14714748
Study of the Long-Term Stability of Two Anomalous X-Ray Pulsars, 4U 0142+61 and 1E 1048.1?5937, with ASCA
We present new observations of two anomalous X-ray pulsars (AXPs), 4U 0142+61 and 1E 1048.1-5937, made in 1998 with ASCA. The energy spectrum of each of these two AXPs is found to consist of two components, a power-law and a blackbody emission from the neutron star surface. These observations, when compared with earlier ASCA observations in 1994, show remarkable stability in the intensities, spectral shapes, and pulse profiles. However, we find that the spin-down rate in 1E 1048.1-5937 is not constant. In this source, we have clearly identified three epochs with spin-down rates different from each other and from the average value. This has very strong implications for the magnetar hypothesis for AXPs. We also note that the spin-down rate and its variations in 1E 1048.1-5937 are much larger than can normally be produced by an accretion disk with a very low mass accretion rate corresponding to its low X-ray luminosity.
14658153
ASCA Observations of the Supernova Remnant IC 443: Thermal Structure and Detection of Overionized Plasma
We present the results of X-ray spatial and spectral studies of the "mixed-morphology" supernova remnant IC 443 using ASCA. IC 443 has a center-filled image in the X-ray band, contrasting with the shell-like appearance in radio and optical bands. The overall X-ray emission is thermal, not from a synchrotron nebula. We observed IC 443 three times with ASCA, covering the whole remnant. From the image analysis, we find that the softness-ratio map reveals a shell-like structure. At the same time, its spectra require two (1.0 and 0.2 keV) plasma components; the emission of the 0.2 keV plasma is stronger in the region near the shell than in the center. These results can be explained by a simple model that IC 443 has a hot (1.0 keV) interior surrounded by a cool (0.2 keV) outer shell. From the emission measures, we infer that the 0.2 keV plasma is denser than the 1.0 keV plasma, suggesting pressure equilibrium between the two. In addition, we find that the ionization temperature of sulfur, obtained from the H-like to He-like Kα intensity ratio, is 1.5 keV, significantly higher than the gas temperature of 1.0 keV suggested from the continuum spectrum. The same can be concluded for silicon. Neither an additional, hotter plasma component nor a multitemperature plasma successfully account for this ratio, and we conclude that the 1.0 keV plasma is overionized. This is the first time that overionized gas has been detected in a supernova remnant (SNR). For the gas to become overionized in the absence of a photoionizing flux, it must cool faster than the ions recombine. Thermal conduction from the 1.0 keV plasma to the 0.2 keV plasma could cause the 1.0 keV plasma to become overionized, which is plausible within an old (3 × 104 yr) SNR.
119940843
Performance of the X-ray CCDs aboard the ASCA satellite after 5-year operation in space
Abstract The performance of the charge coupled devices on-board the ASCA satellite has been traced for five years after the launch. We found the gradual increase of the dark current and the decrease of the charge transfer efficiency. These changes may be explained by charge traps due to the radiation damage. The nature of the radiation damage is investigated in detail using various methods.
119256738
Electron and photon energy deposition in the Universe
We consider energy deposition of high energy electrons and photons in the Universe. We carry out detailed calculations of fractions of the initial energy of the injected electron or photon which are used to heat, ionize, and excite background plasma in the early Universe for various ionization states (ionization $\mathrm{\text{fraction}}={10}^{\ensuremath{-}3}\ensuremath{-}1$) and redshifts ($z=100\char21{}1000$).
472649
Q-ball formation in the gravity-mediated SUSY breaking scenario
We study the formation of Q balls which are made of flat directions that appear in the supersymmetric extension of the standard model in the context of gravity-mediated supersymmetry breaking. The full nonlinear calculations for the dynamics of the complex scalar field are made. Since the scalar potential in this model is flatter than ${\ensuremath{\varphi}}^{2},$ we have found that fluctuations develop and go nonlinear to form nontopological solitons, Q balls. The size of a Q ball is determined by the most amplified mode, which is completely determined by the model parameters. On the other hand, the charge of Q balls depends linearly on the initial charge density of the Affleck-Dine (AD) field. Almost all the charges are absorbed into Q balls, and only a tiny fraction of the charges is carried by a relic AD field. It may lead to some constraints on the baryogenesis and/or parameters in the particle theory. The peculiarity of gravity mediation is the moving Q balls. This results in collisions between Q balls. It may increase the charge of the Q balls, and change its fate.
119073714
Hadronic decay of late-decaying particles and big-bang nucleosynthesis
Abstract We study the big-bang nucleosynthesis (BBN) scenario with late-decaying exotic particles with lifetime longer than ∼1 s. With a late-decaying particle in the early universe, predictions of the standard BBN scenario can be significantly altered. Therefore, we derive constraints on its primordial abundance. We pay particular attention to hadronic decay modes of such particles. We see that the non-thermal production process of D, 3 He and 6 Li provides a stringent upper bound on the primordial abundance of late-decaying particles with hadronic branching ratio.
121696361
Cold dark matter generation by axionic domain wall collapses
The contribution to the cold dark matter density by axionic domain wall collapses is estimated. The dynamics of the axionic domain wall bounded by the axionic string is investigated using numerical simulations. It is found that the collapse proceeds quickly and mildly relativistic axions are emitted. Their energy density increases during radiation dominated era and can account for the dark matter in the universe for F a 10 10 GeV.