2,310 research outputs found
X-ray Emission from the Type Ic Supernova 1994I Observed with Chandra
We present two high-resolution Chandra X-ray observations of supernova (SN)
1994I which show, for the first time, that the interaction of the blast wave
from a Type Ic SN with its surrounding circumstellar material (CSM) can give
rise to soft X-ray emission. Given a 0.3-2 keV band X-ray luminosity of L_x ~ 1
x 10^{37} ergs/s between six and seven years after the outburst of SN 1994I,
and assuming the X-ray emission arises from the shock-heated CSM, we derive a
pre-SN mass-loss rate of \dot{M} ~ 1 x 10^{-5} M_sun/yr (v_w/10 km/s).
Combining the results with earlier ROSAT observations, we construct the X-ray
lightcurve of SN 1994I. A best-fit X-ray rate of decline of L_x \propto t^{-s}
with index s~1 and a CSM density profile of rho_csm \propto r^{-1.9\pm0.1} are
inferred, consistent with what is expected for a constant mass-loss rate and
constant wind velocity profile for the SN progenitor (rho_csm \propto r^{-2}).Comment: 5 pages, 3 figures, accepted for publication in the Astrophysical
Journal Letter
Radiatively Inefficient Accretion Flow in the Nucleus of NGC 1097
We present a model for the accretion flow around the supermassive black hole
in the LINER nucleus of NGC 1097 which fits the optical to X-ray spectral
energy distribution (SED). The X-ray segment of the SED is based on
observations with the Chandra X-Ray Observatory, which are reported here for
the first time. The inner part of the flow is modeled as a radiatively
inefficient accretion flow (RIAF) and the outer part as a standard thin disk.
The value of the transition radius (~225 Schwarzschild radii) between the RIAF
and outer thin disk was obtained from our previous fitting of the double-peaked
Balmer emission line profile, which originates in the thin disk. The black hole
mass was inferred from measurements of the stellar velocity dispersion in the
host galaxy. When these parameters are used in the accretion flow model, the
SED can be successfully reproduced, which shows that the line profile model and
the accretion flow model are consistent with each other. A small remaining
excess in the near-UV is accounted by the contribution of an obscured starburst
located within 9 pc from the nucleus, as we reported in an earlier paper. The
radio flux is consistent with synchrotron emission of a relativistic jet
modeled by means of the internal shock scenario. In an appendix we also analyze
the Chandra X-ray observations of the ~1 kpc circumnuclear star-forming ring
and of an ultraluminous compact X-ray source located outside the ring.Comment: 10 pages and 6 figures formatted with emulateapj, accepted for
publication in Ap
Fluorescent C II* 1335A emission spectroscopically resolved in a galaxy at z = 5.754
We report the discovery of the first spectroscopically resolved C II /C II*
1334, 1335A doublet in the Lyman-break galaxy J0215-0555 at z = 5.754. The
separation of the resonant and fluorescent emission channels was possible
thanks to the large redshift of the source and long integration time, as well
as the small velocity width of the feature, 0.6 +- 0.2A. We model this emission
and find that at least two components are required to reproduce the combination
of morphologies of C II* emission, C II absorption and emission, and
Lyman-alpha emission from the object. We suggest that the close alignment
between the fluorescence and Lyman-alpha emission could indicate an ionisation
escape channel within the object. While the faintness of such a C II /C II*
doublet makes it prohibitively difficult to pursue for similar systems with
current facilities, we suggest it can become a valuable porosity diagnostic in
the era of JWST and the upcoming generations of ELTs.Comment: 5 pages, 3 figures; accepted for publication in MNRAS Letter
Hard X-Ray Spectrum from West Lobe of Radio Galaxy Fornax A Observed with Suzaku
An observation of the West lobe of radio galaxy Fornax A (NGC 1316) with
Suzaku is reported. Since Feigelson et al. (1995) and Kaneda et al. (1995)
discovered the cosmic microwave background boosted inverse-Comptonized (IC)
X-rays from the radio lobe, the magnetic field and electron energy density in
the lobes have been estimated under the assumption that a single component of
the relativistic electrons generates both the IC X-rays and the synchrotron
radio emission. However, electrons generating the observed IC X-rays in the 1
-- 10 keV band do not possess sufficient energy to radiate the observed
synchrotron radio emission under the estimated magnetic field of a few micro-G.
On the basis of observations made with Suzaku, we show in the present paper
that a 0.7 -- 20 keV spectrum is well described by a single power-law model
with an energy index of 0.68 and a flux density of 0.12+/-0.01 micro-Jy at 1
keV from the West lobe. The derived multiwavelength spectrum strongly suggests
that a single electron energy distribution over a Lorentz factor gamma = 300 -
90000 is responsible for generating both the X-ray and radio emissions. The
derived physical quantities are not only consistent with those reported for the
West lobe, but are also in very good agreement with those reported for the East
lobe.Comment: 8 pages, 6 figures; accepted for publication in PASJ (Publications of
the Astronomical Society of Japan) Suzaku 3rd special issue: TYPOS in flux
density unit were correcte
A Chandra Observation of M51: Active Nucleus and Nuclear Outflows
We present a Chandra ACIS-S observation of the nuclear region of the nearby
spiral galaxy M51 (NGC 5194), which has a low-luminosity Seyfert 2 nucleus. The
X-ray image shows the nucleus, southern extranuclear cloud, and northern loop,
the morphology of the extended emission being very similar to those seen in
radio continuum and optical emission line images. The X-ray spectrum of the
nucleus is well represented by a model consisting of soft thermal plasma with
kT ~0.5 keV, a very hard continuum, and an Fe Kalpha emission line at 6.45 keV
with an equivalent width of >2 keV. The very strong Fe line and the flat
continuum indicate that the nucleus is obscured by a column density in excess
of 10^24 cm^-2 and the spectrum is dominated by reflected emission from cold
matter near the nucleus. The X-ray spectra of the extranuclear clouds are well
fitted by a thermal plasma model with kT ~0.5 keV. This spectral shape and
morphology strongly suggest that the clouds are shock heated by the bi-polar
outflow from the nucleus. The shock velocities of the extranuclear cloud and
northern loop inferred from the temperatures of the X-ray gas are 690 km/s and
660 km/s, respectively. By assuming a steady-state situation in which the
emission of the extranuclear clouds is powered by the jets, the mechanical
energy in the jets is found to be comparable to the bolometric luminosity of
the nucleus.Comment: 7 pages, 5 figures, Accepted for publication in the Astrophyscal
Jouna
Suzaku Observations of Local Ultraluminous Infrared Galaxies
We report the results from our analysis of {\it Suzaku} XIS (0.5-10 keV) and
HXD/PIN (15-40 keV) observations of five well-known local ULIRGs: {\em IRAS}
F05189-2524, {\em IRAS} F08572+3915, Mrk 273, PKS 1345+12, and Arp 220. The XIS
observations of F05189-2524 and Mrk 273 reveal strong iron lines consistent
with Fe K and changes in spectral shapes with respect to previous {\it
Chandra} and {\it XMM-Newton} observations. Mrk 273 is also detected by the
HXD/PIN at 1.8-. For F05189-2524, modeling of the data from the
different epochs suggests that the change in spectral shape is likely due to
the central source switching off, leaving behind a residual reflection
spectrum, or an increase in the absorbing column. An increase in the covering
fraction of the absorber can describe the spectral variations seen in Mrk 273,
although a reduction in the intrinsic AGN luminosity cannot be formally ruled
out. The {\it Suzaku} spectra of Mrk 273 are well fit by a ~94% covering
fraction model with a column density of cm. The
absorption-corrected log[ / ] ratio is consistent
with those found in PG Quasars. The 0.5-10 keV spectrum of PKS 1345+12 and Arp
220 seem unchanged from previous observations and their hard X-ray emission is
not convincingly detected by the HXD/PIN. The large column density derived from
CO observations and the large equivalent width of an ionized Fe line in Arp 220
can be reconciled by an ionized reflection model. F08572+3915 is undetected in
both the XIS and HXD/PIN, but the analysis of unpublished {\em Chandra} data
provides a new measurement at low energies.Comment: 37 pages including 4 tables and 10 figures. Accepted for publication
in ApJ. It is tentatively scheduled to appear in the January 20, 2009 issue
of Ap
The Mean Absorption Line Spectra of a Selection of Luminous z~6 Lyman Break Galaxies
We examine the absorption line spectra of a sample of 31 luminous (M_UV=-23)
Lyman break galaxies at redshift z~6 using data taken with the FOCAS and OSIRIS
spectrographs on the Subaru and GTC telescopes. For two of these sources we
present longer exposure data taken at higher spectral resolution from ESO's
X-shooter spectrograph. Using these data, we demonstrate the practicality of
stacking our lower resolution data to measure the depth of various interstellar
and stellar absorption lines to probe the covering fraction of low ionization
gas and the gas-phase and stellar metallicities near the end of the era of
cosmic reionization. From maximum absorption line depths of SiII1260 and
CII1334, we infer a mean covering fraction of >0.85+/-0.16 for our sample. This
is larger than that determined using similar methods for lower luminosity
galaxies at slightly lower redshifts, suggesting that the most luminous
galaxies appear to have a lower escape fraction than fainter galaxies, and
therefore may not play a prominent role in concluding reionization. Using
various interstellar absorption lines we deduce gas-phase metallicities close
to solar indicative of substantial early enrichment. Using selected stellar
absorption lines, we model our spectra with a range of metallicities using
techniques successfully employed at lower redshift and deduce a stellar
metallicity of 0.4 +0.3/-0.1 solar, consistent with the stellar mass - stellar
metallicity relation recently found at z~3-5. We discuss the implications of
these metallicity estimates for the typical ages of our luminous galaxies and
conclude our results imply initial star formation at redshifts z~10, consistent
with independent analyses of earlier objects.Comment: 13 pages, 10 figures, 3 tables, Accepted for Publication in Ap
- …