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We present an analysis of five XMM-Newton 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-Newton observations taken in 2002 and 2003, and find 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 preoutburst, and was certainly hotter. We find a strong correlation between hardness and flux, as seen in other AXPs. We discuss the implications of these results for the magnetar model.

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.

We present a new phase-coherent timing analysis for the young, energetic pulsar PSR B0540-69 using 7.6 yr of data from the Rossi X-Ray Timing Explorer. We measure the braking index, n=2.140+/-0.009, and discuss our measurement in the context of other discordant values reported in the literature. We present an improved source position from the phase-coherent timing of the pulsar, to our knowledge, the first of its kind from X-ray pulsar timing. In addition, we detect evidence for a glitch which has been previously reported but later disputed. The glitch occured at MJD 51335+/-12 with a fractional change in frequency of (1.4+/-0.2)E{-9} and a fractional change in frequency derivative of (1.33+/-0.02)E{-4}. We calculate that the glitch activity parameter for PSR B0540-69 is two orders of magnitude smaller than that of the Crab pulsar which has otherwise very similar properties. This suggests that neutron stars of similar apparent ages, rotation properties and inferred dipolar B fields can have significantly different internal properties., 18 Preprint pages, 6 Figures. Accepted to the Astrophysical Journal

We have discovered four X-ray bursts, recorded with the Rossi X-ray Timing Explorer Proportional Counter Array between 2003 September and 2004 April, that we show to originate from the transient magnetar candidate XTE J1810-197. The burst morphologies consist of a short spike or multiple spikes lasting ~1 s each followed by extended tails of emission where the pulsed flux from XTE J1810-197 is significantly higher. The burst spikes are likely correlated with the pulse maxima, having a chance probability of a random phase distribution of 0.4%. The burst spectra are best fit to a blackbody with temperatures 4-8 keV, considerably harder than the persistent X-ray emission. During the X-ray tails following these bursts, the temperature rapidly cools as the flux declines, maintaining a constant emitting radius after the initial burst peak. During the brightest X-ray tail, we detect a narrow emission line at 12.6 keV with an equivalent width of 1.4 keV and a probability of chance occurrence less than 4 x 10^-6. The temporal and spectral characteristics of these bursts closely resemble the bursts seen from 1E 1048.1-5937 and a subset of the bursts detected from 1E 2259+586, thus establishing XTE J1810-197 as a magnetar candidate. The bursts detected from these three objects are sufficiently similar to one another, yet significantly different from those seen from soft gamma repeaters, that they likely represent a new class of bursts from magnetar candidates exclusive (thus far) to the anomalous X-ray pulsar-like sources., Accepted for publication in ApJ. 26 pages and 11 figures

We report on continued monitoring of the Anomalous X-ray pulsar (AXP) 1E 1048.1-5937 using the Rossi X-ray Timing Explorer. We confirm that this pulsar has exhibited significant pulsed flux variability. The principal features of this variability are two pulsed X-ray flares. Both flares lasted several months and had well-resolved few-week-long rises. The long rise times of the flares are a phenomenon not previously reported for this class of object. The epochs of the flare peaks were MJD 52,218.8+/-4.5 and 52,444.4+/-7.0. Both flares had shorter rise than fall times. The flares had peak fluxes of 2.21+/-0.16 and 3.00+/-0.13 times the quiescent value. We estimate a total 2-10 keV energy release of ~2.7x10^40 ergs and ~2.8x10^41 ergs for the flares, assuming a distance of 5 kpc. We also report large (factor of ~12) changes to the pulsar's spin-down rate on time scales of weeks to months, shorter than has been reported previously. We find marginal evidence for correlation between the flux and spin-down rate variability, with probability of nonrandom correlation 6%. We discuss the implications of our findings for AXP models., 11 pages, 2 figures, ApJ Letters accepted. Modifications to the text, calculations and figures. We corrected a problem which resulted in reducing the scatter in the earlier flux points in Figure 1. Conclusions unchanged

We review the observational properties of the class of young neutron stars known as "anomalous X-ray pulsars," emphasizing the tremendous progress that has been made in recent years, and explain why these objects, like the "soft gamma repeaters," are today thought to be young, isolated, ultrahigh magnetic field neutron stars, or "magnetars.", 10 pages, 5 figures. To appear in Proc. of the BeppoSAX Symposium: "The Restless High-Energy Universe," Eds. E.P.J. van den Heuvel, J.J.M. in't Zand, and R.A.M.J. Wijers

(abridged) An outburst of more than 80 individual bursts, similar to those seen from Soft Gamma Repeaters (SGRs), was detected from the Anomalous X-ray Pulsar (AXP) 1E 2259+586 in 2002 June. Coincident with this burst activity were gross changes in the pulsed flux, persistent flux, energy spectrum, pulse profile and spin down of the underlying X-ray source. We present RXTE and XMM-Newton observations of 1E 2259+586 that show the evolution of the aforementioned source parameters during and following this episode. Specifically, we observe an X-ray flux increase by more than an order of magnitude having two distinct components. The first component is linked to the burst activity and decays within ~2 days during which the energy spectrum is considerably harder than during the quiescent state of the source. The second component decays over the year following the glitch according to a power law in time with an exponent -0.22 +/- 0.01. The pulsed fraction decreased initially to ~15% RMS, and the pulse profile changed significantly during the outburst. A glitch was observed in 1E 2259+586 that preceded the observed burst activity. A fraction of the glitch (~19%) recovered, although the recovery was not purely exponential. An exponential rise of ~20% of the frequency jump with a time scale of ~14 days results in a significantly better fit to the data, however, contamination from a systematic drift in the phase of the pulse profile cannot be excluded. The long-term post-glitch spin-down rate decreased in magnitude relative to the pre-glitch value. A comparison with SGR outburst properties, a physical interpretation of the results, and implications on the number of magnetar candidates in our Galaxy are discussed., Comment: Accepted for publication in ApJ. 51 pages and 13 figures. Figure 1 is modified significantly. Several other minor changes made to the text

We report on 5.4 yr of phase-coherent timing, using the Rossi X-ray Timing Explorer, of the X-ray pulsar 1RXS 1708-4009, a member of the class known as ``anomalous X-ray pulsars.'' This object exhibited a rotational glitch in 1999. Here we report a second much larger rotational glitch which occured ~1.5 yr after the first. We show that the recoveries from the two glitches are different, with the first showing only a possible slow, approximately linear recovery, while the second showed a nearly complete recovery on a time scale of \~50 days. The approximately exponential recovery time scale of the second glitch is similar to that seen recently in 1E 2259+586 at the time of a major outburst. This suggests 1RXS 1708-4009 undergoes similar bursting behavior, although with our sparse observations we have detected no other evidence for bursts from this source., 13 pages, 2 figures. Revised manuscript and Fig 1 following refereeing. Accepted for publication in ApJL Aug 15

We report a major outburst from the Anomalous X-ray Pulsar 1E 2259+586, in which over 80 X-ray bursts were detected in four hours using the Rossi X-ray Timing Explorer. The bursts range in duration from 2 ms to 3 s and have fluences in the 2-10 keV band that range from 3 x 10^{-11} to 5 x 10^{-9} erg cm^{-2}. We simultaneously observed increases of the pulsed and persistent X-ray emission by over an order of magnitude relative to quiescent levels. Both decayed significantly during the course of our 14 ks observation. Correlated spectral hardening was also observed, with the spectrum softening during the observation. In addition, we observed a pulse profile change, in which the amplitudes of the two peaks in the pulse profile were swapped. The profile relaxed back to its pre-outburst morphology after ~6 days. The pulsar also underwent a sudden spin-up (df/f = 4 x 10^{-6}), followed by a large (factor of \~2) increase in spin-down rate which persisted for >18 days. We also observed, using the Gemini-North telescope, an infrared enhancement, in which the K_s (2.15 um) flux increased, relative to that measured in a observation made in 2000, by a factor of ~3, three days post-outburst. The IR counterpart then faded by a factor of ~2 one week later. In addition, we report an upper limit of 50 uJy on radio emission at 1.4 GHz two days post-outburst. The X-ray properties of this outburst are like those seen only in Soft Gamma Repeaters. This conclusively unifies Anomalous X-ray Pulsars and Soft Gamma Repeaters, as predicted uniquely by the magnetar model.

We report on the long-term monitoring of three anomalous X-ray pulsars using the Rossi X-ray Timing Explorer (RXTE). We present a phase-coherent timing ephemeris for 4U 0142+61, and show that it has rotated with high stability over 4.4 yr, with RMS phase deviations of 7% of the pulse period from a simple fit including only $\nu$ and $\dot{\nu}$. We report on the continued timing stability of 1E 2259.1+586, for which phase coherence has now been maintained over 4.5 yr, as well as on the detection of a significant $\ddot{\nu}$ in 1.4 yr of monitoring of RXS J170849.0-400910, consistent with recovery following a glitch. We note a correlation in which timing stability in AXPs decreases with increasing $\dot{\nu}$. The timing stability of soft gamma repeaters in quiescence is consistent with this trend, given their large spin-down rates. This trend is similar to one seen in radio pulsars, suggesting a connection between the three populations. We find no large variability in pulse morphology as a function of time. We present high signal-to-noise ratio average pulse profiles for each AXP, and consider them as a function of energy. We find a variety of different behaviors, and consider possible trends in the data. We also find no large variations in pulsed flux, and set 1 $\sigma$ upper limits of ~20-30% of the mean. Assuming a constant pulsed fraction, either more than one of the AXPs are coincidentally in a much more quiescent state during our RXTE monitoring than in the past, or past claims of large flux variations are incorrect.

We report on a long-term monitoring campaign of 1E 1841-045, the 12 s anomalous X-ray pulsar and magnetar candidate at the center of the supernova remnant Kes 73. We have obtained approximately monthly observations of the pulsar with the Rossi X-Ray Timing Explorer (RXTE) spanning over 2 years, during which time 1E 1841-045 is found to be rotating with sufficient stability to derive a phase-connected timing solution. A linear ephemeris is consistent with measurements of the pulse period made over the last 15 years with the Ginga, ASCA, RXTE, and BeppoSAX observatories. Phase residuals suggest the presence of "timing noise," as is typically observed from young radio pulsars. These results confirm a rapid, constant spin-down for the pulsar, which continues to maintain a steady flux; this is inconsistent with most accretion scenarios.

We report on long-term monitoring of the anomalous X-ray pulsar (AXP) 1E 1048.1-5937 using the Rossi X-ray Timing Explorer (RXTE). The timing behavior of this pulsar is different from that of other AXPs being monitored with RXTE. In particular, we show that the pulsar shows significant deviations from simple spin-down such that phase-coherent timing has not been possible over time spans longer than a few months. We find that the deviations from simple spin down are not consistent with single "glitch" type events, nor are they consistent with radiative precession. We show that in spite of the rotational irregularities, the pulsar exhibits neither pulse profile changes nor large pulsed flux variations. We discuss the implications of our results for AXP models. In the context of the magnetar model, we suggest that 1E 1048.1-5937 may be a transition object between the soft gamma-ray repeater and AXP populations, and the AXP most likely to one day undergo an outburst.

Anomalous X-ray Pulsars (AXPs) are a class of rare X-ray pulsars whose energy source has been perplexing for some 20 years. Unlike other, better understood X-ray pulsars, AXPs cannot be powered by rotation or by accretion from a binary companion, hence the designation ``anomalous.'' AXP rotational and radiative properties are strikingly similar to those of another class of exotic objects, the Soft Gamma Repeaters (SGRs). However, the defining property of SGRs, namely their low-energy gamma-ray and X-ray bursts, have heretofore not been seen in AXPs. SGRs are thought to be ``magnetars,'' young neutron stars powered by the decay of an ultra-high magnetic field. The suggestion that AXPs are magnetars has been controversial. Here we report the discovery, from the direction of AXP 1E 1048-5937, of two X-ray bursts that have many properties similar to those of SGR bursts. These events imply a close relationship between AXPs and SGRs, with both being magnetars., Comment: 14 pages, 2 figures, accepted for publication in Nature. Note: The content of this paper is embargoed until 1900 hrs London time / 1400 US Eastern Time on Sept 11

On 2011 July 14, a new magnetar candidate, Swift J1822.3-1606, was identified via a rate trigger on the Swift/Burst Alert Telescope. Here we present an initial analysis of the X-ray properties of the source, using data from the Rossi X-ray Timing Explorer, Swift, and the Chandra X-ray Observatory, spanning 2011 July 16--September 22. We measure a precise spin period of P=8.43771963(5) s and a spin-down rate of 2.97(28)E-13, at MJD 55761.0, corresponding to an inferred surface dipole magnetic field strength of B=5.1E13 G, the second lowest thus far measured for a magnetar, though similar to 1E~2259+586 as well as to several high-magnetic field radio pulsars. We show that the pulsed X-ray flux decay in the 2--10 keV band is best fit by an exponential with a time constant of 16.4+/-0.3 days. After increasing from ~35% during the first week after the onset of the outburst, the pulsed fraction in the 2--10 keV band remained constant at ~45. We argue that these properties confirm this source to be a new member of the class of objects known as magnetars., 7 pages, 3 figures. Submitted to the Astrophysical Journal Letters

The ∼800 yr‐old pulsar PSR J1846‐0258 in the supernova remnant Kes 75 is a unique transition object between rotation‐powered pulsars and magnetars. While it typically behaves as a rotation‐powered pulsar, in 2006 it exhibited a distinctly magnetar‐like outburst accompanied by a large glitch with an unusual over‐recovery. We present X‐ray timing observations taken with the Rossi X‐ray Timing Explorer after the X‐ray outburst and accompanying glitch had recovered. We observe that the braking index of the pulsar, previously measured to be n = 2.65±0.01 has decreased by 18±5%. We also note a persistent increase in the timing noise relative to the pre‐outburst level, reminiscent of behavior previously observed from some magnetars.

We present an analysis of the extended emission around the anomalous X-ray pulsar 1E 1547.0-5408 using four XMM-Newton observations taken with the source in varying states of outburst as well as in quiescence. We find that the extended emission flux is highly variable and strongly correlated with the flux of the magnetar. Based on this result, as well as on spectral and energetic considerations, we conclude that the extended emission is dominated by a dust-scattering halo and not a pulsar wind nebula (PWN), as has been previously argued. We obtain an upper limit on the 2-10 keV flux of a possible PWN of 4.7e-14 erg/s/cm^2, three times less than the previously claimed value, implying an efficiency for conversion of spin-down energy into nebular luminosity of, 16 pages, 3 tables, 4 figures, published in the Astrophysical Journal

We present results from observations of the magnetar 1E 1547.0-5408 (SGR J1550-5418) taken with the Chandra X-ray Observatory and the Rossi X-ray Timing Explorer (RXTE) following the source's outbursts in 2008 October and 2009 January. During the time span of the Chandra observations, which covers days 4 through 23 and days 2 through 16 after the 2008 and 2009 events, respectively, the source spectral shape remained stable, while the pulsar's spin-down rate in the same span in 2008 increased by a factor of 2.2 as measured by RXTE. The lack of spectral variation suggests decoupling between magnetar spin-down and radiative changes, hence between the spin-down-inferred magnetic field strength and that inferred spectrally. We also found a strong anti-correlation between the phase-averaged flux and the pulsed fraction in the 2008 and 2009 Chandra data, but not in the pre-2008 measurements. We discuss these results in the context of the magnetar model., Comment: 4 figures, accepted for publication in ApJ

The ~800 yr-old pulsar J1846-0258 is a unique transition object between rotation-powered pulsars and magnetars: though behaving like a rotation-powered pulsar most of the time, in 2006 it exhibited a distinctly magnetar-like outburst accompanied by a large glitch. Here we present X-ray timing observations taken with the Rossi X-ray Timing Explorer over a 2.2-yr period after the X-ray outburst and glitch had recovered. We observe that the braking index of the pulsar, previously measured to be n=2.65+/-0.01, is now n=2.16+/-0.13, a decrease of 18+/-5%. We also note a persistent increase in the timing noise relative to the pre-outburst level. Despite the timing changes, a 2009 Chandra X-ray Observatory observation shows that the X-ray flux and spectrum of the pulsar and its wind nebula are consistent with the quiescent levels observed in 2000., Comment: 15 pages, 7 figures. ApJ, in press. Upper limit on blackbody component added, as well as additional discussion

We report a large spin-up glitch in PSR J1846-0258 which coincided with the onset of magnetar-like behavior on 2006 May 31. We show that the pulsar experienced an unusually large glitch recovery, with a recovery fraction of Q=8.7+/- 2.5, resulting in a net decrease of the pulse frequency. Such a glitch recovery has never before been observed in a rotation-powered pulsar, however, similar but smaller glitch over-recovery has been recently reported in the magnetar AXP 4U~0142+61 and may have occurred in the SGR 1900+14. We also report a large increase in the timing noise of the source. We discuss the implications of the unusual timing behavior in PSR J1846-0258 on its status as the first identified magnetically active rotation-powered pulsar., Comment: 14 pages, 5 figures, Accepted for publication in the Astrophysical Journal. Incorporates changes from an anonymous referee; additional analysis and discussion included

We report detection of magnetar-like X-ray bursts from the young pulsar PSR J1846-0258, at the center of the supernova remnant Kes 75. This pulsar, long thought to be rotation-powered, has an inferred surface dipolar magnetic field of 4.9x10^13 G, higher than those of the vast majority of rotation-powered pulsars, but lower than those of the ~12 previously identified magnetars. The bursts were accompanied by a sudden flux increase and an unprecedented change in timing behavior. These phenomena lower the magnetic and rotational thresholds associated with magnetar-like behavior, and suggest that in neutron stars there exists a continuum of magnetic activity that increases with inferred magnetic field strength., 17 pages, 2 figures, accepted for publication in Science. Note: The content of this paper is embargoed until February 21, 2008

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., 3 pages, 4 figures. To appear in the proceedings of the "40 Years of Pulsars: Millisecond Pulsars, Magnetars and More" conference, held 12-17 August 2007, in Montreal QC (AIP, in press, eds: C. Bassa, Z. Wang, A. Cumming, V. Kaspi)

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.

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 (RXTE) monitoring. All the bursts occurred in the interval between 2006 April 6 and 2007 February 7. The bursts had the canonical fast rise slow decay profiles characteristic of SGR/AXP bursts. The burst durations ranged from 8-3x10^3 s as characterized by T90,these are very long durations even when compared to the broad T90 distributions of other bursts from SGRs and AXPs. The first five burst spectra are well modeled by simple blackbodies, with temperature kT ~2-6 keV. However, the sixth 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., To appear in the proceedings of the "40 Years of Pulsars: Millisecond Pulsars, Magnetars and More" conference, held 12-17 August 2007, in Montreal QC (AIP, in press, eds: C. Bassa, Z. Wang, A. Cumming, V. Kaspi)

We report on the serendipitous discovery of a 442-Hz pulsar during a Rossi X-ray Timing Explorer (RXTE) observation of the globular cluster NGC 6440. The oscillation is detected following a burst-like event which was decaying at the beginning of the observation. The time scale of the decay suggests we may have seen the tail-end of a long-duration burst. Low-mass X-ray binaries (LMXBs) are known to emit thermonuclear X-ray bursts that are sometimes modulated by the spin frequency of the star, the so called burst oscillations. The pulsations reported here are peculiar if interpreted as canonical burst oscillations. In particular, the pulse train lasted for ~500 s, much longer than in standard burst oscillations. The signal was highly coherent and drifted down by ~2x10^-3 Hz, much smaller than the ~Hz drifts typically observed during normal bursts. The pulsations are reminiscent of those observed during the much more energetic ``superbursts'', however, the temporal profile and the energetics of the burst suggest that it was not the tail end nor the precursor feature of a superburst. It is possible that we caught the tail end of an outburst from a new `intermittent'' accreting X-ray millisecond pulsar, a phenomenon which until now has only been seen in HETE J1900.1$-$2455 (Galloway et al. 2007). We note that (Kaaret et al. 2003) reported the discovery of a 409.7 Hz burst oscillation from SAX J1748.9-2021, also located in NGC 6440. However, Chandra X-ray Observatory imaging indicates it contains several point-like X-ray sources, thus the 442 Hz object is likely a different source., 4 pages, 3 figures, submitted to ApJ Letters

(Abridged) We report on 8.7 and 7.6 yr of RXTE observations of the Anomalous X-ray Pulsars (AXPs) RXS J170849.0-400910 and 1E 1841-045, respectively. These observations, part of a larger RXTE AXP monitoring program, 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. However, in terms of absolute glitch amplitude, AXP glitches are unremarkable. We show that 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 occurence 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 AXP glitches appear to fall in two classes: radiatively loud and radiatively quiet. The latter, of which the glitches of J170849.0-400910 and 1E 1841-045 are examples, show little evidence for an accompanying radiative event. We also show, however, that pulse profile and pulsed flux changes are common in these AXPs, but do not apprear closely correlated with any timing behavior., 48 pages, 17 figures, 8 tables, To be published in ApJ (accepted)

Pulsar braking indices offer insight into the physics that underlies pulsar spin-down. Only five braking indices have been measured via phase-coherent timing; all measured values are less than 3, the value expected from magnetic dipole radiation. Here we present new measurements for three of the five pulsar braking indices, obtained with phase-coherent timing for PSRs J1846-0258 (n=2.65+/-0.01), B1509-58 (n=2.839+/-0.001) and B0540-69 (n=2.140+/-0.009). We discuss the implications of these results and possible physical explanations for them., 7 pages, 5 figures. To be published in the proceedings of the conference "Isolated Neutron Stars: from the Interior to the Surface" (April 24-28, 2006, London, UK), eds. D. Page, R. Turolla, & S. Zane

We report on 10 years of monitoring of the 8.7-s Anomalous X-ray Pulsar 4U 0142+61 using the Rossi X-Ray Timing Explorer (RXTE). This pulsar exhibited stable rotation from 2000 March until 2006 February: the RMS phase residual for a spin-down model which includes nu, nudot, and nuddot is 2.3%. We report a possible phase-coherent timing solution valid over a 10-yr span extending back to March 1996. A glitch may have occured between 1998 and 2000, but is not required by the existing timing data. The pulse profile has been evolving since 2000. In particular, the dip of emission between its two peaks got shallower between 2002 and 2006, as if the profile were evolving back to its pre-2000 morphology, following an earlier event, which possibly also included the glitch suggested by the timing data. These profile variations are seen in the 2-4 keV band but not in 6-8 keV. We also detect a slow increase in the pulsed flux between 2002 May and 2004 December, such that it has risen by 36+/-3% over 2.6 years in the 2-10 keV band. The pulsed flux variability and the narrow-band pulse profile changes present interesting challenges to aspects of the magnetar model.

We present high-speed, multi-colour optical photometry of the anomalous X-ray pulsar 4U 0142+61, obtained with ULTRACAM on the 4.2-m William Herschel Telescope. We detect 4U 0142+61 at magnitudes of i'=23.7+-0.1, g'=27.2+-0.2 and u'>25.8, consistent with the magnitudes found by Hulleman et al.(2004) and hence confirming their discovery of both a spectral break in the optical and a lack of long-term optical variability. We also confirm the discovery of Kern & Martin (2002) that 4U 0142+61 shows optical pulsations with an identical period (~8.7 s) to the X-ray pulsations. The rms pulsed fraction in our data is 29+-8%, 5-7 times greater than the 0.2-8 keV X-ray rms pulsed fraction. The optical and X-ray pulse profiles show similar morphologies and appear to be approximately in phase with each other, the former lagging the latter by only 0.04+-0.02 cycles. In conjunction with the constraints imposed by X-ray observations, the results presented here favour a magnetar interpretation for the anomalous X-ray pulsars., 6 pages, 4 figures, accepted for publication in MNRAS

Resonant cyclotron scattering of the surface radiation in the magnetospheres of neutron stars may considerably modify the emergent spectra and impede efforts to constraint neutron star properties. Resonant cyclotron scattering by a non-relativistic warm plasma in an inhomogeneous magnetic field has a number of unusual characteristics: (i) in the limit of high resonant optical depth, the cyclotron resonant layer is half opaque, in sharp contrast to the case of non-resonant scattering. (ii) The transmitted flux is on average Compton up-scattered by ~ $1+ 2 beta_T$, where $\beta_T$ is the typical thermal velocity in units of the velocity of light; the reflected flux has on average the initial frequency. (iii) For both the transmitted and reflected fluxes the dispersion of intensity decreases with increasing optical depth. (iv) The emergent spectrum is appreciably non-Plankian while narrow spectral features produced at the surface may be erased. We derive semi-analytically modification of the surface Plankian emission due to multiple scattering between the resonant layers and apply the model to anomalous X-ray pulsar 1E 1048.1--5937. Our simple model fits just as well as the ``canonical'' magnetar spectra model of a blackbody plus power-law., Comment: 37 pages, 10 figures, accepted by MNRAS, minor changes

We report on the 2004 June 29 burst detected from the direction of the Anomalous X-ray Pulsar (AXP) 1E 1048.1-5937 using the Rossi X-ray Timing Explorer (RXTE). We find a simultaneous increase of ~3.5 times the quiescent value in the 2-10 keV pulsed flux of 1E 1048.1-5937 during the tail of the burst which identifies the AXP as the burst's origin. The burst was overall very similar to the two others reported from the direction of this source in 2001. The unambiguous identification of 1E 1048.1-5937 as the burster here confirms it was the origin of the 2001 bursts as well. The epoch of the burst peak was very close to the arrival time of 1E 1048.1-5937's pulse peak. The burst exhibited significant spectral evolution with the trend going from hard to soft. During the 11 days following the burst, the AXP was observed further with RXTE, XMM-Newton and Chandra. Pre- and post-burst observations revealed no change in the total flux or spectrum of the quiescent emission. Comparing all three bursts detected thus far from this source we find that this event was the most fluent (>3.3x10^-8 erg/cm^2 in the 2-20 keV band), had the highest peak flux (59+/-9x10^-10 erg/s/cm^2 in the 2-20 keV band), and the longest duration (>699 s). The long duration of the burst differentiates it from Soft Gamma Repeater (SGR) bursts which have typical durations of ~0.1 s. Bursts that occur preferentially at pulse maximum, have fast-rises and long X-tails containing the majority of the total burst energy have been seen uniquely from AXPs. The marked differences between AXP and SGRs bursts may provide new clues to help understand the physical differences between these objects., 24 pages, 4 figures, submitted to the Astrophysical Journal

An outburst of several tens of SGR‐like bursts was detected from the Anomalous X‐ray Pulsar (AXP) 1E 2259+586 in 2002 June. Coincident with this burst activity were gross changes in the pulsed flux, persistent flux, energy spectrum, pulse profile and spin down of the underlying X‐ray source. We present RXTE and XMM‐Newton observations of 1E 2259+586 that show the evolution of the aforementioned source parameters during and following this episode and identify recovery time scales for each. Specifically, we observe an X‐ray flux increase (pulsed and phase‐averaged) by more than an order of magnitude having two distinct components. The first component is linked to the burst activity and decays within ∼2 days during which the energy spectrum hardens considerably relative to the quiescent state of the source. The second component decays over the year following the glitch/outburst according to a power law in time with an exponent −0.22. The pulsed fraction decreased initially to ∼15% RMS, but recovered rapidly ...

We present an updated timing solution for the young, energetic pulsar PSR B1509-58 based on 21.3 years of radio timing data and 7.6 years of X-ray timing data. No glitches have occurred in this time span, in contrast to other well-studied young pulsars, which show frequent glitches. We report a measurement of the third frequency derivative of (-1.28+/-0.21)x10^(-31) s^(-4). This value is 1.65 standard deviations from, i.e. consistent with, that predicted by the simple constant magnetic dipole model of pulsar spin-down. We measured the braking index to be n=2.839+/-0.003 and show that it varies by 1.5% over 21.3 yr due to contamination from timing noise. Results of a low-resolution power spectral analysis of the significant noise apparent in the data yield a spectral index of alpha=-4.6+/-1.0 for the red noise component., Comment: 21 pages, 4 figures, 2 tables. Accepted by ApJ

We present a statistical analysis of the X‐ray bursts observed from the 2002 June 18 outburst of the Anomalous X‐ray Pulsar (AXP) 1E 2259+586, observed with the Proportional Counter Array aboard the Rossi X‐ray Timing Explorer. We show that the properties of these bursts are similar to those of Soft Gamma‐Repeaters (SGRs). The similarities we find are: the burst durations follow a log‐normal distribution which peaks at 99 ms, the differential burst fluence distribution is well described by a power law of index −1.7, the burst fluences are positively correlated with the burst durations, the distribution of waiting times is well described by a log‐normal distribution of mean 47 s, and the bursts are generally asymmetric with faster rise than fall times. However, we find several quantitative differences between the AXP and SGR bursts. Specifically, there is a correlation of burst phase with pulsed intensity, the AXP bursts we observed exhibit a wider range of durations, the correlation between burst fluence ...

We review the observational properties of the so‐called “anomalous X‐ray pulsars,” a class of young neutron stars having properties very different from most of the population. RXTE has provided observations that have made significant progress in our understanding of these sources, which like the “soft gamma repeaters,” are today thought to be young, isolated, ultrahigh magnetic field neutron stars, or “magnetars.” We briefly discuss the major outstanding questions in this area, and what sort of future X‐ray missions would be most likely to allow progress to be made.

We report on X-ray monitoring of two isolated pulsars within the same RXTE field of view. PSR J1811-1925 in the young supernova remnant G11.2-0.3 has a nearly sinusoidal pulse profile with a hard pulsed spectrum (photon index \~1.2). The pulsar is a highly efficient (~ 1% of spin-down energy) emitter of 2-50 keV pulsed X-rays despite having a fairly typical B ~ 2e12 G magnetic field. PSR J1809-1943/XTE J1810-197 is a newly discovered slow (P=5.54 s), apparently isolated X-ray pulsar which increased in flux by a factor of ~100 in 2003 January. Nine months of monitoring observations have shown a decrease in pulsed flux of ~ 30% without a significant change in its apparently thermal spectrum (kT ~0.7 keV) or pulse profile. During this time, the spin-down torque has fluctuated by a factor of ~ 2. Both the torque and the flux have remained steady for the last 3 months, at levels consistent with a magnetar interpretation., Comment: 3 pages, 4 figures, to appear in the Proceedings of X-ray Timing 2003: Rossi and Beyond, ed. P. Kaaret, F.K. Lamb, & J.H. Swank held in Cambridge, MA, Nov. 3-5, 2003

The X-ray Pulsar PSR J1811-1925 in the historic supernova remnant G11.2-0.3 has a characteristic age over 10 times the age of the remnant. This likely implies that its current spin period, 65 ms, is close to its birth spin period. Alternatively, the pulsar may have an unusually high braking index. We report here on regular Rossi X-ray Timing Explorer/ Proportional Counting Array (RXTE/PCA) timing observations of the pulsar that were designed to measure its braking index. We provide a preliminary phase-coherent timing solution which includes a significant $\ddot{\nu}$. The braking index we measure is >> 3, likely a result of conventional timing noise. We also report on a preliminary analysis of the pulsar's unusually hard spectrum: we determine a photon index of $\Gamma = 1.78\pm0.74$, for the pulsed component of the spectra, consistent within the uncertainties with previous ASCA and Chandra observations. The pulsed emission of PSR J1811-1925 is seen beyond 30 keV, and the pulsations remain sinusoidal up to and beyond this energy., Comment: 6 pages, 3 figures, To appear in the proceedings of the 34th Cospar Scientific Assembly

We present a statistical analysis of the X-ray bursts observed from the 2002 June 18 outburst of the Anomalous X-ray Pulsar (AXP) 1E 2259+586, observed with the Proportional Counter Array (PCA) aboard the Rossi X-ray Timing Explorer. We show that the properties of these bursts are similar to those of Soft Gamma-Repeaters (SGRs). The similarities we find are the burst durations follow a log-normal distribution which peaks at 99 ms, the differential burst fluence distribution is well described by a power law of index -1.7, the burst fluences are positively correlated with the burst durations, the distribution of waiting times is well described by a log-normal distribution of mean 47 s, and the bursts are generally asymmetric with faster rise than fall times. However, we find several quantitative differences between the AXP and SGR bursts. Specifically, the AXP bursts we observed exhibit a wider range of durations, the correlation between burst fluence and duration is flatter than for SGRs, the observed AXP bursts are on average less energetic than observed SGR bursts, and the more energetic AXP bursts have the hardest spectra -- the opposite of what is seen for SGRs. We conclude that the bursts are sufficiently similar that AXPs and SGRs can be considered united as a source class yet there are some interesting differences that may help determine what physically differentiates the two closely related manifestations of neutron stars., Comment: 32 pages, 12 figures, submitted to ApJ

We report on long-term monitoring of anomalous X-ray pulsars (AXPs) using the Rossi X-ray Timing Explorer (RXTE). Using phase-coherent timing, we find a wide variety of behaviors among the sources, ranging from high stability (in 1E 2259.1+586 in quiescence and 4U 0142+61), to instabilities so severe that phase-coherent timing is not possible (in 1E 1048.1-5937). We note a correlation in which timing stability in AXPs decreases with increasing $\dot{\nu}$. The timing stability of soft gamma repeaters (SGRs) in quiescence is consistent with this trend, which is similar to one seen in radio pulsars. We find no significant pulse morphology variations in any AXP in quiescence. We considered high signal-to-noise average pulse profiles for each AXP as a function of energy. We show that, as in the timing properties, there is a variety of different behaviors for the energy dependence. We also used the monitoring and archival data to obtain pulsed flux time series for each source. We have found no large changes in pulsed flux for any source in quiescence, and have set $1\sigma$ upper limits on variations ~20-30% depending on the source. We have recently discovered bursts from the direction of two AXPs: 1E 1048.1-5937 the most SGR-like AXP, and 1E 2259.1+586 the most rotationally stable AXP. We compare the temporal, spectral and flux properties of these events to those of SGR bursts, and show that the two phenomena are very similar. These results imply a close relationship between AXPs and SGRs, with both being magnetars., Comment: 10 pages, 7 figures, to appear in the proceedings of the 34th Cospar Scientific Assembly

We report on long-term monitoring of the anomalous X-ray pulsar (AXP) 1E 1048.1-5937 using the Rossi X-ray Timing Explorer (RXTE). The timing behavior of this pulsar is different from that of other AXPs being monitored with RXTE. In particular, we show that the pulsar shows significant deviations from simple spin-down such that phase-coherent timing has not been possible over time spans longer than a few months. We find that the deviations from simple spin down are not consistent with single "glitch" type events, nor are they consistent with radiative precession. We show that in spite of the rotational irregularities, the pulsar exhibits neither pulse profile changes nor large pulsed flux variations. We discuss the implications of our results for AXP models. In the context of the magnetar model, we suggest that 1E 1048.1-5937 may be a transition object between the soft gamma-ray repeater and AXP populations, and the AXP most likely to one day undergo an outburst., Comment: 27 pages, 4 figures, to appear in August issue of ApJ. Revised text and Figure 3

We report on Chandra X-ray Observatory (CXO) High-Energy Transmission Grating (HETG) spectra of the dipping Low Mass X-ray Binary (LMXB) 1A 1744-361 during its July 2008 outburst. We find that its persistent emission is well modeled by a blackbody (kT ~ 1.0 keV) plus power-law ($��$ ~ 1.7) with an absorption edge at 7.6 keV. In the residuals of the combined spectrum we find a significant absorption line at 6.961+/-0.002 keV, consistent with the Fe XXVI (hydrogen-like Fe) 2 - 1 transition. We place an upper limit on the velocity of a redshifted flow of v < 221 km/s. We find an equivalent width for the line of 27^+2_-3 eV, from which we determine a column density of 7+/-1x10^17 cm^-2 via a curve-of-growth analysis. Using XSTAR simulations, we place a lower limit on the ionization parameter of > 10^3.6 erg cm/s. The properties of this line are consistent with those observed in other dipping LMXBs. Using Rossi X-ray Timing Explorer (RXTE) data accumulated during this latest outburst we present an updated color-color diagram which clearly shows that 1A 1744-361 is an "atoll" source. Finally, using additional dips found in the RXTE and CXO data we provide an updated orbital period estimate of 52+/-5 minutes., 8 pages, 7 figures, submitted to ApJ

We present the results of Rossi X-ray Timing Explorer (RXTE) and Swift monitoring observations of the magnetar 1E 1547.0-5408 following the pulsar's radiative outbursts in 2008 October and 2009 January. We report on a study of the evolution of the timing properties and the pulsed flux from 2008 October 4 through 2009 December 26. We show that the pulsed flux decrease which followed an initial rise in the 2008 outburst was interrupted by a spike ~9 days after the initial outburst. In our timing study, a phase-coherent analysis shows that for the first 29 days following the 2008 outburst, there was a very fast increase in the magnitude of the rotational frequency derivative nudot, such that the second derivative was a factor of ~60 larger than that reported in data from 2007. This nudot magnitude increase occurred in concert with the decay of the pulsed flux following the start of the 2008 event. Following the 2009 outburst, for the first 23 days, the second derivative was consistent with zero, and nudot had returned to close to its 2007 value. In contrast to the 2008 event, the 2009 outburst showed a major increase in persistent flux, relatively little change in the pulsed flux, and sudden significant spectral hardening ~15 days after the outburst. We show that, excluding the month following each of the outbursts, and because of the noise and the sparsity in the data, multiple plausible timing solutions fit the pulsar's frequency behavior. We note similarities in the behavior of 1E 1547.0-5408 following the 2008 outburst to that seen in the AXP 1E 1048.1-5937 following its 2001-2002 outburst and discuss this in terms of the magnetar model., 30 pages, 8 figures, 4 tables, accepted by ApJ

We report on data obtained with the Chandra, XMM-Newton, Suzaku and Swift X-ray observatories, following the 2006 outburst of the Anomalous X-ray Pulsar CXO J164710.2-455216. We find no evidence for the very large glitch and rapid exponential decay as was reported previously for this source. We set a 3 sigma upper limit on any fractional frequency increase at the time of the outburst of Delta nu/nu < 1.5 x 10^{-5}. Our timing analysis, based on the longest time baseline yet, yields a spin-down rate for the pulsar that implies a surface dipolar magnetic field of ~9 x 10^{13} G, although this could be biased high by possible recovery from an undetected glitch. We also present an analysis of the source flux and spectral evolution, and find no evidence for long-term spectral relaxation post-outburst as was previously reported., Submitted to ApJ