## 2 Observations
### Targets  
For the targets of our experiment we have chosen two bright pulsars previously observed with LOFAR (see e.g., [35]). In our previous work we used the data to measurements of sensitivity of the PL612 LOFAR station [31]. Both pulsars were also targets in long term flux density variations study by [PERSON] et al. [36]. The examples with visualization of observing data for both observed pulsars, PSR J0332+5434 and PSR J1509+5531, were presented in Figure 5, where the data of the pulsars are shown in two columns, respectively. At the top, panels with dynamic spectra were presented. The spectra for both pulsars in the frequency range from 118 to 142 MHz were shown. The results in this area were cleaned and they are free of EM interferences. The x axis for all panels in Figure 5 is the pulse phase, but interpretation is different in top and middle panels. In the upper panels the signal is split into channels with appropriate frequency width (0.195313 MHz), while in the middle panels the signal is summed over all frequencies, but was shown as a time series of pulses added up every 10 s--i.e., approximately 13 individual pulses were added together in each time channel. In both the top and center panels, the color intensity indicates the signal level. The bottom boxes in Figure 5 present individual profiles in 2D (relative flux vs. profile phase) visualization summed over 1 min each. The relative flux maximum values used in our data analysis were obtained by fitting to the major component of the Gaussian profile. Gaussian curve fittings are marked in red in the bottom sets of profiles presented in Figure 5.  
Hereafter we present short notes on individual sources summarized in Table 1.  
PSR J0332+5434 (also known as B0329+54) discovered in 1968 [37] is one of the brightest pulsars in the northern hemisphere with the flux of about 1500 mJy (The jansky (symbol: Jy) is a non-SI unit of spectral flux density. 1 Jy = 10\({}^{-26}\) W\(\cdot\)m\({}^{-2}\cdot\)Hz\({}^{-1}\)) at 400 MHz [38; 31]. J0332+5434, rotates with a period of 0.71452 s. The distance to the pulsar, the estimation of which is based on the Galactic electron density distribution, was calculated by [36] to be at 1,43 kpc (The parsec (symbol: pc) is an astronomical unit of length used to measure distances. 1 pc \(\sim\) 3.086 \(\times\) 10\({}^{16}\) m). The DM for this pulsar is 26.7 pc cm\({}^{-3}\) and the independent of dispersion distance estimation indicates a value of 1.18 kpc [39]. Its observations resulted in an interesting information [40], also suggested possibility of planets existing in his surroundings [41] (this assumption was finally denied). Very important for this and possible subsequent works are the pulsar flux measurements at the frequency similar to LOFAR. The spectra presented in [42] indicate that the 154 MHz flux density is at the level of about 700-1000 mJy. The spectrum presented in [43] suggests flux density between 900 and 1100 mJy and [44] showed the flux density at the frequency of 150 MHz is between 700 and 1000 mJy. In Table 1 we have indicated an average value of 900 mJy with an error of about 15%. The spectrum of J0332+5434 in frequency range available for HBA part of LOFAR reaches its maximum. The spectral index for high radio frequencies (1.4-23 GHz) mentioned in [42] is \(-\)2.2. PSR J1509+5531 (also known as B1508+55) has the rotation period of 0.74 s and its DM was determined at 19.62 pc cm\({}^{-3}\)[45]. The calculated model distance [46] is between 1.0 and 1.9 kpc, while new model suggests the pulsar distance of about 2.07 kpc [38]. The flux density measured at the frequency of 400 MHz [38] has been measured as 114 mJy. The value of the flux density at 327 MHz has been estimated at 74 \(\pm\) 15 mJy few years later [36]. The same authors have also estimated distance to J1509+5531 as 0,99 kpc. The value of the flux density has been determined as 800 mJy \(\pm\) 15% error (see Table 1).