[show abstract][hide abstract] ABSTRACT: This white paper describes the LSST Dark Energy Science Collaboration (DESC),
whose goal is the study of dark energy and related topics in fundamental
physics with data from the Large Synoptic Survey Telescope (LSST). It provides
an overview of dark energy science and describes the current and anticipated
state of the field. It makes the case for the DESC by laying out a robust
analytical framework for dark energy science that has been defined by its
members and the comprehensive three-year work plan they have developed for
implementing that framework. The analysis working groups cover five key probes
of dark energy: weak lensing, large scale structure, galaxy clusters, Type Ia
supernovae, and strong lensing. The computing working groups span cosmological
simulations, galaxy catalogs, photon simulations and a systematic software and
computational framework for LSST dark energy data analysis. The technical
working groups make the connection between dark energy science and the LSST
system. The working groups have close linkages, especially through the use of
the photon simulations to study the impact of instrument design and survey
strategy on analysis methodology and cosmological parameter estimation. The
white paper describes several high priority tasks identified by each of the 16
working groups. Over the next three years these tasks will help prepare for
LSST analysis, make synergistic connections with ongoing cosmological surveys
and provide the dark energy community with state of the art analysis tools.
Members of the community are invited to join the LSST DESC, according to the
membership policies described in the white paper. Applications to sign up for
associate membership may be made by submitting the Web form at
http://www.slac.stanford.edu/exp/lsst/desc/signup.html with a short statement
of the work they wish to pursue that is relevant to the LSST DESC.
[show abstract][hide abstract] ABSTRACT: The design of the Large Synoptic Survey Telescope (LSST) requires a
camera system of unprecedented size and complexity. Achieving the
science goals of the LSST project, through design, fabrication,
integration, and operation, requires a thorough understanding of the
camera performance. Essential to this effort is the camera modeling
which defines the effects of a large number of potential mechanical,
optical, electronic or sensor variations which can only be captured with
sophisticated instrument modeling that incorporates all of the crucial
parameters. This paper presents the ongoing development of LSST camera
instrument modeling and details the parametric issues and attendant
analysis involved with this modeling.
[show abstract][hide abstract] ABSTRACT: The precise measurements planned for the Large Synoptic Survey Telescope
(LSST) require careful algorithmic studies before the telescope begins
operating with its unprecedented image production rate. The LSST Image
Simulation group is leading the effort to simulate the LSST system from
end-to-end using a high fidelity framework. We first synthesize input
astrophysical object catalogs that include stars based on a galaxy
model, asteroids, and cosmologically-based galaxy catalogs with
morphological parameters. We then use a novel approach to simulate
images using a photon Monte Carlo approach. We draw photons from the
objects using their spectral energy distributions and propagate those
photons through the Universe, atmosphere, telescope, and camera using
complex wavelength-dependent photon simulation physics. We describe the
simulation framework, and discuss the photon simulation approach that
has been used generate millions of high fidelity images.
[show abstract][hide abstract] ABSTRACT: ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of
metal creation from the epoch of cosmic dawn. Using high-spectral resolution in
the soft X-ray band, ORIGIN will be able to identify the physical conditions of
all abundant elements between C and Ni to red-shifts of z=10, and beyond. The
mission will answer questions such as: When were the first metals created? How
does the cosmic metal content evolve? Where do most of the metals reside in the
Universe? What is the role of metals in structure formation and evolution? To
reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to
study their local environments in their host galaxies. This requires the
capability to slew the satellite in less than a minute to the GRB location. By
studying the chemical composition and properties of clusters of galaxies we can
extend the range of exploration to lower redshifts (z ~ 0.2). For this task we
need a high-resolution spectral imaging instrument with a large field of view.
Using the same instrument, we can also study the so far only partially detected
baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the
WHIM will be studied using absorption lines at low redshift in the spectra for
[show abstract][hide abstract] ABSTRACT: The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, modified Paul-Baker design, with an 8.4-meter primary mirror, a 3.4-m secondary, and a 5.0-m tertiary feeding a refractive camera design with 3 lenses (0.69-1.55m) and a set of broadband filters/corrector lenses. Performance is excellent over a 9.6 square degree field and ultraviolet to near infrared wavelengths. We describe the image quality error budget analysis methodology which includes effects from optical and optomechanical considerations such as index inhomogeneity, fabrication and null-testing error, temperature gradients, gravity, pressure, stress, birefringence, and vibration.
[show abstract][hide abstract] ABSTRACT: Optically fed by LSST's fast and wide-field optics, the camera has a 9.6
square degree FOV in a 3.2 Gigapixel focal plane array. The focal plane
is tiled by 189 4Kx4K CCD science sensors with 10μm (0.2 arcsec)
pixels and also houses four diagnostic ("corner raft") packages that
provide guide- and wavefront-sensors at opposing sides of the field.
The focal plane array is highly modular and features a parallelized
readout scheme, allowing the entire array to be read in 2 seconds.
Dedicated front- and back-end electronics boards housed within the
cryostat vacuum vessel operate sensors in raft groups (3x3 sensors; 144
data channels) while mechanically identical "rafts” are
precision-mounted on a rigid silicon carbide grid structure.
Three large, refractive lens elements act as the optical system's
corrector (the third, L3, provides the vacuum barrier for the cryostat),
and one of six possible band-pass filters is positioned in the beam at
any given time. Mechanisms within the camera include a mechanical
shutter and a carousel filter changer assembly. The camera control
system manages all aspects of camera operation including image capture,
thermal monitoring and control, vacuum control, filter changes, and
communication with the observatory control system.
The data acquisition system records and pre-processes raw images,
provides up to 3 days of storage capacity, and provides very high
throughput data transfer to downstream data management.
[show abstract][hide abstract] ABSTRACT: A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.
[show abstract][hide abstract] ABSTRACT: How structures of various scales formed and evolved from the early Universe up to present time is a fundamental question of astrophysical cosmology. EDGE (Piro et al., 2007) will trace the cosmic history of the baryons from the early generations of massive stars by Gamma-Ray Burst (GRB) explosions, through the period of galaxy cluster formation, down to the very low redshift Universe, when between a third and one half of the baryons are expected to reside in cosmic filaments undergoing gravitational collapse by dark matter (the so-called warm hot intragalactic medium). In addition EDGE, with its unprecedented capabilities, will provide key results in many important fields. These scientific goals are feasible with a medium class mission using existing technology combined with innovative instrumental and observational capabilities by: (a) observing with fast reaction Gamma-Ray Bursts with a high spectral resolution. This enables the study of their star-forming and host galaxy environments and the use of GRBs as back lights of large scale cosmological structures; (b) observing and surveying extended sources (galaxy clusters, WHIM) with high sensitivity using two wide field of view X-ray telescopes (one with a high angular resolution and the other with a high spectral resolution). The mission concept includes four main instruments: a Wide-field Spectrometer (0.1-2.2 eV) with excellent energy resolution (3 eV at 0.6 keV), a Wide-Field Imager (0.3-6 keV) with high angular resolution (HPD = 15") constant over the full 1.4 degree field of view, and a Wide Field Monitor (8-200 keV) with a FOV of A1/4 of the sky, which will trigger the fast repointing to the GRB. Extension of its energy response up to 1 MeV will be achieved with a GRB detector with no imaging capability. This mission is proposed to ESA as part of the Cosmic Vision call. We will outline the science drivers and describe in more detail the payload of this mission.
[show abstract][hide abstract] ABSTRACT: A long 280 ks observation of the Seyfert 1 galaxy NGC 3783 with XMM-Newton is reported. We focus on the oxygen line complex between 17 and 24 Å as measured with the Reflection Grating Spectrometer. Accurate absorption column densities and emission-line fluxes are obtained. We explore several options for the geometry and physical form of the emitting and absorbing gas. The lack of change in ionization in the absorber despite an increase in continuum flux during the observation restricts the high-ionization (O-K) and the low-ionization (Fe-M) gas to distances of at least 0.5 and 2.8 pc, respectively, away from the central source. Given the P Cygni type profiles in the resonance spectral lines and the similar velocity widths, column densities, and ionization structure inferred separately from the emission and absorption lines, it is tempting to relate the X-ray narrow-line emitting plasma with the X-ray-absorbing gas. Under this assumption, the scenario of dense clumped clouds can be ruled out. Conversely, extended ionization cones (r 10 pc) are consistent with the observation independent of this assumption. These findings are in stark contrast to the picture of numerous clumpy (ne 109 cm-3) clouds drawn recently from UV spectra, but they are consistent with the extended X-ray emission cones observed directly in Seyfert 2 galaxies.
The Astrophysical Journal 12/2008; 598(1):232. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report on X-ray observations of the supernova remnant 0509-67.5 in the Large Magellanic Cloud with XMM-Newton X-ray observatory. We use the imaging spectroscopy (EPIC) and Reflective Grating Spectrometer (RGS) data to investigate properties of the remnant and its environment. The X-ray spectra were analyzed with SPEX software package. In addition to this we performed a numerical hydrodynamic simulation of the remnant. The EPIC data show prominent Fe K line emission, but the deduced overall amount of iron in the shocked ejecta is low. The data also show that the remnant has an asymmetric ejecta structure: the bright southwest region of the remnant shows an overabundance of metals. The analysis of the RGS spectrum shows that the remnant has a high lines velocity broadening of ~5000 km/s. We found a hydrodynamical model for the remnant with basic hydrodynamical and spectral parameters similar to the observed ones. The data analysis show that the reverse shock just recently reached iron layers of the ejecta. The brightness enhancement in the southwest region could be a sign of an asymmetric explosion or it could be the result of a density enhancement of the interstellar medium. We constructed numerical models which are in good agreement with the observations, with circumstellar density of 3e-25 g/cm^3, age of ~400 years, velocities of ~5000 km/s and an electron to ion temperature ratio of 0.01. Comment: 10 pages, 11 figures, A&A accepted
Astronomy and Astrophysics 07/2008; · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report on X‐ray observations of the supernova remnant 0509‐67.5 in the Large Magellanic Cloud with XMM‐Newton. The Reflective Grating Spectrometer (RGS) data show that the remnant has a very high expansion velocity of 6000 km/s. The imaging spectroscopy data (EPIC) show that the remnant has an asymmetric ejecta structure: the bright southwest region of the remnant shows an overabundance of Si, S, Fe. This could be a sign of an asymmetric explosion or it could be the result of a density enhancement of the ISM in the Southwest. In addition to the data analysis we also present an hydrodynamical modeling of the remnant. The simulations allow us to put some constraints on its basic parameters.
[show abstract][hide abstract] ABSTRACT: We report on X-ray observations of the supernova remnant 0509-67.5 in Large Maggelanic Clouds with XMM-Newton. The Reflective Grating Spectrometer data show that the remnant has a very high expansion velocity of 6000 km/s. The imaging spectroscopy data (EPIC) show that the remnant has an asymmetric ejecta structure: the bright southwest region of the remnant shows an overabundance of Si, S, Fe. This could be a sign of an asymmetric explosion or it could be the result of a density enhancement of the ISM in the Southwest. In addition to the data analysis we also present a hydrodynamical modeling of the remnant. The simulations allow us to put some additional constraints on the SNR properties and density of the environment.
[show abstract][hide abstract] ABSTRACT: In a series of papers, Nicastro et al. have reported the detection of z > 0 O VII absorption features in the spectrum of Mrk 421 obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS). We evaluate this result in the context of a high-quality spectrum of the same source obtained with the Reflection Grating Spectrometer (RGS) on XMM-Newton. The data comprise over 955 ks of usable exposure time and more than 2.6 × 104 counts per 50 mÅ at 21.6 Å. We concentrate on the spectrally clean region (21.3 < λ < 22.5 ), where sharp features due to the astrophysically abundant O VII may reveal an intervening, warm-hot intergalactic medium (WHIM). We do not confirm detection of any of the intervening systems claimed to date. Rather, we detect only three unsurprising, astrophysically expected features down to the log(Ni) ~ 14.6 (3 σ) sensitivity level. Each of the two purported WHIM features is rejected with a statistical confidence that exceeds that reported for its initial detection. While we cannot rule out the existence of fainter, WHIM related features in these spectra, we suggest that previous discovery claims were premature. A more recent paper by Williams et al. claims to have demonstrated that the RGS data we analyze here do not have the resolution or statistical quality required to confirm or deny the LETGS detections. We show that our analysis resolves the issues encountered by Williams et al. and recovers the full resolution and statistical quality of the RGS data. We highlight the differences between our analysis and those published by Williams et al. as this may explain our disparate conclusions.
The Astrophysical Journal 02/2007; · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present a spectrometer design based on a novel nanofabricated blazed X-ray transmission grating which is modeled to have superior efficiency. Here we outline a full instrument design proposed for Constellation-X which is expected to give resolving powers ~2000 (HEW). The spectrometer advantages include lower mass budget and smaller diffractor area, as well as order-of-magnitude more relaxed alignment tolerances for crucial degrees of freedom than reflection grating schemes considered in the past1,2,3. The spectrometer readout is based on conventional CCD technology adapted to operate with very high speed and low power. This instrument will enable high resolution absorption and emission line spectroscopy in the critical band between 0.2 and 1.5 keV.
[show abstract][hide abstract] ABSTRACT: In a series of papers, the first detection of highly ionized gas associated with two Warm-Hot Intergalactic Medium (WHIM) filaments has been reported by Nicastro et al. (2005). The evidence is based on absorption lines from O VII and other ions towards the bright blazar Mrk 421, measured by the Chandra/LETGS. This result was used to argue that the missing 45% of all baryons have at last been found and are located in the WHIM X-ray forest. We investigate the robustness of this detection by a re-analysis of the original LETGS data, using also more recent LETGS spectra and a thorough analysis of >955 ks of XMM-Newton/RGS data on Mrk 421. We confirm the apparent strength of several features in the original Chandra spectra, but demonstrate that they are statistically not significant. This is due to the number of redshift trials that are made in the search for features and that are not taken into account in the original paper. Moreover, both the RGS data that have a 30% higher sensitivity to line detections than the original LETGS observations as well as the new LETGS spectra do not show any significant feature at the relevant wavelengths. Our careful analysis of the RGS spectra shows that RGS has similar sensitivity to find weak absorption features as LETGS. Finally, we show that a possible association of one of the proposed filaments with a Lyman alpha absorption system lacks sufficient statistical evidence. We conclude that there is insufficient proof for the existence of the proposed WHIM filaments towards Mrk 421, the brightest blazar. Therefore, the highly ionized component of the WHIM still remains to be discovered. Moreover, unless redshifts are known a priori, the unambiguous proof for X-ray absorption lines towards Mrk 421 or any other source is harder than previously thought.
[show abstract][hide abstract] ABSTRACT: The Constellation-X Reflection Grating Spectrometer (RGS) is designed to provide high-throughput, high-resolution spectra in the long wavelength band of 6 to 50 angstrom. In the nominal design an array of reflection gratings is mounted at the exit of the Spectroscopy X-ray Telescope (SXT) mirror module. The gratings intercept and disperse light to a designated array of CCD detectors. To achieve the throughput (Aeff > 1000 cm2 below 0.6 keV) and resolution (Deltalambda/lambda > 300 below 0.6 keV) requirements for the instrument we are investigating two possible grating designs. The first design uses in-plane gratings in a classical configuration that is very similar to the XMM-Newton RGS. The second design uses off-plane gratings in a conical configuration. The off-plane design has the advantage of providing higher reflectivity and potentially, a higher spectral resolution than the in-plane configuration. In our presentation we will describe the performance requirements and the current status of the technology development.
[show abstract][hide abstract] ABSTRACT: In a series of papers, Nicastro et al. have reported the detection of z>0 OVII absorption features in the spectrum of Mrk421 obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS). We evaluate this result in the context of a high quality spectrum of the same source obtained with the Reflection Grating Spectrometer (RGS) on XMM-Newton. The data comprise over 955ks of usable exposure time and more than 26000 counts per 50 milliAngstrom at 21.6 Angstroms. We concentrate on the spectrally clean region (21.3 < lambda < 22.5 Angstroms) where sharp features due to the astrophysically abundant OVII may reveal an intervening, warm--hot intergalactic medium (WHIM). We do not confirm detection of any of the intervening systems claimed to date. Rather, we detect only three unsurprising, astrophysically expected features down to the Log(N_i)~14.6 (3 sigma) sensitivity level. Each of the two purported WHIM features is rejected with a statistical confidence that exceeds that reported for its initial detection. While we can not rule out the existence of fainter, WHIM related features in these spectra, we suggest that previous discovery claims were premature. A more recent paper by Williams et al. claims to have demonstrated that the RGS data we analyze here do not have the resolution or statistical quality required to confirm or deny the LETGS detections. We show that our careful analysis resolves the issues encountered by Williams et al. and recovers the full resolution and statistical quality of the RGS data. We highlight the differences between our analysis and those published by Williams et al. as this may explain our disparate conclusions.
The Astrophysical Journal 05/2006; · 6.73 Impact Factor