High-energy emission and temporal properties of magnetars

Magnetars have been intriguing sources since their discovery, as they opened new avenues on the formation, evolution and emission mechanisms of the neutron stars. Thanks to the long-term observations of these sources, we are able to investigate many aspects of them. In this thesis, we investigate the high-energy gamma-ray emission properties of one of the brightest magnetars in X-ray band, 4U 0142+61. We searched for persistent and pulsed gamma-ray emission using the data obtained with Fermi/LAT. We did not detect significant high-energy gamma-ray emission from this source. Nevertheless, we could place upper limits to the gamma-ray flux and spectral break energy of the source. Together with the earlier works on soft and hard X-ray emission of 4U 0142+61, these upper limits provide a hint on the spectral shape of the source in a wide energy band. Next, we studied the long-term timing and X-ray properties of two frequently glitching magnetars, 1RXS J170849.0- 400910 and 1E 1841-045, with RXTE/PCA. In the analysis of 1RXS J170849.0- 400910 we identified two significant glitch candidates in two data gaps. The source was radiatively stable during the RXTE observations. In the analysis of 1E 1841- 045, we identified a glitch and an anti-glitch ∼1 yr apart from each other. We found no evidence of radiative variability during both the glitch and anti-glitch events. Finally, we discuss our results in the context of glitch models

Peculiar Glitch of PSR J1119-6127 and Extension of the Vortex Creep Model

Glitches are sudden changes in rotation frequency and spin-down rate, observed from pulsars of all ages. Standard glitches are characterized by a positive step in angular velocity ($\Delta\Omega$ $>$ $0$) and a negative step in the spin-down rate ($\Delta \dot \Omega$ $<$ $0$) of the pulsar. There are no glitch-associated changes in the electromagnetic signature of rotation-powered pulsars in all cases so far. For the first time, in the last glitch of PSR J1119-6127, there is clear evidence for changing emission properties coincident with the glitch. This glitch is also unusual in its signature. Further, the absolute value of the spin-down rate actually decreases in the long term. This is in contrast to usual glitch behaviour. In this paper we extend the vortex creep model in order to take into account these peculiarities. We propose that a starquake with crustal plate movement towards the rotational poles of the star induces inward vortex motion which causes the unusual glitch signature. The component of the magnetic field perpendicular to the rotation axis will decrease, giving rise to a permanent change in the pulsar external torque.Comment: accepted by MNRAS, 10 pages, 2 figure

A glitch and an anti-glitch in the anomalous X-ray pulsar 1E 1841-045

We investigated the long-term spin properties of the anomalous X-ray pulsar (AXP) 1E 1841-045 by performing a temporal analysis of archival RXTE observations spanning about 5.2 yr from 2006 September to 2011 December. We identified two peculiar timing anomalies within ~1 yr of each other: a glitch with Delta(nu)/nu ~ 4.8 x 10^{-6} near MJD 54303; and an anti-glitch with Delta(nu)/nu ~ -5.8 x 10^{-7} near MJD 54656. The glitch that we identified, which is the fourth glitch seen in this source in the 13 yr of RXTE monitoring, is similar to the last two detected glitches. The anti-glitch from 1E 1841-045, however, is the first to be identified. The amplitude of the anti-glitch was comparable with that recently observed in AXP 1E 2259+586. We found no significant variations in the pulsed X-ray output of the source during either the glitch or the anti-glitch. We discuss our results in relation to the standard pulsar glitch mechanisms for the glitch, and to plausible magnetospheric scenarios for the anti-glitch.Comment: 6 pages, 3 figures, 3 tables, published in MNRA

Burst Tails from SGR J1550-5418 Observed with Rossi X-ray Timing Explorer

We present the results of our extensive search using the Bayesian block method for long tails following short bursts from a magnetar, SGR J1550-5418, over all RXTE observations of the source. We identified four bursts with extended tails, most of which occurred during its 2009 burst active episode. The durations of tails range between ~13 s and over 3 ks, which are much longer than the typical duration of bursts. We performed detailed spectral and temporal analysis of the burst tails. We find that the spectra of three tails show a thermal nature with a trend of cooling throughout the tail. We compare the results of our investigations with the properties of four other extended tails detected from SGR 1900+14 and SGR 1806-20 and suggest a scenario for the origin of the tail in the framework of the magnetar model.Comment: 10 pages, 7 figures, 4 tables, accepted for publication in Ap