Giant pulses from the Crab pulsar at a frequency of 112 MHz

1. Giant pulses from the Crab pulsar at a frequency of 112 MHz Smirnova T. V.Pushchino Radio Astronomy ObservatoryAstro Space CenterP.N. Lebedev Physical Institute

2. 1. Main properties of giant pulses in Crab 2. Observations 3. Statistical properties of GP at 112 MHz 4. Comparison with data at different frequencies • 5. Conclusion

3. Large brightness temperature, GP can reach 1037K in • nanosecond-resolution observ-s, flux density can exceed 1000 • of times the average pulse-integrated flux • 2) Longitude position coincides with the position of high-energy • emission • 3) Both the main pulse and interpuse exibit the GP phenomenon, • but the precursor doesn’t • 4) The internal width of GP is about 1 mks, although pulse can • have a comlex structure at high frequencies • the narrowest pulses don’t resolved with 2 ns resolution • 5) Power law distribution of GP intensities • 6) Bandwidth of emission at least 0.8 GHz at f = 1 GHz with • spectral indices between -2.2 and -4.9 (Sallmen et al. 1999) • 90% of GP detected at 4.9 GHz were detected at 1.4 GHz (Moffett, • 1997) • The mean spectral index is -2.7 in the range (600-111) MHz and (600 – 23) MHz • (Popov et al. 2006)

4. The advantages of low-frequency observations for study of internal intensity variations Increasing of the the pulsar flux energy more than increasing of noise No influence from diffractive scintillation Refractive time is much more than 1 month

5. Observations BSA, Puchshino Radioastronomy observatory f = 111.88 MHz, Nov. 2005, Jan 2007 and June 2007 T = 3.5 min, time resolution 0.8192 ms 2 days with T = 11 min for calibration 512*5 KHz receiver, B = 2.3 MHz (461 channels) recording of 31 periods in one zone, 200 zones each day DM and timing model from JB monthly ephemeris Postdetection dedispersion

6. Analysis of data finding of zero level and sigma noise in each zone Search for GP with I > 5 sigma noise Normalization of intensities for antenna’s diagram Scattering of pulses Polarization Cumulative probability distribution of GP

7. The mean level and sigma noise in dependence on time. The flux density of the Crab Nebular is 1720 Jy at 112 MHz. 100 c.u. = 6.6 Jy

8. Scattering in January 2007 is in 1.8 times more than in Nov 2005

9. We have RM = (-45.5 ± 0.4) rad/m2, catalog value of RM is (-42.3 ± 0.5) rad/m2. Variations of RM with a time. The degree of polarization at 112 MHz is not more than 12%.

10. The mean ACF from all zones. The distance from MP to IP is (17±1)ms. It is 13.4 ms at 430 MHz. IIP/IMP = 0.3.

11. Cumulative distribution function of GP. Power law with n = -2.3 ± 0.04 (Nov 2005, square), n = -2.43 ± 0.09 (Jan 2007, circles), n = -2.21 ± 0.09 (June 2007, triangle). The number of GP with I > I_0 is proportional to the mean flux density. S_Nov=11Jy, S_Jan=5Jy, S_Jun=7.4Jy. Energy of pulse is: I•We = const

12. Frequency of occurrence of GPs. A pulse that is 50 times more than ampl. of regular pulse can be once in 5000 pulse periods. The brightest GP has a peak amplitude of 1940 Jy and a flux energy of 2.5∙107 Jy∙μks

13. The fluxenergy of brightest pulses (Imax•W) in dependence of frequency. Emax[Jy•ks] = 1012• f-2.2

14. Parameters of GP at 112 MHz

15. Conclusions 1. CPD has a power law with index n=2.3 at 112 MHz . It doesn’t change with a time. Generation mechanism for GP is stable. 2. Changing of pulse scattering affects only on peak amplitude of GP but their energy doesn’t changed. 3. Refractive scintillation affects on the number of GP exceeding some amplitude and statistics of GP can be corrected by multiplication on the ratio of mean flux densities for time separated observations. 4. The dependence of peak energy of GP on frequency has a power low with index -2.2 +- 0.2. 5. Low degree of polarization, RM = 47.5 +- 0.4 rad/m^2.