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Astron. Astrophys. 354, 960-964 (2000)

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2. Observations and data analysis

Timing observations of PSR B1822-09 at the 26-m HartRAO radiotelescope have been carried out since 1985 October at frequencies around 1644 and 2325 MHz at roughly two week intervals, using the system described by Flanagan (1993). The observing bandwidth was 10 MHz. Each observation usually consisted of three integrations. Pulse arrival times were obtained from 15 min on-line integrations of the pulsed signal sampled at 0.15 ms intervals, using a filter time-constant of 300 microsecs. Time was provided by a hydrogen maser, and referenced to UTC via the global positioning system (GPS) network. The pulse was approximated by a Gaussian and referred to as a Gaussian profile template. Such Gaussian templates have a timing reference point, which was chosen to be the centre of the main component. A total of about 830 pulse arrival times were measured for a 13-yr interval between 1985 October and 1999 February.

The observations of PSR B1822-09 at Pushchino Radio Astronomy Observatory were started in 1991 March using the BSA radiotelescope, making up a linearly polarized transit antenna, which operated at 102.5 MHz until 1998 May and at 111.3 MHz since 1998 November after the BSA reconstruction. Observations were performed 2 or 3 times per month, using 32 channel bank of 20 kHz filter receiver. The technique of observation was described in detail in the early paper (Shabanova 1998). The topocentric arrival pulse times were derived by cross-correlating the mean pulse profile from a single observation with a standard, low-noise template. Timing reference point of the template was taken to be the centre of the mean profile.

Fig. 1 presents examples of the mean pulse profiles for PSR B1822-09 for a single observation at three frequencies of 0.1, 1.6 and 2.3 GHz. The pulse profile shapes are similar to the profiles presented in Arzoumanian et al. (1994) and in Kuzmin et al. (1998). The low signal-to-noise ratio of this source allows us to measure the pulse arrival times with uncertainties between 0.3 and 3 ms, which were approximately the same at the three observing frequencies.

[FIGURE] Fig. 1. The mean pulse profile for PSR B1822-09 for a single observation at three observing frequencies of 0.1, 1.6 and 2.3 GHz

The two data sets were analyzed using a standard timing technique (Manchester & Taylor 1977). The topocentric arrival times of the HartRAO and the PRAO data sets were corrected to the barycenter of the Solar System at infinite frequency. Then the two barycentric data sets were combined and a second-order polynomial fit was performed to obtain residuals from a timing model. The JPL ephemeris DE200 was used for the barycentric corrections. Our data analysis procedure is similar to that used in the previous paper (Shabanova 1998). The position of PSR B1822-09 was obtained from Arzoumanian et al. (1994) and the proper motion was taken from Fomalont et al. (1992).

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© European Southern Observatory (ESO) 2000

Online publication: February 25, 2000