118751982
The GLAST LAT Silicon Strip Tracker Converter
The Tracker subsystem of the Large Area Telescope (LAT) science instrument of the Gamma‐ray Large Area Space Telescope (GLAST) mission has been completed and tested. It is the central detector subsystem of the LAT and serves both to convert an incident gamma‐ray into an electron‐positron pair and to track the pair in order to measure the gamma‐ray direction. It also provides the principal trigger for the LAT. The Tracker uses silicon strip detectors, read out by custom electronics, to detect charged particles. The detectors and electronics are packaged, along with tungsten converter foils, in 16 modular, high‐precision carbon‐composite structures. The test program has demonstrated that the system meets or surpasses all of its performance specifications as well as environmental requirements.
122398457
Fermi Gamma‐ray Space Telescope, Introduction and Highlights from the First Eight Months
The Fermi Gamma‐ray Space Telescope, formerly named GLAST, is a mission in low‐Earth orbit to observe gamma rays from the cosmos in the broad energy range from 20 MeV to >300 GeV, with supporting observations of gamma‐ray bursts from 8 keV to 30 MeV. The telescope far surpasses previous generations in its ability to detect and localize faint gamma‐ray sources, as well as its ability to see 20% of the sky at any instant and scan the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi has opened a new and exciting window on a wide variety of exotic astrophysical objects, including pulsars, black holes, active galactic nuclei, and gamma‐ray bursts, and it will enable new research on such topics as the origin and circulation of cosmic rays and searches for hypothetical new phenomena such as annihilation of supersymmetric dark matter.
117775337
The GLAST Gamma‐Ray Telescope Mission
The Gamma‐ray Large Area Space Telescope, GLAST, is an orbital mission under construction to measure the cosmic gamma‐ray flux in the energy range 20 MeV to >300 GeV, with supporting measurements for gamma‐ray bursts from 10 keV to 25 MeV. With its launch in 2007, GLAST will open a new and important window on a wide variety of high energy phenomena, including black holes and active galactic nuclei; gamma‐ray bursts; the origin of cosmic rays and supernova remnants; and searches for hypothetical new phenomena such as supersymmetric dark‐matter annihilations, Lorentz‐invariance violation, and exotic relics from the Big Bang. In addition to a short review of the science opportunities, this talk will describe the high‐energy gamma‐ray telescope and its components and review the mission status.
118623913
A Blind Search for Pulsars in EGRET Data using a Time Differencing Technique
Most of the sources in the galactic plane detected by the EGRET instrument on board the Compton Gamma‐Ray Observatory still remain unidentified. The energy spectra of some of the sources suggest that the gamma‐ray emission originates from pulsars. Detecting pulsed gamma‐ray emission without prior knowledge of the pulsar spin parameters is exceedingly difficult. Standard pulsar blind searches rely on the execution of long FFTs, which use a large amount of computational power. We present a pulsar blind search, based on our Time Differencing Technique, that can be carried out more economically, in this example on a standard office PC. To prove the concept of this search method we conducted a blind periodicity search on all 271 sources from the 3rd EGRET catalog.
208651245
A Monte Carlo Study of the Irreducible Background in the EGRET In- strument
The diffuse extragalactic γ-ray background (EGRB) has been derived by various groups from observations by the Energetic Gamma Ray Experiment Telescope (EGRET) instrument on the Compton Gamma Ray Observatory (CGRO). The derived EGRB consists of γ-rays that may come from astrophysical components, such as from unresolved extragalactic point sources (blazars, normal galaxies, etc.), true extragalactic diffuse emission, misattributed diffuse signals from the Galaxy and other celestial sources, and an irreducible instrumental background due to γ-rays produced by cosmic-ray (CR) interactions in the EGRET instrument. Using the Gamma Ray Large Area Space Telescope (GLAST) simulation and reconstruction software, we have investigated the magnitude of the irreducible instrumental background in the GLAST Large Area Telescope (LAT). We re-scale our results to the EGRET and present preliminary results of our study and its effect on current estimates of the EGRB.
15526014
Dark Matter Searches with Astroparticle Data
The existence of dark matter (DM) was first noticed by Zwicky in the 1930s, but its nature remains one of the great unsolved problems of physics. A variety of observations indicate that it is nonbaryonic and nonrelativistic. One of the preferred candidates for nonbaryonic DM is a weakly interacting massive particle (WIMP) that in most models is stable. WIMP self-annihilation can produce cosmic rays, gamma rays, and other particles with signatures that may be detectable. Hints of anomalous cosmic-ray spectra found by recent experiments, such as PAMELA, have motivated interesting interpretations in terms of DM annihilation and/or decay. However, these signatures also have standard astrophysical interpretations, so additional evidence is needed in order to make a case for detection of DM annihilation or decay. Searches by the Fermi-LAT for gamma-ray signals from clumps, nearby dwarf spheroidal galaxies, and galaxy clusters have also been performed, along with measurements of the diffuse Galactic and extragalactic gammaray emission. In addition, Imaging Air Cherenkov Telescopes like HESS, MAGIC, and VERITAS have reported on searches for gamma-ray emission from dwarf galaxies. In this review, we examine the status of searches for particle DM by these instruments and discuss the interpretations and resulting DM limits.
6698984
The Bulge Globular Cluster NGC 6553: Observations with HST's WFPC2, STIS, and NICMOS
As part of a large HST project to study the formation and evolution of rich star clusters in the Large Magellanic Cloud, we present results for the Galactic bulge metal-rich globular cluster NGC6553. HST observations using WFPC2, NICMOS and STIS were obtained for this cluster. The primarily reason for studying NGC6553 is to allow the possibility to transform our NICMOS and STIS magnitudes directly into stellar masses. This is particularly important for determining the low mass end of the IMF. NGC 6553 was chosen because its metallicity, [Fe/H]$=-0.22\pm 0.05$, is representative of the metallicities
16316489
Constraints on Galaxy Formation from Stars in the Far Outer Disk of M31
Numerical simulations of galaxy formation within the cold dark matter (CDM) hierarchical clustering framework are unable to produce large disk galaxies without invoking some form of feedback to suppress gas cooling and collapse until a redshift of unity or below. An important observational consequence of delaying the epoch of disk formation until relatively recent times is that the stellar populations in the extended disk should be of predominantly young-to-intermediate age. We use a deep Hubble Space Telescope/Wide Field Planetary Camera 2 archival pointing to investigate the mean age and metallicity of the stellar population in a disk-dominated field at 30 kpc along the major axis of M31. Our analysis of the color-magnitude diagram reveals the dominant population to have a significant mean age (greater than or similar to8 Gyr) and a moderately high mean metallicity ([Fe/H] similar to -0.7); tentative evidence is also presented for a trace population of ancient (greater than or equal to 10 Gyr) metal-poor stars. These characteristics are unexpected in CDM models, and we discuss the possible implications of this result as well as alternative interpretations.
16108826
Validation of spallation neutron production and propagation within Geant4
Using simulations to understand backgrounds from muon-induced neutrons is important in designing next-generation low-background underground experiments. Validation of relevant physics within the Geant4 simulation package has been completed by comparing to data from two recent experiments. Verification focused on the production and propagation of neutrons at energies important to underground experiments. Discrepancies were observed between experimental data and the simulation. Techniques were explored to correct for these discrepancies.
18564854
Searching for the Precursors of Life in External Galaxies
Are the organic molecules crucial for life on Earth abundant in early-epoch galaxies? To address this, we searched for organic molecules in extragalactic sources via their absorption features, known as diffuse interstellar bands (DIBs). There is strong evidence that DIBs are associated with polycyclic aromatic hydrocarbons (PAHs) and carbon chains. Galaxies with a preponderance of DIBs may be the most likely places in which to expect life. 
We use the method of quasar absorption lines to probe intervening early-epoch galaxies for the DIBs. We present the equivalent width measurements of DIBs in one neutral hydrogen (HI) abundant galaxy and limits for five DIB bands in six other HI-rich galaxies (damped Lyman-alpha systems--DLAs). Our results reveal that HI-rich galaxies are dust poor and have significantly lower reddening than known DIB-rich Milky Way environments. We find that DIBs in HI-rich galaxies do not show the same correlation with hydrogen abundance as observed in the Milky Way; the extragalactic DIBs are underabundant by as much as 10 times. The lower limit gas-to-dust ratios of four of the HI-rich early epoch galaxies are much higher than the gas-to-dust ratios found in the Milky Way. Our results suggest that the organic molecules responsible for the DIBs are underabundant in HI-rich early epoch galaxies relative to the Milky Way.
9892560
Using STIS to find gamma-ray burst redshifts
A recent spectrum of the optical afterglow of GRB 970508 suggests that gamma-ray bursts (GRBs) are cosmological in origin, and it is of crucial importance to derive an accurate distance to each burst. If GRBs occur near their host galaxies (much less than 40 kpc) then Lyman limit absorption should be observable in roughly half the GRB afterglow spectra. Here we outline the methodology to obtain a redshift from the GRB afterglow spectrum using the recently installed Space Telescope Imaging Spectrograph (STIS) instrument on board HST. A low-resolution spectrum with the Multi-Anode Microchannel Array (MAMA) detector gives complete spectral coverage over the wavelength range 1570-3180 A and 1150-1740 A. Assuming that a Target of Opportunity observation is conducted soon (about 3 wk) after a bright burst, a relatively small integration time (about three orbits) would be sufficient to detect the Lyman limit over a wide redshift range (0.3-2.2). Detection (or nondetection) of the Lyman limit, in concert with ground-based observations of nearby galaxies and Mg II and C IV absorption lines, should provide meaningful constraints on the relationship of GRBs to galaxies.