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3. Results

From our sample of 108 pulsars (with an expected flux density tex2html_wrap_inline1538 mJy at this frequency) we detected 87 pulsars and obtained good quality pulse profiles for most of them. Eight pulsars (B1541+09, B1737+23, B1738-08, B1831-04, B1841-05, B1914+13, B1915+13 and B2111+46) were detected by Seiradakis et al. (1995) but with poor signal-to-noise ratio (S/N) and pulse shapes were not presented. These pulsars were re-observed in the present survey and we obtained good quality profiles in a short integration time. For four other pulsars from our sample (B1900+01, B2016+28, B2045-16, B2310+42), profiles were published by Seiradakis et al. (1995) with poor S/N and are now presented with much better S/N. Eight pulsars which are presented here (B0450-18, B0611+22, B0626-28, B0809+74, B0818-13, B0834+06, B1604-00 and B1818-04), have been observed previously (see Sect. 1) using the old less sensitive system. We observed but did not detect 21 pulsars which are listed in Table 2 (click here). From the 33 pulsars not detected by Seiradakis et al. (1995) we attempted to observe 16 pulsars and detected 14 of them. Only two pulsars (B0320+39, B0531+21) were not detected. It is notable that PSR B0320+39 was observed by Kuzmin et al. (1986) at 4.6 GHz but during the last survey (Seiradakis et al. 1995) and in our observations this pulsar was not detected even after 30 min integration time.


PSR B N Time tex2html_wrap_inline1552 PSR B N Time tex2html_wrap_inline1552
[min] [mJy] [min] [mJy]
0320+39 1 30 0.03 1732-07 1 10 0.04
0353+52 1 15 0.06 1754-24 2 31 0.04
0410+69 2 30 0.02 1811+40 1 30 0.04
0531+21 3 40 0.02 1820-14 2 20 0.02
0613-021 10 1834-04 1 15 0.04
0621-043 41 0.01 1848+04 1 10
0751+18 1 35 1848+12 1 10 0.04
0841+80 1 10 1859+01 1 25 0.03
1322+83 2 30 0.05 2044+15 3 50 0.03
1534+12 3 31 2229+26 1 15
1700-181 20 0.03
Table 2: Pulsars not detected at 4.85 GHz. The pulsar name, number of observations, total observing time and upper limits tex2html_wrap_inline1552 for the flux density are listed

The detection limit at 1.4 GHz for the survey by Seiradakis et al. (1995) lies around tex2html_wrap_inline1572 mJy. The 4.85 GHz survey has yielded a lower limit of tex2html_wrap_inline1574 0.05 mJy, as is visible from Table 1 (click here) and the upper limits for not detected pulsars (see Table 2 (click here)).

Scatter broadening makes it difficult to detect pulsars with high dispersion measure at low frequencies, and only 11 pulsars with dispersion measures DM> 600 cm-3pc are known. All of them were discovered at 1.4 GHz (Clifton et al. 1992) or at 1.5 GHz (Johnston et al. 1992). However, scattering is still a limiting factor even at these frequencies. Using the new receiver at 6 cm we detected 9 pulsars with DM> 500 cm-3pc. We easily measured, for instance, B1758-23, which has presently the largest known DM of 1074 cm-3pc (see Fig. 1 (click here) and Table 1 (click here)). B1750-24 (tex2html_wrap_inline1588cm-3pc) shows a double (more likely complex) component profile at 4.85 GHz, whereas the components are completely smeared out at 1.4 GHz due to scatter broadening (Clifton et al. 1992). Finally, we observed four millisecond pulsars at this frequency (for more detailes see Kijak et al. 1997).

  figure312 figure317 figure321 figure325 figure329 figure333

Figure 1: Pulse shapes for 87 pulsars at 4.85 GHz

In Fig. 1 (click here) we present all pulse shapes obtained as result of our observations. The errors in flux density and pulse width were estimated by taking into account the calibration results, the signal-to-noise ratio and the resolution of the profiles. The error of the pulse width after smoothing is indicated by the width of the error box at the lower, right corner of each figure. The results are given in Table 1 (click here). For each pulsar, Col. (5) and (6) contain the pulse widths W50 and W10. The flux densities S and their errors are listed in Col. (7) and (8), respectively. The spectral index tex2html_wrap_inline1598 for flux densities between 1.4 and 4.85 GHz is given in Col. (9) with errors in Col. (10). We assumed that the pulsar flux spectra are well described by a power law of the form tex2html_wrap_inline1600. An index was obtained between 1.4 and 4.85 GHz using data from Lorimer et al. (1995) at 1.4 and 1.6 GHz, Sieber (1973) at 2.7 GHz, Seiradakis et al. (1995) at 1.4 and 4.75 GHz and this paper.

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