J/A+A/694/A96ivo://CDS.VizieR/J/A+A/694/A96doi:10.26093/cds/vizier.36940096CDSMarchili N.Witzel G.Aller M.F.2025-05-21T20:02:19Z2025-02-05T08:51:31ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.fractive-galactic-nucleiradio-sourcesthe-sunCompact radio sources can show remarkable flux density variations at GHz frequencies on a wide range of timescales. The origin of the variability is a mix of source-intrinsic mechanisms and propagation effects, the latter being generally identified with scattering from the interstellar medium. Some of the most extreme episodes of variability, however, show characteristics that are not consistent with any of the explanations commonly proposed. An in-depth analysis of variability at radio frequencies has been carried out on light curves from the impressive database of the US Navy's extragalactic source monitoring program at the Green Bank Interferometer (GBI) - a long-term project mainly aimed at the investigation of extreme scattering events - complemented by UMRAO light curves for selected sources. The purpose of the present work is to identify events of flux density variations that appear to correlate with the position of the Sun. The 2GHz and 8GHz light curves observed in the framework of the GBI monitoring program have been inspected in a search for one-year periodic patterns in the data. Variations on timescales below one year have been isolated through a de-trending algorithm and analysed, looking for possible correlations with the Sun's position relative to the sources. Objects at ecliptic latitude below ~20{deg} show one-year periodic drops in flux densities, centred close to the time of minimum solar elongation; both interplanetary scintillation and instrumental effects may contribute to these events. However, in some cases the drops extend to much larger angular distances, affecting sources at high ecliptic latitudes, and causing variability on timescales of months. Three different kinds of such events have been identified in the data. Their exact nature is not yet known. In the present study we show that the variability of compact radio sources is heavily influenced by effects that correlate with solar angular distance; this unexpected contribution significantly alters the sources' variability characteristics estimated at GHz frequencies. In particular, we found that many extreme scattering events previously identified in the GBI monitoring program are actually the consequence of Sun-related effects; others occur simultaneously in several objects, which excludes interstellar scattering as their possible cause. These discoveries have a severe impact on our understanding of extreme scattering events. Furthermore, Sun-related variability, given its amplitude and timescale, can significantly alter results of variability studies, which are very powerful tools for the investigation of active galactic nuclei. Without a thorough comprehension of the mechanisms that cause these variations, the estimation of some essential information about the emitting regions, such as their size and all the derived quantities, might be seriously compromised.2025A&A...694A..96Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/694/A96CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/ApJS/136/265 : Monitoring compact radio sources at 2.5+8.2GHz (Lazio+, 2001)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/694/A96https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/694/A96http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/694/A96https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/694/A96https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/694/A96http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/694/A96GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/694/A96/table3 (*Main variability characteristics of the sources included in the US Navy's extragalactic source monitoring program (NESMP), Lazio et al., 2001ApJS..136..265L, Cat. J/ApJS/136/265)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/694/A96/table3?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/694/A96/table3?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/694/A96/table3?GETtext/xml+votable180.050000true1.488230838.33754140.0055555555555555566/60 124 579 677 1154 1263 1521 1544 1546 1701 1782 2098 2143 2214 2245 2710 2836 3096 3402 3675 3820 3886 3965 4054 4361 4436 4448 4695 4754 4820 5371 5448 5693 5767 6033 6167 6641 6686 7570 7873 7896 7911 7969 8017 8031 8123 8487 8615 8705 8717 8858 8977 8997 9073 9442 9633 9813 9976 10006 10288 10321 10422 10432 10566 10743 10795 11203 11639 12301 12352 12444 12466 12987 13156 13410 13545 13789 13927 13995 14737 15067 15286 15494 16059 16093 16281 16298 16301 17351 17414 17541 17836 18271 19101 19341 19523 19609 19723 19970 20099 20202 20213 20468 21117 21298 21373 21758 21885 22047 22375 22658 22943 22950 23121 23291 24084 24571 24936 25302 25503 25937 26115 26131 26547 26642 27060 27290 27702 28167 28383 28453 28830 29675 29963 30542 30942 31334 31529 31559 31857 31894 32527 32594 36417 40692 40730 44670 485951.325213914061602e-24 5.300855656246408e-24https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/694/A96?format=asciiRadiodefaultJ/A+A/694/A96/table3*Main variability characteristics of the sources included in the US Navy's extragalactic source monitoring program (NESMP), Lazio et al., 2001ApJS..136..265L, Cat. J/ApJS/136/265S2GHzAverage flux density at 2GHzJyphot.flux.density;em.radio.1500-3000MHzfloatELATEcliptic latitudedegpos.ecliptic.latfloatrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSEminTime of the year in which solar elongation reaches the minimumatime.epochfloats_S2GHzStandard deviation of the 2 GHz flux densityJystat.stdev;phot.flux.density;em.radio.1500-3000MHzfloatS8GHzAverage flux density at 8GHzJyphot.flux.density;em.radio.6-12GHzfloats_S8GHzStandard deviation of the 8GHz flux densityJystat.stdev;phot.flux.density;em.radio.6-12GHzfloat2Gdip? Amplitude of the dip at minimum solar elongation in the 2GHz light curveJysrc.var.amplitudefloatnullablee_2Gdip? Uncertainty in the 2GHz dip estimationJystat.errorfloatnullableAutoProb? Probability that the number of SRV events is consistent with an homogeneous distribution of dips across the yearstat.fit.goodnessdoublenullableSRVA2SRV classification at 2 GHz according to automatic detectionsrc.classcharAutoProbT? Probability that the number of TDV events is consistent with an homogeneous distribution of dips across the yearstat.fit.goodnessfloatnullableTDVA[Y] TDV classification according to automatic detectionmeta.codechar_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.mainSourceSource name (HHMM+DDm)meta.id;meta.maincharSRVV2SRV classification at 2GHz according to visual inspectionsrc.classcharSRVV8SRV classification at 8GHz according to visual inspectionsrc.classcharTDVV[Y] TDV classification according to visual inspectionmeta.codecharSimbadNameSimbad column added by the CDSmeta.idcharnullable