289 research outputs found
The XMM-Newton Slew Survey: Towards The Whole X-ray Sky and the Rarest X-ray Events
The data collected by XMM-Newton as it slews between pointings currently
cover almost half the entire sky, and many familiar features and new sources
are visible. The soft-band sensitivity limit of the Slew is close to that of
the RASS, and a large-area Slew-RASS comparison now provides the best
opportunity for discovering extremely rare high-variability objects.Comment: To appear in Proceedings of "X-ray Astronomy 2009: Present Status,
Multi-Wavelength Approach and Future Perspectives", Bologna, Italy, September
7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelin
The XMM-Newton Slew Survey
XMM-Newton, with the huge collecting area of its mirrors and the high quantum
efficiency of its EPIC detectors, is the most sensitive X-ray observatory ever
flown. This is strikingly evident during slew exposures, which, while yielding
only at most 14 seconds of on-source exposure time, actually constitute a 2-10
keV survey ten times deeper than all other "all-sky" surveys. The current
(April 2005) XMM archive contains 374 slew exposures which give a uniform
coverage over around 10,000 square degrees (approx. 25% of the sky). Here we
describe the results of pilot studies, the current status of the XMM-Newton
Slew Survey, up-to-date results and our progress towards constructing a
catalogue of slew detections in the full 0.2-12 keV energy band.Comment: 3 pages, 4 figures, XMM-Newton EPIC Consortium Meeting, Schloss
Ringberg, Germany, April 2005, to appear in MPE Repor
A high Eddington-ratio, true Seyfert 2 galaxy candidate: implications for broad-line-region models
A bright, soft X-ray source was detected on 2010 July 14 during an
XMM--Newton slew at a position consistent with the galaxy GSN 069 (z=0.018).
Previous ROSAT observations failed to detect the source and imply that GSN 069
is now >240 times brighter than it was in 1994 in the soft X-ray band. We
report here results from a ~1 yr monitoring with Swift and XMM-Newton, as well
as from optical spectroscopy. GSN 069 is an unabsorbed, ultra-soft source in
X-rays, with no flux detected above ~1 keV. The soft X-rays exhibit significant
variability down to timescales of hundreds of seconds. The UV-to-X-ray spectrum
of GSN 069 is consistent with a pure accretion disc model which implies an
Eddington ratio of ~0.5 and a black hole mass of ~ 1.2 million solar masses. A
new optical spectrum, obtained ~3.5 months after the XMM-Newton slew detection,
is consistent with earlier spectra and lacks any broad line component,
classifying the source as a Seyfert 2 galaxy. The lack of cold X-ray absorption
and the short timescale variability in the soft X-rays rule out a standard
Seyfert 2 interpretation of the X-ray data. We discuss our results within the
framework of two possible scenarios for the broad-line-region (BLR) in AGN,
namely the two-phase model (cold BLR clouds in pressure equilibrium with a
hotter medium), and models in which the BLR is part of an outflow, or
disc-wind. Finally, we point out that GSN 069 may be a member of a population
of super-soft AGN whose SED is completely dominated by accretion disc emission,
as it is the case in some black hole X-ray binary transients during their
outburst evolution. The disc emission for a typical AGN with larger black hole
mass than GSN 069 does not enters the soft X-ray band, so that GSN 069-like
objects would likely be missed by current X-ray surveys, or mis-classified as
Compton-thick candidates. (ABRIDGED)Comment: Accepted for publication in MNRA
Extended sources in the XMM-Newton slew survey
The low background, good spatial resolution and great sensitivity of the
EPIC-pn camera on XMM-Newton give useful limits for the detection of extended
sources even during the short exposures made during slewing maneouvers. In this
paper we attempt to illustrate the potential of the XMM-Newton slew survey as a
tool for analysing flux-limited samples of clusters of galaxies and other
sources of spatially extended X-ray emission.Comment: 2 pages, 4 figures, to appear in the proceedings of "The X-ray
Universe 2005", San Lorenzo de El Escorial (Spain), 26-30 September 200
The XMM-Newton Slew Survey: towards the XMMSL1 catalogue
The XMM-Newton satellite is the most sensitive X-ray observatory flown to
date due to the great collecting area of its mirrors coupled with the high
quantum efficiency of the EPIC detectors. It performs slewing manoeuvers
between observation targets tracking almost circular orbits through the
ecliptic poles due to the Sun constraint. Slews are made with the EPIC cameras
open and the other instruments closed, operating with the observing mode set to
the one of the previous pointed observation and the medium filter in place.
Slew observations from the EPIC-pn camera in FF, eFF and LW modes provide
data, resulting in a maximum of 15 seconds of on-source time. These data can be
used to give a uniform survey of the X-ray sky, at great sensitivity in the
hard band compared with other X-ray all-sky surveys.Comment: 2 pages, 2 figures, to appear in the proceedings of "The X-ray
Universe 2005", San Lorenzo de El Escorial (Spain), 26-30 September 200
Processing challenges in the XMM-Newton slew survey
The great collecting area of the mirrors coupled with the high quantum
efficiency of the EPIC detectors have made XMM-Newton the most sensitive X-ray
observatory flown to date. This is particularly evident during slew exposures
which, while giving only 15 seconds of on-source time, actually constitute a
2-10 keV survey ten times deeper than current "all-sky" catalogues. Here we
report on progress towards making a catalogue of slew detections constructed
from the full, 0.2-12 keV energy band and discuss the challenges associated
with processing the slew data. The fast (90 degrees per hour) slew speed
results in images which are smeared, by different amounts depending on the
readout mode, effectively changing the form of the point spread function. The
extremely low background in slew images changes the optimum source searching
criteria such that searching a single image using the full energy band is seen
to be more sensitive than splitting the data into discrete energy bands. False
detections due to optical loading by bright stars, the wings of the PSF in very
bright sources and single-frame detector flashes are considered and techniques
for identifying and removing these spurious sources from the final catalogue
are outlined. Finally, the attitude reconstruction of the satellite during the
slewing manoeuver is complex. We discuss the implications of this on the
positional accuracy of the catalogue.Comment: 12 pages, 16 figures, presented at the SPIE 2005 conference, San
Diego, C
Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068
We present sub-arcsecond 7.513 m imaging- and spectro-polarimetric
observations of NGC 1068 using CanariCam on the 10.4-m Gran Telescopio
CANARIAS. At all wavelengths, we find:
(1) A 90 60 pc extended polarized feature in the northern ionization
cone, with a uniform 44 polarization angle. Its polarization
arises from dust and gas emission in the ionization cone, heated by the active
nucleus and jet, and further extinguished by aligned dust grains in the host
galaxy. The polarization spectrum of the jet-molecular cloud interaction at
24 pc from the core is highly polarized, and does not show a silicate
feature, suggesting that the dust grains are different from those in the
interstellar medium.
(2) A southern polarized feature at 9.6 pc from the core. Its
polarization arises from a dust emission component extinguished by a large
concentration of dust in the galaxy disc. We cannot distinguish between dust
emission from magnetically aligned dust grains directly heated by the jet close
to the core, and aligned dust grains in the dusty obscuring material
surrounding the central engine. Silicate-like grains reproduce the polarized
dust emission in this feature, suggesting different dust compositions in both
ionization cones.
(3) An upper limit of polarization degree of 0.3 per cent in the core. Based
on our polarization model, the expected polarization of the obscuring dusty
material is 0.1 per cent in the 813 m wavelength range. This
low polarization may be arising from the passage of radiation through aligned
dust grains in the shielded edges of the clumps.Comment: 17 pages, 10 figures, accepted for publication at MNRA
The XMM-Newton Slew Survey: a wide-angle survey in the 0.2 - 12 keV band
The scientific data collected during slews of the XMM-Newton satellite are
used to construct a slew survey catalogue. This comprises of the order of 4000
sources detected in the EPIC-pn 0.2-12 keV band with exposures of less than 15s
and a sky coverage of about 6300 square degrees (source density ~0.65 per
square degree). Below 2 keV the sensitivity limit is comparable to the ROSAT
PSPC All-Sky Survey and the XMM-Newton slew survey offers long-term variablity
studies. Above 2 keV the survey will be a factor of 10 more sensitive than all
previous all-sky X-ray surveys. The slew survey is almost complementary to the
serendipitous survey compiled from pointed XMM-Newton observations. It is aimed
to release the first source catalogue by the end of 2005. Later slew
observations and detections will continuously be added. This paper discusses
the XMM-Newton slew survey also in a historical context.Comment: 6 pages, 6 figures, to appear in the proceedings of "The X-ray
Universe 2005", San Lorenzo de El Escorial (Spain), 26-30 September 200
Relativistic tidal compressions of a star by a massive black hole
Aims: We investigate the stellar pancake mechanism during which a solar-type
star is tidally flattened within its orbital plane passing close to a 10^6
solar masses black hole. We simulate the relativistic orthogonal compression
process and follow the associated shock waves formation.
Methods: We consider a one-dimensional hydrodynamical stellar model moving in
the relativistic gravitational field of a non-rotating black hole. The model is
numerically solved using a Godunov-type shock-capturing source-splitting method
in order to correctly reproduce the shock waves profiles.
Results: Simulations confirm that the space-time curvature can induce several
successive orthogonal compressions of the star which give rise to several
strong shock waves. The shock waves finally escape from the star and repeatedly
heat up the stellar surface to high energy values. Such a shock-heating could
interestingly provide a direct observational signature of strongly disruptive
star - black hole encounters through the emission of hard X or soft gamma-ray
bursts. Timescales and energies of such a process are consistent with some
observed events such as GRB 970815.Comment: 8 pages, 11 figures, submitted to Astron. Astrophy
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