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Register a new userProperties and observability of glitches and anti-glitches in accreting pulsars
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Several glitches have been observed in young, isolated radio pulsars, while a clear detection in accretion-powered X-ray pulsars is still lacking. We use the Pizzochero snowplow model for pulsar glitches as well as starquake models to determine for the first time the expected properties of glitches in accreting pulsars and their observability. Since some accreting pulsars show accretion-induced long-term spin-up, we also investigate the possibility that anti-glitches occur in these stars. We find that glitches caused by quakes in a slow accreting neutron star are very rare and their detection extremely unlikely. On the contrary, glitches and anti-glitches caused by a transfer of angular momentum between the superfluid neutron vortices and the non-superfluid component may take place in accreting pulsars more often. We calculate the maximum jump in angular velocity of an anti-glitch and we find that it is expected to be about 1E-5 - 1E-4 rad/s. We also note that since accreting pulsars usually have rotational angular velocities lower than those of isolated glitching pulsars, both glitches and anti-glitches are expected to have long rise and recovery timescales compared to isolated glitching pulsars, with glitches and anti-glitches appearing as a simple step in angular velocity. Among accreting pulsars, we find that GX 1+4 is the best candidate for the detection of glitches with currently operating X-ray instruments and future missions such as the proposed Large Observatory for X-ray Timing (LOFT).
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The abrupt change in the pulse period of a pulsar is called a pulsar glitch. In this paper, we present eleven pulsar glitches detected using the Ooty Radio Telescope (ORT) and the upgraded Giant Metrewave Radio Telescope (uGMRT) in high cadence timing observations of 8 pulsars. The measured relative amplitude of glitches ($Delta u/ u$) from our data ranges from $10^{-6}$ to $10^{-9}$. Among these glitches, three are new discoveries, being reported for the first time. We also reanalyze the largest pulsar glitch in the Crab pulsar (PSR J0534+2200) by fitting the ORT data to a new phenomenological model including the slow rise in the post-glitch evolution. We measure an exponential recovery of 30 days after the Vela glitch detected on MJD 57734 with a healing factor $Q=5.8times 10^{-3}$. Further, we report the largest glitch ($Delta u/ u = 3147.9 times 10^{-9}$) so far in PSR J1731$-$4744.
Data are gathered from the Parkes pulsar data archive of twelve young radio pulsars, with the intervals of data for each pulsar ranged between 2.8 years and 6.8 years. 31 glitches are identified by using phase connection from pulsar timing technology, ranging from $1.7times10^{-9}$ to $8.5times10^{-6}$ at the change in relative glitch sizes $Delta u/ u$, where $ u=1/P$ is the pulse frequency. 8 post-glitch behaviours of 13 published glitches are updated with 4 exponential recoveries observed. Detecting 18 new glitches has great significance, but only one exponential relaxation was discovered in these new glitches. The bimodal distribution of $Delta u/ u$, as before, is validated with peaks at $sim 10^{-6}$ and $sim 10^{-9}$. Moreover, all exponential decays were observed in large glitches, and have very low $Q$. It takes short time toward the extrapolation of the pre-glitch pulse frequency with the timescale of 40 or 80 days. Besides, most glitches exhibit a linear decrease in slow-down rate $|dot{ u}|$ and a permanent change in $ddot{ u}$ after glitch. In special, PSR J1341-6220 was detected 4 new glitches to compose a total of 27 glitches, rising in third place of the most actively glitching pulsars known with a glitch rate of $1.17$ glitches per year. Unusual post-glitch behaviours demonstrate long-lasting increase of $ u$ for hundreds of days in PSR J1112--6103 and PSR J1614--5048.
We suggest that the collision of a small solid body with a pulsar can lead to an observable glitch/anti-glitch. The glitch amplitude depends on the mass of the small body and the impact parameter as well. In the collision, a considerable amount of potential energy will be released either in the form of a short hard X-ray burst or as a relatively long-lasting soft X-ray afterglow. The connection between the glitch amplitude and the X-ray energetics can help to diagnose the nature of these timing anomalies.
Timing observations from the Parkes 64-m radio telescope for 165 pulsars between 1990 and 2011 have been searched for period glitches. A total of 107 glitches were identified in 36 pulsars, where 61 have previously been reported and 46 are new discoveries. Glitch parameters were measured by fitting the timing residual data. Observed relative glitch sizes Delta u_g/ u range between 10^-10 and 10^-5, where u = 1/P is the pulse frequency. We confirm that the distribution of Delta u_g/ u is bimodal with peaks at approximately 10^-9 and 10^-6. Glitches are mostly observed in pulsars with characteristic ages between 10^3 and 10^5 years, with large glitches mostly occurring in the younger pulsars. Exponential post-glitch recoveries were observed for 27 large glitches in 18 pulsars. The fraction Q of the glitch that recovers exponentially also has a bimodal distribution. Large glitches generally have low Q, typically a few per cent, but large Q values are observed in both large and small glitches. Observed time constants for exponential recoveries ranged between 10 and 300 days with some tendency for longer timescales in older pulsars. Shorter timescale recoveries may exist but were not revealed by our data which typically have observation intervals of 2 - 4 weeks. For most of the 36 pulsars with observed glitches, there is a persistent linear increase in dot u in the inter-glitch interval. Where an exponential recovery is also observed, the effects of this are superimposed on the linear increase in dot u. In some cases, the slope of the linear recovery changes at the time of a glitch. The ddot u values characterising the linear changes in dot u are almost always positive and, after subtracting the magnetospheric component of the braking, are approximately proportional to the ratio of |dot u| and the inter-glitch interval, as predicted by vortex-creep models.
The rotation of more than 700 pulsars has been monitored using the 76-m Lovell Telescope at Jodrell Bank. Here we report on a new search for glitches in the observations, revealing 128 new glitches in the rotation of 63 pulsars. Combining these new data with those already published we present a database containing 315 glitches in 102 pulsars. The database was used to study the glitch activity among the pulsar population, finding that it peaks for pulsars with a characteristic age tau_c ~ 10kyr and decreases for longer values of tau_c, disappearing for objects with tau_c > 20Myr. The glitch activity is also smaller in the very young pulsars (tau_c <~ 1kyr). The cumulative effect of glitches, a collection of instantaneous spin up events, acts to reduce the regular long term spindown rate |nudot| of the star. The percentage of |nudot| reversed by glitch activity was found to vary between 0.5% and 1.6% for pulsars with spindown rates |nudot| between 10^(-14) and 3.2*10^(-11) Hz/s, decreasing to less than 0.01% at both higher and lower spindown rates. These ratios are interpreted in terms of the amount of superfluid involved in the generation of glitches. In this context the activity of the youngest pulsar studied, the Crab pulsar, may be explained by quake-like activity within the crust. Pulsars with low spindown rates seem to exhibit mostly small glitches, matching well the decrease of their crustal superfluid. Through the analysis of glitch sizes it was found that the particular glitching behaviour of PSR J0537-6910 and the Vela pulsar may be shared by most Vela-like pulsars. These objects present most of their glitches with characteristic frequency and frequency derivative jumps, occurring at regular intervals of time. Their behaviour is different from other glitching pulsars of similar characteristic age.
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