197 research outputs found
Multiwavelength campaign on Mrk 509. VI. HST/COS observations of the far-ultraviolet spectrum
We present medium resolution (R~20,000) HST/COS ultraviolet spectra covering
1155-1760 A of the Seyfert 1 Mrk 509 obtained simultaneously with a
Chandra/LETGS spectrum as part of a multiwavelength campaign in 2009 that
included observations with XMM-Newton, SWIFT, and Integral. Our high S/N
spectrum detects additional complexity in the absorption troughs from a variety
of sources in Mrk 509, including the outflow from the active nucleus, the ISM
and halo of the host galaxy, and infalling clouds or stripped gas from a merger
that are illuminated by the AGN. Variability between the STIS and COS
observation of the -400 km/s component allows us to set an upper limit on its
distance of < 250 pc. Similarly, variability of a component at +150 km/s
between two prior FUSE observations limits its distance to < 1.5 kpc. The UV
absorption only partially covers the emission from the AGN nucleus. Covering
fractions are lower than those previously seen with STIS, and are comparable to
those seen with FUSE. Given the larger apertures of COS and FUSE compared to
STIS, we favor scattered light from an extended region near the AGN as the
explanation for the partial covering. As observed in prior X-ray and UV
spectra, the UV absorption has velocities comparable to the X-ray absorption,
but the bulk of the ultraviolet absorption is in a lower ionization state with
lower total column density than the gas responsible for the X-ray absorption.
We conclude that the outflow from the active nucleus is a multiphase wind.Comment: 21 pages, 9 figures. Accepted for publication in Astronomy &
Astrophysics, 26 May 201
The filter wheel and filters development for the X-IFU instruments onboard Athena
Athena is the large mission selected by ESA in 2013 to investigate the science theme "Hot and Energetic Universe" and presently scheduled for launch in 2028. One of the two instruments located at the focus of the 12 m-long Athena telescope is the X-ray Integral Field Unit (X-IFU). This is an array of TES microcalorimeters that will be operated at temperatures of 50 mK in order to perform high resolution spectroscopy with an energy resolution down to 2.5 eV at energies < 7 keV. In order to cope with the large dynamical range of X-ray fluxes spanned by the celestial objects Athena will be observing, the X-IFU will be equipped with a filter wheel. This will allow the user to fine tune the instrument set-up based on the nature of the target, thus optimizing the scientific outcomes of the observation. A few positions of the filter wheel will also be used to host a calibration source and to allow the measurement of the instrument intrinsic background
ROSAT PSPC spectra of X-ray selected Narrow Emission Line Galaxies
We analyse the ROSAT PSPC spectrum of 19 X-ray selected Narrow Emission Line
Galaxies (NELGs) discovered during the optical identification of sources in the
ROSAT UK Deep Survey. Their properties are compared to those of broad line
Active Galactic Nuclei (AGN) in the same sample. Counts in three spectral bands
have been extracted for all the sources, and have been fitted with a power-law
model assuming the Galactic value for NH. The average slope of NELGs is
\alpha=0.45+-0.09, whilst for the AGN it is \alpha=0.96+-0.03. The power-law
model is a good fit for ~90% of NELGs and ~75% of AGN. Recent work shows that
the fractional surface density of NELGs increases with respect to AGN at faint
fluxes. Thus they are expected to be an important component of the residual
soft (<2 keV) X--ray background. The slope of the X--ray background
(\alpha~0.4, 1-10 keV) is harder than that of AGN (\alpha~1) but our results
show that it is consistent with the summed spectrum of the NELGs in the deep
survey (\alpha~0.4). This may finally reconcile the spectrum of the background
with the properties of the sources that constitute it.Comment: Uuencoded compressed LaTex file and three PS figures plus mn.sty.
Accepted in MNRA
Optical Multicolor WBVR-Observations of the X-Ray Star V1341 Cyg = Cyg X-2 in 1986-1992
We present the results of observations of the low-mass X-ray binary
V1341 X--2. Our observations include a total of
2375 individual measurements in four bands on 478 nights in 1986-1992. We tied
the comparison and check stars used for the binary to the catalog using
their magnitudes. The uncertainty of this procedure was 3 in the
and bands and 8%-10% for the and bands. In quiescence, the
amplitude of the periodic component in the binary's brightness variations
is within ( in ); this is due
to the ellipsoidal shape of the optical component, which is distorted with
gravitational forces from the X-ray component. Some of the system's active
states (long flares) may be due to instabilities in the accretion disk, and
possibly to instabilities of gas flows and other accretion structures. The
binary possesses a low-luminosity accretion disk. The light curves reveal no
indications of an eclipse near the phases of the upper and lower conjunctions
in quiescence or in active states during the observed intervals. We conclude
that the optical star in the close binary V1341
X-2 is a red giant rather than a blue straggler. We studied the long-term
variability of the binary during the seven years covered by our observations.
The optical observations presented in this study are compared to X-ray data
from the Ginga observatory for the same time intervals.Comment: 35 pages, 8 figure
Anatomy of the AGN in NGC 5548: I. A global model for the broadband spectral energy distribution
An extensive multi-satellite campaign on NGC 5548 has revealed this
archetypal Seyfert-1 galaxy to be in an exceptional state of persistent heavy
absorption. Our observations taken in 2013-2014 with XMM-Newton, Swift, NuSTAR,
INTEGRAL, Chandra, HST and two ground-based observatories have together enabled
us to establish that this unexpected phenomenon is caused by an outflowing
stream of weakly ionised gas (called the obscurer), extending from the vicinity
of the accretion disk to the broad-line region. In this work we present the
details of our campaign and the data obtained by all the observatories. We
determine the spectral energy distribution of NGC 5548 from near-infrared to
hard X-rays by establishing the contribution of various emission and absorption
processes taking place along our line of sight towards the central engine. We
thus uncover the intrinsic emission and produce a broadband continuum model for
both obscured (average summer 2013 data) and unobscured ( 2011) epochs of
NGC 5548. Our results suggest that the intrinsic NIR/optical/UV continuum is a
single Comptonised component with its higher energy tail creating the 'soft
X-ray excess'. This component is compatible with emission from a warm,
optically-thick corona as part of the inner accretion disk. We then investigate
the effects of the continuum on the ionisation balance and thermal stability of
photoionised gas for unobscured and obscured epochs.Comment: Accepted for publication in A&A, 19 pages, 13 figure
X-rays Studies of the Solar System
X-ray observatories contribute fundamental advances in Solar System studies
by probing Sun-object interactions, developing planet and satellite surface
composition maps, probing global magnetospheric dynamics, and tracking
astrochemical reactions. Despite these crucial results, the technological
limitations of current X-ray instruments hinder the overall scope and impact
for broader scientific application of X-ray observations both now and in the
coming decade. Implementation of modern advances in X-ray optics will provide
improvements in effective area, spatial resolution, and spectral resolution for
future instruments. These improvements will usher in a truly transformative era
of Solar System science through the study of X-ray emission.Comment: White paper submitted to Astro2020, the Astronomy and Astrophysics
Decadal Surve
Evening choruses in the Perth Canyon and their potential link with Myctophidae fishes
An evening chorus centered at near 2.2 kHz was detected across the years 2000 to 2014 from seabed receivers in 430-490 m depth overlooking the Perth Canyon, Western Australia. The chorus reached a maximum level typically 2.1 h post-sunset and normally ran for 2.1 h (between 3 dB down points). It was present at lower levels across most of the hours of darkness. Maximum chorus spectrum levels were 74-76 dB re 1 µPa2/Hz in the 2 kHz 1/3 octave band, averaging 6-12 dB and up to 30 dB greater than pre-sunset levels. The chorus displayed highest levels over April to August each year with up to 10 dB differences between seasons. The spatial extent of the chorus was not determined but exceeded the sampling range of 13-15 km offshore from the 300 m depth contour and 33 km along the 300 m depth contour. The chorus comprised short damped pulses. The most likely chorus source is considered to be fishes of the family Myctophidae foraging in the water column. The large chorus spatial extent and its apparent correlation with regions of high productivity suggest it may act as an acoustic beacon to marine fauna indicating regions of high biomass
A fast and long-lived outflow from the supermassive black hole in NGC 5548
Supermassive black holes in the nuclei of active galaxies expel large amounts
of matter through powerful winds of ionized gas. The archetypal active galaxy
NGC 5548 has been studied for decades, and high-resolution X-ray and UV
observations have previously shown a persistent ionized outflow. An observing
campaign in 2013 with six space observatories shows the nucleus to be obscured
by a long-lasting, clumpy stream of ionized gas never seen before. It blocks
90% of the soft X-ray emission and causes simultaneous deep, broad UV
absorption troughs. The outflow velocities of this gas are up to five times
faster than those in the persistent outflow, and at a distance of only a few
light days from the nucleus, it may likely originate from the accretion disk.Comment: 25 pages, 8 figures. This is the author's version of the work. It is
posted here by permission of the AAAS for personal use, not for
redistribution. The definitive version was published in Science,
electronically available at Science Express (June 19, 2014). For a brief
video explaining the key results of this paper, please visit
http://www.issibern.ch/teams/ngc5548/?page_id=2
- …