X-Ray Evidence of an AGN in M82

An X-ray spectrum of the famous starburst galaxy M82 consists of three components: soft, medium, and hard components (Tsuru et al. 1997). The spectrum of the hard component, which is spatially unresolved, is well represented by an absorbed thermal bremsstrahlung, or an absorbed power-law model. However the origin of the hard component was unclear. Thus, we made a monitoring observation with ASCA in 1996. Although the X-ray flux of the soft and medium components remained constant, a significant time variability of the hard component was found between $3\times10^{40}$ erg/s and $1\times10^{41}$ erg/s at various time scales from 10 ks to a month. The temperature or photon index of the hard component also changed. We proved that the spatial position of the hard component is the center of M82. The spectrum of the variable source obtained by subtracting the spectrum of the lowest state from the highest state suggests the strong absorption of $N_{\rm H} \sim 10^{22}$ cm$^2$, which means the variable source is embedded in the center of M82. All these suggest that a low-luminosity AGN exists in M82.Comment: 15pages for text and tables. 13pages for figure

ASCA observations of massive medium-distant clusters of galaxies. II

We have selected seven medium-distant clusters of galaxies (z ~ 0.1 - 0.3) for multi-wavelength observations with the goal of investigating their dynamical state. Following Paper I (Pierre et al. 1999) which reported the ASCA results about two of them, we present here the analysis of the ASCA observations of the other five clusters; RXJ1023.8-2715 (A3444), RXJ1031.6-2607, RXJ1050.5-0236 (A1111), RXJ1203.2-2131(A1451), and RXJ1314.5-2517. Except for RXJ1031.6, whose X-ray emission turned out to be dominated by an AGN, the ASCA spectra are well fitted by a one-temperature thin thermal plasma model. We compare the temperature-luminosity relation of our clusters with that of nearby ones (z<0.1). Two clusters, RXJ1050.5 and RXJ1023.8, show larger luminosities than the bulk of clusters at similar temperatures, which suggests the presence of a cooling flow. The temperature vs. iron-abundance relationship of our sample is consistent with that of nearby clusters.Comment: 9 pages, 20 figures, A&AS in pres

Discovery of the compact X-ray source inside the Cygnus Loop

We detected an X-ray compact source inside the Cygnus Loop during the observation project of the whole Cygnus Loop with the ASCA GIS. The source intensity is 0.11 c s$^{-1}$ for GIS and 0.15 c s$^{-1}$ for SIS, which is the strongest in the ASCA band. The X-ray spectra are well fitted by a power law spectrum of a photon index of \error{-2.1}{0.1} with neutral H column of (\error{3.1}{0.6})${\rm \times 10^{21} cm^{-2}}$. Taking into account the interstellar absorption feature, this source is X-ray bright mainly above 1 keV suggesting either an AGN or a rotating neutron star. So far, we did not detect intensity variation nor coherent pulsation mainly due to the limited observation time. There are several optical bright stellar objects within the error region of the X-ray image. We carried out the optical spectroscopy for the brightest source (V=+12.6) and found it to be a G star. The follow up deep observation both in optical and in X-ray wavelengths are strongly required.Comment: Accepted for Publications of the Astronomical Society of Japan 17 pages, 3 figur

A Chandra View of the Normal SO Galaxy NGC 1332: II: Solar Abundances in the Hot Gas and Implications for SN Enrichment

We present spectral analysis of the diffuse emission in the normal, isolated, moderate-Lx S0 NGC 1332, constraining both the temperature profile and the metal abundances in the ISM. The characteristics of the point source population and the gravitating matter are discussed in two companion papers. The diffuse emission comprises hot gas, with an ~isothermal temperature profile (~0.5 keV), and emission from unresolved point-sources. In contrast with the cool cores of many groups and clusters, we find a small central temperature peak. We obtain emission-weighted abundance contraints within 20 kpc for several key elements: Fe, O, Ne, Mg and Si. The measured iron abundance (Z_Fe=1.1 in solar units; >0.53 at 99% confidence) strongly excludes the very sub-solar values often historically reported for early-type galaxies but agrees with recent observations of brighter galaxies and groups. The abundance ratios, with respect to Fe, of the other elements were also found to be ~solar, although Z_o/Z_Fe was significantly lower (<0.4). Such a low O abundance is not predicted by simple models of ISM enrichment by Type Ia and Type II supernovae, and may indicate a significant contribution from primordial hypernovae. Revisiting Chandra observations of the moderate-Lx, isolated elliptical NGC 720, we obtain similar abundance constraints. Adopting standard SNIa and SNII metal yields, our abundance ratio constraints imply 73+/-5% and 85+/-6% of the Fe enrichment in NGC 1332 and NGC 720, respectively, arises from SNIa. Although these results are sensitive to the considerable systematic uncertainty in the SNe yields, they are in good agreement with observations of more massive systems. These two moderate-Lx early-type galaxies reveal a consistent pattern of metal enrichment from cluster scales to moderate Lx/Lb galaxies. (abridged)Comment: 12 pages, 4 figures, accepted for publication in ApJ. Minor changes to match published versio

Scaling laws of solar and stellar flares

In this study we compile for the first time comprehensive data sets of solar and stellar flare parameters, including flare peak temperatures T_p, flare peak volume emission measures EM_p, and flare durations t_f from both solar and stellar data, as well as flare length scales L from solar data. Key results are that both the solar and stellar data are consistent with a common scaling law of EM_p ~ T_p^4.7, but the stellar flares exhibit ~250 times higher emission measures (at the same flare peak temperature). For solar flares we observe also systematic trends for the flare length scale L(T_p) ~ T_p^0.9 and the flare duration t_F(T_p) ~ T_p^0.9 as a function of the flare peak temperature. Using the theoretical RTV scaling law and the fractal volume scaling observed for solar flares, i.e., V(L) ~ L^2.4, we predict a scaling law of EM_p ~ T_p^4.3, which is consistent with observations, and a scaling law for electron densities in flare loops, n_p ~ T_p^2/L ~ T_p^1.1. The RTV-predicted electron densities were also found to be consistent with densities inferred from total emission measures, n_p=(EM_p/q_V*V)^1/2, using volume filling factors of q_V=0.03-0.08 constrained by fractal dimensions measured in solar flares. Our results affect also the determination of radiative and conductive cooling times, thermal energies, and frequency distributions of solar and stellar flare energies.Comment: 9 Figs., (paper in press, The Astrophsycial Journal

Suzaku Observation of HESS J1825-137: Discovery of Largely-Extended X-rays near from PSR J1826-1334

We observed the brightest part of HESS J1825-137 with the Suzaku XIS, and found diffuse X-rays extending at least up to 15' (~ 17 pc) from the pulsar PSR J1826-1334. The spectra have no emission line, and are fitted with an absorbed power-law model. The X-rays, therefore, are likely due to synchrotron emission from a pulsar wind nebula. The photon index near at the pulsar (r<1.5') is 1.7 while those in r=1.5-16 are nearly constant at Gamma=2.0. The spectral energy distribution of the Suzaku and H.E.S.S. results are naturally explained by a combined process; synchrotron X-rays and gamma-rays by the inverse Compton of the cosmic microwave photons by high-energy electrons in a magnetic field of 7 micro G. If the electrons are accelerated at the pulsar, the electrons must be transported over 17 pc in the synchrotron life time of 1900 yr, with a velocity of > 8.8 times 10^3 km s^{-1}.Comment: 9 pages, 10 figure