1. Introduction

Observations of integrated pulse profiles over a wide frequency range are important for an understanding of many aspects of radio pulsars. Mean pulse profiles of pulsars exhibit great stability but there are large morphological differences from pulsar to pulsar (Backer 1976; Morris et al. 1981; Rankin 1983; Lyne & Manchester 1988; Seiradakis et al. 1995). This fact has become the basis for a classification system first proposed by Huguenin et al. (1971) and finally developed by Rankin (1983). The morphological characteristics of observed pulse shapes provide us information on both the geometry and the mechanism of pulsar radiation. In the hollow-cone beam model for pulsar radio emission (Sturrock 1971; Ruderman & Sutherland 1975) the observed pulse shapes represent cuts across the radiated beam. Most pulsars show considerable changes of pulse shape and profile width with frequency. Simple profiles at low frequency are often resolved into several components at higher frequencies (Kramer 1994). These differences are partly due to the various ways in which the line of sight cuts across the radiated beam and partly due to the intrinsic asymmetries or irregulaties within the actual pulsar beams. The narrowing of profiles with increasing frequency is compatible with the hollow-cone model and supports the concept of a radius-to-frequency mapping (Cordes 1978).

Dispersion smearing and in particular, scatter broadening prohibit the detection of pulsars with high dispersion measures at low frequencies. However, the general steepness of pulsar spectra demands a highly sensitive observing system at high frequencies. The flux density of observed pulsars is known to be frequency dependent at lower frequencies with an average power-law index of -1.6 (Lorimer et al. 1995).

The profile morphology develops with increasing frequency either from a simple to a multiple component structure or vice versa. A classification scheme based on this fact (Rankin 1983) distinguishes between core and cone dominated profiles, depending on the radiating part of the emission cone. The so-called core component is identified with a central component of the pulse profile, which shows no drift in the corresponding sub-pulses. In contrast, cone components generally located at the outer edges of the pulse profiles, often exhibit drifting sub-pulses. In the hollow-cone model, the mean pulsar beam consists of a multiple cone structure nested around a core component located at the magnetic axis. This model describes simple and complex structures of pulse profiles well (Oster & Sieber 1976; Gil & Krawczyk 1997). In general, a core component is observed mainly at low frequencies and fades progressively towards higher frequencies. At the same time "conal outriders'' become the dominant features in pulse profiles at high frequencies. This can be explained by geometrical effects (Kramer et al. 1994; Sieber 1997). Several studies present arguments for the multi-conal beam structure which is implied by average pulsar profiles (Gil et al. 1993; Rankin 1993; Kramer et al. 1994; Gil & Krawczyk 1996). However, Lyne & Manchester (1988) claim that the components in the mean profile correspond to patchy beams fixed to the neutron star surface.

Nevertheless, both models assume that integrated profiles represent a true "long exposed'' image of the radio beam. Thus, the study of flux densities, pulse widths and pulse shapes over a wide frequency range are very important for the understanding of the radio emission properties of pulsars. Therefore we have started a project to collect pulse shapes and flux densities in the widest range of frequencies possible. Up to now, 64 different pulsar profiles have been observed and presented at a wavelength of 6 cm using the 100-m radio telescope of the Max-Planck-Institut für Radioastronomie (see Sieber et al. 1975; Kuzmin et al. 1986; Izvekova et al. 1994; Seiradakis et al. 1995). In this paper we present a further 87 pulse shapes at 4.85 GHz. We have measured pulse widths at a level of 50 and 10 per cent of the pulse peak as well as mean flux densities (see Table 1 (click here)). The results are used to discuss the profile development and the narrowing of pulse widths with frequency. The new data are combined with data from the literature to make a statistical study of the spectral behaviour of flux density.

   

PSR B P DM N W₅₀  W₁₀  S

(s) (pulses)  (deg)  (deg)  (mJy) (mJy) (1.41 - 4.85 GHz)

0037+56 1.118 91 1339 3.2 7.7 0.08 0.01 -1.7 0.1

0053+47 0.472 18 6293 8.4 13.7 0.06 0.01

0138+59 1.222 35 480 15.8 27.8 0.31 0.03 -2.4 0.1

0144+59 0.196 39 4864 3.2 9.5 0.35 0.11 -0.6 0.1

0301+19 1.387 16 430 6.0 14.4 0.44 0.05 -2.5 0.2

0402+61 0.594 65 1000 5.6 17.2 0.29 0.03 -1.8 0.1

0450-18 0.548 40 540 20.0 26.7 0.97 0.10 -1.4 0.1

0559-05 0.395 81 4625 11.2 20.0 0.31 0.03 -1.7 0.1

0609+37 0.297 27 2000 7.7 13.0 0.11 0.02 -2.1 0.2

0611+22 0.334 97 1980 9.5 21.5 0.38 0.04 -1.3 0.1

0626+24 0.476 84 4464 14.1 20.0 0.89 0.09 -1.0 0.1

0628-28 1.244 34 72 13.7 26.7 9.19 0.90 -0.6 0.2

0643+80 1.214 33 1956 3.2 7.4 0.06 0.01 -1.5 0.2

0751+32 1.442 39 1160 21.1 24.3 0.15 0.02 -1.4 0.2

0756-15 0.682 64 2583 3.9 6.0 0.20 0.02 -1.7 0.1

0809+74 1.292 6 693 14.7 29.3 2.45 0.25 -1.3 0.1

0818-13 1.238 41 480 6.0 9.8 0.33 0.03 -2.4 0.1

0834+06 1.273 13 2772 7.7 10.2 0.07 0.02 -3.5 0.2

0906-17 0.401 16 4329 15.1 20.7 0.44 0.05 -1.6 0.2

0942-13 0.570 13 4134 6.0 8.4 0.05 0.01 -2.9 0.2

J1022+10  0.016 10 138472 8.4 27.0 0.39 0.05 -1.7 0.2

1039-19 1.386 32 1210 10.9 15.1 0.55 0.06 -1.1 0.2

1254-10 0.617 29 960 8.4 19.0 0.21 0.02 -1.5 0.1

1541+09 0.748 35 480 9.5 21.6 0.10 0.01 -3.4 0.1

1552-23 0.532 51 2240 6.7 12.3 0.09 0.02 -2.0 0.1

1604-00 0.421 11 700 6.5 11.4 1.64 0.16 -0.7 0.2

1612+07 1.206 21 1056 1.8 3.2 0.04 0.01 -3.0 0.2

1620-09 1.276 70 1067 3.5 7.4 0.05 0.20 -2.0 0.2

1702-19 0.298 23 1800 11.6 16.5 1.10 0.11 -1.6 0.3

0.298 23 1800 4.9 8.8 0.14

1709-15 0.868 58 1003 5.3 9.5 0.08 0.01 -1.8 0.2

J1713+07  0.004 16 361020 17.2 82.6 0.80 0.04 -1.7 0.1

1717-16 1.565 42 558 3.2 6.3 0.06 0.01 -2.4 0.3

1737+13 0.803 49 738 11.3 20.7 0.37 0.04 -1.8 0.1

1738-08 2.043 75 287 7.0 14.4 0.14 0.02 -2.1 0.1

1745-12 0.394 100 1520 14.8 20.7 1.42 0.14 -0.6 0.1

1750-24 0.528 800 1036 17.6 23.7 0.37 0.04 -1.3 0.1

1753+52 2.391 35 750 11.6 16.9 0.08 0.01 -2.4 0.2

1758-23 0.415 1140 1440 4.9 16.9 0.43 0.04 -2.1 0.1

1805-20 0.918 609 1296 9.8 13.0 0.21 0.02 -1.8 0.6

1815-14 0.291 595 1020 8.1 17.6 0.51 0.06 -2.1 0.1

1817-13 0.921 750 928 4.2 10.6 0.20 0.03 -2.2 0.2

1818-04 0.598 84 1000 6.7 14.4 0.43 0.04 -2.4 0.1

1819-22 1.874 121 312 8.4 15.1 0.14 0.02 -2.5 0.1

1820-11 0.279 428 1431 34.5 51.3 0.64 0.06 -1.4 0.1

Table 1: Parameters for detected pulsars at 4.85 GHz. The pulsar name, period, dispersion measure, number of pulses, pulse width at 50%, pulse width at 10%, flux density with error and spectral index with error are listed

PSR B P DM N W₅₀  W₁₀  S

(s) (pulses)  (deg)  (deg)  (mJy) (mJy) (1.41 - 4.85 GHz)

1821+05 0.752 67 779 23.2 30.9 0.84 0.09 -1.1 0.1

1821-11 0.435 620 6222 3.9 14.4 0.09 0.01 -2.5 0.1

1822-14 0.279 360 3392 4.2 8.8 1.20 0.11 -0.7 0.1

1823-13 0.101 231 5880 78.0 105.1 2.60 0.26 -0.4 0.1

1829-08 0.647 301 920 11.9 23.6 0.15 0.02 -2.8 0.1

1830-08 0.085 411 15925 49.9 71.0 0.90 0.08 -1.3 0.1

1831-04 0.290 79 2040 126.6 139.9 2.11 0.23 -1.6 0.1

1839+09 0.381 49 1560 10.6 13.7 0.22 0.03 -1.6 0.1

1839+56 1.652 27 360 6.0 10.9 0.36 0.04 -2.0 0.2

1841-05 0.255 400 4698 9.5 19.7 0.32 0.03 -1.7 0.1

1849+00 2.180 680 168 22.9 29.5 0.28 0.03 -2.4 0.1

1855+02 0.415 504 1584 4.9 14.4 0.51 0.05 -1.1 0.1

1855+09 0.005 13 385986 31.6 60.0 1.12 0.09 -1.4 0.2

0.005 13 385986 14.0 70.0

1859+07 0.644 253 920 10.6 19.7 0.12 0.02 -2.4 0.1

1900+01 0.729 246 380 6.7 12.7 0.59 0.06 -1.0 0.2

1900+06 0.673 530 1386 2.5 4.6 0.13 0.02 -2.2 0.2

1905+39 1.235 30 2004 15.1 23.9 0.17 0.02 -1.9 0.1

1907+03 2.330 79 876 50.6 62.3 0.35 0.04 -1.3 0.2

1911+13 0.521 144 1708 9.1 17.9 0.15 0.02 -1.7 0.1

1911-04 0.825 89 720 6.7 8.8 0.37 0.04 -2.0 0.1

1913+10 0.404 246 1480 9.8 16.5 0.15 0.02 -2.3 0.1

1914+09 0.270 61 7865 9.8 20.7 0.12 0.01 -1.7 0.1

1914+13 0.281 237 8374 6.7 12.0 0.21 0.02 -1.8 0.1

1915+13 0.194 95 9240 10.6 17.9 0.16 0.02 -2.7 0.1

1916+14 1.181 30 1356 7.0 12.0 0.13 0.01 -1.9 0.3

1923+04 1.074 102 945 6.0 8.4 0.16 0.02

2000+32 0.696 135 945 6.7 15.1 0.42 0.04 -0.9 0.1

2000+40 0.905 128 656 5.6 16.2 0.13 0.01 -3.0 0.1

2002+31 2.111 235 791 10.5 15.8 0.10 0.02 -2.4 0.1

2011+38 0.230 239 1040 22.2 39.7 0.72 0.07 -1.9 0.1

2016+28 0.557 14 1612 7.9 15.4 0.83 0.09 -3.0 0.2

2045-16 1.961 12 602 1.9 13.7 1.05 0.12 -2.8 0.1

2053+36 0.221 98 2680 8.4 16.5 0.28 0.03 -1.8 0.1

2110+27 1.202 25 1248 3.5 5.3 0.08 0.02 -2.5 0.1

J2145-07  0.016 9 112080 12.0 96.0 0.44 0.03 -2.9 0.2

2111+46 1.014 141 1764 54.1 69.3 1.89 0.19 -1.9 0.1

2148+52 0.332 146 3870 13.0 18.3 0.38 0.04 -1.6 0.1

2148+63 0.380 128 3861 9.8 18.3 0.26 0.05 -1.9 0.1

2154+40 1.525 71 1125 15.9 22.9 0.57 0.06 -2.8 0.1

2303+30 1.575 50 378 4.6 8.1 0.37 0.04 -1.2 0.1

2310+42 0.349 17 2646 9.1 14.8 0.50 0.05 -3.0 0.1

2315+21 1.222 21 1020 3.2 7.0 0.08 0.01 -2.8 0.2

2334+61 0.495 58 1200 15.5 22.2 0.29 0.03 -1.0 0.1

Table 1: Continued