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

Abstract

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.

arXiv commentAccepted for publication as a Letter in Astronomy and Astrophysics

References in corpus (11)

• The Swift X-ray Telescope
• The Nuclear Spectroscopic Telescope Array (NuSTAR) Mission
• TEMPO2, a new pulsar timing package. I: Overview
• 45 Years of Rotation of the Crab Pulsar
• Observations of a Series of Six Recent Glitches in the Crab Pulsar
• Absolute Timing of the Crab Pulsar with RXTE
• Broadband X-ray Imaging and Spectroscopy of the Crab Nebula and Pulsar with NuSTAR
• Timing accuracy of the Swift X-Ray Telescope in WT mode
• RXTE/HEXTE Analysis of the Crab Pulsar Glitch of July 2000
• The 1997 Event in the Crab Pulsar in X-rays
• Did the Crab Pulsar Undergo a Small Glitch in 2006 late March/early April?

Cited by in corpus (4)

• Insights into the physics of neutron star interiors from pulsar glitches
• NICER observations of the Crab pulsar glitch of 2017 November
• The persistent shift in spin-down rate following the largest Crab pulsar glitch rules out external torque variations due to starquakes
• Irregularities in the rate of generation of giant pulses from the Crab pulsar observed at 111 MHz