The signs of the active star formation in the Orion region are mainly found in the direction of the two giant molecular clouds - Ori A and Ori B -. Recent objective prism survey in the Orion region shows large number of Hα emission-line stars distributed outside of the giant molecular clouds (Nakano et al., 1995). Many weak-lined T Tauri star candidates are also discovered by the discrimination analysis of the X-ray sources found in the ROSAT all sky survey (RASS) (Sterzik et al., 1995). Although such huge number of pre-main sequence stars outside of the molecular cloud was not expected, their nature is still in controversial (Neuhäuser, 1997). To know the X-ray properties of these sources in the Orion region, we have carried out the ASCA observations.

By using ASCA, Koyama et al. (1994, 1996) carried out a systematic survey of hard X-ray sources in molecular clouds and revealed that protostars are strong hard X-ray emitting sources. Some of them show flare-like activities. Protostellar flares differ from solar flares in their total energy(1035-36 erg), size(several times the radius of protostar), and higher temperature(8keV). Protostellar flares are also observed in lower energy band by ROSAT in YLW15 (Grosso et al. 1997). By extending the model of solar flares associated with footpoint shearing motion, we proposed a model of protostellar flares in which the magnetic field connecting the protostar and the disk disrupt by twist injection from the rotating disk(Hayashi et al. 1996).

R CrA molecular cloud, at a distance of 130pc(Marraco, Rydgren 1981), is one of the active low-to-middle mass star forming regions. The core of this cloud, named Coronet, contains five protostar candidates. In 1994, we observed the Coronet Cluster using the X-ray satellite ASCA, and discovered hard X-rays from protostar candidates(Koyama et al. 1996).

On 1993 August 20, we observed the Rho-Oph dark cloud and detected hard X-rays from Class I sources (Koyama et al.(1994), Kamata et al.(1997)). One of the sources (EL29) showed a flare-like variability, while another (WL6) exhibited sinusoidal variation with no large spectral change. The later would be due to a spin of the protostar. The sinusoidal period of about 1 day is shorter than spin periods of TTSs of ~3-7 day.

The radioactive isotopes, such as 44Ti and 56Ni, are synthesized as a result of rapid nucleosynthesis in supernova explosions. The gamma-ray photons coming out from the decay sequence of 44Ti is now a strong candidate to explain the the late light curve of SN 1987A. It is noted here that the energy release from the 44Ti decay depends strongly on its half-life. However, the published values for 44Ti half-life display a large spread, ranging from ~ 35 to ~ 68 years. In this paper (Kumagai et al. 1997; see also Kumagai et al. 1993), we discuss the value of the half-life by comparing the theoretical light curves and the observations in SN 1987A. The unestablished half-life value is related to the ratio of the abundance of 44Ti to that of 56Ni.

Massive stars in a certain mass range (20 – 40M⊙) may form low mass black holes after supernova explosions. In such massive stars, fall back of ~ 0.1M⊙ materials onto a black hole is expected due to a deep gravitational potential or a reverse shock propagating back from the outer composition interface. We study hydrodynamical disk accretion onto a new-born low mass black hole in a supernova using the SPH (Smoothed Particle Hydrodynamics) method.

SN1993J is very unique object which was discovered in the nearby Sb galaxy M81 (NGC 3031) on March 28. The first detection of the radio emission was at 22.5 GHz by the VLA only 5 days after the optical outburst. Subsequently X-ray emission was detected by ROSAT and ASCA at 6 days and 8 days after the explosion respectively. These emissions are expected when the SN shock front sweeps out the circumstellar matter (CSM). The early detection of radio and X-ray emission implies the existence of high-density CSM in the vicinity of the supernova(e.g.).

In this paper we discuss the results of extensive comparison of the Boltzmann solver recently developed by us and the Monte Carlo method coded by Janka. The aim of our project is to improve the treatment of the neutrino transfer and to study the neutrino reactions systematically, since the numerical treatment of neutrino transfer and neutrino reaction rates in the hot dense medium are two of the greatest uncertainties in the supernova simulations.

Observations of the soft X-Ray background and interstellar UV absorption lines have indicated that a large fraction of interstellar space is filled with a high temperature low density “coronal” gas. In such low density environments SNRs will expand up to 200 pc in radius without thin shell formation which occurs due to radiative cooling effects. Such SNRs can occupy a large fraction of volume of Galaxy and can be the main source of background emissions. In the present work we examine the evolution of the radio emission of shell-like SNR evolving in the hot ISM.

One major objective of our ASCA Galactic Plane Survey Project (AGPSP) is, utilizing the wide and high energy band (up to 10 keV) X-ray imaging capability and the high spectral resolving power of ASCA, to search possible X-ray SNRs in the Galactic inner disk. The observation of the field including G352.7-0.1 reported in this paper, was performed on 1996 March 14 during the first AO4 survey. We report on the X-ray SNR G352.7-0.1 found in AGPSP. G352.7-0.1 is one of the radio SNRs (Green 1996), and is classified as a shell-like SNR with the size of 8' x 6'.

IRAS observations of supernova remnants (SNRs) reported that infrared luminosity from SNRs are very different, though some of them have same temperature. This is because infrared emittion depends on density of the dust grains.

The Cygnus Loop is the prototype shell-like supernova remnant (SNR) and one of the brighest SNRs in X-ray wavelength. We have observed the entire Cygnus Loop with the X-ray satellite, ASCA. Its large apparent size, high surface brightness, and low absorption features have made the Cygnus Loop to be an ideal target for the study of the spatially-resolved spectroscopic structure in detail. Part of this work was summarized in Miyata (1996). Here, we present the first X-ray image of the Cygnus Loop obtained with ASCA.

From many Galactic supernova remnants (SNRs), X-ray emissions consisting of non-equilibrium ionization (NEI) plasma and additional hard component are detected. The hard emission have been usually interpreted as a high temperature plasma of = 10 keV. However, the recent observation with ASCA made it clear that the hard components of some SNRs are of non-thermal origin. Here we report the ASCA results of SN 1006 and IC 443 observations as an example of such SNRs.

We have presented X-ray observations of Crab-like supernova remnants (SNRs) (plerions) and (non-thermal) composite SNRs. We have observed several objects including 3C58, CTA1, and G292.0+1.8. Since space is limited, here we summarize results on G292.0+1.8. For the other objects, please refer to each publication (Slane et al. 1997; Torii et al. 1997).

Recently, many unusual morphologies of supernova remnants (SNRs) have been discovered: semicircular shell; center-brightened but without center point source; two-lobed; bipolar; irregular, etc. To understand these varieties of morphologies, we have made theoretical models. One of the main reasons of their unusualness is the multiphase structure of the interstellar medium (ISM) and circumstellar medium (CSM) where they evolved, and the CSM is connected with their progenitor.

RX J1713.7-3946 is a new and bright supernova remnant (SNR) in soft X-rays discovered by Pfeffermann & Aschenbach (1996, hereafter PA 1996). Its visual position as shown on its name is within the asterism Wei where the AD393 guest star occured (Wang et al. 1997).

Radio supernova remnants(SNRs) of large angular diameter are obvious objects for multifrequency spectral studies from long wavelengths to short wavelengths, as resolutions at low frequency are usually about several arcminutes. An international cooperation consists of MRAO, BAO, DRAO, MPI, and astronomers from Beijing University, Beijing Normal University, China and Calgary University, Canada. This international collaboration is also a part of the Panorramic Spectral Imaging of the Milky Way (PI R. Taylor). Some results on HB21, G78.2+2.1, and HB9 are presented in this paper.

X-ray images of rotation-powered pulsars were examined using ASCA Gas Imaging Spectrometer (GIS). The data sets are taken from those available in the ASCA public archive in the performance verification (PV) phase and the guest-observing (GO) phase 1. We detected diffuse X-ray sources in the vicinity of nine pulsars including five new detections. There are large variety in their morphology and spatial size. The high probability of finding such diffuse sources around pulsars suggests that they exist universally for all the active pulsars, and that they are powered by the pulsars. We propose that the pulsar-powered nebula is a good probe to measure the otherwise invisible energy flux dissipating from a pulsar into the surrounding space.

Recent observation with ASCA reveals that radio pulsars own X-ray diffuse nebulae around them. 11 such nebulae have been reported (Harrus, Hughes & Helfand 1996, Shibata et al. 1997, Kawai, Tamura & Shibata 1997). It is most likely that these nebulae are synchrotron nebuale powered by the pulsar wind, the outflow of relativistic particles. Kawai, Tamura and Shibata (1997) reduced an empirical law for the nebula luminosity Lx as a function of the rotation power Ėrot of the central pulsar: Lx/Ėrot = −12.3 + 0.27 log Ėrot.

We present a scenario for the origin of the hot plasma in our Galaxy, as a model of a strong X-ray emission (LX(2 – 10keV) ~ 1038 erg s−1), called Galactic Ridge X-ray Emission (GRXE), which has been observed near the Galactic plane. GRXE is thermal emission from hot component (~ 7 keV) and cool component (~ 0.8 keV). Observations suggest that the hot component is diffuse, and is not escaping away freely. Both what heats the hot component and what confines it in the Galactic ridge are still remained puzzling, while the cool component is believed to be made by supernovae. We propose a new scenario: the hot component of GRXE plasma is heated by magnetic reconnection, and confined in the helical magnetic field produced by magnetic reconnection or in the current sheet and magnetic field. We solved also the 2-dimensional magnetohydrodynamic (MHD) equations numerically to study how the magnetic reconnection creates hot plasmas and magnetic islands (helical tubes), and how the magnetic islands confine the hot plasmas in Galaxy. We conclude that the magnetic reconnection is able to heat up the cool component to hot component of GRXE plasma if the magnetic field is localized into intense flux tube with Blocal ~ 30 μG (the volume filling factor of f ~ 0.1).