Using XMM-Newton and Chandra, we measure period derivatives for the second and third known pulsars in the class of Central Compact Objects (CCOs) in supernova remnants, proving that these young neutron stars have exceptionally weak dipole magnetic field components. For the 112 ms PSR J0821−4300 in Puppis A,Ṗ = (9.28 ± 0.36) × 10 −18 . Its proper motion, µ = 61 ± 9 mas yr −1 , was also measured using Chandra. This contributes a kinematic term to the period derivative via the Shklovskii effect, which is subtracted fromṖ to derive dipole B s = 2.9 × 10 10 G, a value similar to that of first measured CCO PSR J1852+0040 in Kes 79, which has B s = 3.1 × 10 10 G. Antipodal surface hot spots with different temperatures and areas are deduced from the X-ray spectrum and pulse profiles. Paradoxically, such nonuniform surface temperature appears to require strong crustal magnetic fields, probably toroidal or quadrupolar components much stronger than the external dipole. A spectral feature, consisting of either an emission line at ≈ 0.75 keV or absorption at ≈ 0.46 keV, is modulated in strength with the rotation. It may be due to a cyclotron process in a magnetic field on the surface that is slightly stronger than the dipole deduced from the spin-down. We also timed anew the 424 ms PSR J1210−5226, resolving previous ambiguities about its spin-down rate. Itṡ P = (2.22 ± 0.02) × 10 −17 , corresponding to B s = 9.8 × 10 10

We report on timing, flux density, and polarimetric observations of the transient magnetar and 5.54 s radio pulsar XTEJ1810−197 using the Green Bank, Nançay, and Parkes radio telescopes beginning in early 2006, until its sudden disappearance as a radio source in late 2008. Repeated observations through 2016 have not detected radio pulsations again. The torque on the neutron star, as inferred from its rotation frequency derivativeṅ, decreased in an unsteady manner by a factor of three in the first year of radio monitoring, until approximately mid-2007. By contrast, during its final year as a detectable radio source, the torque decreased steadily by only 9%. The periodaveraged flux density, after decreasing by a factor of 20 during the first 10 months of radio monitoring, remained relatively steady in the next 22 months, at an average of 0.7±0.3 mJy at 1.4 GHz, while still showing day-to-day fluctuations by factors of a few. There is evidence that during this last phase of radio activity the magnetar had a steep radio spectrum, in contrast to earlier flat-spectrum behavior. No secular decrease presaged its radio demise. During this time, the pulse profile continued to display large variations; polarimetry, including of a new profile component, indicates that the magnetic geometry remained consistent with that of earlier times. We supplement these results with X-ray timing of the pulsar from its outburst in 2003 up to 2014. For the first 4 years, XTEJ1810 −197 experienced non-monotonic excursions in frequency derivative by at least a factor of eight. But since 2007, itsṅ has remained relatively stable near its minimum observed value. The only apparent event in the X-ray record that is possibly contemporaneous with the radio shutdown is a decrease of ≈20% in the hot-spot flux in 2008-2009, to a stable, minimum value. However, the permanence of the high-amplitude, thermal X-ray pulse, even after the (unexplained) radio demise, implies continuing magnetar activity.

We present the earliest X-ray observations of the 2018 outburst of XTE J1810−197, the first outburst since its 2003 discovery as the prototypical transient and radio-emitting anomalous X-ray pulsar (AXP). The Monitor of All-sky X-ray Image (MAXI ) detected XTE J1810−197 immediately after a November 20-26 visibility gap, contemporaneous with its reactivation as a radio pulsar, first observed on December 8. On December 13 the Nuclear Spectroscopic Telescope Array (NuSTAR) detected Xray emission up to at least 30 keV, with a spectrum well-characterized by a blackbody plus power-law model with temperature kT = 0.74 ± 0.02 keV and photon index Γ = 4.4 ± 0.2 or by a two-blackbody model with kT = 0.59 ± 0.04 keV and kT = 1.0 ± 0.1 keV, both including an additional power-law component to account for emission above 10 keV, with Γ h = −0.2±1.5 and Γ h = 1.5±0.5, respectively. The latter index is consistent with hard X-ray flux reported for the non-transient magnetars. In the 2−10 keV bandpass, the absorbed flux is 2 × 10 −10 erg s −1 cm −2 , a factor of 2 greater than the maximum flux extrapolated for the 2003 outburst. The peak of the sinusoidal X-ray pulse lags the radio pulse by ≈ 0.13 cycles, consistent with their phase relationship during the 2003 outburst. This suggests a stable geometry in which radio emission originates on magnetic field lines containing currents that heat a spot on the neutron star surface. However, a measured energy-dependent phase shift of the pulsed X-rays suggests that all X-ray emitting regions are not precisely co-aligned.

We report on X-ray observations of the 5.54 s transient magnetar XTE J1810−197 using the XMM-Newton and Chandra observatories, analyzing new data from 2008 through 2014, and re-analyzing data from 2003 through 2007 with the benefit of these six years of new data. From the discovery of XTE J1810−197 during its 2003 outburst to the most recent 2014 observations, its 0.3 − 10 keV X-ray flux has declined by a factor of about 50 from 4.1 × 10 −11 to 8.1 × 10 −13 erg cm −2 s −1 . Its X-ray spectrum has now reached a steady state. Pulsations continue to be detected from a 0.3 keV thermal hot-spot that remains on the neutron star surface. The luminosity of this hot-spot exceeds XTE J1810−197's spin down luminosity, indicating continuing magnetar activity. We find that XTE J1810−197's X-ray spectrum is best described by a multiple component blackbody model in which the coldest 0.14 keV component likely originates from the entire neutron star surface, and the thermal hot-spot is, at different epochs, well described by an either one or two-component blackbody model. A 1.2 keV absorption line, possibly due to resonant proton scattering, is detected at all epochs. The X-ray flux of the hot spot decreased by ≈ 20% between 2008 March and 2009 March, the same period during which XTE J1810−197 became radio quiet.

After 15 yr, in late 2018, the magnetar XTE J1810−197 underwent a second recorded X-ray outburst event and reactivated as a radio pulsar. We initiated an X-ray monitoring campaign to follow the timing and spectral evolution of the magnetar as its flux decays using Swift, XMM–Newton, NuSTAR, and NICER observations. During the year-long campaign, the magnetar reproduced similar behaviour to that found for the first outburst, with a factor of 2 change in its spin-down rate from ∼7.2 × 10−12 to ∼1.5 × 10−11 s s−1 after two months. Unique to this outburst, we confirm the peculiar energy-dependent phase shift of the pulse profile. Following the initial outburst, the spectrum of XTE J1810−197 is well modelled by multiple blackbody components corresponding to a pair of non-concentric, hot thermal caps surrounded by a cooler one, superposed to the colder star surface. We model the energy-dependent pulse profile to constrain the viewing and surface emission geometry and find that the overall geometry of XTE J1810−197 has likely evolved relative to that found for the 2003 event.