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See also Second quadrant SNRs
Bull. of SAO, 1996, 41, 65--80

Multi--frequency observations of supernova remnants with the RATAN--600 radio telescope

S. A. Trushkin


The results of multi--frequency observations of about 90 Galactic supernova remnants (SNR) in the Galactic quadrants I and IV at 2--6 frequencies are presented. The main goals are to determine accurately sizes, structure and radio spectra. The observations were carried out with the Northern sector of the RATAN--600 radio telescope at 0.96, 2.3, 3.65, 3.9, 7.7 and 11.2 GHz in 1987--1995. Flux densities of the most SNRs have been measured at 0.96 and 3.9 GHz. The new suspected SNRs were included in the recent runs of observations (1992--1996). The spectra of many new SNRs have been defined with a higher accuracy. The one--dimensional brightness distributions of all SNRs have been analyzed comparing with the available radio maps.

The interesting variable point source 1820--239 was identified with the confirmed SNR G8.7-5.0. It has a non--thermal spectrum and shows flux variability on a time scale of 3--4 months. In the confused region G10.3-0.3 we have clearly found a non--thermal detail in the new observations. G12.0-0.1 resolved into two sources: W--detail has a flat spectrum and E--detail has a steep one. Suspected G36.6-0.7 has the spectral index -0.8, it seems to be a background extragalactic source because the spectral index is too steep for SNR.

For 18 SNRs (G5.9+3.1, G8.7-5.0, G11.2-1.2, G13.5+0.2, G16.7+0.1, G16.8-1.1, G17.4-2.3, G23.6+0.3, G42.8+0.6, G45.9+1.6, G49.2-0.7, G57.2+0.8, G59.5+0.1, G59.8+1.8, G68.6-1.2, G344.7-0.1, G348.5-0.0 and G352.7-0.1) the non--thermal spectra (alpha < -0.3) have been confirmed. Another 16 shell SNRs (G0.9+0.1, G1.4-0.1, G4.2-3.5, G5.2-2.6, G5.4-1.2, G6.4+4.0, G15.1+1.6, G17.8-2.6, G32.8-0.1, G40.5-0.5, G43.9+1.6, G73.9+0.9, G85.2-1.2, G351.2+0.1, G357.7+0.3, G359.1-0.5 have a flatter, critical spectral index alpha > -0.3 as it follows from our flux points. The new spectra of 12 SNRs have strongly changed (Delta_alpha > 0.1). In the region of the SNR G5.4-1.2 the compact source G5.27-0.90, associated with the pulsar PSR 1758-24, has shown the inverse spectrum with the spectral index alpha=+0.33, which is consistent with the optically thin synchrotron source with a mono-energetic spectrum of relativistic electrons. Unusual SNR G18.9-1.1 has a prominent feature with a flat spectrum, and the rest of the remnant has a steep one. The central W--E ``plateau'' within the remarkable SNR CTB80 has the spectral index alpha=-0.52+-0.06. But the 40" x 30" ``core'' near the 40 ms pulsar from 1 to 15 GHz has shown a flat spectrum, at the level of 1.0 Jy, and during the last six years this level has not changed. However a turnover at high frequencies is possible. There are no variations of the spectral index from the brighter W-region to the weak E-part of the G357.7-0.1, rejecting possible speculations about ``aging'' of radio emission within the remnant from the bright filamentary region to the faint smoothed one. During the last years the RATAN-600 has been used to carry out a new survey of the Galactic plane at 960 and 3900 MHz from l=342^o to l=19^o, |b| < 5.5^o, to search for new SNRs and to study the SNRs that have just been detected.

Column (1) lists Galactic notation names of the new and well--known SNRs from Green's catalog;

columns (2) and (3) give Right Ascension and Declination (epoch 1950.0),

column (4) contains angular sizes of a source: MAX x MIN and the new measured size in parentheses, if it is different;

columns (5), (6), (7) present measured flux densities (S_nu) at 2.7, 7.6 and 13 cm wavelengths; column (8) contains nu at 960 MHz and estimated values at 1 GHz from Green's catalog; in column (9) the ``old'' spectral indices from Green's Table 1

in column (10) the ``new'' ones (here S_nu ~ nu(-alpha) ) evaluated from the available and measured points S_nu are given. The sign ``?'' means sparse data or great uncertainty. The sign ``var'' means variable spectral index over remnants.