Abstract Details
| Name: Kaustubh Rajwade Affiliation: West Virginia University Conference ID: ASI2015_706 Title : Probing nulling in milli second pulsars with the GMRT Authors and Co-Authors : Yashwant Gupta, Ujjwal Kumar - National Centre for Radio Astrophysics-Pune and Mihir Arjunwadkar - Centre for modeling and simulation, University of Pune, Pune Abstract Type : Poster Abstract Category : Stars, The Milky Way Galaxy and its neighbours Abstract : Over the past several years, the phenomenon of pulse nulling has been studied for many 'normal' period pulsars. These studies, which require measurement of single pulse energies, have revealed a wealth of information which has helped in improving our understanding of the emission mechanism of pulsars. Studies of pulse nulling for Milli-Second Pulsars (MSPs) are relatively more difficult as they are much fainter in flux. Till date, results are available in literature for only one MSP -- PSR J0437-4715. Pulse nulling studies of MSPs will be crucial in understanding their emission behaviour and to see if phenomena like pulse nulling are relevant in the regime of lower magnetic fields and faster spin rates. The GMRT, due to its high sensitivity, offers a good option to probe nulling in MSPs. In this paper, we present results of the nulling analysis of five MSPs using data from the GMRT at 325 MHz. For each pulsar, we do an analysis of the energy histograms to estimate the limits of the Null Fraction (NF), which is the measure of the fraction of pulses in a pulse sequence which null. We confirm that PSR J0437-4715 does not null after analysing 1000000 pulses. In cases of other MSPs, where the Signal to noise ratio (S/N) is not sufficient, we integrate subsequent pulses so that the S/N is high enough to obtain an upper limit on the nulling timescale. As there are limitations of S/N on the above method of estimation of NF, we explore new ways of analysis. Using novel technique of gaussian mixture modelling, we are able to get stronger constraints on the NF of these pulsars. Our results show, with good statistical certainty, that 3 of the 5 pulsars do not show evidence of nulling. For the remaining 2, we get an upper limit on the nulling timescale. In conclusion, we are able to get NF estimates for the largest sample of MSPs so far, and the results suggest that nulling is absent in these MSPs. |