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Variability study of flat-spectrum radio Variability study of flat-spectrum radio sources sample at the RATAN-600sources sample at the RATAN-600
Sotnikova Yu.V., Erkenov A.K.
● 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 characteristics of compact radio sources in the near-polar region of the celestial sphere.
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.
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
FAST VARIABILITY
2007.07.27 23:21:29 '7725r 7280021.r 1937+83 Marat': Start
2007.07.27 23:21:47 Failures:
174A 86.8 251.0 Fail: Nmov
2007.07.27 23:22:20 '7725r 7280021.r 1937+83 Marat': Stop
2007.07.28 0:37:43 '7725r 7280053.r 2005+77 Marat': Start
2007.07.28 0:37:55 Failures:
174A 86.8 251.0 Fail: Nmov
2007.07.28 0:42:10 '7725r 7280053.r 2005+77 Marat': Stop
2007.07.28 1:01:22 '7725r 7280112.r 2022+76 Marat': Start
2007.07.28 1:03:04 '7725r 7280112.r 2022+76 Marat': Stop
an output file-protocol of the condition of antennasurfaces state
format of the output file with observant data
name
1.38 cm 2.7 сm 3.9 cm 6.3 cm
relative errors of antenna temperature [%]
0410+76 1.11.1 0.170.17 0.210.21 0.330.330410+76 cor 1.11.1 0.160.16 0.200.20 0.300.300016+79 4.64.6 0.510.51 0.240.24 0.360.360016+79 cor 4.54.5 0.510.51 0.220.22 0.360.362344+82 6.46.4 0.610.61 0.260.26 0.470.472344+82 cor 6.46.4 0.600.60 0.250.25 0.450.45
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)
Long-term variability (1999-2007)Long-term variability (1999-2007)
VarVarΔΔSS = (Smax–Smin)/Smin = (Smax–Smin)/Smin
Approximate classificationApproximate classification
20 sources – flat spectra which can be described by a power law, 20 sources – flat spectra which can be described by a power law, withwith 0 0 ≥≥ αα ≥ -0.5 ≥ -0.5
mainly Galaxies mainly Galaxies
5 sources with peaked spectra5 sources with peaked spectra (candidates in GPS) (candidates in GPS)Quasars – core/core-jetQuasars – core/core-jetGalaxies – compact symmetrical structureGalaxies – compact symmetrical structure
99 sources with complex or powerfully changing sources with complex or powerfully changing shapeshape
Varied VLBI-morphologyVaried VLBI-morphology
Approximate classificationApproximate classification
17 sources with rising spectra 17 sources with rising spectra mainly Quasars - coremainly Quasars - core
The statistical analysis of fast variability of the obtained data was based on methods described
in [Quirrenbach A. 2000]:
Tam 1100[%]
2
1
2
1
1
N
i i
i
Ta
TaTa
N
2
0
23[%] mmY
- 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 test2
- 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
““Light curves” of the selected reference sources and (lower) Light curves” of the selected reference sources and (lower) relation between the modulation index and declination of a relation between the modulation index and declination of a source.source.
*322.032.24[%]7.21,0 m *078.074.5[%]2.11,0 m *009.05.0[%]7.7,0 m *027.081.1[%]8.4,0 m
ResultsResults
ConclusionsConclusions1. It was obtained simultaneous multi-frequency radio spectra of objects (from flux-density full 1. It was obtained simultaneous multi-frequency radio spectra of objects (from flux-density full
sample ) of near-polar region at several epochs (sample ) of near-polar region at several epochs (1999, 2005, 2006, 20071999, 2005, 2006, 2007).).
2. As a result of statistical analyze 15 objects were detected with presence of variability of radio 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 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 and 4.8 GHz. Most of them are quasars. The variability amplitude of these sources is not above 7%. Four sources from them above 7%. Four sources from them (J(J0626+8202, 0626+8202, JJ1153+8058, 1153+8058, JJ1800+7828, 1800+7828, JJ2005+7752 2005+7752 )) are are already known as fast-variations sources [already known as fast-variations sources [DD..SS. . Heeschen 1987; A. QuirrenbashHeeschen 1987; A. Quirrenbash 2001; A. Kraus2001; A. Kraus 20032003]. ].
3. On the results of statistical analyze both objects with significant long-term variability and ones 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 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 days and more. For example, three radio sources with peaked spectrum, were earlier candidates in GPS-sources candidates in GPS-sources J0626+82, J0726+79J0626+82, J0726+79 and and J1044+80.J1044+80.
4. 4. More than half of sources with rapid variability demonstrate the rise of the variability amplitude More than half of sources with rapid variability demonstrate the rise of the variability amplitude with the frequency. with the frequency.
____________________________________________________________________________________________________________________________________________Publications:1. Mingaliev M.G., et al., Astron. J., 2007, 84, N5, 1-22.2. Mingaliev M.G., et al., Astron. J., 2008, in prepare.
THE END
ReferencesReferences
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