Victoria M. Kaspi

ON THE X-RAY SPECTRA OF ANOMALOUS X-RAY PULSARS AND SOFT GAMMA REPEATERS

We revisit the apparent correlation between soft X-ray band photon index and spin-down rate ύ previously reported for Anomalous X-ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs) by Marsden & White. Our analysis, improved thanks to new source discoveries, better spectral parameter measurements in previously known sources, and the requirement of source quiescence for parameter inclusion, shows evidence for the previously noted trend, although with greater scatter. This trend supports the twisted magnetosphere model of magnetars although the scatter suggests that factors other than ύ are also important.We also note possible correlations involving the spectra of AXPs and SGRs in the hard X-ray band. Specifically, the hard-band photon index shows a possible correlation with inferred ύ and B, as does the degree of spectral turnover. If the former trend is correct, then the hard-band photon index for AXP 1E 1048.1 − 5937 should be ∼0–1. This may be testable with long integrations by the International Gamma-Ray Astrophysics Laboratory, or by the upcoming focusing hard X-ray mission NuSTAR.

THE 2006 OUTBURST OF THE MAGNETAR CXOU J164710.2 - 455216

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 CXOU J164710.2–455216. Using a more complete and higher signal-to-noise data set, we find no evidence for the very large glitch and rapid exponential decay as was reported previously for this source. We set a 3σ upper limit on any fractional frequency increase at the time of the outburst of Δν/ν < 1.5 × 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 × 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.

10 Years of RXTE Monitoring of Five Anomalous X‐Ray Pulsars

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.

Long-term RXTE monitoring of the anomalous X-ray pulsar 1E 1048.1–5937

We report on long-term monitoring of the anomalous X-ray pulsar 1E 1048.1-5937 using the Rossi X-ray Timing Explorer. This pulsars timing behavior is different from that of other AXPs. In particular, 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 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. 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.