 350­400 mJy at 1.4 GHz assuming an average spectral index of 0.7 (S - ) for the sources. Accordingly, the adopted "complete sample" criteria for the sources selected from the NVSS catalogue were: 1. Flux density S 400 mJy at the NVSS frequency of 1.4 GHz; 2. 00h 24h; 3. +75 +88 . In total we have selected for observation 182 ob jects which satisfy these criteria.

(0.325­42 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 possible, 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 RATAN-600 frequency bands the spectra of the calibrators were interpolated to the desired frequencies by second order polynomial.

4.1. The calibration errors, c
The flux density measurement procedure at the RATAN600 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

3. The observations
The observations were made in February-March 1999 using the South sector of the RATAN-600 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, Tphys is the physical temperature of the radiometer amplifier, Tampl is the noise temperature of the amplifier and Tsys is the noise temperature of the whole system at the given frequency. All of the radiometers have HEMT first-stage amplifiers. Information about FWH M can be found in the article by Kovalev et al. (1999). For example at 11.2 GHz the FWH M is about 17 â 2 at the elevations of the NCP observations. Usually each source was observed 5­8 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.

g (e) = 1/f (e Tant, F ,f e = 90 - + = 43 65333 .

)-

elevation calibration function; antenna temperature; arbitrary functions; antenna elevation; latitude of the telescope site.

In order to get the flux density from Tant, we have to multiply 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 calibration sources of known flux density spanning a wide range of declination, . Having the list of values g (ei ) = S,i /T
ant,,i

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 information about source fluxes in a wide frequency range

for different sources we can approximate the functions g (e) by a second order polynomial with the help of minimization 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 assumed 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
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M. G. Mingaliev et al.: Observations in the NCP region
c= 2.3 G H z c= 3.9 G H z

g(e), Jy/K

4 3 2 1 0 6 5

c= 7.7 G H z

c= 11.2 G H z

g(e), Jy/K

4 3 2 1 0 25 30 35 40 45 50 55 60 25 30 35 40 45 50 55 60

Elevation e, deg.

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 of the source J0017+815 J0229+777 J0410+769 J0626+820 J1435+760 J1459+716 J2022+761 S (c = 21.7 GHz), Jy 0.48 ­ 1.14 0.31 ­ 1.00 0.42 S (c = 11.2 GHz), Jy 0.78 ­ 1.77 0.56 0.31 1.72 0.41 S (c = 7.7 GHz), Jy 0.94 0.41 2.23 0.74 0.44 2.27 0.43 S (c = 3.9 GHz), Jy 1.00 1.05 3.35 1.01 0.74 3.69 0.44 S (c = 2.3 GHz), Jy 0.9 1.8 4.49 0.95 1.03 5.33 0.46

4.2. The errors of Tant measurements, m
The specifics of the RATAN-600 observations lead to the fact that the errors of the antenna temperature measurements 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

3.9 GHz, = +75, t = 4 s and N = 5, T to 0.56 mK.

rec

is equal

= T/(tN k )1/2

(2)

Unfortunately the contribution of atmospheric fluctuations increases as t increases corresponding to larger angular scales thereby partially reducing the growth of sensitivity expected from longer integration times. The errors 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 Tant for the N observations of the data set can give us the measurement error, m , including all of the components listed above.

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 beam-switching 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 different for different 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 1­15 s. As an example for

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 where t c m S g (e) = 1/f (e Tant, )total standard error; standard error of calibration; standard error of Tant, measurement; flux density; elevation calibration function; antenna temperature.
2

=

c g (e)

2

+

m Tant,

2

(3)

A number of the sources in the NVSS target list were not fully resolved in the RATAN-600 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 multifrequency data for this NCP survey in which 171 individual sources were identified.

The values of the standard error of Tant, measurement, m , are 2­3% for 11.2, 7.7 and 3.9 GHz, 3­5% for 2.3 GHz and 7­11% 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.

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. 4.4. Comparison with the other catalogues The chosen limit to the flux density at 5 GHz was 150 mJy The RATAN-600 results described in this paper are in which corresponds to a signal amplitude of 10 µK in the good accordance with the flux densities given by NVSS at interferometer. The ma jority of sources (80 percent) were 1.4 GHz, the Westerbork Northern Sky Survey (WENSS; stronger than this limit and would make a significant conRengelink et al. 1997) at 0.325 GHz and the earlier data tribution to the CMB foreground and should be removed of the Kuehr (1981) Catalogue. Four sample spectra are from the interferometer survey. shown in Fig. 2 which compare the RATAN-600 data with The question then arises as to the further contributhose from the three above catalogues. The sources illus- tion from flat spectrum and rising spectrum sources not trated all have steep spectra and as a consequence are not included in our survey which would have a 5 GHz flux denlikely to be variable. The few discrepancies in the plotted sity of 150 mJy. Remembering that our source selection spectra are all in the older Kuehr data. 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 5. Results our sources chosen at 1.4 GHz have spectral indices flatter The spectra for 171 sources in the present RATAN-600 than this value. Accordingly there will be a further conNCP survey are given in Table 4. Data from WENSS tribution from such sources with flux densities at 1.4 GHz and NVSS are included. Nearly all the sources have com- of 200­400 mJy. Assuming the fraction of flat spectrum plete data at 2.3, 3.9, 7.7 and 11.2 GHz; 40 sources have sources stays constant with decreasing frequency, we may 21.7 GHz flux densities. Only a few of these sources have expect 5 sources in this category. Yet another contribeen observed previously over this wide frequency range. bution will come from Gigahertz Peaked Spectrum (GPS) The columns in the table are: sources; likewise there will be 5 extra sources with a flux Column 1 : The source name (NVSS notation), cor- density above 150 mJy at 5 GHz. responding to epoch J2000 coordinates; Columns 2-3 : The flux density in Jy and standard er- 6.2. Statistics of sources sp ectra ror at 0.325 GHz (WENSS catalogue, Although this is a modest sample of GHz spectra, it Rengelink et al. 1997); Columns 4-5 : The flux density in Jy and standard error provides an indication of the spectral properties of the at 1.4 GHz (NVSS catalogue, Condon brightest radio sources in the NCP region (+75 +88 ). We would expect them to follow the trends in et al. 1998); Columns 6-15 : The flux density in Jy and total stan- the general field. One particular advantage of the present dard error, t , at 2.3, 3.9, 7.6, 11.2 and catalogue is that all the sources were observed simultaneously at all frequencies to provide an instantaneous 21.7 GHz respectively; Column 16 : The spectral index = - log(S (1 )/ spectrum unaffected by source variability. The histograms S (2 ))/ log(1 /2 ), computed between of spectral index values estimated over the frequency fluxes at 0.325 and 11.2 GHz (or the 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. 3­6 respectively. nearest available frequencies).


82
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M. G. Mingaliev et al.: Observations in the NCP region
J001631+791651 Kuehr RATAN-600 W EN SS and N VSS
10 10

J041045+765645 Kuehr RATAN-600 W EN SS and N VSS

Flux, Jy
1

1

0,1

10

J144709+765621 Kuehr RATAN-600 W EN SS and N VSS

10

J234403+862640 Kuehr RATAN-600 W EN SS and N VSS

Flux, Jy

1

1

0,1

0,1

1

10

0,1

1

10

Frequency, G Hz

Frequency, G Hz

Fig. 2. Four sample source spectra from Kuehr catalogue compared with RATAN-600, NVSS and WENSS data Table 3. Complex sources Name in NVSS J022235+861727 J022248+861851 J022249+862027 J074246+802741 J074305+802544 J101330+855411 J101412+855349 Name in the Table 4 J0222XX+861XXX Name in NVSS J184142+794752 J184151+794727 J184214+794613 J184226+794517 J204257+750428 J204259+750306 J101XXX+855XXX J211814+751203 J211817+751112 J235521+795552 J235525+795442 J2118XX+751XXX Name in the Table 4 J184XXX+794XXX

J074XXX+802XXX J20425X+750XXX

J2355XX+795XXX

The ma jority 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 indices which indicates that the turn-over 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 result 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. 4­6, is 20­25 percent. This family of flattish spectrum sources is of particular concern as a foreground in the measurement of fluctuations in the cosmic microwave background.

6.3. Individual sources with compact comp onents
The spectral signature of compact radio sources is a flat component arising from synchrotron self-absorption. 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 low-frequency 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 Table 4. Fluxes of the sources in the NCP region
Name, NVSS J000943+772440 J001236+854313 J001311+774846 J001631+791651 J001708+813508 J001816+782743 J003812+844727 J004617+751752 J011045+873822 J013156+844612 J015207+755035 J020537+752207 J020723+795602 J0222XX+861XXX J022454+765554 J022914+774316 J023010+814129 J025100+791359 J025417+791147 J030011+820238 J030454+772731 J035150+800437 J035446+800929 J035629+763742 J035817+783719 J040652+763354 J041045+765645 J041426+761243 J041531+842457 J041946+755915 J042205+762708 J042408+765341 J042918+770911 J044545+783856 J050731+791257 J050842+843204 J061837+782123 J062205+871948 J062602+820225 J063012+763245 J063012+763245 J063825+841106 J064045+781327 J064558+775502 J071452+815153 J072611+791130 J073433+765813 J074XXX+802XXX J075058+824158 J080626+812620 J080734+784610 J082550+765313 J083236+800601 J084833+783003 J085834+750121 J090112+780930 J090842+834543 J092016+862845 J093239+790629 J093817+781528 J093923+831526 J094440+825408 J095559+791134 J100005+812702 J100741+813150 J100949+810719 J101015+825014 J101037+765052 J101XXX+855XXX J101734+810517 J102326+803255 J102926+785241 J104423+805439 S0.325 Jy, 2.059 1.605 4.517 9.959 0.688 2.16 0.972 1.371 2.215 2.072 2.823 0.86 3.89 20.538 5.949 8.067 2.285 2.475 2.186 2.415 0.164 1.534 1.243 1.969 1.334 1.592 9.406 1.359 1.965 1.491 3.75 1.614 4.702 1.807 1.859 0.149 2.511 2.105 0.199 2.187 1.512 3.834 1.605 2.054 1.704 0.092 1.361 9.574 3.741 1.506 1.574 1.903 2.019 5.369 0.239 1.422 1.039 2.122 9.234 2.062 11.592 1.904 1.295 2.541 3.632 1.5 0.741 3.076 1.973 2.894 6.905 2.559 0.643 t WENSS 0.082 0.064 0.181 0.398 0.028 0.086 0.039 0.055 0.089 0.083 0.113 0.035 0.156 0.822 0.238 0.323 0.091 0.099 0.088 0.097 0.008 0.061 0.05 0.079 0.053 0.064 0.376 0.054 0.079 0.06 0.15 0.065 0.188 0.072 0.074 0.007 0.101 0.084 0.009 0.088 0.061 0.153 0.064 0.082 0.068 0.005 0.055 0.383 0.15 0.06 0.063 0.076 0.081 0.215 0.01 0.057 0.042 0.085 0.369 0.083 0.464 0.076 0.052 0.102 0.145 0.06 0.03 0.123 0.079 0.116 0.276 0.102 0.026 S1.4 Jy, 0.628 0.691 2.101 3.651 0.693 0.707 0.406 0.444 0.686 0.777 0.839 1.151 1.363 6.478 1.927 2.683 1.048 0.713 0.643 1.379 0.977 0.546 0.644 0.629 0.508 0.527 5.62 0.405 0.578 0.427 1.043 0.408 0.945 0.65 0.629 0.295 1.075 0.645 0.681 0.783 0.481 1.1 0.688 0.608 0.551 0.501 0.475 3.322 1.845 0.406 0.525 0.689 0.867 1.509 0.948 0.447 0.448 0.519 2.241 0.699 2.953 0.735 0.415 0.864 0.855 0.455 0.504 0.806 0.81 1.172 1.807 1.111 0.828 t NVSS 0.021 0.023 0.071 0.123 0.023 0.024 0.014 0.015 0.023 0.026 0.028 0.039 0.046 0.217 0.065 0.09 0.035 0.024 0.022 0.046 0.033 0.018 0.022 0.021 0.017 0.018 0.189 0.014 0.019 0.014 0.035 0.014 0.032 0.022 0.021 0.01 0.036 0.022 0.023 0.026 0.016 0.037 0.023 0.02 0.018 0.017 0.016 0.112 0.062 0.014 0.018 0.023 0.029 0.051 0.032 0.015 0.015 0.017 0.075 0.023 0.099 0.025 0.014 0.029 0.029 0.015 0.017 0.027 0.027 0.039 0.061 0.037 0.028 S2.3 Jy 0.447 0.539 1.578 2.46 0.853 0.428 0.332 0.273 0.467 0.603 0.526 0.873 0.932 4.006 1.271 1.663 0.783 0.475 0.463 1.078 0.926 0.368 0.499 0.397 0.367 0.384 4.538 0.259 0.453 0.273 0.598 0.223 0.517 0.46 0.496 0.302 0.733 0.534 0.962 0.7 ­ 0.737 0.403 0.458 0.419 0.75 0.282 2.408 1.579 0.251 0.39 0.491 0.638 0.86 0.578 0.252 0.325 0.345 1.333 0.426 1.802 0.54 0.254 0.561 0.496 0.328 0.507 0.522 0.537 0.838 1.144 0.741 0.829 t 0.04 0.048 0.141 0.183 0.067 0.038 0.03 0.025 0.042 0.054 0.047 0.078 0.072 0.422 0.095 0.124 0.07 0.043 0.041 0.102 0.07 0.033 0.045 0.036 0.033 0.034 0.336 0.023 0.041 0.025 0.053 0.02 0.044 0.041 0.044 0.031 0.066 0.048 0.086 0.063 ­ 0.066 0.036 0.041 0.037 0.057 0.025 0.185 0.119 0.023 0.035 0.044 0.057 0.077 0.052 0.023 0.029 0.031 0.119 0.038 0.134 0.048 0.023 0.05 0.044 0.029 0.045 0.047 0.045 0.075 0.102 0.066 0.074 S3.9 Jy 0.267 0.246 0.981 1.422 1.022 0.252 0.223 0.163 0.206 0.361 0.285 0.611 0.582 3.006 0.744 0.95 0.544 0.226 0.212 0.586 0.634 0.211 0.371 0.252 0.226 0.195 3.512 0.147 0.235 0.166 0.309 0.146 0.266 0.292 0.307 0.242 0.501 0.251 0.947 0.339 0.193 0.426 0.249 ­ 0.255 0.904 0.217 1.699 1.421 0.127 0.218 0.303 0.392 0.508 0.302 0.165 0.221 0.173 0.667 0.272 0.917 0.358 0.152 0.304 0.257 0.195 0.622 0.235 0.303 0.512 0.627 0.525 0.961 t 0.017 0.018 0.056 0.087 0.058 0.015 0.017 0.012 0.015 0.027 0.016 0.036 0.033 0.261 0.042 0.054 0.031 0.013 0.013 0.034 0.036 0.012 0.023 0.016 0.016 0.012 0.197 0.011 0.015 0.01 0.018 0.011 0.015 0.022 0.019 0.019 0.038 0.019 0.054 0.025 0.015 0.029 0.018 ­ 0.016 0.051 0.013 0.124 0.08 0.008 0.013 0.018 0.023 0.029 0.017 0.012 0.013 0.013 0.038 0.016 0.052 0.023 0.009 0.017 0.015 0.012 0.035 0.02 0.034 0.03 0.036 0.03 0.054 S7.7 Jy 161 148 467 643 919 109 108 074 118 186 095 309 252 137 334 401 284 089 105 265 344 078 279 127 102 095 215 061 128 076 0.1 0.035 0.085 0.156 0.155 0.246 0.227 0.1 0.763 0.152 0.085 0.197 0.092 0.098 0.141 0.818 0.098 0.954 0.959 0.045 0.106 0.159 0.184 0.203 0.097 0.069 0.118 0.065 0.235 0.125 0.304 0.173 0.061 0.122 0.096 0.081 0.607 0.071 0.109 0.194 0.185 0.25 1.212 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 1. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 2. 0. 0. 0. t 0.007 0.005 0.012 0.017 0.023 0.005 0.005 0.004 0.005 0.005 0.005 0.009 0.008 0.133 0.009 0.011 0.008 0.003 0.006 0.008 0.009 0.004 0.008 0.007 0.003 0.004 0.054 0.003 0.004 0.004 0.006 0.002 0.004 0.004 0.004 0.008 0.012 0.006 0.019 0.009 0.004 0.005 0.004 0.006 0.004 0.02 0.006 0.05 0.024 0.002 0.003 0.004 0.005 0.006 0.006 0.003 0.003 0.003 0.006 0.004 0.009 0.006 0.003 0.007 0.003 0.004 0.015 0.004 0.007 0.006 0.005 0.006 0.029 S11.2 Jy 0.14 0.099 0.314 0.422 0.788 0.054 0.084 0.04 0.081 0.136 0.054 0.202 0.18 0.813 0.21 0.259 0.213 0.036 0.067 0.177 0.262 0.041 0.259 0.098 0.065 0.068 1.769 0.04 0.09 0.045 0.05 0.019 0.026 0.113 0.122 0.25 0.119 0.072 0.717 0.092 0.053 0.155 0.048 0.067 0.127 0.742 0.074 0.681 0.881 0.033 0.084 0.121 0.132 0.127 0.048 0.059 0.099 0.036 0.127 0.075 0.171 0.129 0.047 0.069 0.05 0.062 0.628 0.033 0.066 0.12 0.093 0.164 1.362 t 0.016 0.011 0.034 0.044 0.082 0.006 0.01 0.005 0.009 0.016 0.006 0.021 0.021 0.095 0.023 0.028 0.023 0.004 0.008 0.022 0.028 0.005 0.028 0.011 0.007 0.008 0.182 0.005 0.01 0.005 0.006 0.002 0.003 0.013 0.014 0.027 0.014 0.008 0.074 0.011 0.006 0.018 0.005 0.008 0.014 0.077 0.009 0.076 0.091 0.004 0.01 0.014 0.015 0.014 0.005 0.007 0.011 0.004 0.014 0.009 0.02 0.015 0.005 0.008 0.006 0.007 0.066 0.004 0.008 0.014 0.011 0.019 0.14 S21.7 Jy ­ ­ 0.202 0.145 0.441 ­ ­ ­ ­ ­ ­ 0.097 ­ ­ 0.085 0.111 0.212 ­ ­ ­ 0.157 ­ 0.211 ­ ­ ­ 1.279 ­ ­ ­ ­ ­ ­ 0.068 0.066 0.169 ­ ­ 0.521 ­ ­ ­ ­ ­ ­ 0.48 ­ ­ 0.643 ­ ­ 0.028 0.051 0.038 ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ 0.548 ­ ­ ­ ­ ­ 1.206 t ­ ­ 0.03 0.022 0.065 ­ ­ ­ ­ ­ ­ 0.015 ­ ­ 0.013 0.016 0.031 ­ ­ ­ 0.024 ­ 0.031 ­ ­ ­ 0.142 ­ ­ ­ ­ ­ ­ 0.01 0.01 0.025 ­ ­ 0.06 ­ ­ ­ ­ ­ ­ 0.054 ­ ­ 0.095 ­ ­ 0.004 0.008 0.006 ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ 0.064 ­ ­ ­ ­ ­ 0.134

83

Sp. index 0.325/11.2 0. 0. 0. 0. ­0. 1. 0. 76 79 75 89 04 04 69 1 0.93 0.77 1.12 0.41 0.87 0.91 0.94 0.97 0.67 1.2 0.98 0.74 ­0.13 1.02 0.44 0.85 0.85 0.89 0.47 1 0.87 0.99 1.22 1.25 1.47 0.78 0.77 ­0.15 0.86 0.95 ­0.36 0.9 0.95 0.91 0.99 0.97 0.73 ­0.59 0.82 0.75 0.41 1.08 0.83 0.78 0.77 1.06 0.45 0.9 0.66 1.15 1.21 0.94 1.19 0.76 0.94 1.02 1.21 0.9 0.05 1.28 0.96 0.9 1.22 0.78 ­0.21


84 Table 4. continued
1 J105150+791341 J110405+793253 J110412+765859 J111342+765449 J112342+773123 J114829+782721 J115312+805829 J115504+753439 J115522+815709 J115608+823505 J115713+811824 J122015+792732 J122340+804004 J122518+860839 J123708+835704 J125736+834231 J130035+805438 J130538+815626 J130609+800825 J130705+764918 J130811+854424 J131723+821916 J132053+845011 J132145+831613 J132331+780947 J132351+794251 J135639+794340 J135755+764320 J141419+790547 J141718+805939 J141947+760033 J142248+770416 J142613+794607 J143547+760526 J144314+770726 J144709+765621 J150008+751851 J150207+860811 J151304+814326 J153112+770604 J153700+815431 J160222+801558 J160929+793954 J161940+854921 J163051+823345 J163226+823220 J163925+863153 J164843+754628 J165752+792808 J171416+761245 J172359+765312 J172529+770805 J172550+772624 J173021+794916 J173734+844543 J175056+814736 J180045+782804 J183712+851449 J184XXX+794XXX J184502+765230 J185750+774636 J190350+853647 J190919+781330 J193419+795606 J193739+835629 J194136+850138 J194340+785829 J194420+781602 J194958+765413 J200531+775243 J202235+761126 J2042XX+750XXX 2 1.894 0.338 7.554 1.534 1.516 0.97 1.39 1.822 2.017 1.4 1.269 1.409 1.204 1.532 1.909 1.145 4.837 1.734 2.218 1.178 1.711 3.126 0.702 0.829 1.192 0.574 2.121 0.419 1.445 1.519 3.216 1.094 1.257 2.644 6.648 6.168 3.858 0.863 2.144 1.446 0.2 4.507 2.806 3.965 ­ ­ 2.234 5.799 2.458 1.916 0.216 0.979 3.077 4.444 1.971 1.139 1.918 1.852 30.187 1.517 1.636 2.533 0.823 2.721 0.844 2.477 1.107 1.631 1.827 0.806 0.567 ­ 3 0.076 0.014 0.302 0.061 0.061 0.039 0.056 0.073 0.081 0.056 0.051 0.056 0.048 0.061 0.076 0.046 0.194 0.069 0.089 0.047 0.069 0.125 0.028 0.033 0.048 0.023 0.085 0.017 0.058 0.061 0.129 0.044 0.05 0.106 0.266 0.247 0.154 0.035 0.086 0.058 0.009 0.18 0.112 0.159 ­ ­ 0.089 0.232 0.098 0.077 0.009 0.039 0.123 0.178 0.079 0.046 0.077 0.074 1.207 0.061 0.066 0.101 0.033 0.109 0.034 0.099 0.044 0.065 0.073 0.032 0.023 ­

M. G. Mingaliev et al.: Observations in the NCP region

4 0.525 0.514 2.341 0.471 0.407 0.42 1.343 0.817 0.671 0.404 0.981 0.517 0.705 0.453 0.778 0.475 1.251 0.49 0.785 0.754 0.593 0.869 0.436 0.565 0.482 0.599 0.579 0.647 0.424 0.541 0.981 0.541 0.407 1.304 1.882 1.667 0.784 0.416 0.782 0.566 0.433 1.016 1.239 1.643 0.875 0.802 0.852 1.942 0.872 0.459 0.424 0.565 1.163 1.02 0.444 0.44 2.224 0.69 12.944 0.536 0.474 0.905 0.465 0.765 0.43 0.662 0.499 0.503 0.51 1.061 0.429 1.144

5 0.018 0.017 0.079 0.016 0.014 0.014 0.045 0.027 0.023 0.014 0.033 0.017 0.024 0.015 0.026 0.016 0.042 0.016 0.026 0.025 0.02 0.029 0.015 0.019 0.016 0.02 0.019 0.022 0.014 0.018 0.033 0.018 0.014 0.044 0.063 0.056 0.026 0.014 0.026 0.019 0.015 0.034 0.042 0.055 0.029 0.027 0.029 0.065 0.029 0.015 0.014 0.019 0.039 0.034 0.015 0.015 0.075 0.023 0.435 0.018 0.016 0.03 0.016 0.026 0.014 0.022 0.017 0.017 0.017 0.036 0.014 0.038

6 0.314 0.491 1.518 0.29 0.228 0.3 1.887 0.594 0.428 0.25 0.766 0.334 0.701 0.294 0.667 0.375 0.777 0.32 0.597 0.531 0.418 0.46 0.484 0.485 0.346 0.642 0.349 0.575 0.251 0.356 0.635 0.329 0.266 0.979 1.069 0.997 0.395 0.379 0.554 0.346 0.39 0.515 0.965 1.322 0.378 0.777 0.633 1.246 0.599 0.268 0.342 0.425 0.795 0.648 0.258 0.269 2.679 0.526 9.44 0.347 0.291 0.63 0.33 0.518 0.392 0.596 0.444 0.322 0.312 1.343 0.5 1.172

7 0.028 0.044 0.113 0.026 0.02 0.027 0.146 0.053 0.038 0.023 0.06 0.03 0.063 0.026 0.051 0.034 0.069 0.029 0.053 0.048 0.037 0.041 0.044 0.043 0.031 0.057 0.031 0.051 0.023 0.032 0.057 0.029 0.024 0.087 0.095 0.089 0.035 0.034 0.05 0.031 0.035 0.046 0.086 0.098 0.034 0.064 0.057 0.111 0.054 0.024 0.03 0.038 0.071 0.058 0.023 0.024 0.205 0.047 0.859 0.031 0.026 0.056 0.03 0.046 0.035 0.053 0.04 0.029 0.028 0.102 0.045 0.1

8 0.179 0.377 0.887 0.183 0.151 0.206 1.922 0.407 0.227 0.175 0.556 0.214 0.752 0.164 0.333 0.27 0.386 0.17 0.365 0.359 0.236 0.29 0.28 0.333 0.23 0.575 0.189 0.7 0.153 0.217 0.388 0.173 0.168 0.724 0.552 0.559 0.19 0.229 0.302 0.18 0.314 0.255 0.711 0.801 0.259 0.644 0.418 0.746 0.399 0.139 0.358 0.262 0.499 0.309 0.128 0.161 2.883 0.246 5.94 0.251 0.166 0.411 0.202 0.231 0.239 0.29 0.205 0.147 0.164 1.463 0.449 0.842

9 0.01 0.021 0.05 0.011 0.009 0.012 0.108 0.025 0.019 0.02 0.033 0.012 0.043 0.016 0.02 0.019 0.022 0.01 0.022 0.021 0.015 0.017 0.021 0.025 0.014 0.033 0.011 0.04 0.01 0.016 0.022 0.01 0.012 0.041 0.034 0.032 0.011 0.014 0.022 0.01 0.018 0.015 0.04 0.046 0.019 0.037 0.026 0.042 0.024 0.008 0.02 0.016 0.028 0.033 0.009 0.011 0.162 0.016 0.416 0.016 0.01 0.03 0.012 0.016 0.015 0.02 0.014 0.009 0.009 0.083 0.025 0.062 0. 0. 0. 0. 0. 0. 1. 0.

10 078 237 395 095 055 088 715 201 0.1 0.065 0.301 0.084 0.767 0.082 0.186 0.176 0.166 0.077 0.18 0.18 0.156 0.114 0.211 0.275 0.106 0.476 0.072 0.769 0.082 0.115 0.192 0.063 0.067 0.428 0.225 0.226 0.076 0.108 0.134 0.056 0.2 ­ 0.431 0.433 0.086 0.555 0.233 0.365 0.179 0.056 0.343 0.134 0.27 0.126 0.054 0.054 2.674 0.113 3.63 0.101 0.074 0.192 0.094 0.101 0.22 0.129 0.111 0.044 0.074 1.453 0.414 0.555

11 0.004 0.006 0.01 0.005 0.003 0.005 0.042 0.006 0.004 0.003 0.009 0.004 0.019 0.004 0.005 0.005 0.004 0.004 0.007 0.006 0.009 0.007 0.007 0.015 0.003 0.012 0.004 0.02 0.004 0.005 0.007 0.003 0.003 0.011 0.006 0.006 0.004 0.003 0.004 0.003 0.005 ­ 0.012 0.011 0.005 0.014 0.006 0.01 0.006 0.003 0.011 0.005 0.007 0.004 0.003 0.003 0.067 0.004 0.37 0.006 0.004 0.005 0.003 0.006 0.008 0.007 0.004 0.002 0.004 0.035 0.01 0.028

12 0.06 0.172 0.224 0.066 0.036 0.074 1.696 0.137 0.065 0.056 0.222 0.043 0.808 0.041 0.122 0.164 0.107 0.054 0.142 0.124 0.108 0.08 0.189 0.262 0.072 0.435 0.036 0.819 0.056 0.077 0.137 0.029 0.036 0.323 0.131 0.144 0.044 0.087 0.088 0.021 0.163 0.049 0.333 0.319 0.052 0.615 0.173 0.245 0.123 0.031 0.315 0.096 0.206 0.064 0.029 0.033 2.69 0.057 ­ 0.061 0.042 0.147 0.057 0.049 0.265 0.094 0.078 ­ 0.051 1.428 0.393 ­

13 0.007 0.018 0.023 0.007 0.004 0.009 0.175 0.016 0.007 0.007 0.023 0.005 0.083 0.005 0.014 0.019 0.012 0.006 0.016 0.014 0.012 0.009 0.022 0.03 0.008 0.046 0.004 0.085 0.007 0.009 0.016 0.003 0.004 0.034 0.015 0.016 0.005 0.01 0.01 0.002 0.019 0.005 0.035 0.034 0.006 0.065 0.019 0.026 0.014 0.004 0.033 0.011 0.023 0.007 0.003 0.004 0.278 0.007 ­ 0.007 0.005 0.017 0.007 0.005 0.028 0.011 0.009 ­ 0.006 0.147 0.041 ­

14 ­ 0.11 ­ ­ ­ ­ 1.251 ­ ­ ­ ­ ­ 0.775 ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ 0.331 ­ 0.761 ­ ­ 0.058 ­ ­ 0.191 ­ ­ ­ ­ ­ ­ 0.095 ­ 0.193 ­ ­ 0.647 ­ 0.109 ­ ­ 0.279 ­ 0.132 ­ ­ ­ 2.427 ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ 1.324 0.369 ­ 0.

15 ­ 016 ­ ­ ­ ­ 138 ­ ­ ­ ­ ­ 087 ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ 042 ­ 085 ­ ­ 009 ­ ­ 028 ­ ­ ­ ­ ­ ­ 014 ­ 028 ­ ­ 096 ­ 016 ­ ­ 042 ­ 019 ­ ­ ­ 272 ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ 146 055 ­ 0. 0. 0. 0. 1. 0. ­0. 0. 0. 0. 0. 0. 0. 1. 0. 0. 1. 0. 0. 0. 0. 1. 0. 0. 0. 0. 1. ­0. 0. 0. 0. 1.

16 98 19 99 89 06 73 06 73 97 91 49 99 11 02 78 55 08 98 78 64 78 04 37 33 79 08 15 19 92 84 89 03 1 0.59 1.11 1.06 1.26 0.65 0.9 1.2 0.06 1.28 0.6 0.71 1.36 0.13 0.72 0.89 0.85 1.17 ­0.11 0.66 0.76 1.2 1.19 1 ­0.1 0.98 0.85 0.91 1.03 0.8 0.75 1.13 0.33 0.92 0.75 1.45 1.01 ­0.16 0.1 0.71

0.

0.

0. 0.

0.

0.

0. 0.

0. 0.

0. 0.

0.

0. 0.


M. G. Mingaliev et al.: Observations in the NCP region Table 4. continued
1 J204541+762510 J205033+752622 J210407+763307 J2118XX+751XXX J211956+765734 J212926+845326 J213008+835730 J213139+843011 J213334+823905 J213929+833953 J214928+754045 J215657+833714 J215712+764642 J220955+835356 J222800+753219 J224714+855542 J230122+795406 J230138+820015 J232503+791715 J232640+823158 J232803+761738 J234403+822640 J234914+751744 J235413+804753 J2355XX+795XXX J235622+815252 2 3.238 2.107 15.52 4.717 1.188 3.514 5.098 0.445 1.93 1.418 1.735 0.474 2.283 1.787 2.039 1.432 1.447 1.518 0.705 2.964 1.466 5.667 1.428 1.634 6.463 0.569 3 0.13 0.084 0.621 0.189 0.048 0.141 0.204 0.018 0.077 0.057 0.069 0.019 0.091 0.072 0.082 0.057 0.058 0.061 0.028 0.119 0.059 0.227 0.057 0.065 0.259 0.023 4 0.953 0.556 3.891 1.261 0.432 1.274 1.798 0.677 0.915 0.48 0.524 0.474 0.777 0.578 0.651 0.516 0.431 0.45 1.136 1.001 0.459 3.777 0.43 0.482 1.706 0.521 5 0.032 0.019 0.131 0.042 0.015 0.043 0.06 0.023 0.031 0.016 0.018 0.016 0.026 0.019 0.022 0.017 0.014 0.015 0.038 0.034 0.015 0.127 0.014 0.016 0.057 0.017 6 0.603 0.365 2.27 0.66 0.307 0.809 1.332 0.647 0.809 0.306 0.329 0.442 0.56 0.4 0.429 0.356 0.291 0.378 0.912 0.728 0.26 2.904 0.322 0.307 0.967 0.454 7 0.054 0.032 0.169 0.059 0.027 0.072 0.119 0.058 0.072 0.027 0.029 0.039 0.05 0.036 0.038 0.032 0.026 0.034 0.082 0.065 0.023 0.259 0.029 0.027 0.073 0.041 8 0.474 0.182 1.314 0.419 0.15 0.482 0.846 0.422 0.617 0.217 0.202 0.285 0.309 0.191 0.289 0.205 0.154 0.196 0.578 0.35 0.172 1.787 0.2 0.178 0.603 0.5 9 0.027 0.012 0.074 0.027 0.011 0.035 0.048 0.032 0.035 0.012 0.012 0.022 0.018 0.018 0.018 0.013 0.01 0.016 0.037 0.022 0.01 0.102 0.013 0.01 0.034 0.032 10 0.257 0.082 0.486 0.135 0.082 0.168 0.382 0.241 0.433 0.107 0.104 0.214 0.149 0.09 0.142 0.098 0.077 0.085 0.285 0.16 0.072 0.896 0.117 0.075 0.196 0.586 11 0.008 0.004 0.012 0.004 0.004 0.007 0.01 0.007 0.01 0.006 0.006 0.009 0.006 0.005 0.005 0.006 0.004 0.004 0.007 0.009 0.004 0.022 0.007 0.004 0.007 0.016 12 0.201 0.046 0.259 0.078 0.05 0.072 0.279 0.185 0.39 0.081 0.073 0.184 0.091 0.069 0.111 0.076 0.044 0.046 0.189 0.066 0.053 0.65 0.096 0.058 0.094 0.667 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 13 023 005 027 009 006 008 032 021 045 009 009 021 011 008 013 009 005 005 021 007 006 067 011 007 011 071 14 ­ ­ ­ ­ ­ ­ ­ ­ 0.192 ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ 0.292 ­ ­ ­ 0.713 15 ­ ­ ­ ­ ­ ­ ­ ­ 0.028 ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ 0.043 ­ ­ ­ 0.08 16 0.79 1.08 1.16 1.16 0.89 1.1 0.82 0.25 0.45 0.81 0.9 0.27 0.91 0.92 0.82 0.83 0.99 0.99 0.37 1.07 0.94 0.61 0.76 0.94 1.2 ­0.04

85

Number of sources, N

Number of sources, N

60

60

40

40

20

20

0 -1,2 -0,8 -0,4 0 ,0 0,4 0 ,8 1,2

0 -0,8 -0,4

Spectral index,

0.325/1.4 GHz

Spectral index, 0.

0 ,0

0,4

0 ,8
325/3.9 GHz

1,2

Fig. 3. Spectral index distribution between 0.325 and 1.4 GHz

Fig. 4. Spectral index distribution between 0.325 and 3.9 GHz

40

whole frequency range measured; of these, 4 show weak GPS behavior (see below) and 3 show weakly rising spectra 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 ob jects with a peak in their spectra at GHz frequencies in the redshift frame of emission. They are characterized by a difference 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 characteristics. It is possible that several may be giant radio galaxies with low frequency absorption (for

Number of sources, N

30

20

10

0 -0,4 0 ,0 0,4 0 ,8 1,2 1 ,6 2,0 2 ,4

Spectral index,

3.9/11.2 GHz

Fig. 5. Spectral index distribution between 3.9 and 11.2 GHz


86

M. G. Mingaliev et al.: Observations in the NCP region 25th General Assembly of the International Union of Radio Science abstracts, Lille, France, 750 Berlin, A., Maksyasheva, A., Nizhelskij, N., et al. 1997, Spread spectrum radiometers of RATAN-600 radio telescope, in The problems of Modern Radio Astronomy, 27th Radio Astronomy Conference, Sankt-Peterburg, 115 Condon, J. J., Cotton, W. D., Greisen, E. W., et al. 1998, AJ, 115, 1693 Giardino, G., Asareh, H., Melhuish, S. J., et al. 2000, MNRAS, 313, 689 Gregory, P. C., Scott, W. K., Douglas, K., & Condon, J. J. 1996, ApJS, 103, 427 Korolkov, D. V, & Pariiskii, Yu. N. 1979, Sky Telesc., 57, 324 Kovalev, Y. Y, Nizhelsky, N. A., Kovalev, Yu. A., et al. 1999, A&AS, 139, 545 Kuehr, H., Witzel, A., Pauliny-Toth, I. I. K., & Nauber, U. 1981, A&AS, 45, 367 Marecki, A., Falcke, H., Niezgoda, J., Garrington, S. T., & Patnaik, A. R. 1999, A&AS, 135, 273 Melhuish, S. J., Davies, R. D., Mingaliev, M. G., & Stolyarov, V. A. 2001, in preparation Mingaliev, M., Botashev, A., & Stolyarov, V. 1998, Multifrequency monitoring of a sample of extragalactic radio sources, In IAU Colloquium 164: Radio Emission from Galactic and Extragalactic Compact Sources, ed. J. A. Zensus, G. B. Taylor, & J. M. Wrobel, ASP Conf. Ser., 144, 279 Parijskij, Yu. 1993, IEEE Antennas Propagation Magazine (IAPM), 35, 7 Pauliny-Toth, I. I. K., Witzel, A., Preuss, E., Baldwin, J. E., & Hills, R. E. 1978, A&AS, 34, 253 Perley, R., & Taylor, G. 1999, VLA Calibrator Manual, http://www.nrao.edu/~gtailor/calibr.html Rengelink, R. B., Tang, Y., de Bruyn, A. G., et al. 1997, A&AS, 124, 259 Trushkin, S. 1985, Ph.D. Thesis, Special Astrophysical Observatory of Russian Academy of Sciences Verkhodanov, O., Trushkin, S., Andernach, H., & Chernenkov, V. 1997, The CATS database to operate with astrophysical catalogs, in Astronomical Data Analysis Software and Systems VI, ed. G. Hunt, & H. E. Payne, ASP Conf. Ser, 125, 322 Verkhodanov, O. 1997, Multiwaves continuum data reduction at RATAN-600, in Astronomical Data Analysis Software and Systems VI, ed. G. Hunt, & H. E. Payne, ASP Conf. Ser., 125, 46 de Vries, W. H., Barthel, P. D., & O'Dea, C. P. 1997, A&A, 321, 105

Number of sources, N

40

20

0 - 0 ,4 0,0 0 ,4 0,8
0.325/11.2 GHz

1 ,2

1,6

Spectral index,

Fig. 6. Spectral index distribution between 0.325 and 11.2 GHz

example 085834+750121); mapping will be required to establish 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.
Acknow ledgements. This research is partially supported by the Russian Foundation for Basis Research Pro ject No. 9802-16428 and Russian Federal Program "Astronomy" Pro ject 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 counterparts in the radio catalogues.

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