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Register a new userX-ray observations of the high magnetic field radio pulsar PSR J1814-1744
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PSR J1814-1744 is a 4 s radio pulsar with surface dipole magnetic field strength 5.5*10^13 G, inferred assuming simple magnetic dipole braking. This pulsars spin parameters are very similar to those of anomalous X-ray pulsars (AXPs), suggesting that this may be a transition object between the radio pulsar and AXP population, if AXPs are isolated, high magnetic field neutron stars as has recently been hypothesized. We present archival X-ray observations of PSR J1814-1744 made with ROSAT and ASCA. X-ray emission is not detected from the position of the radio pulsar. The derived upper flux limit implies an X-ray luminosity significantly smaller than those of all known AXPs. This conclusion is insensitive to the possibility that X-ray emission from PSR J1814-1744 is beamed or that it undergoes modest variability. When interpreted in the context of the magnetar mechanism, these results argue that X-ray emission from AXPs must depend on more than merely the inferred surface magnetic field strength. This suggests distinct evolutionary paths for radio pulsars and AXP, despite their proximity in period--period derivative phase space.
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Recent radio observations have unveiled the existence of a number of radio pulsars with spin-down derived magnetic fields in the magnetar range. However, their observational properties appears to be more similar to classical radio pulsars than to magnetars. To shed light on this puzzle we first have to determine whether the spin-down derived magnetic field values for these radio pulsars are indeed representative of the actual neutron star magnetic field or if they are polluted, e.g. by the effects of a torque from a fallback disk. To investigate this possibility, we have performed deep IR observations of one of these high magnetic field radio pulsars (PSR J1119-6127) with the ESO VLT to search for IR emission which can be associated with a disk. No IR emission is detected from the pulsar position down to J=24, H=23, Ks=22. By comparing our flux upper limits with the predictions of fallback disk models, we have found that we can only exclude the presence of a disk with accretion rate dot M >3x10^16 g/s. This lower limit cannot rule out the presence of a substantial disk torque on the pulsar, which would then lead to overestimate the value of the magnetic field inferred from P and dot P.
We report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822-09 with ESAs XMM-Newton and the WSRT, GMRT and Lovell radio telescopes. PSR B1822-09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation timescale within the modes. We discovered X-ray (energies 0.2-1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 +/- 0.017, with an energy-dependent pulsed fraction varying from ~0.15 at 0.3 keV to ~0.6 at 1 keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ~ 0.96 x 10^6 K, hot-spot radius R ~ 2.0 km) and a hot component (T ~ 2.2 x 10^6 K, R ~ 100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822-09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055-52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi LAT data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In the X-ray skymap we found a harder source at only (5.1+/- 0.5 )arcsec from PSR B1822-09, which might be a pulsar wind nebula.
We report on the detection of PSR 1706-44 in two ROSAT-PSPC observations. The recorded source counts are unpulsed with a $2sigma$ pulsed fraction upper limit of 18%. Spectral analysis did not distinguish between black-body and power law models; however, we argue that the lack of pulsations and the similarity in the pulsars spin parameters to those of the Vela pulsar favour a power law model $dN/dEpropto E^{-2.4pm 0.6}$ and indicate synchrotron emission from a pulsar-powered nebula as the origin of the detected X-radiation. The X-ray flux derived for the power law model is f_x=3.2^{+6.5}_{-1.8} x E-12 erg/ s/ cm^2 within the 0.1-2.4 keV energy range. An upper limit for the neutron stars surface temperature is put at Log T_s^infty sim 6.03 K for a neutron star with a medium stiff equation of state (FP-model with M=1.4 Mo, R=10.85 km). Slightly different values for $T_s^infty$ are computed for the various neutron star models available in the literature, reflecting the difference in the equation of state. No soft X-ray emission is detected from the supernova remnant G343.1-2.3, proposed to be associated with PSR 1706-44.
Observations obtained in the last years challenged the widespread notion that rotation-powered neutron stars are steady X-ray emitters. Besides a few allegedly rotation-powered neutron stars that showed magnetar-like variability, a particularly interesting case is that of PSR B0943+10. Recent observations have shown that this pulsar, well studied in the radio band where it alternates between a bright and a quiescent mode, displays significant X-ray variations, anticorrelated in flux with the radio emission. The study of such synchronous radio/X-ray mode switching opens a new window to investigate the processes responsible for the pulsar radio and high-energy emission. Here we review the main X-ray properties of PSR B0943+10 derived from recent coordinated X-ray and radio observations.
We present X-ray observations of the redback eclipsing radio millisecond pulsar and candidate radio pulsar/X-ray binary transition object PSR J1723-2837. The X-ray emission from the system is predominantly non-thermal and exhibits pronounced variability as a function of orbital phase, with a factor of ~2 reduction in brightness around superior conjunction. Such temporal behavior appears to be a defining characteristic of this variety of peculiar millisecond pulsar binaries and is likely caused by a partial geometric occultation by the main-sequence-like companion of a shock within the binary. There is no indication of diffuse X-ray emission from a bow shock or pulsar wind nebula associated with the pulsar. We also report on a search for point source emission and $gamma$-ray pulsations in Fermi Large Area Telescope data using a likelihood analysis and photon probability weighting. Although PSR J1723-2837 is consistent with being a $gamma$-ray point source, due to the strong Galactic diffuse emission at its position a definitive association cannot be established. No statistically significant pulsations or modulation at the orbital period are detected. For a presumed source detection, the implied $gamma$-ray luminosity is $lesssim$5% of its spin-down power. This indicates that PSR J1723-2837 is either one of the least efficient $gamma$-ray producing millisecond pulsars or, if the detection is spurious, the $gamma$-ray emission pattern is not directed towards us.
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