Previous XMM-Newton observations of the thermally emitting isolated neutron star RX J1605.3+3249 provided a candidate for a shallow periodic signal and evidence of a fast spin down, which suggested a ...high dipolar magnetic field and an evolution from a magnetar. We obtained a large programme with XMM-Newton to confirm its candidate timing solution, understand the energy-dependent amplitude of the modulation, and investigate the spectral features of the source. We performed extensive high-resolution and broadband periodicity searches in the new observations, using the combined photons of the three EPIC cameras and allowing for moderate changes of pulsed fraction and the optimal energy range for detection. We also investigated the EPIC and RGS spectra of the source with unprecedented statistics and detail. A deep 4σ upper limit of 1.33(6)% for modulations in the relevant frequency range conservatively rules out the candidate period previously reported. Blind searches revealed no other periodic signal above the 1.5% level (3σ; P > 0.15 s; 0.3–1.35 keV) in any of the four new observations. While theoretical models fall short at physically describing the complex energy distribution of the source, best-fit X-ray spectral parameters are obtained for a fully or partially ionized neutron star hydrogen atmosphere model with B = 1013 G, modified by a broad Gaussian absorption line at energy ϵ = 385 ± 10 eV. A double-temperature blackbody model, although a good fit to the source spectrum, is disfavoured as it would require a particularly improbable viewing geometry to explain the lack of X-ray pulsations associated with small hotspots on the surface of the neutron star. We identified a low significance (1σ) temporal trend on the parameters of the source in the analysis of RGS data dating back to 2002, which may be explained by unaccounted calibration issues and spectral model uncertainties. The new dataset also shows no evidence of the previously reported narrow absorption feature at ϵ ∼ 570 eV, whose possible transient nature disfavours an atmospheric origin.
I present an analysis of the XMM-Newton observations of four millisecond pulsars, J0437-4715, J2124-3358, J1024-0719, and J0034-0534. The new data provide strong evidence of thermal emission in the ...X-ray flux detected from the first three objects. This thermal component is best interpreted as radiation from pulsar polar caps covered with a nonmagnetic hydrogen atmosphere. A nonthermal power-law component, dominating at energies E 3 keV, can also be present in the detected X-ray emission. For PSR J0437-4715, the timing analysis reveals that the shape and pulsed fraction of the pulsar light curves are energy dependent. This, together with the results obtained from the phase-resolved spectroscopy, supports the two-component (thermal plus nonthermal) interpretation of the pulsar's X-ray radiation. Highly significant pulsations have been found in the X-ray flux of PSRs J2124-3358 and J1024-0719. For PSR J0034-0534, a possible X-ray counterpart of the radio pulsar has been suggested. The inferred properties of the detected thermal emission are compared with predictions of radio pulsar models.
We report on the discovery of gamma-ray pulsations from five millisecond pulsars (MSPs) using the Fermi Large Area Telescope (LAT) and timing ephemerides provided by various radio observatories. We ...also present confirmation of the gamma-ray pulsations from a sixth source, PSR J2051−0827. Five of these six MSPs are in binary systems: PSRs J1713+0747, J1741+1351, J1600−3053 and the two black widow binary pulsars PSRs J0610−2100 and J2051−0827. The only isolated MSP is the nearby PSR J1024−0719, which is also known to emit X-rays. We present X-ray observations in the direction of PSRs J1600−3053 and J2051−0827. While PSR J2051−0827 is firmly detected, we can only give upper limits for the X-ray flux of PSR J1600−3053. There are no dedicated X-ray observations available for the other three objects.
The MSPs mentioned above, together with most of the MSPs detected by Fermi, are used to put together a sample of 30 gamma-ray MSPs. This sample is used to study the morphology and phase connection of radio and gamma-ray pulse profiles. We show that MSPs with pulsed gamma-ray emission which is phase-aligned with the radio emission present the steepest radio spectra and the largest magnetic fields at the light cylinder among all MSPs. Also, we observe a trend towards very low, or undetectable, radio linear polarization levels. These properties could be attributed to caustic radio emission produced at a range of different altitudes in the magnetosphere. We note that most of these characteristics are also observed in the Crab pulsar, the only other radio pulsar known to exhibit phase-aligned radio and gamma-ray emission.
We observed the gamma -ray pulsar Geminga with the FUV-MAMA and NUV-MAMA detectors of the Space Telescope Imaging Spectrometer to measure Geminga's spectrum and pulsations in the ultraviolet. The ...slope of the far-ultraviolet (FUV) spectrum is close to that of a Rayleigh-Jeans spectrum, suggesting that the FUV radiation is dominated by thermal emission from the neutron star (NS) surface. The measured FUV flux, F sub(FUV) = (3.7 plus or minus 0.2) x 10 super(-15) ergs cm super(-2) s super(-1) in the 1155-1702 AA band, corresponds to a brightness temperature T sub(RJ) approximately (0.3-0.4)(d sub(200)/R sub(13)) super(2) MK, depending on the interstellar extinction (d = 200d sub(200) pc and R = 13R sub(13) km are the distance and the NS radius, respectively). The soft thermal component of Geminga's X-ray spectrum measured with the XMM-Newton observatory corresponds to a temperature T sub(s) = 0.49 plus or minus 0.01 MK and radius R sub(s) = (12.9 plus or minus 1.0)d sub(200) km. Contrary to other NSs detected in the UV-optical, for which the extrapolation of the X-ray thermal component into the optical underpredicts the observed flux of thermal radiation, the FUV spectrum of Geminga lies slightly below the extrapolation of the soft thermal component, which might be associated with Geminga's very low temperature. Surprisingly, the thermal FUV radiation is strongly pulsed, showing a narrow dip at a phase close to that of a broader minimum of the soft X-ray light curve. The strong pulsations might be attributed to partial occultations of the thermal UV radiation by regions of the magnetosphere filled with electron/positron plasma. In contrast to the FUV spectrum, the near-infrared (NIR) through near-ultraviolet (NUV) spectrum of Geminga is clearly nonthermal. It can be described by a power-law model, F sub( upsilon ) proportional to upsilon super(- Gamma +1), with a photon index Gamma = 1.43 plus or minus 0.15, close to the slope Gamma = 1.56 plus or minus 0.24 of the hard X-ray (E > 2.5 keV) magnetospheric component. The extrapolation of the X-ray magnetospheric spectrum into the optical is marginally consistent with (or perhaps lies slightly above) the observed NIR-optical-NUV spectrum. The NUV pulsations, however, do not show a clear correlation with the hard X-ray pulsations.
ESO 4 m class telescope and VLT deep imaging of the isolated neutron star RX J0720.4–3125 reveals a proper motion of $\mu = 97\pm12$ mas/yr and a blue $U-B$ color index. We show that a neutron star ...atmosphere model modified to account for a limited amount of hydrogen on the star's surface can well represent both the optical and X-ray data without invoking any additional thermal component. The large proper motion almost completely excludes the possibility that accretion from the interstellar medium is the powering mechanism of the X-ray emission. It also implies that the proposed spin down is entirely due to magnetic dipole losses. RX J0720.4–3125 is thus very likely a middle aged cooling neutron star. Its overall properties are quite similar to some of the long period radio pulsars recently discovered, giving further support to the idea that RX J0720.4–3125 may be a pulsar whose narrow radio beam does not cross the Earth.
The superb spatial resolution of Chandra has allowed us to detect a 20 long tail behind the Geminga pulsar, with a hard spectrum (photon index = 1.0 c 0.2) and a luminosity of (1.3 c 0.2) x 10 ...super(29) ergs s super(-1) in the 0.5-8 keV band, for an assumed distance of 200 pc. The tail could be either a pulsar jet, confined by a toroidal magnetic field of 6100 kPG, or it could be associated with the shocked relativistic wind behind the supersonically moving pulsar confined by the ram pressure of the oncoming interstellar medium. We also detected an arclike structure 5-7 ahead of the pulsar, extended perpendicular to the tail, with a factor of 3 lower luminosity. We see a 3 s enhancement in the Chandra image apparently connecting the arc with the southern outer tail that has been possibly detected with XMM-Newton. The observed structures imply that the Geminga's pulsar wind is intrinsically anisotropic.
We present the timing and spectral analyses of the XMM-Newton data on the 17 Myr old, nearby radio pulsar B0950+08. This observation revealed pulsations of the X-ray flux of PSR B0950+08 at its radio ...period, P 253 ms. The pulse shape and pulsed fraction are apparently different at lower and higher energies of the observed 0.2-10 keV energy range, which suggests that the radiation cannot be explained by a single emission mechanism. The X-ray spectrum of the pulsar can be fitted with a power-law model with a photon index = 1.75 c 0.15 and an (isotropic) luminosity L sub(X) = (9.8 c 0.2) x 10 super(29) ergs s super(-1) in the 0.2-10 keV range. Better fits are obtained with two-component, power-law plus thermal models with = 1.30 c 0.10 and L sub(X) = (9.7 c 0.1) x 10 super(29) ergs s super(-1) for the power-law component, which presumably originates from the pulsar's magnetosphere. The thermal component, dominating at E 0.7 keV, can be interpreted as radiation from heated polar caps on the neutron star surface covered with a hydrogen atmosphere. The inferred effective temperature, radius, and bolometric luminosity of the polar caps are T sub(PC) - 1 MK, R sub(PC) - 250 m, and L sub(PC) - 3 x 10 super(29) ergs s super(-1). Optical through X-ray nonthermal spectrum of the pulsar can be described as a single power law with = 1.3-1.4 for the two-component X-ray fit. The ratio of the nonthermal X-ray (1-10 keV) luminosity to the nonthermal optical (4000-9000 AA) luminosity, -360, is within the range of 10 super(2)-10 super(3) observed for younger pulsars, which suggests that the magnetospheric X-ray and optical emissions are powered by the same mechanism in all pulsars, independent of age and spin-down power. Assuming a standard neutron star radius, the upper limit on the temperature of the bulk of the neutron star surface, inferred from the optical and X-ray data, is about 0.15 MK. We also analyze X-ray observations of several other old pulsars, B2224+65, J2043+2740, B0628-28, B1813-36, B1929+10, and B0823+26, and compare their properties with those of PSR B0950+08.
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