We report on new and archival X-ray and near-IR observations of the anomalous X-ray pulsar 1E 1048.1À5937 performed between 2001 and 2007 with the Rossi X-Ray Telescope Explorer (RXTE ), the Chandra X-Ray Observatory, the Swift Gamma-Ray Burst Explorer, the Hubble Space Telescope (HST ), and the Very Large Telescope. Monitoring with RXTE revealed that following its $2001Y2004 active period, 1E 1048.1À5937 entered a phase of timing stability; at the same time, simultaneous observations with Chandra and HST in 2006 showed that its X-ray and near-IR radiative properties, all variable prior to 2005, stabilized. Specifically, the 2006 X-ray spectrum is consistent with a two-component blackbody plus power law, with an average kt ¼ 0:52 keV and À ¼ 2:8, at a mean flux level of $6:5 ; 10 À12 erg cm À2 s À1 (2Y10 keV ). The near-IR counterpart in 2005Y2006 was detected at H $ 22:7 mag and K s $ 21:0 mag, considerably fainter than previously measured. In 2007 March, this newfound quiescence was interrupted by sudden X-ray flux, spectral, and pulse morphology changes, simultaneous with a large glitch and near-IR enhancement. Our RXTE observations revealed a factor of $3 increase in pulsed flux (2Y10 keV ), while observations with Chandra and Swift saw the total X-ray flux increase much more than the pulsed flux, reaching a peak value of >7 times the quiescent value (2Y10 keV ). We find a strong anticorrelation between X-ray flux and pulsed fraction, and a correlation between X-ray spectral hardness and flux. Simultaneously with the radiative and timing changes, we observed the X-ray pulse profile change significantly from nearly sinusoidal to having multiple peaks. We compare these remarkable events with other magnetar outbursts and discuss implications in the context of AXP emission models.

We present the results of a near-infrared monitoring program of the anomalous X-ray pulsar 1E 2259ϩ586, performed at the Gemini Observatory. This program began 3 days after the pulsar's 2002 June outburst and spans ∼1.5 yr. We find that after an initial increase associated with the outburst, the near-infrared flux decreased continually and reached the preburst quiescent level after about 1 yr. We compare both the near-infrared flux enhancement and its decay to those of the X-ray afterglow and find them to be remarkably consistent. Fitting simple power laws to the Rossi X-Ray Timing Explorer pulsed flux and near-infrared data for day postburst, t 1 1 we find the following decay indices:(X-ray) and (near-infrared), where a p Ϫ0.21 ‫ע‬ 0.01 a p Ϫ0.21 ‫ע‬ 0.02 flux is a function of time such that . This suggests that the enhanced infrared and X-ray fluxes have a a F ∝ t physical link postoutburst, most likely from the neutron star magnetosphere.

We present an X-ray and radio study of the wind nebula surrounding the central pulsar PSR J1811À1925 in the supernova remnant G11.2À0.3. Using high-resolution data obtained with the Chandra X-Ray Observatory and with the VLA radio telescope, we show the X-ray and radio emission is asymmetric around the pulsar, despite the latter's central position in the very circular shell. The new X-ray data allow us to separate the synchrotron emission of the pulsar wind nebula from the surrounding thermal emission and that from the pulsar itself. On the basis of X-ray data from two epochs, we observe temporal variation of the location of X-ray hot spots near the pulsar, indicating relativistic motion. We compare thermal emission observed within the shell, which may be associated with the forward shock of the pulsar wind nebula, to thermal emission from a nearby portion of the remnant shell, the temperature of which implies an expansion velocity consistent with the identification of the remnant with the historical event of 386 A.D. The measured X-ray and radio spectral indices of the nebula synchrotron emission are found to be consistent with a single synchrotron cooling break. The magnetic field implied by the break frequency is anomalously large, given the apparent size and age of the nebula, if a spherical morphology is assumed but is consistent with a bipolar morphology.

We have conducted a radio pulsar survey of 56 unidentified -ray sources from the third EGRET catalog that are at intermediate Galactic latitudes (5 < jbj < 73 ). For each source, four interleaved 35 minute pointings were made with the 13 beam, 1400 MHz multibeam receiver on the Parkes 64 m radio telescope. This covered the 95% error box of each source at a limiting sensitivity of $0.2 mJy to pulsed radio emission for periods P k 10 ms and dispersion measures P50 pc cm À3. Roughly half of the unidentified -ray sources at jbj > 5 with no proposed active galactic nucleus counterpart were covered in this survey. We detected nine isolated pulsars and four recycled binary pulsars, with three from each class being new discoveries. Timing observations suggest that only one of the pulsars has a spin-down luminosity that is even marginally consistent with the inferred luminosity of its coincident EGRET source. Our results suggest that population models, which include the Gould Belt as a component, overestimate the number of isolated pulsars among the midlatitude Galactic -ray sources, and that it is unlikely that Gould Belt pulsars make up the majority of these sources. However, the possibility of steep pulsar radio spectra and the confusion of terrestrial radio interference with long-period pulsars (P k 200 ms) having very low dispersion measures (P10 pc cm À3, expected for sources at a distance of less than about 1 kpc) prevent us from strongly ruling out this hypothesis. Our results also do not support the hypothesis that millisecond pulsars make up the majority of these sources. Nonpulsar source classes should therefore be further investigated as possible counterparts to the unidentified EGRET sources at intermediate Galactic latitudes.

We present the results of Chandra X-Ray Observatory observations of the transient anomalous X-ray pulsar candidate AX J1845.0À0258 in apparent quiescence. Within the source's error circle, we find a point source and possible counterpart, which we designate CXOU J184454.6À025653. No coherent pulsations are detected, and no extended emission is seen. The source's spectrum is equally well described by a blackbody model of temperature kT $ 2:0 keV or a power-law model with photon index À $ 1:0. This is considerably harder than was seen for AX J1845.0À0258 during its period of brightening in 1993 (kT $ 0:6 keV) despite being at least $13 times fainter. This behavior is opposite to that observed in the case of the established transient AXP, XTE J1810À197. We therefore explore the possibility that CXOU J184454.6À025653 is an unrelated source and that AX J1845.0À0258 remains undetected since 1993, with a flux 260Y430 times fainter than at that epoch. If so, this would represent an unprecedented range of variability in AXPs.