Multi range study of the radio sources of the RATAN-600 surveys O.P. Zhelenkova, E.K. Majorova SAO RAS, Nizhnij Arkhyz Terscol, 03.07.2017

Search for variables and transient radio sources in archival data and blind surveys To search for the variability of radio sources, archival data began to be used and specialized blind surveys were carried out, for example: RATAN-600: Cold experiment (1980-2000), GAISH Zelenchukskij survey; VLA (Very Large Array): archival data of NVSS and FIRST surveys; MOST (Molonglo Observatory Synthesis Telescope): 22-year survey of the southern sky; ATCA (Australia Telescope Compact Array): pilot survey; Allen Telescope Array: ATATS (Allen Telescope Array Twenty-centimeter Survey), includes 12 epochs of observations; PiGSS (Pi GHz Sky Survey) .

RATAN-600 «Cold» blind surveys 1980-1994 The strategy of conducting of the deep blind survey of the “Cold-80” experiment on the RATAN-600 radio telescope in 1980 was primarily aimed at obtaining data to search for microwave background fluctuations. The survey covered the strip of sky centered on SS 433 (Dec2000 = +4d54m) with width of 40m on declination and 24 hours range on right accession. The catalog RC (RATAN Cold) with a detection threshold of 10 mJy on 3.94 GHz was produced based on the observations of the survey (Parijskij et al. 1991A&AS...87....1P; Parijskij+, 1993A&AS...98..391P). To refine flux densities and coordinates of the sources of the catalog, several more observing runs were carried out in 1982–1999 on RATAN-600 at the same frequency and declination.(Parijskij+, 1991A&AS...87....1P; Parijskij+, 1993A&AS...98..391P) Refined RC (RCR) – on data 1980-1999 for the right ascension interval R.A.=02h–17h, the coordinates and flux densities of the detected sources were refined; coverege area ~154 кв.град.; на 3.9GHz Slim~10mJy; Completeness 90% S>15mJy; (Soboleva+, 2010AstBu..65...42S, Zhelenkova+, 2017AstBu).

RATAN-600 «Cold» blind surveys 1980-1994 H date t, days N σ, mK Flim3.94GHz, mJy 1980 51°08' 15.03.1980-06.06.1980 84 25-50 0.7 8.0±0.5 1988 51°09' 16.12.1987-12.01.1988 28 25 1.1 10.6±1.3 1993 51°10' 17.09.1993-01.11.1993 46 1.6 10.4±1.2 51°22' 01.04.1994-25.05.1994 55 40 1.2 11.1±2.0 (Soboleva+, 2010AstBu..65…44) The ability to detect variable sources based on blind RATAN-600 surveys (Majorova&Zhelenkova, 2012AstBu..67..318); Search candidates of variables sources in the range 7h<RA<17h (Majorova&Zhelenkova, 2013AstBu..68..371) and in 2h<RA<7h (Majorova+, 2015AstBu..70…34); Search sources which were observed only in one survey, including the transient events (Zhelenkova&Majorova, 2016); 05.02.2016

RATAN-600 «Cold» blind surveys 1980-1994 The RATAN-600 power beam pattern (PBP) differs from that of a parabolic dish. The PBP broadens with increasing angular distance from its central section. The farther the sources is from the PBP center the broader the responce width and weaker the signal. One-dimensional scan is a superposition of the sources that have crossed different horizontal sections of PBP. We needed to derive the calibration curves that can be used to compute the source flux densities and to estimate the flux density errors.

RATAN-600 «Cold» blind surveys 1980-1994 The reduction of the data of these surveys revealed that flux densities of a number of the objects vary from one observing run to another. To examine this issue, we use the data of the surveys carried out in 1980, 1988, 1993, and 1994. To find variable sources in the data of the deep surveys we performed a more thorough selection of calibration sources. Criteria for selection of calibration sources: There is information on the flux densities at several frequencies; Sufficiently bright objects with a minimum scatter of points on the spectrum; Sources with steep spectra.

RATAN-600 «Cold» blind surveys 1980-1994 The detection thresholds (or average 3 r.m.s. values) in these surveys were equal to 8.0±0.5 mJy for the 1980 survey; 10.6±1.3 (1988); 10.4±3.7 (1993); 11.1±2.0 (1994). We estimated the long-term variability index V of each studied source, its relative variability amplitude Vχ , and the χ2 probability p. We detected significant flux density variations for 73 objects with a probability of p > 0.6 by the χ2 criterion in the studied region, which is equal to 17% of the number of the sources (429 objects) that were studied for variability. Criteria for variability (I) VR= Fi/Fj (de Vries+, 2004AJ..127. 2565); (II) VF= (Fi-Fj)/√(σ2i+ σ2j) (Wang+, 2006ApJ./645..856); (III) V = [(Fi-σi)-(Fj+σj)]/[(Fi-σi)+(Fj+σj)] (Gorshkov+, 2010ARep..54.908); (IV) Vχ= ΔF/‹F›, ‹F›=√((n-1)[χ2-(n-1)]/∑(Fi/σi)

Variable source candidates

Search of radio transients in RATAN-600 blind surveys 1980-1994 The archive data of the surveys are also used for searching and estimating the frequency of radio transients. They are frequently thought to be associated with different types of events and objects. They can be supernovae or afterglows of gamma-ray bursts, tidal disruption events (TDE), tidal disruption flares (TDF) and others. The activity of stars and compact objects in the Galaxy can be also detected as a transient event in the radio range. As a criterion of the transient nature of a source, apart from its absence in the NVSS and other catalogs, we adopted the condition of its detection in scans of only one single survey of 1980, 1988, 1993, and 1994 provided that the sensitivity of at least one another survey would be enough for its detection. We detected three events at a level of 3–5 r.m.s.

Radio transient candidates in the blind surveys 1980-1994 Using the data from radio, optical and infrared surveys, we made assumptions on the possible nature of these events. The first transient is probably associated with AGN activity, the second with a cataclysmic GRB event or with a supernova, the origin of the third is not determined.

RCR-sources with significant flux density variations Variable sources have a variety of morphological types, although point sources and sources with a core are 10-17% larger than those of non-variable objects. 70% - compact objects that are not resolved in NVSS and FIRST. 10% have significant angular and linear size (from 100 to 500 kpc), and their morphological structure has features that are most likely generated by the re-start of an active phase of the radio source. All extended sources are identified with galaxies that have neighbors.

RCR sources with significant flux density variations RCR sources with significant flux density variations. Variability search in the optical range Half of the variable radio sources were detected a variability in the optical and / or infrared range, and all the hosts of the variable radio sources brighter than R = 18m turned out to be also variables in optics. Variable radio sources with ultra-steep spectra show no variability in the optical and / or infrared range due to the weak magnitude of the parent objects.

Comparison of variables and non-variable sources G/Q k=-Mr/log(L3.94ГГц) log(L3.94ГГц)

Comparison of variables and non-variable sources Left – redshifts and radio luminosities L1.4GHz W/Hz for studied radio sources (stars) with significant variations of integrated flux densities (suspected variable) and without ones (circles). In the center - percentage for the same sources as a function of the radio luminosity. Right - percentage for the same sources as a function of the integrated flux density on 3.94 GHz.