1,883 research outputs found
The 4MOST facility simulator: instrument and science optimisation
This paper describes the design and implementation of a facility simulator
for the 4 metre Multi-Object Spectroscopic Telescope (4MOST) project, a new
survey instrument proposed for the ESO VISTA telescope. The 4MOST Facility
Simulator (4FS) has several roles, firstly to optimise the design of the
instrument, secondly to devise a survey strategy for the wide field design
reference surveys that are proposed for 4MOST, and thirdly to verify that
4MOST, as designed, can indeed achieve its primary science goals. We describe
the overall structure of the 4FS, together with details of some important 4FS
subsystems. We present the initial results from the 4FS which illustrate
clearly the value of having a functioning facility simulator very early in the
conceptual design phase of this large project.Comment: 7 pages, 7 figures, 1 tabl
The Largest Blueshifts of [O III] emission line in Two Narrow-Line Quasars
We have obtained optical intermediate resolution spectra (R = 3000) of the
narrow-line quasars DMS 0059-0055 and PG 1543+489. The [O III] emission line in
DMS 0059-0055 is blueshifted by 880 km/s relative to Hbeta. We also confirm
that the [O III] emission line in PG 1543+489 has a relative blueshift of 1150
km/s. These two narrow-line quasars show the largest [O III] blueshifts known
to date among type 1 active galactic nuclei (AGNs). The [O III] emission lines
in both objects are broad (1000 - 2000 km/s) and those in DMS 0059-0055 show
strong blue asymmetry. We interpret the large blueshift and the profile of the
[O III] lines as the result of an outflow interacting with circumnuclear gas.
Among type 1 AGNs with large blueshifted [O III], there is no correlation
between the Eddington ratios and the amount of [O III] blueshifts. Combining
our new data with published results, we confirm that the Eddington ratios of
the such AGNs are the highest among AGNs with the same black hole masses. These
facts suggest that the Eddington ratio is a necessary condition or the [O III]
blueshifts weakly depend on the Eddington ratio. Our new sample suggests that
there are possible necessary conditions to produce an outflow besides a high
Eddington ratio: large black hole mass (> 10^7 M_solar) or high mass accretion
rate (> 2 M_solar/yr) or large luminosity (lambda L_{lambda} (5100A) > 10^44.6
erg/s).Comment: Accepted for publication in The Astrophysical Journa
A direct view of the AGN powering IRAS12393+3520
We report the first direct X-ray evidence that an AGN is hidden in the center
of IRAS12393+3520. An ASCA observation of this target unveiled a bright (0.5-10
keV luminosity 3.9 x 10^42 erg/s) and variable source, with minimum observed
doubling/halving time scale comprised in the range 30-75 ks. A model composed
by a simple power-law, with photon index ~1.8 and an absorption edge, whose
threshold energy is consistent with K-shell photoionization of OVII, provides
an adequate fit of the spectrum. This suggests that we are observing the
emission from the nuclear region through a warm absorber of N_H a few
10^{21}/cm/cm. If it has internal dust with Galactic gas-to-dust ratio, it
could explain the lack of broad Hbeta emission, even in the episodic presence
of a broad Halpha emission line. Optical spectra obtained over several years
show indeed variations in the strength of this broad Halpha component. A
distribution of dusty, optically thick matter on spatial scales a few hundreds
parsec, which does not intercept the line of sight towards the nucleus, is
probably required to account simultaneously for the relative [OIII] luminosity
deficit in comparison to the X-rays. The high IR to X-ray luminosity ratio is
most likely due to intense star formation in the circumnuclear region.
IRAS12393+3520 might thus exhibit simultaneously nuclear activity and
remarkable star formation.Comment: 9 Latex pages, 8 figures, Accepted for publication in Astronomy &
Astrophysic
Ray-tracing in pseudo-complex General Relativity
Motivated by possible observations of the black hole candidate in the center
of our galaxy and the galaxy M87, ray-tracing methods are applied to both
standard General Relativity (GR) and a recently proposed extension, the
pseudo-complex General Relativity (pc-GR). The correction terms due to the
investigated pc-GR model lead to slower orbital motions close to massive
objects. Also the concept of an innermost stable circular orbit (ISCO) is
modified for the pc-GR model, allowing particles to get closer to the central
object for most values of the spin parameter than in GR. Thus, the
accretion disk, surrounding a massive object, is brighter in pc-GR than in GR.
Iron K emission line profiles are also calculated as those are good
observables for regions of strong gravity. Differences between the two theories
are pointed out.Comment: revised versio
X-ray Spectral Variability and Rapid Variability of the Soft X-ray Spectrum Seyfert 1 Galaxies Ark 564 and Ton S180
The bright, soft X-ray spectrum Seyfert 1 galaxies Ark 564 and Ton S180 were
monitored for 35 days and 12 days with ASCA and RXTE (and EUVE for Ton S180).
The short time scale (hours-days) variability patterns were very similar across
energy bands, with no evidence of lags between any of the energy bands studied.
The fractional variability amplitude was almost independent of energy band. It
is difficult to simultaneously explain soft Seyferts stronger variability,
softer spectra, and weaker energy-dependence of the variability relative to
hard Seyferts. The soft and hard band light curves diverged on the longest time
scales probed, consistent with the fluctuation power density spectra that
showed relatively greater power on long time scales in the softest bands. The
simplest explanation is that a relatively hard, rapidly-variable component
dominates the total X-ray spectrum and a slowly-variable soft excess is present
in the lowest energy channels of ASCA. Although it would be natural to identify
the latter with an accretion disk and the former with a corona surrounding it,
a standard thin disk could not get hot enough to radiate significantly in the
ASCA band, and the observed variability time scales are much too short. The
hard component may have a more complex shape than a pure power-law. The most
rapid factor of 2 flares and dips occurred within ~1000 sec in Ark 564 and a
bit more slowly in Ton S180. The speed of the luminosity changes rules out
viscous or thermal processes and limits the size of the individual emission
regions to <~15 Schwarzschild radii (and probably much less), that is, to
either the inner disk or small regions in a corona
ROSAT PSPC detection of soft X-ray absorption in GB 1428+4217: The most distant matter yet probed with X-ray spectroscopy
We report on a ROSAT PSPC observation of the highly-luminous z = 4.72
radio-loud quasar GB 1428+4217 obtained between 1998 December 11 and 17, the
final days of the ROSAT satellite. The low-energy sensitivity of the PSPC
detector was employed to constrain the intrinsic X-ray absorption of the
currently most distant X-ray detected object. Here we present the detection of
significant soft X-ray absorption towards GB 1428+4217, making the absorbing
material the most distant matter yet probed with X-ray spectroscopy. X-ray
variability by 25+-8 per cent is detected on a timescale of 6500 s in the rest
frame. The X-ray variation requires an unusually high radiative efficiency of
at least 4.2, further supporting the blazar nature of the source.Comment: 6 pages incl. 6 figures, accepted for publication in Monthly Notice
Spectropolarimetry of the Luminous Narrow-Line Seyfert Galaxies IRAS 20181-2244 and IRAS 13224-3809
We observed the narrow-line Seyfert 1 galaxies IRAS 20181-2244 and IRAS
13324-3809 with a new spectropolarimeter on the RC spectrograph at the CTIO 4m
telescope. Previously it had been suggested that IRAS 20181-2244 was a Type 2
QSO and thus might contain an obscured broad-line region which could be
detected by the presence of broad Balmer lines in the polarized flux. We found
the object to be polarized at about 2%, and constant with wavelength, (unlike
most narrow-line Seyfert 1s), but with no evidence of broad Balmer lines in
polarized flux. The spectropolarimetry indicates that the scattering material
is inside the BLR. IRAS 13224-3809, notable for its high variability in X-ray
and UV wavelengths, has a low polarization consistent with a Galactic
interstellar origin.Comment: 19 pages using (AASTEX) aaspp4.sty and 5 postscript figures To be
published in the Astrophysical Journa
Soft X-ray properties of a spectroscopically selected sample of interacting and isolated Seyfert galaxies
We present a catalogue of ROSAT detected sources in the sample of spectroscopically selected Seyfert 1 and Seyfert 2 galaxies of Rafanelli et al. (1995). The catalogue contains 102 Seyfert 1 and 36 Seyfert 2 galaxies. The identification is based on X-ray contour maps overlaid on optical images taken from the Digitized Sky Survey. We have derived the basic spectral and timing properties of the X-ray detected Seyfert galaxies. For Seyfert 1 galaxies a strong correlation between photon index and X-ray luminosity is detected. We confirm the presence of generally steeper X-ray continua in narrow-line Seyfert 1 galaxies (NLS1s) compared to broad-line Seyfert 1 galaxies. Seyfert 2 galaxies show photon indices similar to those of NLS1s. Whereas a tendency for an increasing X-ray luminosity with increasing interaction strength is found for Seyfert 1 galaxies, such a correlation is not found for Seyfert 2 galaxies. For Seyfert 1 galaxies we found also a strong correlation for increasing far-infrared luminosity with increasing interaction strength. Both NLS1s and Seyfert 2 galaxies show the highest values of far-infrared luminosity compared to Seyfert 1 galaxies, suggesting that NLS1s and Seyfert 2 galaxies host strong (cirumnuclear) starformation. For variable Seyfert galaxies we present the X-ray light curves obtained from the ROSAT All-Sky Survey and from ROSAT PSPC and HRI pointed observations. Besides the expected strong short- and long-term X-ray variability in Seyfert 1 galaxies, we find indications for X-ray flux variations in Seyfert 2 galaxies
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