The quasar 3C273 was observed from 18th to 21st July 1996 with the Narrow Field Instruments (NFIs) onboard BeppoSAX satellite (Boella et al 1997). The total exposure time was 12 ksec for LECS, 131 ksec for MECS and 64 ksec for HPGSPC and PDS.

We report the results of the search for the change in the warm absorber of the quasar MR 2251-178 with ASCA. We detected its change along with the X-ray intensity change. In the bright phase in 1993, its X-ray spectra showed the absorption edge features by OVII and OVIII edges. In contrast, in the medium intensity (in 1996), the absorption apparently increased and the edge energy was shifted to the lower energy. These results are well explained by the ionization change of the same absorber. The timescale of the change requires moderately high density and the location to be nearer to the center than the Narrow Line Region. We briefly discuss the stability of the warm absorber.

There are several regions where a group of quasars are significantly clustered in the physical space. In the “CFHT grens survey” conducted by Crampton et al. (Crampton et al. 1989 and references therein), the 23 quasars between z=1.036 and 1.185 were found to be clustered over ~ 2° × 2° in the region denoted as 1338+27 At the mean redshift zave = 1.113, the angular extent 6000 arcsec (CHH89) of this cluster corresponds to 60 h−1Mpc(q0 = 0.5) and the dispergion of the redshift λz = 0.044 to 45 h−1Mpc.

The detection by EGRET of gamma-rays from more than 50 active galactic nuclei (AGNs) allowed us to expect these objects to be the sources of extragalactic cosmic rays at very high energy. The TeV gamma-rays from nearby BL Lac objects of the AGNs examined were detected by the Whipple Observatory collaboration. In this paper, we present the results given by the Tibet air shower array on the search for 10 TeV gamma-ray emission from 18 relatively nearby AGNs with redshifts of z < 0.07.

Like many radio-selected blazars, 0716+714 shows a high level of variability on different time scales, as short as a few days (e.g. Wagner et al 1996, Ghisellini et al. 1997). The mechanism of the emission in the optical band, in the general scheme of a relativistic plasma jet highy collimated toward the observer, is generally believed to be synchrotron radiation from electrons in a strong magnetic field. Our monitoring of S5 0716+714 is aimed to clarify whether the flux variations are chromatic or achromatic. In the first case, one could guess that variations in the spectrum of the injected electrons are responsible for the flux variations; in the second case, geometrical effects like small changes in the angle between the jet and the line of sight could be more likely (Wagner et al. 1993).

We present ASCA spectra of low luminosity AGNs with X-ray luminosities of 1040-41 ergs s−1. Their X-ray continua are very similar to Seyfert galaxies. Although iron K emissin centered at 6.4 keV or 6.7 keV is detected from a few objects, iron K emission is weak on average. Possible reasons for variety of iron line properties are discussed.

Fornax A (NGC 1316) is a radio galaxy with prototypical double lobes. Feigelson et al. (1995 ApJ 449, L149) and Kaneda et al. (1995 ApJ 454, L13) detected inverse Compton X-rays for the first time from its radio lobes, and unambiguously derived the lobe magnetic field intensity of 2-4 μG. Accordingly, the radio-emitting electrons in the lobes are inferred to have a Lorentz factor of 104, and hence a synchrotron life time of ~108 yr. This means that Fornax A was highly active at least 108 years ago.

4C46.09 is the radio source that shows up as a point-like x-ray source inside the supernova remnant HB9 (Leahy, 1987). Leahy, 1987 found a 0.2-4 keV Einstein IPC flux of approximately 1.5 × 10−12erg cm−2s−1 and a significantly higher hardness ratio than the rest of HB9. Too few counts were available for any spectral analysis. Seward et al, 1991, found 4C46.09 to be a large radio galaxy at redshift 0.195 and distance 1280 Mpc (Ho = 50 km s−1Mpc−1). 4C46.09 is of further interest due to the observation of a high energy component in the spectrum of HB9 observed by GINGA (Yamauchi and Koyama, 1993). Whether this was due to HB9 or to 4C46.09 could not be determined.

We propose an alternative model for the powering of active galactic nuclei (AGN), based on the assumption that all AGN have experienced mergers. In our model (Kaburaki and Taniguchi 1996; Taniguchi and Kaburaki 1996), a close pair of super-massive black holes (the black hole grazer) orbit one another in a plane roughly perpendicular to the galactic center magnetic field. The orbital motion induces surface charges on the black holes which produce an electric field. This field is strong enough to cause pair creation so that the Roche lobe of the binary system is filled with pair plasmas. Rigid-body rotation of the Roche-lobe magnetosphere drives electrodynamically a powerful synchrotron jet emanating from the center of mass of the binary. Furthermore, a pair of equatorial jets flow from the outer Lagrangian points of the binary system. Although these jets are not so collimated, they interact with the accreting gas ring formed around the orbital plane of the binary, causing broad line regions or H2O maser emission regions (Taniguchi et al. 1996). In addition to the primary jet, two secondary jets are also driven by local accretion disks around the two black holes. The interaction among the primary and the secondary jets may explain detailed jet morphology observed by VLBI facilities.

Aperiodic optical variability is a common property of Active Galactic Nuclei (AGN), though its physical origin is still open to question. We have compared light curves among the following two models and observation of quasar 0957+561A,B (Kundić et al. 1997) in terms of structure function analysis (§2).

It is very important to estimate the relationship between the central blackhole mass MBH and bolometric luminosity Lbol of AGNs, because such a relation may be useful to judge the validity of various models for AGNs (Koratkar & Gaskell 1991, hereafter KG91). The predictions of various models are summerized in Table 1, where B is the magnetic field around the central object.

Active galactic nuclei(AGN) produce many type of active phenomena, powerful X-ray emission, UV hump, narrow beam ejection, gamma-ray emission. Energy of these phenomena is thought to be brought out binding energy between a black hole and surrounding matter. What condition around a black hole produces many type of active phenomena? We investigated dynamical evolution of accretion flow onto a black hole by using a general-relativistic, hydrodynamic code which contains a viscosity based on the alpha-model. We find three types of flow's pattern, depending on thickness of accretion disk. In a case of the thin disk with a thickness less than the radius of the event horizon at the vicinity of a marginally stable orbit, the accreting flow through a surface of the marginally stable orbit becomes thinner due to additional cooling caused by a general-relativistic Roche-lobe overflow and horizontal advection of heat. An accretion disk with a middle thickness, 2rh ≤ h ≤ 3rh, divides into two flows: the upper region of the accreting flow expands into the atmosphere of the black hole, and the inner region of the flow becomes thinner, smoothly accreting onto the black hole. The expansion of the flow generates a dynamically violent structure around the event horizon. The kinetic energy of the violent motion becomes equivalent to the thermal energy of the accreting disk. The shock heating due to violent motion produces a thermally driven wind which flows through the atmosphere above the accretion disk. A very thick disk, 4rh ≤ h, forms a narrow beam whose energy is largely supplied from hot region generated by shock wave. The accretion flowing through the thick disk, h ≥ 2rh, cannot only form a single, laminar flow falling into the black hole, but also produces turbulent-like structure above the event horizon. The middle disk may possibly emit the X-ray radiation observed in active galactic nuclei. The thin disk may produce UV hump of Seyfert galaxy. Thick disk may produce a jet observed in radio galaxy. The thickness of the disk is determined by accretion rate, such as h κ κes/cṁf(r) κ 10rhṁf(r), at the inner region of the disk where the radiation pressure dominates over the gas pressure. Here, Ṁ is the accretion rate and ṁ is the normarized one by the critical-mass flux of the Eddington limit. κes and c are the opacity by electron scattering and the velocity of light. f(r) is a function with a value of unity far from the hole.

We made a search of quiescent X-ray counterparts of two Gamma-Ray Bursts (GRBs), GRB930131 and GRB940217. These GRBs were detected with BATSE, EGRET, COMPTEL on board CGRO together with the GRB detector on Ulysses spacecraft, then they were localized in small error regions. These observations showed that the bursts were remarkably bright accompanying delayed high energy gamma-rays. ASCA observations have found a single X-ray source for each GRB on the possible location determined with the above instruments.

Extensive data bases on Gamma-Ray Burst (GRB) properties such as the BATSE 3B catalog (Meegan et al. 1996) contain a wealth of statistical information. The nine entries of the 3B database for each GRB consist of two durations, T50, T90, which contain 50% and 90% of the burst energy, respectively; four fluences (time-integrated energy fluxes) F1, F2, F3, F4, defined over different energy channels; and three measures of the peak flux (each summed over the four energy channels), measured over three different resolution timescales (64 ms, 256 ms and 1024 ms). Thus the initial number of variables is n = 9. There is, of course, some incompleteness in the catalog. There are 625 GRBs having all 9 non-zero quantities, and only they are considered here.

To reveal the origin of the cosmic X-ray background (CXB) in the hard band, we are now conducting a wide (~ 7 deg2) and deep (~ 1 × 10−13 erg sec−1 cm−2 in the 2-10 keV band) survey with the ASCA (the ASCA Large Sky Survey, hereafter LSS). We have detected 83 sources above 4 sigma level in the 0.7-10 keV band with the GIS and resolved ~30% of the CXB in the 2-10 keV band into discrete sources (Ueda 1996). AGNs (type 1 and type 2) and clusters of galaxies are expected to be major contributers to these X-ray sources.

We are constructing the ASCA GIS source catalog from the ASCA public archive, mainly for extra-galactic sky. The large field of view and the low-background characteristics of the GIS make it suitable for a search for serendipitous sources in a wide energy band of 0.7-10 keV. Sources to be detected by the project will provide valuable information on the log N-log S relation over the entire sensitivity band, which has never been available before. About this project, also refer to Ishisaki et al. (1995), Ueda et al. (1997) and Takahashi et al. (1997). There is the SIS source catalog project, too (Gotthelf et al., 1996). These catalogs are going to appear on the WEB.

ASCA DSS was intended to carry out unbiased surveys in wide energy range of 0.5-10 keV. The strategy of this project is to survey small sky region with extremely high sensitivity reaching to the source confusion limit of ASCA XRT, in contrast to the Large Sky Survey project (Ueda 1996) which covers much larger sky area with relatively shallow exposure.

Since the bulk of the energy density of the Cosmic X-ray Background (CXB) resides in the harder energy band than that of the ROSAT band (0.5-2 keV) and since the X-ray sources identified in the ROSAT band have X-ray spectra softer than that of the CXB, investigation of nature of the X-ray sources at the harder energy band is indispensable to solve the origin of the CXB. However, only 2-3% of the CXB in the hard band (2-10 keV) had been resolved into discrete sources (Piccinotti et al. 1982, ApJ 253, 485). We present our preliminary results of optical follow-up observations of the ASCA Lynx deep survey.

The Rosat All-Sky Survey (Trümper 1991, Adv. Spce Res., 2, 241) has its largest exposure times, approaching 10 ks, at the ecliptic poles where the scan circles overlap. The North Ecliptic Pole (NEP) region covers a 9° X 9° field, and contains a total of 465 X-ray sources detected at > 4σ in the 0.1-2.4 keV. We are identifying all sources in the field. The principal derivative is a statistically complete sample of galaxy clusters appropriate for more fully characterizing X-ray Luminosity Function (XLF) evolution. We report preliminary results for two subregions which are identified to the 95% level. These subregions are observed to approximately the median NEP survey exposure. They enclose 16% of the survey area and contain 96 X-ray sources representing 21% of the total NEP. The typical mix of sources is consistent with the Einstein Extended Medium Sensisitivity Survey (EMSS; Gioia et al., 1990a, ApJS, 72, 567). In particular there are 56% AGN/ELG (59% in the EMSS), 25% stars (27% in the EMSS) and 14% clusters against 13% clusters in the EMSS.