342 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
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
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
First Results from the XMM-Newton Slew Survey
We have attempted to analyse all the available data taken by XMM-Newton as it
slews between targets. This slew survey, the resultant source catalogue and the
analysis procedures used are described in an accompanying paper. In this letter
we present the initial science results from the survey. To date, detailed
source-searching has been performed in three X-ray bands (soft, hard and total)
in the EPIC-pn 0.2-12 keV band over ~6300 sq.degrees (~15% of the sky), and of
order 4000 X-ray sources have been detected (~55% of which have IDs). A great
variety of sources are seen, including AGN, galaxies, clusters and groups,
active stars, SNRs, low- and high-mass XRBs and white dwarfs. In particular, as
this survey constitutes the deepest ever hard-band 2-12 keV all-sky survey, a
large number of hard sources are detected. Furthermore, the great sensitivity
and low-background of the EPIC-pn camera are especially suited to emission from
extended sources, and interesting spatial structure is observed in many
supernova remnants and clusters of galaxies. The instrument is very adept at
mapping large areas of the X-ray sky. Also, as the slew survey is well matched
to the ROSAT all-sky survey, long-term variability studies are possible, and a
number of extremely variable X-ray sources, some possibly due to the tidal
disruption of stars by central supermassive black holes, have been discovered.Comment: 4 Pages, 3 Figs, to appear in PASJ (2006) 58, No 6. Colour version
available at http://www.star.le.ac.uk/~amr30/publications.htm
Resolving the AGN and host emission in the mid-infrared using a model-independent spectral decomposition
We present results on the spectral decomposition of 118 Spitzer Infrared
Spectrograph (IRS) spectra from local active galactic nuclei (AGN) using a
large set of Spitzer/IRS spectra as templates. The templates are themselves IRS
spectra from extreme cases where a single physical component (stellar,
interstellar, or AGN) completely dominates the integrated mid-infrared
emission. We show that a linear combination of one template for each physical
component reproduces the observed IRS spectra of AGN hosts with unprecedented
fidelity for a template fitting method, with no need to model extinction
separately. We use full probability distribution functions to estimate
expectation values and uncertainties for observables, and find that the
decomposition results are robust against degeneracies. Furthermore, we compare
the AGN spectra derived from the spectral decomposition with sub-arcsecond
resolution nuclear photometry and spectroscopy from ground-based observations.
We find that the AGN component derived from the decomposition closely matches
the nuclear spectrum, with a 1-sigma dispersion of 0.12 dex in luminosity and
typical uncertainties of ~0.19 in the spectral index and ~0.1 in the silicate
strength. We conclude that the emission from the host galaxy can be reliably
removed from the IRS spectra of AGN. This allows for unbiased studies of the
AGN emission in intermediate and high redshift galaxies -currently inaccesible
to ground-based observations- with archival Spitzer/IRS data and in the future
with the Mid-InfraRed Instrument of the James Webb Space Telescope. The
decomposition code and templates are available at
http://www.denebola.org/ahc/deblendIRS.Comment: 16 pages, 15 figures, 2 tables, accepted for publication in Ap
A tidal disruption-like X-ray flare from the quiescent galaxy SDSS J120136.02+300305.5
SDSS J120136.02+300305.5 was detected in an XMM-Newton slew from June 2010
with a flux 56 times higher than an upper limit from ROSAT, corresponding to
Lx~3x10^44 ergs/s. It has the optical spectrum of a quiescent galaxy (z=0.146).
Overall the X-ray flux has evolved consistently with the canonical t^-5/3
model, expected for returning stellar debris from a tidal disruption event,
fading by a factor ~300 over 300 days. In detail the source is very variable
and became invisible to Swift between 27 and 48 days after discovery, perhaps
due to self-absorption. The X-ray spectrum is soft but is not the expected tail
of optically thick thermal emission. It may be fit with a Bremsstrahlung or
double-power-law model and is seen to soften with time and declining flux.
Optical spectra taken 12 days and 11 months after discovery indicate a deficit
of material in the broad line and coronal line regions of this galaxy, while a
deep radio non-detection implies that a jet was not launched during this event.Comment: Accepted for publication in Astronomy and Astrophysics. 11 pages, 11
figure
Higher prevalence of X-ray selected AGN in intermediate age galaxies up to z~1
We analyse the stellar populations in the host galaxies of 53 X-ray selected
optically dull active galactic nuclei (AGN) at 0.34<z<1.07 with ultra-deep
(m=26.5) optical medium-band (R~50) photometry from the Survey for High-z
Absorption Red and Dead Sources (SHARDS). The spectral resolution of SHARDS
allows us to consistently measure the strength of the 4000 AA break, Dn(4000),
a reliable age indicator for stellar populations. We confirm that most X-ray
selected moderate-luminosity AGN (L_X<10^44 erg/s) are hosted by massive
galaxies (typically M*>10^10.5 M_sun) and that the observed fraction of
galaxies hosting an AGN increases with the stellar mass. A careful selection of
random control samples of inactive galaxies allows us to remove the stellar
mass and redshift dependencies of the AGN fraction to explore trends with
several stellar age indicators. We find no significant differences in the
distribution of the rest-frame U-V colour for AGN hosts and inactive galaxies,
in agreement with previous results. However, we find significantly shallower
4000 AA breaks in AGN hosts, indicative of younger stellar populations. With
the help of a model-independent determination of the extinction, we obtain
extinction-corrected U-V colours and light-weighted average stellar ages. We
find that AGN hosts have younger stellar populations and higher extinction
compared to inactive galaxies with the same stellar mass and at the same
redshift. We find a highly significant excess of AGN hosts with Dn(4000)~1.4
and light weighted average stellar ages of 300-500 Myr, as well as a deficit of
AGN in intrinsic red galaxies. We interpret failure in recognising these trends
in previous studies as a consequence of the balancing effect in observed
colours of the age-extinction degeneracy.Comment: Accepted for publication in MNRAS, 12 pages, 8 figures, 1 tabl
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
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