High-resolution single-pulse studies of the Vela pulsar

Abstract

We present high‐resolution multi‐frequency single‐pulse observations of the Vela pulsar, PSR B0833 − 45, aimed at studying micro‐structure, phase‐resolved intensity fluctuations and energy distributions at 1.41 and 2.30 GHz. We find micro‐structure in about 80 per cent of all pulses independent of observing frequency. The width of a micro‐pulse seems to depend on its peak flux density, whilst quasi‐periodicities observed in micro‐pulses remain constant. The width of the micro‐pulses may decrease with increasing frequency, but confirmation is needed at higher frequencies. The fraction of pulses showing quasi‐periodic micro‐pulses may become smaller at higher frequencies. We show that the micro‐pulse width in pulsars has a period dependence which suggests a model of sweeping micro‐beams as the origin of the micro‐pulses. Like individual pulses, the micro‐pulses of Vela are highly elliptically polarized. There is a strong correlation between Stokes parameters V and I in the micro‐structure. We do not observe any micro‐pulses where the handedness of the circular intensity changes within a micro‐pulse, although flips within a pulse are not uncommon. We show that the V/I distribution is Gaussian with a narrow width and that this width appears to be constant as a function of pulse phase. The phase‐resolved intensity distributions of I are best fitted with log‐normal statistics. Extra emission components, i.e. ‘bump’ and ‘giant micro‐pulses’, discovered by Johnston et al. at 0.6 and 1.4 GHz are also present at the higher frequency of 2.3 GHz. The bump component seems to be an extra component superposed on the main pulse profile but does not appear periodically. The giant micro‐pulses are time‐resolved and have significant jitter in their arrival times. Their flux density distribution is best fitted by a power‐law, indicating a link between these features and ‘classical’ giant pulses as observed for the Crab pulsar (PSR B0531 + 21), PSR B1937 + 21 and PSR B1821 − 24. We find that Vela contains a mixture of emission properties representing both ‘classical’ properties of radio pulsars (e.g. micro‐structure, high degree of polarization, S‐like position angle swing, orthogonal modes) and features which are most likely related to high‐energy emission (e.g. extra profile components, giant micro‐pulses). It hence represents an ideal test case to study the relationship between radio and high‐energy emission in significant detail.

Variability, polarimetry, and timing properties of single pulses from PSR J1713+0747 using the Large European Array for Pulsars

“…While similar phenomena are known to occur in canonical pulsars (e.g. Kramer et al 2002), this is the first time a phase-dependent periodicity of intensity variations has been reported for a MSP. In the 2DFS, the two local maxima at 0.14 and 0.34 cpp are clearly offset from the vertical axis of zero, indicating the association of the two periodicities with systematic drifting of emission power in pulse phase.…”

Detection of Polarized Quasi-Periodic Microstructure Emission in Millisecond Pulsars

“…Since we find micropulses to be mostly unresolved from the underlying quasi-periodicity, it is difficult to estimate their intrinsic widths, and hence we do not discuss the micropulse width-rotation period relationship. We use previously reported microstructure periodicities in Kramer et al (2002 , Table 2) and Mitra et al (2015 , Table 3) along with our new results to extend the relationship. Note that previous reports combine observations from multiple frequencies of observation, and in cases where multiple reports were present (at different frequencies, different analysis techniques, or for different subpulse components), we only used the results with reported uncertainty estimates and averaged their timescales for our analysis.…”

“…Note that previous reports combine observations from multiple frequencies of observation, and in cases where multiple reports were present (at different frequencies, different analysis techniques, or for different subpulse components), we only used the results with reported uncertainty estimates and averaged their timescales for our analysis. While there is some weak evidence for change in microstructure timescales across frequencies, the dependence is known to be very weak (e.g., Hankins et al 1976;Ferguson & Seiradakis 1978;Kramer et al 2002). Hence, we do not expect such averaging to change the properties of the relationship significantly.…”

“…In particular, microstructure emission has been long known to be a common feature of single pulse emission (first detected by Craft et al 1968) and typically involves intensity variations at milli-period timescales, corresponding to timescales of a few hundred microseconds for normal period pulsars (e.g., Hankins 1972). Previous studies have shown that these features have typical widths for a given pulsar and often appear as a train of quasi-periodic pulses, with their timescales showing a strong correlation with the pulsar period (e.g., Kramer et al 2002;Mitra et al 2015).…”

Polarized Quasiperiodic Structures in Pulsar Radio Emission Reflect Temporal Modulations of Non-Stationary Plasma Flow

“…Cordes (1979) and Kramer et al (2002) further show that the measured temporal width (t µ ) of a micropulse is related linearly to the rotation period P approximately as t µ (msec) ∼ 10 −3 P (sec) and t µ (msec) ∼ 0.7 × 10 −3 P (sec) respectively. Polarized microstructure has been investigated for a few pulsars (Ferguson & Seiradakis 1978;Cordes 1979), and only for the Vela pulsar B0833-45 does some quantitative description exist (Kramer et al 2002). Further observations, analyses, and phenomenological assessments are needed to establish how microstructure is connected physically with the mechanisms of pulsar emission.…”