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3.0 FY06 PROGRESS IN THE PARTICLE ASTROPHYSICS PROGRAM
by Roger Blandford
Appendix B Self-Evaluation FY2006

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The Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) has completed its third full academic year. The KIPAC faculty has been joined by Professor Risa Wechsler who works in the area of cosmic structure formation and by Panofsky Fellow Saurabh Jha, whose work focuses on supernovae and their use as cosmological probes.

As of Oct 2006 there are 18 postdoctoral researchers in KIPAC. The new recruits are Marcelo Alvarez, Andres Escala, Stelios Kazantzidis, Masamune Oguri and Lukasz Stawarz. KIPAC continues to hire the very best young scientists, working across the wide range of topics under the KIPAC mandate. (This year's hires were selected from an outstanding field of approximately 120 applicants.) Over 30 graduate students are now associated with the group and morale among students and postdoc members is very high. At the administrative level, Ziba Mahdavi has joined the group. The current KIPAC membership can be found at http://www-group.slac.stanford.edu/kipac/ .

The six postdoc members who came to the end of their time at KIPAC in the past year have all moved on to prestigious positions. Anatoly Spitkovsky has moved to Princeton University as Assistant Professor in the Department of Astrophysical Sciences. Andrei Frolov has moved on to Simon Fraser University as Assistant Professor in the Department of Physics. John Peterson has moved on to Purdue University as Assistant Professor of Physics. Masao Sako has moved to the University of Pennsylvania as Assistant Professor of Physics and Astronomy. Phil Marshall is the TABASGO Fellow at UC Santa Barbara. Ted Baltz has taken up a staff scientist position at SLAC. Three grad students have moved on to postdoc positions at other universities. The success rate in the job market for KIPAC student and postdoctoral members is clearly very high.

KIPAC has become well-integrated into the SLAC-campus physics community. Joint astrophysics seminars take place on Thursday afternoons, the venue alternating between campus and SLAC; these are well attended. There is good coordination with other lecture series at SLAC and on campus. There are twice-weekly KIPAC `morning teas,' one on campus and one at SLAC, where recent papers and `hot topics' are discussed and short research presentations are made by group members and visitors. Attendance at these meetings typically varies between 50 and 70. KIPAC has achieved the goal of providing a lively and open scientific forum, connecting SLAC with campus. Further outreach has also occurred into the Bay Area astrophysics community.

Administratively, the KIPAC-Physics department has been running smoothly. More than 80 individuals are now associated with KIPAC Physics, with 27 individuals receiving partial or full funding support through the department (6 faculty, 7 staff, 8 postdocs and 6 students). The various subdepartments of KIPAC-Physics have continued to operate efficiently within their FY06 budgets.

The new Fred Kavli Building has been a tremendous success. The open design of the building has enhanced the spirit of lively, open discussion and has fostered further collaboration and the sense of `team' within the Institute. The new Physics-Astrophysics Building on campus will be completed in early October 2006 and bring further opportunities.

The scientific program at KIPAC is diverse with wide-ranging efforts on observational, theoretical, computational and experimental fronts.

Given the nature of modern particle astrophysics and cosmology, this maximizes the opportunity for significant progress. In addition to the work directly related to major projects, reported below, over 100 scientific papers, including conference proceedings, have been written by KIPAC members over the past year and a comparable number of talks has been delivered. Major research concentrations include, in no particular order:

• cosmological studies of clusters of galaxies, combining observations made using X-ray, optical and radio telescopes.
• projects in weak and strong gravitational lensing as well as microlensing, investigations of particle dark matter
• studies of dark matter, dark energy and cosmological parameters
• participation in the Sloan Digital Sky Survey, particularly in the discovery and analysis of supernovae
• participation in radio observations of the sources likely to be studied by GLAST
• modeling of pulsars, especially the recently discovered double pulsar
• modeling of gamma ray bursts
• numerical simulations of the growth of structure in the early universe
• analysis of microwave background observations
• calculations of atomic transitions for use in X-ray astronomy
• new ideas in black hole astrophysics
• studies of astrophysical jets, accretion and galaxy formation.

KIPAC looks forward to further growth over the coming year.

GLAST

The Gamma-ray Large Area Space Telescope, GLAST, is a satellite-based experiment under construction to measure the cosmic gamma-ray flux in the energy range 20 MeV to >300 GeV, with supporting measurements for gamma-ray burst (GRB) transients in the energy range 10 keV to 30 MeV. With a sensitivity that is more than a factor of 30 greater than that of the EGRET detector on the previous Compton GRO mission, GLAST will open a new and important window on a wide variety of high-energy phenomena, including super-massive black holes and active galactic nuclei, GRBs, supernova remnants and cosmic ray acceleration, and searches for new phenomena such as super-symmetric dark matter annihilations, Lorentz invariance violations and big-bang particle relics. The GLAST launch is scheduled for late 2007.

The Large Area Telescope (LAT) is the primary science instrument on GLAST. The LAT collaboration is a novel teaming of particle physicists and high energy astrophysicists. The collaboration now numbers 86 scientific members, 85 affiliated members and 23 postdocs and many graduate students (5 currently at SLAC-Stanford). The LAT Principal Investigator (PI) and Spokesperson is Professor Peter Michelson (Stanford and SLAC). The LAT has been developed in a partnership between NASA and the DOE, with substantial contributions from Italy, Japan, France and Sweden. The LAT project is managed at SLAC.

The LAT collaboration had a 3-day meeting in Stockholm in August 2006, preceded by splinter meetings of many of the 9 science groups organized in the collaboration, and followed by a one-day science symposium on gamma-ray bursts.

The integration of all 16 towers, the Anti-coincidence Detector and data acquisition electronics onto the LAT support grid was completed at SLAC in May 2006. The LAT was then trucked to the Naval Research Laboratory in Washington, DC for environmental testing, including vibration, acoustic, electromagnetic interference and thermal-vacuum testing. These tests verified that the LAT successfully operated after being subjected to launch-like stresses and the expected temperature extremes of on-orbit operating conditions. After a successful post-test review on 15 September 2006, the LAT arrived at General Dynamics C4 Systems in Gilbert, AZ on 18 September 2006 ready to be integrated onto the GLAST spacecraft. The development of the LAT flight software is nearing completion. The final launch-ready version of the software will be installed on the LAT in November, before initial testing of the integrated GLAST. The integration and test of GLAST will last approximately 9-10 months at General Dynamics before GLAST is transported to Cape Canaveral for launch.

Preparations for the operation of the LAT continue at SLAC. The LAT Instrument Science Operations Center (ISOC) at SLAC will operate the LAT in conjunction with the GLAST Mission Operations Center (MOC) and GLAST Science Support Center (GSSC) at NASA Goddard Space Flight Center, and will process LAT detected event data and provide reduced data to NASA and the LAT collaboration. Most of the ISOC staff have been consolidated into the Central Lab Annex building at SLAC. Construction has started on the LAT ISOC Operations Facility in the Central Lab Annex, comprising an operations control room, office area for operations staff, and a dataflow lab housing a full-scale replica of the LAT flight electronics and eventually the flight-spare detectors. The construction of the Operations Facility is scheduled for completion in January 2007.

Data Challenge 2 (DC2) was held during March-June 2006, following on from DC1 in 2004. DC2 used a simulation of 55 days of LAT data generated using 200,000 CPU hours on 400 CPUs in the SLAC computer farm. DC2 provided end-to-end testing of instrument simulation, event reconstruction and science analysis tools including pulsar timing, GRB detection, and the analysis pipeline for generating the LAT source catalog.

From July to September of 2006 a beam test was conducted at CERN in the Swiss-French border, using spare modules of the LAT assembled into a mechanical support grid. The test article, hereafter calibration unit (CU), consists of 2 complete LAT towers (tracker, calorimeter and tower electronics module), a third calorimeter and tower electronics module, a trigger module, and 5 plastic scintillator tiles from the anti-coincidence detector. Data were collected in the CERN PS beam line during the months of July and August using low-energy beams (up to 10 GeV) of photons (tagged and untagged), electrons, positrons and hadrons. Data were collected with the CU in the SPS beam line in early September using beams of photons, electrons and hadrons at several energies up to 280 GeV. Further data taking with the LAT CU will be conducted with heavy ion beams at GSI/Germany in November.

Work to understand the LAT acceptance, proton rejection, and response functions using ground Cosmic Ray data and beam test data is ongoing. Preparations at SLAC are ongoing in three broad areas of GLAST science.

1. Dark Matter and New Physics
2. Particle Interactions and Acceleration in Astrophysical Sources
3. Relativistic Outflows.

Figure 1. 16 towers installed on the LAT

Figure 2. The LAT in the thermal-vacuum chamber at NRL Figure 3. The LAT ready to ship to General Dynamics for integration onto GLAST

Figure 3. The LAT ready to ship to General Dynamics for integration onto GLAST

Figure 4. Sky map of gamma rays detected by the LAT in the Data Challenge 2 simulation.

Figure 5. The Calibration Unit (CU) used for the beam test at CERN.

LSST

The prime goal of LSST is a precision measure of the nature of dark energy though a suite of techniques using a homogeneous imaging data set. Central of these is weak lens shear of galaxy shapes to z=3 by mass at z<3, giving a unique probe of dark energy. This will be done through a combination of deep-wide multiband imaging data over 20,000 sq.deg. in a weak lensing survey of unprecedented sensitivity x volume and quality. By measuring the gravitational lens distorted shapes of billions of galaxies as a function of angle on the sky and photometric red shift out to z=3, and using galaxy P(k) from these same data together with WMAP and Planck data, LSST will constrain six eigenmodes of the dark energy equation of state parameter. The shear power spectra and 3-point correlations depend on the growth function and angular diameter distances, which are both sensitive to the equation of state of dark energy. The technique used in these forecasts is lensing tomography with the auto- and cross-power spectra of the lensing shear. LSST will also measure with record precision: baryon acoustic oscillations, hundreds of thousands of SNe, and clusters of galaxies — three additional cosmological diagnostics providing independent constraints on dark energy.

LSST will be a large, wide-field ground-based telescope designed to obtain sequential images of the entire visible sky every few nights. The optical design involves a 3-mirror system with an 8.4 m primary, which feeds three refractive correcting elements inside a camera, providing a 10 square degree field of view sampled by a 3 gigapixel focal plane array. The total effective system throughput, AΩ = 318 m 2 deg2, is nearly two orders of magnitude larger than that of any existing facility. The survey will yield contiguous overlapping imaging of 20,000 – 23,000 square degrees of sky in 6 optical bands covering the wavelength regime 350–1100 nm.

A collaboration led by SLAC is building the LSST camera which is a wide-field optical (0.35-1 µm) imager designed to provide a 3.5 degree FOV with better than 0.2 arcsecond sampling. The camera includes a filter mechanism and shuttering capability. It is positioned in the middle of the telescope where cross-section area is constrained by optical vignetting and heat dissipation must be controlled to limit thermal gradients in the optical beam. The fast, f/1.2 beam will require tight tolerances on the focal plane mechanical assembly. SLAC personnel occupy several leadership positions within the project. Steven Kahn is the Deputy Director of the LSST project overall, and is the Lead Scientist for the Camera. Kirk Gilmore is the Camera Project Manager. Roger Blandford, the Director of KIPAC, is a member of the LSST Corporation Board of Directors.

During the past year, substantial progress has been made on the camera development. Camera body/cryostat modeling as well as overall metrology is currently being developed by SLAC designers and engineers. The current level of design is leading to several years of R&D that will include extensive prototyping of the major components of the camera. Part of the prototyping effort is motivated by retiring the risk associated with state of the art components.

The LSST Camera focal plane contains a large array of imagers. The challenge is the development of imagers which meet LSST’s specifications on pixel size, QE, flatness, dead area and readout speed. All the specifications have been achieved in previously used CCD arrays; the development task involves integrating all the required features into a single sensor. The LSST sensor working group, which includes members of the LSST at SLAC team, currently has several vendors under contract to develop study sensors that will help determine the final operating characteristics of the science detectors. LSST’s fast optics produce a very narrow depth of field which requires that the focal plane be flat within 10 µm. The R&D program for the LSST camera will focus on understanding the best techniques to employ to keep the focal plane flat to the high precision tolerances required. Initial studies will include the development of various motion control scenarios to actively maintain flatness of the raft (3x3 detector array) under a variety of thermal and mechanical conditions.

LSST filters present special fabrication challenges to achieving spatially uniform passband characteristics necessary to do <1% photometry. These include achieving the necessary thermal and mechanical stability. A development program spearheaded by SLAC personnel is currently under way with the ultimate goal of fabricating a full-scale prototype which demonstrates the necessary performance characteristics over the full field.

In terms of scientific investigations, science collaboration groups have been formed to address the issues associated with the major scientific projects of the LSST. These Science Collaborations will work closely with the LSST Project as it builds the telescope, camera, and software, and will be expected to play a substantial role in the scientific commissioning of the project. The major input of the science collaboration groups will help identify and resolve key scientific issues. KIPAC is heavily represented on most of the collaborations.

A camera face-face meeting was held at SLAC in FY06 and was attended by 48 LSST personnel with 37 people from partner institutions and 11 people from SLAC. SLAC also hosted an LSST simulations workshop and operations simulator workshop in FY06.

Below is an image of the LSST camera body with the cryostat. The raft tower contains the detector and the electronics. The diameter of the L1/L2 housing is about 1.7 meters.

SNAP

The Supernova Acceleration Probe (SNAP) is a proposal for a space-based wide-field telescope designed to study the physics of dark energy using calibrated Type 1a supernovae as standard candles. The mission will also enable weak lensing studies with high precision over moderate angular scales. The SNAP design includes a large focal plane tiled with both visible-light and infrared-imaging sensors, as well as a visible/IR spectrograph suitable for following up detected supernovae.

SLAC/Stanford proposed to join the SNAP collaboration in August of 2003. That application was formally approved in March 2004. Within the collaboration, SLAC is responsible for the design and development of the SNAP Instrument Control Unit (ICU) and the focal plane guiding system. SLAC scientists also provide significant support of the strong lensing abilities of the SNAP telescope.

The ICU performs electronic supervision of the entire SNAP instrument, executes the science mission, manages the operation of instrument mechanisms and thermal controls, and controls the flow of commands and data between the focal plane electronics, mass memory and spacecraft. This effort is led by Gunther Haller who has been hosting semimonthly electronics exchange (elex) meetings between SLAC, FNAL and LBL. The SNAP mission desires to have all focal plane components maintained at a common temperature without thermal control on each device. Over the last year the ICU team have been studying of the thermal properties of the focal plane and developing communications protocols between the warm electronics and the cold focal plane components. The level 3 electronic requirements document and on deck component layout studies are being developed.

The focal plane guiding system will allow the SNAP observatory to track its science fields to an accuracy of better than 20 milliarcseconds. SNAP intends to use a new technical approach, consisting of four asynchronously operated imaging devices, controlled by a central processor. This system will collect sufficient photons to generate an appropriate error signal for the spacecraft pointing system. By operating the sensors asynchronously, the integration time for each device can be tailored to the number and brightness of stars available with the field of view. This approach was simulated and compared with worst-case star field density and shown to meet the accuracy requirements. In collaboration with Lockheed Martin LLC, Bill Craig, Kevin Reil and Johnny Ng have been developing a test-bed prototype to confirm the pointing requirements. Studies using this test-bed should be completed over the next year.

SLAC scientists have also played a significant role in formulating the detailed scientific program for SNAP, especially with regard to strong lensing investigations. The SNAP database should reveal a large number of new strong lenses. Measurements of the properties of these lensed images will yield a number of interesting constraints on cosmological models. SLAC scientists including Phil Marshall, Roger Blandford, Masao Sako [see 2005-01-16 New Astronomy Reviews 49 387 (2005)], have provided support for strong lensing science from SNAP. Currently, in support of the scientific promise of SNAP, studies of existing data in the HST ACS archive are underway. Information on their search for lenses in this existing data can found in http://arxiv.org/abs/astro-ph/0607239.

Computing

KIPAC members have strong research programs spanning much of high energy astrophysics and cosmology including gamma-ray, X-ray and radio astronomy, modeling of gamma-ray bursts, active galactic nuclei, pulsars and supernova remnants. Generic, high energy astrophysics processes, such as relativistic shock waves and particle acceleration are also being studied. Most of these scientific programs require high performance computing and this has been a major feature of KIPAC's plans since its inception. Data handling, data analysis and numerical modeling activities are driving this development. In 2006, major efforts included searching the Hubble Space Telescope database for gravitational lenses and cosmic strings, analysis of X-ray observational rich clusters of galaxies, numerical modeling of the kinetic structure of supersonic and relativistic shock fronts, determining the properties and consequences of the first stars to form in the universe and modeling the production of gamma-ray bursts during the collapse of massive stars. A more complete tour of computational activities at KIPAC is available on the web at: http://www-group.slac.stanford.edu/kipac/comp_physics.htm .

Using adaptive mesh refinement cosmological hydrodynamics calculations the collapse of primordial gas is followed over 25 orders of magnitude in density with a maximal dynamic range of 1015. Simulations are being carried out on the KIPAC, 72 processor SGI Altix supercomputer.

To support these activities KIPAC has established a computing department with 2006 as its first full year. Development has begun of a sustained computing program comprising four elements: processing cycles, data/storage management, visualization, and personnel.

Current processing capability includes a 72-processor SGI Altix SMP system, KIPAC's 12-node set of Apple compute servers, access to the Advanced Computation Department’s myrinet clusters for MPI jobs, SLAC's batch servers, and individual users’ desktops. These resources have been used aggressively to carry out many projects but to date, computing capability has been a source of limitations. These systems will be augmented with a 64-node cluster in late 2006 specifically tailored for numerical astrophysics computations. Additionally, KIPAC’s SGI Altix is being upgraded with additional memory specifically to facilitate cosmological simulations that require larger dynamic range.

This year (2006) development began of a long term “Data Lifecycle Management” program which includes tiered storage and planned growth. KIPAC purchased 30 TB of storage and plan for approximately constant annual costs (As cost per unit storage decreases ) to keep up with increasing demand. An implementation is currently being tested of a high performance storage system to support the compute cluster environment where I/O performance can be a significant enabling factor in scientific output.

Visualization capabilities have also been developed in 2006 with prototype 3-D projection and 2D tiled display systems suitable for software development and modest data interaction. Use of these facilities includes creating three-dimensional movies, using multiscreen displays of high dimensional parameter spaces and exploring new methods to exhibit three-dimensional vectors like magnetic field. The strong graphical content of observational and theoretical astrophysics and cosmology makes it ideal for education and public outreach.

With the move into the Fred Kavli Building in mid 2006, the process of building personnel resources and communication mechanisms has been enhanced. Five FTEs are currently resident at KIPAC and SLAC’s Scientific Computing and Computing Services (SCCS) group supporting computing. Regular meetings are held with SCCS twice per month and an external review of our computing plan was held in March 2006. An expert in scientific visualization is being recruited to join KIPAC. Additionally, substantial use is made of our SU campus location at kipac.stanford.edu to host KIPAC-specific computing documentation and group communications.

As the year closes, negotiations with vendors are in progress to obtain a low-latency compute cluster with 64 nodes (each with 4 cpu cores), 512 GB total memory and 10 TB of parallel disk storage. KIPAC staff are collaborating with SCCS to develop the specialized configurations needed for numerical astrophysics. Staff are also working closely with SCCS to design and integrate this new system with the existing storage and visualization capabilities. This system will augment substantially the existing research programs and provide a significant capability to the incoming group of postdocs.

Other Activities

NuSTAR

NuSTAR is a satellite-based instrument to image hard X-ray radiation from celestial sources. This experiment is led by Caltech (Fiona Harrison, PI), but with a substantial involvement of KIPAC scientists (W. Craig, G. Madejski, R. Blandford) in addition to participants from JPL, UCSC, and Columbia University. The technical approach is via the use of multilayer grazing incidence optics focusing hard X-rays onto pixilated CdZnTe detectors. This approach dramatically reduces the particle- and Cosmic X-ray background, resulting in at least a 100-fold sensitivity improvement over any previous instruments. The science goals of the mission are: to study the production of heavy elements in supernovae; to determine the origin of the celestial hard X-ray background (where most of its energy is detected); and to provide for a tool to study relativistic jets in celestial sources via simultaneous observations with the GLAST satellite (also involving SLAC personnel).

This instrument was selected by NASA via a competitive process for the extended definition study in the Explorer program, with the goal of launch in 2009. Unfortunate budgetary constraints at NASA led to the termination of funding for the project. However, since this experiment was the top-rated astrophysics mission in the Explorer class, and the science objectives remain extremely compelling, it is anticipated that it will be either reinstated, or will be highly competitive in the next Announcement of Opportunity, expected next year. The NuSTAR team is fully committed to its success.

Even if NASA chooses not to be involved in the sensitive exploration of the hard X-ray sky, there is a highly competitive international program with similar goals. The most viable is the Japanese-led mission NeXT, which is identified as the next high energy astrophysics effort of the Japanese Space Agency JAXA. With the intended launch of 2012-2013, NeXT will include an imaging hard X-ray instrument similar in design to NuSTAR, but also will include detectors sensitive in soft X-ray, and soft gamma-ray bands. KIPAC scientists are part of the NeXT collaboration, and fully intend to participate, since such work is likely to enhance the scientific return of the GLAST (and LSST!) projects.

PoGO

PoGO is a balloon-borne hard X-ray polarimeter that consists of well-type phoswich scintillation counters to study polarization of hard X-ray flux from celestial sources. PoGO is funded by a Stanford Campus fund in the US, the Warrenburg Foundation in Sweden (PI is Mark Pearce of the Royal Institute of Technology), three grants from Grants-in-Aid in Japan (PI¹s are Jun Kataoka of Tokyo Institute of Technology, Yasushi Fukazawa of Hiroshima University and Tune Kamae as a professor emeritus of University of Tokyo). A proposal was also submitted to NASA, which is being reviewed right now.

A beam test has been completed using synchrotron light to study the performance and another beam test using proton beam to study the effect of cosmic rays. Developments of detector elements, readout electronics, data acquisition system, gondola and pointing system are on track for the first balloon flight in 2009 spring.