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After 6 years of quiescence, Anomalous X-ray Pulsar (AXP) 4U 0142+61 entered an active phase in 2006 March that lasted several months. During the active phase, several bursts were detected, and many aspects of the X-ray emission changed. We report on the discovery of six X-ray bursts, the first ever seen from this AXP in ∼10 years of Rossi X-ray Timing Explorer monitoring. All the bursts occurred in the interval between 2006 April 6 and 2007 February 7. The burst durations ranged from 8–3×103 s as characterized by T90. These are very long durations even when compared to the broad T90 distributions of other bursts from AXPs and Soft Gamma Repeaters (SGRs). The first five burst spectra are well modeled by simple blackbodies, with temperature kT∼2–6 keV. However, the sixth and most energetic burst had a complicated spectrum consisting of at least three emission lines with possible additional emission and absorption lines. The most significant feature was at ∼14 keV. Similar 14-keV spectral features were seen in bursts from AXPs 1E 1048.1–5937 and XTE J1810–197. If this feature is interpreted as a proton cyclotron line, then it supports the existence of a magnetar-strength field for these AXPs. Several of the bursts were accompanied by a short-term pulsed flux enhancement. We discuss these events in the context of the magnetar model. [ABSTRACT FROM AUTHOR]

After 10 years of RXTE monitoring of 5 Anomalous X-ray Pulsars, we report the detection of 10 glitches and 5 glitch candidates. Armed with sufficient data for a meaningful comparison of AXP and radio pulsar glitch properties, 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. We show that three of the largest AXP glitches observed thus far 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. These observations are challenging to interpret in standard glitch models, as is the frequent occurrence of large glitches given AXPs' high measured temperatures. We speculate that the stellar core may be involved in the largest AXP glitches. Furthermore we show that unlike in radio pulsars, AXP glitches sometimes, but not necessarily always, involve major radiative events. [ABSTRACT FROM AUTHOR]

We present the results of X-ray and near-IR observations of the anomalous X-ray pulsar 1E 1048.1–5937, believed to be a magnetar. This AXP underwent a period of extreme variability during 2001–2004, but subsequently entered an extended and unexpected quiescence in 2004–2006, during which we monitored it with RXTE, CXO, and HST. Its timing properties were stable for >3 years throughout the quiescent period. 1E 1048.1–5937 again went into outburst in March 2007, which saw a factor of >7 total X-ray flux increase which was anti-correlated with a pulsed fraction decrease, and correlated with spectral hardening, among other effects. The near-IR counterpart also brightened following the 2007 event. We discuss our findings in the context of the magnetar and other models. [ABSTRACT FROM AUTHOR]

Anomalous X-ray Pulsars are believed to be magnetars: young, isolated neutron stars powered by a large magnetic energy reservoir. Here, we review recent observational progress on five anomalous X-ray pulsars based on a 10-year long monitoring project done using the Rossi X-Ray Timing Explorer (RXTE). In particular, we discuss timing behavior including glitches, radiative variability including bursts, pulsed flux changes, and pulse profile changes. We compare the timing properties to those of regular rotation-powered pulsars, and we consider the observed radiative phenomena in the context of the magnetar model. [ABSTRACT FROM AUTHOR]

We present an analysis of five X-ray Multi-Mirror Mission (XMM) observations of the Anomalous X-ray Pulsar (AXP) 1E 2259+586 taken in 2004 and 2005 during its relaxation following its 2002 outburst. We compare these data with those of five previous XMM observations taken in 2002 and 2003, and find that the observed flux decay is well described by a power-law of index -0.69±0.03. As of mid-2005, the source may still have been brighter than pre-outburst, and was certainly hotter. We find a strong correlation between hardness and flux, as seen in other AXP outbursts. We discuss the implications of these results for the magnetar model. [ABSTRACT FROM AUTHOR]