A review of x-ray spectral evolution in Crab pulsar

Pravdo et al (1997) claimed that the phase resolved x-ray spectrum in Crab pulsar (PSR B0531+21) shows a spectral hardening at the leading edge of the first peak of its integrated profile; this was a new and unexpected result. This article reanalyzes their data, as well as some other related data, and argues that the spectrum is as likely to be unvarying (i.e., neither hardening nor softening).Comment: 12 pages, 4 figures, accepted for publication in A&

A non-glitch speed-up event in the Crab Pulsar

Context: The rotation history of the Crab Pulsar is well described by (1) a rotation frequency $\nu$ and a slowdown model that is specified by its first two time derivatives $\dot \nu$ and $\ddot \nu$, known as the secular slowdown model, (2) occasional (once in $\approx 2$ years) significant and abrupt increases in the magnitude of $\nu$ and $\dot \nu$ (occurring on timescales of minutes), known as glitches, and (3) much slower increases and decreases in $\nu$ and $\dot \nu$ (occurring over months and years) that are an order of magnitude smaller, known as timing noise. Aims: This work reports a speed-up event in the Crab Pulsar that occurred around $2015$ February that is distinct from glitches and timing noise. Methods: Monthly $\nu$s and $\dot \nu$s of the Crab Pulsar, obtained at radio frequencies and published by Jodrell Bank Observatory (JBO), are used to demonstrate the speed-up event. Monthly arrival times of the Crab Pulsar's pulse, also published by JBO, combined with X-ray data from the RXTE, SWIFT, and NUSTAR observatories are used to verify the result. Results: The speed-up event is caused by a persistent increase in $\dot \nu$, which results in a monotonic increase in $\nu$. Over the last $\approx 550$ days, $\nu$ has increased monotonically by an amount that is $\approx 10$ times larger than the timing noise level. Conclusions: This is a unique event in the Crab Pulsar. This is probably due to a small increase in the Crab Pulsar's internal temperature. In its absence, the next large glitch in the Crab Pulsar is expected to occur around $2019$ March. However, this event could have an important bearing on its occurrence.Comment: Accepted for publication as a Letter in Astronomy and Astrophysic

RXTE observations of single pulses of PSR B0531+21: II Test for radio behavior

This article is the second in the series that analyze about 1.87 million periods of Crab pulsar, observed by the PCA detector aboard the RXTE x-ray observatory. At these energies the pulsar displays none of the three phenomena that are often seen in normal radio pulsars -- ``pulse nulling'', ``systematic sub pulse drifting'' and ``mode changing''. Presence or absence of these three behavior in the Crab pulsar, at radio wavelengths, something that has not been rigorously established yet, might be important for a satisfactory understanding of the above three phenomena.Comment: 6 pages, 4 figure

Time-scales of Radio Emission in PSR J0437-4715 at 327 MHz

Time-scales of radio emission are studied in PSR J0437-4715 at 327 MHz using almost half a million periods of high quality data from Ooty Radio Telescope. The radio emission in this milli second pulsar occurs on a short (s) time-scale of approximately 0.026 +- 0.001 periods, and on a (l) time-scale that is much longer than the widths of the components of the integrated profile (approximately 0.05 periods). The width of the s emission increases with its increasing relative contribution to the total radio emission. This may provide constraints for the details of discharge of vacuum gaps above pulsar polar caps. The s emission occasionally takes place in the form of intense spikes, which are confined to the main component of the integrated profile for 90 per cent of the time. The positions of spikes within a component of the integrated profile have no simple relation to the shape of that component. This may have impact on the interpretation of the integrated profile components in terms of independent regions of emission on the polar cap.Comment: Accepted for publication in Vol 543 (1 Nov 2000) of The Astrophysical Journa