An unusual pulsar - PSR 0826 - 34

Abstract. Pulsars with drifting subpulses are thought to be an important key to unlocking the mystery of how radio pulsars work. We present new results from high sensitivity GMRT observations of PSR B0826−34 -a wide profile pulsar that exhibits an interesting but complicated drifting pattern. We provide a model to explain the observed subpulse drift properties of this pulsar, including the apparent reversals of the drift direction. In this model, PSR B0826−34 is close to being an aligned rotator. Using information about the polarization and frequency evolution of the pulse profile, we solve for the emission geometry of this pulsar and show that the angle between the rotation axis and the dipole magnetic axis is less than 5• . As a result, our line of sight samples a circular path that is entirely within the emission beam. We see evidence for as many as 6 to 7 drifting bands in the main pulse at 318 MHz, which are all part of a circulating system of about 15 spark-associated subpulse emission beams that form, upon averaging, one conal ring of the mean emission. We also see evidence for a second ring of emission, which becomes dominant at higher frequencies (above 1 GHz) due to the nature of the emission geometry. We model the subpulse drift behaviour of this pulsar in detail, providing quantitative treatments of the aliasing problem and various effects of geometry which play an important role. The observed drift rate is an aliased version of the true drift rate which is such that a subpulse drifts to the location of the adjacent subpulse (or a multiple thereof) in about one pulsar period. We show that small variations, of the order of 3-8%, in the mean drift rate are then enough to explain the apparent reversals of drift direction seen in the data. We find the mean circulation time of the drift pattern to be significantly longer than the predictions of the original Ruderman & Sutherland (1975) model and propose an explanation for this, which relates to modified models with temperature regulated partial ion flow in the polar vacuum gap. The small variations in drift rate are then explained by very small heating and cooling effects -less than 3500 K change in the ∼2.5 × 10 6 K surface temperature of the neutron star polar cap. From a detailed consideration of the variation of the mean subpulse separation across the main pulse window, we show that the circulating spark pattern is not centred around the dipole axis, but around a point much closer (within a degree or so) to the rotation axis. This is an indicator of the presence of a "local pole" corresponding to the non-dipolar magnetic fields that are expected to be present close to the neutron star surface. PSR B0826−34 thus provides a very rich and powerful system in which to explore important aspects of the physics of pulsar radio emission and neutron star magnetospheres.

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“…In addition, there is evidence for faint emission in the Biggs et al (1985) and Durdin et al (1979).…”

Section: Observations and Data Analysismentioning

confidence: 99%

“…However, it is not a widely studied pulsar, probably because of the fact that it nulls for as much as 70% of time (Durdin et al 1979), making it a difficult case to observe. The study reported by Biggs et al (1985) is the most exhaustive study published to date for this pulsar.…”

Section: Introductionmentioning

confidence: 99%

Unraveling the drift behaviour of the remarkable pulsar PSR B0826–34

Gupta¹,

Gil

Kijak

et al. 2004

A&A

108

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“…Many pulsars are known to exhibit the phenomenon of "nulling", where the emission appears to cease, or is greatly diminished, for a certain number of pulse periods. Typical time scales of nulling are of the order of a few pulse periods, however it may last for up to many hours in certain pulsars; for example, PSR B0826-34 which is active for only ∼20% of the time (Durdin et al 1979). …”

Section: Introductionmentioning

confidence: 99%

Simultaneous single-pulse observations of radio pulsars

Bhat¹,

Gupta

Krämer

et al. 2006

A&A

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Aims. In this paper we revisit the well-known phenomenon of pulse nulling using high-quality single-pulse data of PSR B1133+16 from simultaneous multifrequency observations. Methods. Observations were made at 325, 610, 1400 and 4850 MHz as part of a joint program between the European Pulsar Network (EPN) and the Giant Metrewave Radio Telescope (GMRT). 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. Results. 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 the statistics of such "selective nulling" as a function of frequency, separation in frequency, and combination of frequencies. The most remarkable case of such selective nulling seen in our data is a significantly large number of nulls (≈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". We characterise the properties of high frequency (HF) emission at the occurrence of LF nulls, and compare and contrast them with that of "normal emission" at 4850 MHz. 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.

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“…The drift rate of its drifting subpulses shows wide variations include sign reversals. Durdin et al (1979) noted that the pulsar exhibited nulls for 70 per cent of the time. Further investigations of this pulsar by Biggs et al (1985) at 408 MHz and 645 MHz found emission at all longitudes, implying that this pulsar is an almost aligned rotator viewed from near the rotation axis.…”

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confidence: 99%