M. Pilia et al., "Wide-band, low-frequency pulse profiles of 100 radio pulses with LOFAR," Astronomy & Astrophysics, V586, no. A92, pp1-34, February 2016.
Context. LOFAR offers the unique capability of observing
pulsars across the 10 - 240 MHz frequency range with a fractional
bandwidth of roughly 50%. This spectral range is well suited for
studying the frequency evolution of pulse profile morphology caused by
both intrinsic and extrinsic effects such as changing emission
altitude in the pulsar magnetosphere or scatter broadening by the
interstellar medium, respectively.
Aims. The magnitude of most of these effects increases rapidly
towards low frequencies. LOFAR can thus address a number of open
questions about the nature of radio pulsar emission and its
propagation through the interstellar medium.
Methods. We present the average pulse profiles of 100 pulsars
observed in the two LOFAR frequency bands: high band (120 - 167 MHz,
100 profiles) and low band (15 - 62 MHz, 26 profiles). We compare them
with Westerbork Synthesis Radio Telescope (WSRT) and Lovell Telescope
observations at higher frequencies (350 and 1400 MHz) to study the
profile evolution. The profiles were aligned in absolute phase by
folding with a new set of timing solutions from the Lovell Telescope,
which we present along with precise dispersion measures obtained with
Results. We find that the profile evolution with decreasing
radio frequency does not follow a specific trend; depending on the
geometry of the pulsar, new components can enter into or be hidden
from view. Nonetheless, in general our observations confirm the
widening of pulsar profiles at low frequencies, as expected from
radius-to-frequency mapping or birefringence theories.
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