Millisecond Pulsar Scintillation Studies with LOFAR: Initial Results


High-precision timing of millisecond pulsars (MSPs) over years to decades is a promising technique for direct detection of gravitational waves at nanohertz frequencies. Time-variable, multi-path scattering in the interstellar medium is a significant source of noise for this detector, particularly as timing precision approaches 10 ns or better forMSPs in the pulsar timing array. Formany MSPs, the scattering delay above 1 GHz is at the limit of detectability; therefore, we study it at lower frequencies. Using the LOw-Frequency ARray (LOFAR) radio telescope, we have analyzed short (5-20 minutes) observations of 3 MSPs in order to estimate the scattering delay at 110-190 MHz, where the number of scintles is large and, hence, the statistical uncertainty in the scattering delay is small. We used cyclic spectroscopy, still relatively novel in radio astronomy, on baseband-sampled data to achieve unprecedented frequency resolution while retaining adequate pulse-phase resolution. We detected scintillation structure in the spectra of theMSPs PSR B1257+12, PSR J1810+1744, and PSR J2317+1439 with diffractive bandwidths of 6 +/- 3, 2.0 +/- 0.3, and similar to 7 kHz, respectively, where the estimate for PSR J2317+1439 is reliable to about a factor of two. For the brightest of the three pulsars, PSR J1810+1744, we found that the diffractive bandwidth has a powerlaw behavior Delta nu(d) proportional to nu(alpha) where. is the observing frequency and alpha = 4.5 +/- 0.5, consistent with a Kolmogorov inhomogeneity spectrum. We conclude that this technique holds promise for monitoring the scattering delay of MSPs with LOFAR and other high-sensitivity, low-frequency arrays like the low-frequency component of the Square Kilometre Array.


IOP Publishing

Publication Date


Publication Title

Astrophysical Journal Letters


Physics and Astronomy

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ISM, Pulsars, Individual (PSR B1257+12, PSR J1810+1744, PSR J2317+1439), Cyclic spectral-analysis, Interstellar plasma, Scattering density, Spectroscopic