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Variability study of flat-spectrum radio sources sample at the RATAN-600

Variability study of flat-spectrum radio sources sample at the RATAN-600. Sotnikova Yu.V., Erkenov A.K.

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Variability study of flat-spectrum radio sources sample at the RATAN-600

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  1. Variability study of flat-spectrum radio sources sample at the RATAN-600 Sotnikova Yu.V., Erkenov A.K.

  2. ● The aim: to study variations of radio emission of AGNs on time scales from days to 8 years to determine characteristics of their variability. The paper presents results of observations of compact radio sources with flat spectra near the Celestial North Pole (75° ≤ δ ≤ 88°) ●All observations of sources were carried out with the radio telescope RATAN-600(21.7, 11.2, 7.7, 4.8, 2.3 and 1.1 GHz)during several observational sessions in the period 1999-2007. The main task was to obtain simultaneous multi-frequency spectra and spectral characteristicsof compact radio sources in the near-polar region of the celestial sphere.

  3. OBSERVATIONS1. 1999, 182 sources SNVSS ≥ 400 mJy, 75° ≤ Decl ≤ 88°. The work was provoked by a necessity to take account of discrete radio sources in the study of background.2. 2005, 504 sources, SNVSS ≥ 200 mJy, 75° ≤ Decl ≤ 88°. This resulted in detection of 51 sources with flat spectra.3. October 2006, April and September 2007, separate objects of the sample with flat spectra were observed additionally.4. August 2007, 33 objects of the list under investigation were observed during 30 days daily.

  4. FAST VARIABILITY format of the output file with observant data an output file-protocol of the condition of antenna surfaces state NAXIS1=7080CTYPE1=TIMECRVAL1=7051.683CRPIX1=1CDELT1=0.1BSCALE=0.4571429BZERO=0OBJECT=0203+81DATE-OBS=25/07/07LAMBDA=0.027TM-END=7759.683TTYPE1=CHANNEL 2OBSRA=2.06725253333333OBSDEC=81.13616AZIMUTH=180ELEVAT=52.709923ELEV-AN=52.709923ELEV-SH=0EPOCH=2000RA=2.05216666666667DEC=81.103528NUT-RA=4.263864e-01CMPRS-CF=1NOISE-T=4.8CALIBR1=11CALIBR2=10 2007.07.27 23:21:29 '7725r 7280021.r 1937+83 Marat': Start2007.07.27 23:21:47 Failures:174A 86.8 251.0 Fail: Nmov2007.07.27 23:22:20 '7725r 7280021.r 1937+83 Marat': Stop2007.07.28 0:37:43 '7725r 7280053.r 2005+77 Marat': Start2007.07.28 0:37:55 Failures:174A 86.8 251.0 Fail: Nmov2007.07.28 0:42:10 '7725r 7280053.r 2005+77 Marat': Stop2007.07.28 1:01:22 '7725r 7280112.r 2022+76 Marat': Start2007.07.28 1:03:04 '7725r 7280112.r 2022+76 Marat': Stop

  5. Relative errors of antenna temperature of reference sources averaged over the observational cycle, before and after introduction of corrections for the antenna surface state (the correction was calculated by Lena Majorova)

  6. Long-term variability (1999-2007) VarΔS = (Smax–Smin)/Smin

  7. Approximate classification 20 sources – flat spectra which can be described by a power law, with0 ≥α ≥ -0.5 mainly Galaxies 5 sources with peaked spectra (candidates in GPS) Quasars – core/core-jet Galaxies – compact symmetrical structure

  8. http://lacerta.gsfc.nasa.gov/vlbi/images/

  9. Approximate classification 9 sources with complex or powerfully changing shape Varied VLBI-morphology 17 sources with rising spectra mainly Quasars - core

  10. The statistical analysis of fast variability of the obtained data was based on methods described in [Quirrenbach A. 2000]: - we used the modulation index m, which is related to the mean antenna temperature end their standard deviation - as a criterion whether a source is variable or not, we perform a test - the variability amplitude for the variable sources, where m0 – is the modulation index of a non-variable sources (reference sources). But our statistical analysis differs a little bit from classical one… 55 minutes for Decl=88º … 0410+76 0016+79 2344+82

  11. “Light curves” of the selected reference sources and (lower) relation between the modulation index and declination of a source.

  12. Results

  13. Conclusions 1. It was obtained simultaneous multi-frequency radio spectra of objects (from flux-density full sample ) of near-polar region at several epochs (1999, 2005, 2006, 2007). 2. As a result of statistical analyze 15 objects were detected with presence of variability of radio emission on scales of days and more (in system of the observer) at frequencies 21.7, 11.2, 7.7 and 4.8 GHz. Most of them are quasars. The variability amplitude of these sources is not above 7%. Four sources from them (J0626+8202, J1153+8058, J1800+7828, J2005+7752 ) are already known as fast-variations sources [D.S. Heeschen 1987; A. Quirrenbash2001; A. Kraus2003]. 3. On the results of statistical analyze both objects with significant long-term variability and ones without long-term variability show presence of variability of radiation at the time scales on days and more. For example, three radio sources with peaked spectrum, were earlier candidates in GPS-sources J0626+82, J0726+79 and J1044+80. 4. More than half of sources with rapid variability demonstrate the rise of the variability amplitude with the frequency. ______________________________________________________________________ Publications: • Mingaliev M.G., et al., Astron. J., 2007, 84, N5, 1-22. • Mingaliev M.G., et al., Astron. J., 2008, in prepare.

  14. THE END

  15. References S.J. Tingay, D.L. Launcey, E.A. King, et al., PASJ, 55, 351 (2003).

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