IPS Observations Using the Big Scanning Array of the Lebedev Physical Institute: Recent Results and Future Prospects I.V.Chashei, V.I.Shishov, S.A.Tyul’bashev, V.V.Oreshko Lebedev Physical Institute, Pushchino Radio Astronomy Observatory

Abstract Since 2006 IPS observations with the BSA LPI radio telescope at the frequency 111 MHz have been carried out in a monitoring regime. All the sources, about several hundred daily, with a scintillating flux greater than 0.2 Jy are recorded over 24 hours in the 16 beams of the radio telescope covering a sky strip of 8 o declination width. We present some results of IPS observations for the recent period of low solar activity. The solar radial dependence of scintillation index for two selected strong radio sources, 3C 298 and 3C 48, are considerably weaker than the expected dependence for a spherically symmetric heliosphere geometry. This same statistical non-radial dependence was found for the mean scintillation index of the radio source ensemble, and was especially pronounced in the year 2008 during the very deep solar activity minimum period. These features are explained by the influence of heliospheric current sheet that is revealed as a strong concentration of turbulent solar wind plasma aligned with the solar equatorial plane. Solar wind speeds were estimated using the IPS temporal power spectra. These estimates are in a good agreement with values found by IPS measurements of the same sources using the spaced radio telescopes of STEL, Japan. A new beam system of the BSA LPI radio telescope has been especially designed and constructed for IPS observations using 128 beams. The new beam system will allow an increase of the instantaneous view field of up to 64 o in declination angle and the measurement of the number of daily observed scintillating sources to more than one thousand.

Radio telescope BSA LPI Collecting area m 2, dipoles Frequency 111 MHz Two independent 16-beams systems One of them – monitoring of turbulent solar wind using IPS

IPS observations Measurable – intensity fluctuations 24 hours, every day Sky strip covering 8 o in declination Frequency bandwidth 600 kHz Sampling rate 0.1 s All scintillating sources, several hundred daily, with flux more than 0.2 Jy Strong reference sources: 3C 48 in summer time; 3C298 in winter time

Trajectory of the strip in the ecliptic coordinates

Example of IPS record

IPS data processing Traditional: scintillation indexes, temporal spectra To produce g-maps we need information on sources angular structure NA for great number of weak sources Statistical approach in assumption of sources ensemble uniformity

IPS data processing Structure function D I ( , t) = D I (  =1 s) = 2(  2 IPP +  2 noise ) Typical values  IPP  0.2 Jy  noise  1 Jy Structure function is passed through diagram filter to extract sources  2 lgD I,i (  =1s, t) = - (1/2)[ lgD I,i (  =1 s, t-3 min) -2 lgD I,i (  =1 s, t) + lgD I,i (  =1 s, t+3min)] One positive and two negative fringes,  2 lgD I,i (  =1s, t) = lg ( 1 +  2 IPP /  2 noise ) at maximum of positive fringe. Version 1. The number of scintillating sources is proportional to the averaged over ensemble scintillation index N(  IPP >  0 )   0 -2  N  [m(t)] 2 Version 2. Mean variance of scintillating flux Σ I (t) = Σ  2 lgD I,i (  =1s, t) is also proportional to [m(t)] 2 Σ I (t)  [m(t)] 2

Temporal dependence of IPS structure function, 16 beams, averaging over – ; structures with fringes are scintillating sources

Averaged over 0.5 hr x 8 deg (64 deg 2 ) sky area scintillating flux, Feb.2008

Averaged over 0.5 hr x 8 deg (60 deg 2 ) sky area scintillating flux, Feb.2011

m = (sin  ) -p, p=1, more flat than expected p=3/2 Mar. – Oct. 2007

m = (sin  ) -p, p=1, more flat than expected p=3/2 Oct.2006-Mar.2007

V STEL = k V spectr, k=1,007 (Manoharan et al, 1995)

V STEL = k V spectr, k=1,012

Averaged number of scintillating sources vs daytime, 2006 and 2008

Averaged dependence of scintillating flux on daytime in Feb. of years 2007, 2008,2009,2010,2011

New BSA beams system, 128 beams, 64 deg coverage in declination

Conclusions Week m(  ),  I (t) – pronounced low latitude high density current sheet, especially in years (L.Yang et al, 2011). Secondary maximum in anti-solar direction. IPS at our wavelength (3 m) are sensitive to close region of the solar wind, especially at descending phase and minimum of solar activity. Anticipated new beams system: almost whole daily coverage of northern sky and increase in the number of sources from few hundreds up to more than 1000 daily.