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Register a new userROSAT observations of the radio and gamma-ray pulsar PSR 1706-44
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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.
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Observations made with the University of Durham Mark 6 atmospheric Cerenkov telescope confirm that PSR B1706-44 is a very high energy gamma-ray emitter. There is no indication from our dataset that the very high energy gamma-rays are pulsed, in contrast to the findings at < 20 GeV, which indicate that more than 80% of the flux is pulsed. The flux at E > 300 GeV is estimated to be (3.9 +/- 0.7 (statistical)) x 10^-11 cm^-2 s^-1.
We report the results of the observations of the three gamma-ray pulsars PSR B0656+14, PSR B1055-52 and PSR B1706-44 performed with BeppoSAX. We detected a pulsed emission only for PSR B1055-52: in the range 0.1-6.5 keV the pulse profile is sinusoidal and the statistical significance is 4.5 sigma. The pulsed fraction was estimated 0.64+/-0.17. This pulsation was detected also at energies greater than 2.5 keV suggesting either a non-thermal origin or a quite high temperature region on the neutron star surface. Spectral analysis showed that only the X-ray spectrum of PSR B1706-44 can be fitted by a single power-law component, while that of PSR B1055-52 requires also a blackbody component (kT = 0.075 keV) and that of PSR B0656+14 two blackbody components (kT_1 = 0.059, kT_2 = 0.12 keV).
We present the results of new Agile observations of PSR B1509-58 performed over a period of 2.5 years following the detection obtained with a subset of the present data. The modulation significance of the lightcurve above 30 MeV is at a 5$sigma$ confidence level and the lightcurve is similar to those found earlier by Comptel up to 30 MeV: a broad asymmetric first peak reaching its maximum 0.39 +/- 0.02 cycles after the radio peak plus a second peak at 0.94 +/- 0.03. The gamma-ray spectral energy distribution of the pulsed flux detected by Comptel and Agile is well described by a power-law (photon index alpha=1.87+/-0.09) with a remarkable cutoff at E_c=81 +/- 20 MeV, representing the softest spectrum observed among gamma-ray pulsars so far. The pulsar luminosity at E > 1 MeV is $L_{gamma}=4.2^{+0.5}_{-0.2} times10^{35}$ erg/s, assuming a distance of 5.2 kpc, which implies a spin-down conversion efficiency to gamma-rays of $sim 0.03$. The unusual soft break in the spectrum of PSR B1509-58 has been interpreted in the framework of polar cap models as a signature of the exotic photon splitting process in the strong magnetic field of this pulsar. In this interpretation our spectrum constrains the magnetic altitude of the emission point(s) at 3 km above the neutron star surface, implying that the attenuation may not be as strong as formerly suggested because pair production can substitute photon splitting in regions of the magnetosphere where the magnetic field becomes too low to sustain photon splitting. In the case of an outer-gap scenario, or the two pole caustic model, better constraints on the geometry of the emission would be needed from the radio band in order to establish whether the conditions required by the models to reproduce Agile lightcurves and spectra match the polarization measurements.
The predicted nature of the candidate redback pulsar 3FGL,J2039.6$-$5618 was recently confirmed by the discovery of $gamma$-ray millisecond pulsations (Clark et al. 2020, hereafter Paper,I), which identify this $gamma$-ray source as msp. We observed this object with the Parkes radio telescope in 2016 and 2019. We detect radio pulsations at 1.4,GHz and 3.1,GHz, at the 2.6ms period discovered in $gamma$-rays, and also at 0.7,GHz in one 2015 archival observation. In all bands, the radio pulse profile is characterised by a single relatively broad peak which leads the main $gamma$-ray peak. At 1.4,GHz we found clear evidence of eclipses of the radio signal for about half of the orbit, a characteristic phenomenon in redback systems, which we associate with the presence of intra-binary gas. From the dispersion measure of $24.57pm0.03$,pc,cm$^{-3}$ we derive a pulsar distance of $0.9pm 0.2$,kpc or $1.7pm0.7$,kpc, depending on the assumed Galactic electron density model. The modelling of the radio and $gamma$-ray light curves leads to an independent determination of the orbital inclination, and to a determination of the pulsar mass, qualitatively consistent to the results in Paper,I.
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.
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