Noriaki Shibazaki

Neutron star evolution with internal heating

The thermal evolution predicted by current models of the superfluid-crust interaction is noted to differ substantially from the thermal evolution predicted by models without internal heating as well as previous models of heating. Heating rates approaching the maximum predicted by current models enhance the photon luminosity of the star in the neutrino cooling era, and dramatically alter the thermal evolution in the photon cooling era. Standard cooling models are consistent with current pulsar temperature estimates and upper limits, except those for the Vela pulsar, which are lower than predicted. 77 refs.

DISCOVERY OF X-RAY EMISSION FROM THE CRAB PULSAR AT PULSE MINIMUM

The Chandra X-Ray Observatory observed the Crab pulsar using the Low-Energy Transmission Grating with the High-Resolution Camera. Time-resolved zeroth-order images reveal that the pulsar emits X-rays at all pulse phases. Analysis of the flux at minimum—most likely nonthermal in origin—places an upper limit (T∞ < 2.1 MK) on the surface temperature of the underlying neutron star. In addition, analysis of the pulse profile establishes that the error in the Chandra-determined absolute time is quite small, -0.2 ± 0.1 ms.

Thermal evolution of neutron stars with internal frictional heating

It has been suggested that the frictional interaction of neutron superfluids with normal matter in the inner crust of neutron stars dissipates rotational energy of superfluids and generates heat. Incorporating of general formula of internal heating into the detailed numerical codes of thermal evolution, we examine the effects of the internal heating on thermal evolution of neutron stars. We find that when a very stiff equation of state is used, it takes as long as ∼2×10 4 yr for the interior of a neutron star to reach the isothermal state, even if a strong heat source is placed in a thin layer of the inner crust

Accurate Position of SGR 1900+14 by Bursts and Changes in Pulse Period and Folded Pulse Profile with ASCA

The Advanced Satellite for Cosmology and Astrophysics (ASCA) observed the soft gamma repeater SGR 1900+14 on 1998 April 30-May 1 and discovered a pulsar with a period of 5.1589715(8) s from the known X-ray source of RX J190714.2+0919.3. Four months later, on September 16-17, ASCA observed SGR 1900+14 again just after the giant burst on 1998 August 27. Comparing the observations in September with those in April, there are several changes in characteristics. The pulse period changed to 5.160295(3) s, and thus the long-term period derivative is 1.1 × 10-10 s s-1. This strongly supports a magnetar model. The folded pulse profile in 2-10 keV largely changed from three peaks in April to one simple peak, while the steady intensity increased by a factor of 2. Finally, we successfully determined the accurate location of SGR 1900+14 by the bursts with an accuracy of 15 in diameter.

Subaru optical observations of the two middle-aged pulsars PSR B0656+14 and Geminga

Aims. We carried out a deep subarcsecond BRI imaging of the two middle-aged pulsars to establish their properties in the optical range Methods. Astrometry and photometry methods are applied to identify the pulsars and to measure their fluxes. We also reanalyze arch ival ESO/NTT and HST broadband data and find that some published fluxes f or Geminga were estimated inaccurately. The resulting dereddened broadband spectra in the near-IR-UV range are analyzed and compared with available data from the radio through gamma-rays. Results. Both pulsars are detected at>10σ level. Geminga is for the first time reliably detected in the I band with a magnitude of 25. 10±0.14. The dereddened spectra of both pulsars are remarkably similar to each other and show significant flux increases towards th e far-UV and near-IR, and a wide flux excess in V-I bands. This suggests a multicomponent structure of the optical emission. The nonthermal power law component of the pulsar magnetospheric origin dominates in the most part of the optical range. For PSR B0656+14 it is compatible with a low energy extension of the power law tail seen in hard X-rays. For Geminga the respective extension overshoots by a factor of 100 the nonthermal optical flux, which has a less steep spectral slope than in X-r ays. This implies a spectral break at a photon energy∼1 keV. The flux increases towards the far-UV are compatible with contributions of the Rayleigh-Jeans parts of the blackbody components from whole surfaces of the neutron stars dominating in soft X-rays. The V-I excess, which is most significant for PSR B0656+14, suggests a third spectral component of still unidentified origin. Faint, a few arcseconds in size ne bulae extended perpendicular to the proper motion directions of the pulsars, are seen around both objects in our deepest I band images. They can be optical counterparts of the bow-shock head of Geminga and of the tentative pulsar wind nebula of PSR B0656+14 observed in X-rays.

A Pulse Profile Change Possibly Associated with a Glitch in the Anomalous X-Ray Pulsar 4U 0142+61

We report a glitchlike pulse-frequency deviation from the simple spin-down law in an anomalous X-ray pulsar (AXP), 4U 0142+61, detected by ASCA observations. We also found a significant change in pulse profile after the putative glitch. The glitch parameters resemble those found in another AXP, 1RXS J170849.0-400910, and in the Vela and other radio pulsars. This suggests that radio pulsars and AXPs have the same internal structure and glitch mechanism. It must be noted, however, that the pulse-frequency anomaly can also be explained by a gradual change of the spin-down rate without invoking a glitch.

The effects of mixing of the ejecta on the hard X-ray emissions from SN 1987A

The X-ray and gamma-ray emissions expected from SN 1987A have been calculated, taking into account mixing of material in the ejecta. Nuclear gamma rays emitted by Co-56 are scattered down to the hard X-ray band by multiple Compton scatterings. Nomotos 11E1Y6 model for the ejecta of SN 1987A is used. X-ray light curves in the 10-30 keV band and spectra above 20 keV calculated with an inner mixed region of 5 + or - 1 solar mass are consistent with the observations performed with the Ginga satellite and the Kvant/Roentgen mission. On the basis of this comparison, further evolutions of the hard X-ray, gamma-ray, and optical/infrared emissions are discussed. 28 references.

Thermal Response of a Neutron Star to a Glitch

In a glitch, some energy must be liberated in the neutron star interior. We examine the thermal response of a neutron star to a sudden energy release in the interior. A part of the released energy diffuses outward and is emitted promptly as thermal afterglow from the surface of the star. The appearance of the thermal afterglow exhibits significant variations depending on the magnitude and depth of the energy release and on the equation of state for dense matter. We especially show how the thermal response varies according to whether the released energies are a small or large fraction of the heat content of the star. We also discuss how observations of thermal afterglow can be used to set constraints on the transient energy release and on the equation of state.

Soft and Hard X-Ray Emissions from the Anomalous X-Ray Pulsar 4U 0142+61 Observed with Suzaku

The anomalous X-ray pulsar 4U 0142+61 was observed with Suzaku on 2007 August 15 for a net exposure of � 100 ks, and was detected in a 0.4 to � 70 keV energy band. The intrinsic pulse period was determined to be 8.68878 ˙ 0.00005 s, in agreement with an extrapolation from previous measurements. The broadband Suzaku spectra enabled a first simultaneous and accurate measurement of the soft and hard components of this object by a single satellite. The former can be reproduced by two blackbodies, or slightly better by a resonant cyclotron scattering model. The hard component can be approximated by a power-law of photon index of Γh � 0.9 when the soft component is represented by the resonant cyclotron scattering model, and its high-energy cutoff is constrained as > 180 keV. Assuming an isotropic emission at a distance of 3.6 kpc, the unabsorbed 1–10 keV and 10–70 keV luminosities of the soft and hard components were calculated to be 2.8 � 10 35 erg s � 1 and 6.8 � 10 34 erg s � 1 , respectively. Their sum becomes � 10 3 times as large as the estimated spin-down luminosity. On a time scale of 30 ks, the hard

Subaru optical observations of the old pulsar PSR B0950+08 ⋆

We report the B band optical observations of an old (τ ∼ 17.5 Myr) radiopulsar PSR B0950+08 obtained with the Suprime-Cam at the Subaru telescope. We detected a faint object, B = 27. m 07 ± 0.16. Within our astrometrical accuracy it coincides with the radio position of the pulsar and with the object detected earlier by Pavlov et al. (1996) in UV with the HST/FOC/F130LP. The positional coincidence and spectral properties of the object suggest that it is the optical counterpart of PSR B0950+08. Its flux in the B band is two times higher than one would expect from the suggested earlier Rayleigh-Jeans interpretation of the only available HST observations in the adjacent F130LP band. Based on the B and F130LP photometry of the suggested counterpart and on the available X-ray data we argue in favour of nonthermal origin of the broad-band optical spectrum of PSR B0950+08, as it is observed for the optical emission of the younger, middle-aged pulsars PSR B0656+14 and Geminga. At the same time, the optical efficiency of PSR B0950+08, estimated from its spin-down power and the detected optical flux, is by several orders of magnitude higher than for these pulsars, and comparable with that for the much younger and more energetic Crab pulsar. We cannot exclude the presence of a compact, ∼1 �� , faint pulsar nebula around PSR B0950+08, elongated perpendicular to the vector of its proper motion, unless it is not a projection of a faint extended object on the pulsar position.