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.
15057663
Linac Coherent Light Source Undulator RF BPM System
The Linac Coherent Light Source (LCLS) will be the world's first x-ray free-electron laser (FEL) when it becomes operational in 2009. The LCLS is currently in the construction phase. The beam position monitor (BPM) system planned for the LCLS undulator will incorporate a high-resolution X-band cavity BPM system described in this paper. The BPM system will provide high-resolution measurements of the electron beam trajectory on a pulse-to-pulse basis and over many shots. The X-band cavity BPM size, simple fabrication, and high resolution make it an ideal choice for LCLS beam position detection. We will discuss the system specifications, design, and prototype test results.
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.
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.
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.
15325639
A Fresh Look at Diffuse Gamma-ray Emission from the Inner Galaxy
The Energetic Gamma-Ray Experiment Telescope (EGRET) experiment onboard the Compton Gamma-Ray Observatory (CGRO) has provided the most precise measurements of the -ray sky to date. The EGRET measurements of the diffuse emission across the sky show an excess above 1 GeV. This "GeV excess" has been a topic of great debate and interest since its original discovery by Hunter et al. in 1997. We have modified the GLAST simulation and reconstruction software to model the EGRET instrument. This detailed modeling has allowed us to explore the parameters of the EGRET instrument, in both its beam-test configuration and in-orbit on CGRO, in greater detail than has previously been published. We have found that the GeV excess is significantly increased when previously unaccounted for instrumental effects are considered. We will present a new measurement of diffuse -ray emission in the inner Galaxy.
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.
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
122426348
Pion Charge Exchange Scattering at High-Energies
We report on a study of pion charge-exchange scattering carried out at Fermilab in the energy range 20 to 200 GeV. The results can be described remarkably well by a simple Regge-pole model. The charge-exchange cross sections in the forward direction lead to a prediction for the difference in total cross sections of ..pi../sup -/p and ..pi../sup +/p which is in satisfactory agreement with direct measurements of this difference in another experiment at Fermilab. (AIP)
22684568
MaGe-a Geant4-Based Monte Carlo Application Framework for Low-Background Germanium Experiments
We describe a physics simulation software framework, MaGe, that is based on the Geant4 simulation toolkit. MaGe is used to simulate the response of ultra-low radioactive background detectors to ionizing radiation, specifically the Majorana and Gerda neutrinoless double-beta decay experiments. Majorana and Gerda use high-purity germanium detectors to search for the neutrinoless double-beta decay of 76Ge and MaGe is jointly developed between these two collaborations. The MaGe framework contains the geometry models of common objects, prototypes, test stands and the actual experiments. It also implements customized event generators, Geant4 physics lists and output formats. All of these features are available as class libraries that are typically compiled into a single executable. The user selects the particular experimental setup implementation at run-time via macros. The combination of all these common classes into one framework reduces duplication of efforts, eases comparison between simulated data and experiment and simplifies the addition of new detectors to be simulated. This paper focuses on the software framework, custom event generators and physics lists.
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.