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A LOFAR Census of Millisecond Pulsars

Submitter: Vlad Kondratiev and LOFAR PWG
Description: Studies of millisecond pulsars (MSPs) at low radio frequencies are very valuable as they expand our ability to probe the compactness of radio emission regions in pulsar magnetospheres by comparing radio emission properties between MSPs and non-recycled pulsars. However, until recently there have been only a few studies of MSPs at frequencies below 200 MHz, mainly due to the high background sky temperature and large pulse broadening (caused by both scattering and dispersion in the interstellar medium). At the same time, as result of Fermi discoveries and ongoing pulsars surveys, the number of known MSPs in the Galactic field grew substantially over the past few years.

Here we present the results of LOFAR MSP census. Within this project, we accumulated the largest sample of MSPs ever observed at frequencies below 200 MHz with a single radio telescope, with half of the detected MSPs being observed for the first time at these low frequencies. Out of 75 MSPs, observed in the frequency range 110-188 MHz, we detected 49, and three of those MSPs were also detected at 38-77 MHz.

In our paper (Kondratiev et al. 2016, A&A, 585, 128) we present the average pulse profiles of the detected MSPs, their dispersion measures, effective pulse widths, and flux densities, and compare these with higher observing frequencies. A qualitative comparison of the LOFAR MSP profiles with those at higher radio frequencies shows constant separation between profile components. Similarly, the profile widths are consistent with those observed at higher frequencies, unless scattering dominates at the lowest frequencies. This is very different from what is observed for normal pulsars and suggests more compact emission region in the MSP magnetosphere.

"Postal stamps" of the LOFAR total-intensity average profiles from the best individual observations are shown here. The horizontal axis shows the pulse phase, and the vertical axis is the flux density in arbitrary units.
Copyright: Vlad Kondratiev
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