Simultaneous Single-Pulse Observations of Radio Pulsars: V. On the
Broadband Nature of The Pulse Nulling Phenomenon in PSR B1133+16
ArXiv astro-ph/0610929 (2006)
Authors:
NDR Bhat, Y Gupta, M Kramer, A Karastergiou, AG Lyne, S Johnston
Abstract:
We revisit the phenomenon of pulse nulling using high-quality single-pulse
data of PSR B1133+16 from simultaneous multifrequency observations.
Observations were made at 325, 610, 1400 and 4850 MHz as part of a joint
program between the European Pulsar Network and the Giant Metrewave Radio
Telescope. The pulse energy time series are analysed to derive improved
statistics of nulling pulses as well as to investigate the frequency dependence
of the phenomenon. The pulsar is observed to be in null state for approximately
15% of the time; however, we find that nulling does not always occur
simultaneously at all four frequencies of observation. We characterise this
"selective nulling'' as a function of frequency, separation in frequency, and
combination of frequencies. The most remarkable case is a significantly large
number of nulls ($\approx$6%) at lower frequencies, that are marked by the
presence of a fairly narrow emission feature at the highest frequency of 4850
MHz. We refer to these as "low frequency (LF) nulls." Our analysis shows that
this high frequency emission tends to occur preferentially over a narrow range
in longitude and with pulse widths typically of the order of a few
milliseconds. We discuss the implications of our results for the pulsar
emission mechanism in general and for the broadbandness of nulling phenomenon
in particular. Our results signify the presence of an additional process of
emission which does not turn off when the pulsar nulls at low frequencies, and
becomes more prominent at higher frequencies. Our analysis also hints at a
possible outer gap origin for this new population of pulses, and thus a likely
connection to some high-energy emission processes that occur in the outer parts
of the pulsar magnetosphere.
