1,771 research outputs found
The nature of the fluorescent iron line in V 1486 Ori
The fluorescent 6.4 keV iron line provides information on cool material in
the vicinity of hard X-ray sources as well as on the characteristics of the
X-ray sources themselves. First discovered in the X-ray spectra of the flaring
Sun, X-ray binaries and active galactic nuclei (AGN), the fluorescent line was
also observed in a number of stellar X-ray sources. The young stellar object
(YSO) V1486 Ori was observed in the framework of the Chandra Ultra Deep Project
(COUP) as the source COUP 331. We investigate its spectrum, with emphasis on
the strength and time variability of the fluorescent iron K-alpha line, derive
and analyze the light curve of COUP 331 and proceed with a time-resolved
spectral analysis of the observation. The light curve of V 1486 Ori shows two
major flares, the first one lasting for (approx) 20 ks with a peak X-ray
luminosity of 2.6*10^{32} erg/s (dereddened in the 1-10 keV band) and the
second one -- only partially observed -- for >60 ks with an average X-ray
luminosity of 2.4*10^{31} erg/s (dereddened). The spectrum of the first flare
is very well described by an absorbed thermal model at high temperature, with a
pronounced 6.7 keV iron line complex, but without any fluorescent K-alpha line.
The X-ray spectrum of the second flare is characterized by even higher
temperatures (>= 10 keV) without any detectable 6.7 keV Fe XXV feature, but
with a very strong fluorescent iron K-alpha line appearing predominantly in the
20 ks rise phase of the flare. Preliminary model calculations indicate that
photoionization is unlikely to account for the entire fluorescent emission
during the rise phase.Comment: 4 pages, letter, accepted for publication in A&
A Radio Perspective on the Wet Merger Remnant NGC 34
We present VLA observations of the neutral hydrogen and radio continuum of
NGC 34 (= NGC 17 = Mrk 938). This object is an ideal candidate to study the
fate of gas in mergers, since, as shown by an optical study done by Schweizer &
Seitzer (2007), it is a gas-rich ("wet") merger remnant of two disk galaxies of
unequal mass hosting a strong central starburst and a weak AGN. We detect HI
emission from both tidal tails and from nearby galaxies, suggesting that NGC 34
is actually part of a gas-rich group and might have recently interacted with
one of its companions. The kinematics of the gas suggests this remnant is
forming an outer disk of neutral hydrogen from the gas of the northern tail. We
also detect broad HI absorption (514 +/- 21 km/s wide) at both negative and
positive velocities with respect to the systemic velocity. This absorption
could be explained by the motions of the tidal tails or by the presence of a
circumnuclear disk. In addition, we present radio-continuum images that show
both nuclear (62.4 +/- 0.3 mJy) and extra-nuclear emission (26.5 +/- 3.0 mJy).
The extra-nuclear component is very diffuse and in the shape of two radio
lobes, spanning 390 kpc overall. This emission could be a signature of an AGN
that has turned off, or it could originate from a starburst-driven superwind.
We discuss the possible scenarios that explain our observations, and what they
tell us about the location of the gas and the future evolution of NGC 34.Comment: 29 pages, 12 figures, 2 tables. Accepted for publication in the
Astronomical Journal. Figs. 1, 2 & 6 degraded to reduce file size
Subaru Spectroscopy and Spectral Modeling of Cygnus A
We present high angular resolution (0.5) MIR spectra
of the powerful radio galaxy, Cygnus A, obtained with the Subaru telescope. The
overall shape of the spectra agree with previous high angular resolution MIR
observations, as well as previous Spitzer spectra. Our spectra, both on and off
nucleus, show a deep silicate absorption feature. The absorption feature can be
modeled with a blackbody obscured by cold dust or a clumpy torus. The deep
silicate feature is best fit by a simple model of a screened blackbody,
suggesting foreground absorption plays a significant, if not dominant role, in
shaping the spectrum of Cygnus A. This foreground absorption prevents a clear
view of the central engine and surrounding torus, making it difficult to
quantify the extent the torus attributes to the obscuration of the central
engine, but does not eliminate the need for a torus in Cygnus A
Infrared 3-4 Micron Spectroscopic Investigations of a Large Sample of Nearby Ultraluminous Infrared Galaxies
We present infrared L-band (3-4 micron) nuclear spectra of a large sample of
nearby ultraluminous infrared galaxies (ULIRGs).ULIRGs classified optically as
non-Seyferts (LINERs, HII-regions, and unclassified) are our main targets.
Using the 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission and
absorption features at 3.1 micron due to ice-covered dust and at 3.4 micron
produced by bare carbonaceous dust, we search for signatures of powerful active
galactic nuclei (AGNs) deeply buried along virtually all lines-of-sight. The
3.3 micron PAH emission, the signatures of starbursts, is detected in all but
two non-Seyfert ULIRGs, but the estimated starburst magnitudes can account for
only a small fraction of the infrared luminosities. Three LINER ULIRGs show
spectra typical of almost pure buried AGNs, namely, strong absorption features
with very small equivalent-width PAH emission. Besides these three sources, 14
LINER and 3 HII ULIRGs' nuclei show strong absorption features whose absolute
optical depths suggest an energy source more centrally concentrated than the
surrounding dust, such as a buried AGN. In total, 17 out of 27 (63%) LINER and
3 out of 13 (23%) HII ULIRGs' nuclei show some degree of evidence for powerful
buried AGNs, suggesting that powerful buried AGNs may be more common in LINER
ULIRGs than in HII ULIRGs. The evidence of AGNs is found in non-Seyfert ULIRGs
with both warm and cool far-infrared colors. These spectra are compared with
those of 15 ULIRGs' nuclei with optical Seyfert signatures taken for
comparison.The overall spectral properties suggest that the total amount of
dust around buried AGNs in non-Seyfert ULIRGs is systematically larger than
that around AGNs in Seyfert 2 ULIRGs.Comment: 56 pages, 9 figures, accepted for publication in ApJ (20 January
2006, vol 637 issue
The structure of the Au(111)/methylthiolate interface : new insights from near-edge X-ray absorption spectroscopy and X-ray standing waves
The local structure of the Au(111)([square root of]3×[square root of]3)R30°-methylthiolate surface phase has been investigated by S K-edge near-edge s-ray absorption fine structure (NEXAFS) both experimentally and theoretically and by experimental normal-incidence x-ray standing waves (NIXSW) at both the C and S atomic sites. NEXAFS shows not only excitation into the intramolecular sigma* S–C resonance but also into a sigma* S–Au orbital perpendicular to the surface, clearly identifying the local S headgroup site as atop a Au atom. Simulations show that it is not possible, however, to distinguish between the two possible adatom reconstruction models; a single thiolate species atop a hollow-site Au adatom or a dithiolate moiety comprising two thiolate species bonded to a bridge-bonded Au adatom. Within this dithiolate moiety a second sigma* S–Au orbital that lies near parallel to the surface has a higher energy that overlaps that of the sigma* S–C resonance. The new NIXSW data show the S–C bond to be tilted by 61° relative to the surface normal, with a preferred azimuthal orientation in , corresponding to the intermolecular nearest-neighbor directions. This azimuthal orientation is consistent with the thiolate being atop a hollow-site Au adatom, but not consistent with the originally proposed Au-adatom-dithiolate moiety. However, internal conformational changes within this species could, perhaps, render this model also consistent with the experimental data
Energy Diagnoses of Nine Infrared Luminous Galaxies Based on 3--4 Micron Spectra
The energy sources of nine infrared luminous galaxies (IRLGs) are diagnosed
based on their ground-based 3--4 m spectra. Both the equivalent width of
the 3.3 m polycyclic aromatic hydrocarbon (PAH) emission feature and the
3.3 m PAH to far-infrared luminosity ratio () are
analyzed. Assuming nuclear compact starburst activity in these sources produces
the 3.3 m PAH emission as strongly as that in starburst galaxies with
lower far-infrared luminosities, the followings results are found: For six
IRLGs, both the observed equivalent widths and the ratios
are too small to explain the bulk of their far-infrared luminosities by compact
starburst activity, indicating that active galactic nucleus (AGN) activity is a
dominant energy source. For the other three IRLGs, while the 3.3 m PAH
equivalent widths are within the range of starburst galaxies, the
ratios after correction for screen dust extinction are a
factor of 3 smaller. The uncertainty in the dust extinction correction
factor and in the scatter of the intrinsic ratios for
starburst galaxies do not allow a determination of the ultimate energy sources
for these three IRLGs.Comment: 29 pages, 2 figures, Accepted for publication in Ap
Sub-arcsecond CO(1-0) and CO(2-1) observations of the ultraluminous infrared galaxy IRAS 10190+1322
We present the results of high resolution mapping of the CO(1-0) and CO(2-1)
emission of the ultraluminous infrared galaxy (ULIRG) IRAS 10190+1322, with the
IRAM interferometer, down to an angular resolution of ~0.3 arcsec. This object
is composed of two interacting galaxies with a projected nuclear separation of
6 kpc, and was selected to analyze the physical and dynamical properties of the
molecular gas in each galaxy in order to study the conditions that lead a
galaxy pair to become ultraluminous in the infrared. With the exception of Arp
220, the closest ULIRG, this is the first time that the CO emission is
morphologically and kinematically resolved in the two interacting galaxies of a
ULIRG system. In one of the galaxies the molecular gas is highly concentrated,
distributed in a circumnuclear disk of 1.7 kpc in size. The molecular gas in
the presumably less infrared luminous galaxy is distributed in a more extended
disk of 7.4 kpc. The molecular gas mass accounts for ~10% of the dynamical mass
in each galaxy. Both objects are rich enough in molecular gas, Mgas ~ 4 10^9
Msun, as to experience an infrared ultraluminous phase.Comment: 4 pages, 3 figures. Accepted for publication in A&A Letters Special
Issue for the new extended configuration of the Plateau de Bure
Interferomete
Higher order effects in the and transfer reactions
Full Coupled Channels Calculations were performed for the
and transfer reactions at several deuteron incident
energies from MeV up to 3.27 MeV. A strong polarization effect
between the entrance channel and the transfer channels
and was
observed. This polarization effect had to be taken into account in order to
obtain realistic spectroscopic factors from these reactions.Comment: 15 papes, 13 figures, accepted for publication in Phys. Rev.
- …