Glitch Amplitudes Research Articles

Classification of pulsar glitch amplitudes using extreme deconvolution

We carry out a classification of the glitch amplitudes of radio pulsars using Extreme Deconvolution technique based on the Gaussian Mixture Model, where the observed uncertainties in the glitch amplitudes (Δνν) are taken into account. Our dataset consists of 699 glitches from 238 pulsars. We then use information theory criteria such as AIC and BIC to determine the optimum number of glitch classes. We find that both AIC and BIC show that the pulsar glitch amplitudes can be optimally described using a bimodal distribution. The mean values of (Δνν) for the two components are equal to 4.79×10−9 and 1.28×10−6, respectively with standard deviation given by 1.01 and 0.55 dex. We also applied this method to classify the pulsar inter-glitch time intervals, and we find that AIC prefers two components, whereas BIC prefers a single component. The unified data set and analyses codes used in this work have been made publicly available.

The Jodrell bank glitch catalogue: 106 new rotational glitches in 70 pulsars

ABSTRACT Pulsar glitches are rapid spin-up events that occur in the rotation of neutron stars, providing a valuable probe into the physics of the interiors of these objects. Long-term monitoring of a large number of pulsars facilitates the detection of glitches and the robust measurements of their parameters. The Jodrell Bank pulsar timing programme regularly monitors more than 800 radio pulsars and has accrued, in some cases, over 50 yr of timing history on individual objects. In this paper, we present 106 new glitches in 70 radio pulsars as observed up to the end of 2018. For 70 per cent of these pulsars, the event we report is its only known glitch. For each new glitch, we provide measurements of its epoch, amplitude, and any detected changes to the spin-down rate of the star. Combining these new glitches with those listed in the Jodrell Bank glitch catalogue, we analyse a total sample of 543 glitches in 178 pulsars. We model the distribution of glitch amplitudes and spin-down rate changes using a mixture of two Gaussian components. We corroborate the known dependence of glitch rate and activity on pulsar spin-down rates and characteristic ages, and show that younger pulsars tend to exhibit larger glitches. Pulsars with spin-down rates between 10−14 and 10−10.5 Hz s−1 show a mean reversal of 1.8 per cent of their spin-down as a consequence of glitches. Our results are qualitatively consistent with the superfluid vortex unpinning models of pulsar glitches.

Effects of general relativity on glitch amplitudes and pulsar mass upper bounds

Pinning of vortex lines in the inner crust of a spinning neutron star may be the mechanism that enhances the differential rotation of the internal neutron superfluid, making it possible to freeze some amount of angular momentum which eventually can be released, thus causing a pulsar glitch. We investigate the general relativistic corrections to pulsar glitch amplitudes in the slow-rotation approximation, consistently with the stratified structure of the star. We thus provide a relativistic generalization of a previous Newtonian model that was recently used to estimate upper bounds on the masses of glitching pulsars. We find that the effect of general relativity on the glitch amplitudes obtained by emptying the whole angular momentum reservoir is less than 30\%. Moreover we show that the Newtonian upper bounds on the masses of large glitchers obtained from observations of their largest recorded event differ by less than a few percent from those calculated within the relativistic framework. This work can also serve as a basis to construct more sophisticated models of angular momentum reservoir in a relativistic context. In particular, we present two alternative scenarios for "rigid" and "slack" vortex lines, and we generalize the Feynman-Onsager relation to the case when both entrainment coupling between the fluids and a strong gravitational field are present.

Characterizing the rotational irregularities of the Vela pulsar from 21 yr of phase-coherent timing

Pulsars show two classes of rotational irregularities that can be used to understand neutron-star interiors and magnetospheres: glitches and timing noise. Here we present an analysis of the Vela pulsar spanning nearly 21 yr of observation and including 8 glitches. We identify the relative pulse number of all of the observations between glitches, with the only pulse-number ambiguities existing over glitch events. We use the phase coherence of the timing solution to simultaneously model the timing noise and glitches in a Bayesian framework, allowing us to select preferred models for both. We find the glitches can be described using only permanent and transient changes in spin frequency, i.e., no step changes in frequency derivative. For all of the glitches, we only need two exponentially decaying changes in spin frequency to model the transient components. In contrast to previous studies, we find that the dominant transient components decay on a common $\approx$ 1300 d time scale, and that a larger fraction ( $\gtrsim 25\%$) of glitch amplitudes are associated with these transient components. We also detect shorter-duration transient components of $\approx$ 25 d, as previously observed, but are limited in sensitivity to events with shorter durations by the cadence of our observations. The timing noise is well described by a steep power-law process that is independent of the glitches and subdominant to the glitch recovery. The braking index is constrained to be $<$ 8 with 95% confidence. This methodology can be used to robustly measure the properties of glitches and timing noise in other pulsars.

Observations of four glitches in the young pulsar J1833−1034 and study of its glitch activity

We present the results from timing observations with the Giant Metrewave Radio Telescope of the young pulsar J1833−1034 in the Galactic supernova remnant G21.5−0.9. We detect the presence of four glitches in this pulsar over a period of 5.5 yr, making it one of a set of pulsars that show fairly frequent glitches. The glitch amplitudes, characterized by the fractional change of the rotational frequency, range from 1 × 10−9 to 7 × 10−9, with no evidence for any appreciable relaxation of the rotational frequency after the glitches. The fractional changes observed in the frequency derivative are of the order of 10−5. We show conclusively that, in spite of having significant timing noise, the sudden irregularities like glitches detected in this pulsar cannot be modelled as smooth timing noise. Our timing solution also provides a stable estimate of the second derivative of the pulsar spin-down model, and a plausible value for the braking index of 1.857, which, like the value for other such young pulsars, is much less than the canonical value of 3.0. PSR J1833−1034 appears to belong to a class of pulsars exhibiting fairly frequent occurrence of low amplitude glitches. This is further supported by an estimate of the glitch activity parameter, , which is found to be significantly lower than the trend of glitch activity versus characteristic age (or spin frequency derivative) that a majority of the glitching pulsars follow. We present evidence for a class of such young pulsars, including the Crab, where higher internal temperature of the neutron star could be responsible for the nature of the observed glitch activity.

29 glitches detected at Urumqi Observatory

Glitches detected in pulsar timing observations at the Nanshan radio telescope of Urumqi Observatory between 2002 July and 2008 December are presented. In total, 29 glitches were detected in 19 young pulsars, with this being the first detection of a glitch in 12 of these pulsars. Fractional glitch amplitudes range from a few parts in 10−11 to 3.9 × 10−6. Three ‘slow’ glitches are identified in PSRs J0631+1036, B1822−09 and B1907+10. Post-glitch recoveries differ greatly from pulsar to pulsar and for different glitches in the same pulsar. Three small glitches in PSRs B0402+61, B0525+21 and J1853+0545 show evidence for normal post-glitch recovery, but for PSRs B0144+59 and B2224+65 the spin frequency ν continually increases relative to the pre-glitch solution for hundreds of days after their small glitches. Most large glitches show some evidence for exponential post-glitch recovery on time-scales of 100–1000 d, but in some cases, e.g. PSR B1758−23, there is little or no recovery, i.e. no detectable increase in at the time of the glitch. Beside exponential recoveries, permanent increases in slowdown rate are seen for the two large glitches in PSRs B1800−21 and B1823−13. These and several other pulsars also show a linear increase in following the partial exponential recovery, which is similar to the Vela pulsar post-glitch behaviour. However, the rate of increase, ⁠, is an order of magnitude less than for the Vela pulsar. We present improved positions for 14 of the glitching pulsars. Analysis of the whole sample of known glitches shows that fractional glitch amplitudes are correlated with characteristic age with a peak at about 105 yr, but there is a spread of two or three orders of magnitude at all ages. Glitch activity is positively correlated with spin-down rate, again with a wide spread of values. For some (but not all) pulsars, there is a correlation between glitch amplitude and the duration of the following interglitch interval. In no case is there a correlation of glitch amplitude with the duration of the preceding interglitch interval.

Observational features of pulsar glitches

Pulsar glitches are sudden increases in the rotation rate which probably result from angular momentum transfer within the neutron star. We review the observational features of the 39 glitches detected at Nanshan from 2000 to 2008, including several events which appear to be slow glitches. A wide variety of post-glitch behavior is observed with very little recovery in some pulsars and over-recovery in others. Analysis of the whole sample of known glitches shows that fractional glitch amplitudes are correlated with characteristic age with a peak at about 105 years, but there is a spread of two or three orders of magnitude at all ages. For individual pulsars with many glitches, the time until the next glitch is sometimes proportional to the fractional glitch amplitude.

Glitches in Anomalous X‐Ray Pulsars

We report on 8.7 and 7.6 yr of Rossi X-Ray Timing Explorer (RXTE) observations of the anomalous X-ray pulsars (AXPs) RXS J170849.0–400910 and 1E 1841–045, respectively. These observations have allowed us to study the long-term timing, pulsed flux, and pulse profile evolution of these objects. We report on four new glitches, one from RXS J170849.0–400910 and three from 1E 1841–045. With nearly all known persistent AXPs now seen to glitch, such behavior is clearly generic to this source class. We show that in terms of fractional frequency change, AXPs are among the most actively glitching neutron stars, with glitch amplitudes in general larger than in radio pulsars. However, in terms of absolute glitch amplitude, AXP glitches are unremarkable. Unlike radio pulsar glitches, AXP glitches can sometimes, though not always, be accompanied by radiative events. We show that the largest observed AXP glitches have recoveries that are unusual among those of radio pulsar glitches, with the combination of recovery time scale and fraction yielding changes in spin-down rates following the glitch similar to, or larger than, the long-term average. We also observed a large long-term fractional increase in the magnitude of the spin-down rate of 1E 1841–045, following its largest glitch, with $Δ d{ν }/d{ν } = 0.1$ -->. These observations are challenging to interpret in standard glitch models, as is the frequent occurence of large glitches given AXPs' high measured temperatures. We speculate that the stellar core may be involved in the largest AXP glitches.

Observations of six glitches in PSR B1737−30

Six glitches have been recently observed in the rotational frequency of the young pulsar PSR B1737-30 (J1740-3015) using the 25-m Nanshan telescope of Urumqi Observatory. With a total of 20 glitches in 20 years, it is one of the most frequently glitching pulsars of the about 1750 known pulsars. Glitch amplitudes are very variable with fractional increases in rotation rate ranging from 10^{-9} to 10^{-6}. Inter-glitch intervals are also very variable, but no relationship is observed between interval and the size of the preceding glitch. There is a persistent increase in |\dot\nu|, opposite in sign to that expected from slowdown with a positive braking index, which may result from changes in the effective magnetic dipole moment of the star during the glitch.

Quakes in solid quark stars

A starquake mechanism for pulsar glitches is developed in the solid quark star model. It is found that the general glitch natures (i.e., the glitch amplitudes and the time intervals) could be reproduced if solid quark matter, with high baryon density but low temperature, has properties of shear modulus μ=10 30–34 erg/cm 3 and critical stress σ c=10 18∼24 erg/cm 3. The post-glitch behavior may represent a kind of damped oscillations.

The Glitches of the Anomalous X‐Ray Pulsar 1RXS J170849.0−400910

We report on a timing analysis of archival observations of the anomalous X-ray pulsar 1RXS J170849.0-400910 made with the RXTE Proportional Counter Array. We detect a new large glitch (Δν/ν 3 × 10-6) that occurred between 2001 March 27 and May 6, with an associated large increase in the spin-down rate (Δ/ 0.3). The short time (1.5 yr) elapsed from the previously detected glitch and the large amplitude of the new spin-up place this source among the most frequent glitchers, with large average glitch amplitudes, similar to those of the Vela pulsar. The source shows different recoveries after the glitches: in the first one it is well described by a long-term linear trend similar to those seen in Vela-like glitches; in the second case the recovery is considerably faster and is better described by an exponential plus a fractional change in the long-term spin-down rate of the order of 1%. No recovery of the latter is detected, but additional observations are necessary to confirm this result. We find minor but significant changes in the average pulse profile after both glitches. No bursts were detected in any light curve, but our search was limited in sensitivity with respect to short (t < 60 ms) bursts. Observed glitch properties are compared to those of radio pulsar glitches; current models are discussed in light of our results. It appears that glitches may represent yet another peculiarity of anomalous X-ray pulsars. Starquake-based models appear to be preferred on qualitative grounds. Alternative models can be applied to individual glitches but fail in explaining both. Thus the two events may as well arise from two different mechanisms.

Observations of a Series of Six Recent Glitches in the Crab Pulsar

From 1995 to 1999, daily monitoring of the radio emission from the Crab pulsar at the Green Bank and Jodrell Bank observatories revealed a series of six sudden rotational spin-ups or glitches, doubling the number of glitches observed for this pulsar since 1969. With these observations, the range of time intervals between significant Crab glitches has widened considerably, indicating that the occurrence of Crab glitches may be more random than previously thought. The new glitch amplitudes Δν/ν span an order of magnitude from 2 × 10-9 to 3 × 10-8. Except in one case, which we suggest may represent an aftershock event, the frequency jumps display an exponential recovery with a timescale of ~3 days for the smaller glitches and ~10 days for the largest (1996) glitch. In the largest event, a portion of the spin-up was resolved in time, as was previously reported for the 1989 glitch. A pronounced change in also occurs after each glitch and is correlated with the size of the initial frequency jump, although for some of the smaller glitches this appears to be a temporary effect. We discuss the properties of the ensemble of observed Crab glitches and compare them with the properties of Vela glitches, highlighting those differences that must be explained by evolutionary models.