The KHOLOD Experiment: A Search for a New Population of Radio Sources

Published data from long-term observations of a strip of sky at declination +5 degrees carried out at 7.6 cm on the RATAN-600 radio telescope are used to estimate some statistical properties of radio sources. Limits on the sensitivity of the survey due to noise imposed by background sources, which dominates the radiometer sensitivity, are refined. The vast majority of noise due to background sources is associated with known radio sources (for example, from the NVSS with a detection threshold of 2.3 mJy) with normal steep spectra ({\alpha} = 0.7-0.8, S \propto {\nu}^{- \alpha}), which have also been detected in new deep surveys at decimeter wavelengths. When all such objects are removed from the observational data, this leaves another noise component that is observed to be roughly identical in independent groups of observations. We suggest this represents a new population of radio sources that are not present in known catalogs at the 0.6 mJy level at 7.6 cm. The studied redshift dependence of the number of steep-spectrum objects shows that the sensitivity of our survey is sufficient to detect powerful FRII radio sources at any redshift, right to the epoch of formation of the first galaxies. The inferred new population is most likely associated with low-luminosity objects at redshifts z < 1. In spite of the appearance of new means of carrying out direct studies of distant galaxies, searches for objects with very high redshifts among steep and ultra-steep spectrum radio sources remains an effective method for studying the early Universe.Comment: 13 pages, 10 figure

Flaring variability of Microquasars

We discuss flaring variability of radio emission of microquasars, measured in monitoring programs with the RATAN-600 radio telescope. We carried out a multi-frequency (1-30 GHz) daily monitoring of the radio flux variability of the microquasars SS433, GRS1915+105, and Cyg X-3 during the recent sets in 2005-2007. A lot of bright short-time flares were detected from GRS 1915+105 and they could be associated with active X-ray events. In January 2006 we detected a drop down of the quiescent fluxes from Cyg X-3 (from 100 to $\sim$20 mJy), then the 1 Jy-flare was detected on 2 February 2006 after 18 days of quenched radio emission. The daily spectra of the flare in the maximum were flat from 2 to 110 GHz, using the quasi-simultaneous observations at 110 GHz with the RT45m telescope and the NMA millimeter array of NRO in Japan. Several bright radio flaring events (1-15 Jy) followed during the continuing state of very variable and intensive 1-12 keV X-ray emission ($\sim$0.5 Crab), which was monitored in the RXTE ASM program. Swift/BAT ASM hard X-ray fluxes correlated strongly with flaring radio data. The various spectral and temporal characteristics of the light curves from the microquasars could be determined from such comparison. We conclude that monitoring of the flaring radio emission is a good tracer of jet activity X-ray binaries.Comment: 6 pages, 8 figures, published in the proceedings of the Second Kolkata conference on Observational Evidence for Black Holes in the Universe, ed. S.K. Chakrabarti (AIP

Radio emission of the Galactic X-rays binaries with relativistic jets

Variable non-thermal radio emission from Galactic X-ray binaries is a trace of relativistic jets, created near accretion disks. The spectral characteristics of a lot of radio flares in the X-ray binaries with jets (RJXB) is discussed in this report. We carried out several long daily monitoring programs with the RATAN-600 radio telescope of the sources: SS433, Cyg X-3, LSI+61o303, GRS 1915+10 and some others. We also reviewed some data from the GBI monitoring program at two frequencies and hard X-ray BATSE (20-100 keV) and soft X-ray RTXE (2-12 keV) ASM data. We confirmed that flaring radio emission of Cyg X-3 correlated with hard and anti-correlated with soft X-ray emission during the strong flare (>$Jy) in May 1997. During two orbital periods we investigated radio light curves of the remarkable X-binary LSI+61o303. Two flaring events near a phase 0.6 of the 26.5-day orbital period have been detected for first time at four frequencies simultaneously. Powerful flaring events of SS433 were detected at six frequencies in May 1996 and in May 1999. The decay of the flare is exactly fitted by an exponential law and the rate of the decay$\tau$ depends upon frequency as tau \propto \nu^{-0.4} in the first flare and does not depend upon frequency in the second flare, and is equal to \tau=6+-1 days at frequencies from 0.96 to 21.7 GHz in the last flare in May 1999. Many flaring RJXB show two, exponential and power, laws of flare decay. Moreover, these different laws could be present in one or several flares and commonly flare decays are faster at a higher frequency. The decay law seems to change because of geometric form of the conical hollow jets. The synchrotron and inverse Compton losses could explain general frequency dependences in flare evolution. In conclusion we summarized the general radio properties of RJXB.Comment: 10 pages, LaTeX, 14 Postscript figures, talk given at the Gamov Memorial International Conference (GMIC'99) "Early Universe: Cosmological Problems and Instrumental Technologies" in St.Petersburg, 23-27 August, 1999, to appear in Astron. Astrophys. Trans., 200

Observations of the bright radio sources in the North Celestial Pole region at the RATAN-600 radio telescope

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 5-10 percent including calibration errors. About 20 percent of the sources have flat spectra or a flat component.Comment: 21 pages, 7 figures; to be published in Astronomy and Astrophysics (without last figure with the spectra of the observed sources