121348159
Measurement of the Crab spectrum with Milagro
Through use of new algorithms for estimating γ-ray and cosmic ray primary energies of events in Milagro we determine the energy spectra of gamma rays from the Crab nebula and spectra of Milagro background triggers have been determined in the energy range 1 to 100 TeV. The measured spectra are compared with those measured by ACT techniques and direct measurements of cosmic ray spectra.
117206415
Event‐by‐Event Energy Estimation and Spectral Determination with Milagro
The observed characteristics of a TeV gamma ray shower which triggers Milagro depend on core location, zenith angle, and primary energy. An algorithm to estimate the primary energy on an event‐by‐event basis based upon observed quantities has been devised. This algorithm is applied to signals observed from sources to determine energy spectra in the energy range 1 to 100 TeV. Results for spectral determination are presented for the Crab nebula. For the Crab nebula our results are similar to atmospheric Cherenkov telescope measurements.
9139935
ProtoEXIST: advanced prototype CZT coded aperture telescopes for EXIST
ProtoEXIST1 is a pathfinder for the EXIST-HET, a coded aperture hard X-ray telescope with a 4.5 m2 CZT detector plane a 90x70 degree field of view to be flown as the primary instrument on the EXIST mission and is intended to monitor the full sky every 3 h in an effort to locate GRBs and other high energy transients. ProtoEXIST1 consists of a 256 cm2 tiled CZT detector plane containing 4096 pixels composed of an 8x8 array of individual 1.95 cm x 1.95 cm x 0.5 cm CZT detector modules each with a 8 x 8 pixilated anode configured as a coded aperture telescope with a fully coded 10° x 10° field of view employing passive side shielding and an active CsI anti-coincidence rear shield, recently completed its maiden flight out of Ft. Sumner, NM on the 9th of October 2009. During the duration of its 6 hour flight on-board calibration of the detector plane was carried out utilizing a single tagged 198.8 nCi Am-241 source along with the simultaneous measurement of the background spectrum and an observation of Cygnus X-1. Here we recount the events of the flight and report on the detector performance in a near space environment. We also briefly discuss ProtoEXIST2: the next stage of detector development which employs the NuSTAR ASIC enabling finer (32×32) anode pixilation. When completed ProtoEXIST2 will consist of a 256 cm2 tiled array and be flown simultaneously with the ProtoEXIST1 telescope.
19868552
Tiled Array of Pixelated CZT Imaging Detectors for ProtoEXIST2 and MIRAX-HXI
We have assembled a tiled array (220 cm2) of fine pixel (0.6 mm) imaging CZT detectors for a balloon borne wide-field hard X-ray telescope, ProtoEXIST2. ProtoEXIST2 is a prototype experiment for a next generation hard X-ray imager MIRAX-HXI on board Lattes, a spacecraft from the Agencia Espacial Brasilieira. MIRAX will survey the 5 to 200 keV sky of Galactic bulge, adjoining southern Galactic plane and the extragalactic sky with 6 ' angular resolution. This survey will open a vast discovery space in timing studies of accretion neutron stars and black holes. The ProtoEXIST2 CZT detector plane consists of 64 of 5 mm thick 2 cm × 2 cm CZT crystals tiled with a minimal gap. MIRAX will consist of 4 such detector planes, each of which will be imaged with its own coded-aperture mask. We present the packaging architecture and assembly procedure of the ProtoEXIST2 detector. On 2012, Oct 10, we conducted a successful high altitude balloon experiment of the ProtoEXIST1 and 2 telescopes, which demonstrates their technology readiness for space application. During the flight both telescopes performed as well as on the ground. We report the results of ground calibration and the initial results for the detector performance in the balloon flight.
119196181
The REgolith X-Ray Imaging Spectrometer (REXIS) for OSIRIS-REx: identifying regional elemental enrichment on asteroids
The OSIRIS-REx Mission was selected under the NASA New Frontiers program and is scheduled for launch in September of 2016 for a rendezvous with, and collection of a sample from the surface of asteroid Bennu in 2019. 101955 Bennu (previously 1999 RQ36) is an Apollo (near-Earth) asteroid originally discovered by the LINEAR project in 1999 which has since been classified as a potentially hazardous near-Earth object. The REgolith X-Ray Imaging Spectrometer (REXIS) was proposed jointly by MIT and Harvard and was subsequently accepted as a student led instrument for the determination of the elemental composition of the asteroid's surface as well as the surface distribution of select elements through solar induced X-ray fluorescence. REXIS consists of a detector plane that contains 4 X-ray CCDs integrated into a wide field coded aperture telescope with a focal length of 20 em for the detection of regions with enhanced abundance in key elements at 50 m scales. Elemental surface distributions of approximately 50-200 m scales can be detected using the instrument as a simple collimator. An overview of the observation strategy of the REXIS instrument and expected performance are presented here.
29786670
Pulsar Discovery by Global Volunteer Computing
Einstein@Home, a distributed computing project, discovered a rare, isolated pulsar with a low magnetic field. Einstein@Home aggregates the computer power of hundreds of thousands of volunteers from 192 countries to mine large data sets. It has now found a 40.8-hertz isolated pulsar in radio survey data from the Arecibo Observatory taken in February 2007. Additional timing observations indicate that this pulsar is likely a disrupted recycled pulsar. PSR J2007+2722’s pulse profile is remarkably wide with emission over almost the entire spin period; the pulsar likely has closely aligned magnetic and spin axes. The massive computing power provided by volunteers should enable many more such discoveries.
118374435
An example of the Vilkovisky-DeWitt effective action in one loop quantum gravity
39584401
Cosmic strings confront COBE
We investigate large-angle anisotropies in the cosmic microwave radiation background which are induced by cosmic strings. We numerically evolve a string network from a redshift Z-100 to the present day and we use this data to generate a full-sky temperature map using sophisticated Green's function methods. Based on a limited number of realizations, we have compared the results of our simulations with the observations of the COBS-DMR experiment, demonstrating broad consistency. We have obtained a preliminary normalization for the string mass-per-unit-length μ in the cosmic string scenario.
117985245
Structure Formation Seeded by Cosmic Strings
We describe the results of high-resolution numerical simulations of structure formation seeded by a cosmic string network with a large dynamical range taking into account, for the first time, modifications due to the radiation-matter transition [1]. The resulting linear power spectrum of density perturbations is calculated with either cold or hot dark matter backgrounds and compared with the linear power spectrum inferred from various galaxy surveys [2]. Finally, we investigate the performance of cosmic string models in open universes and those with a non-zero cosmological constant. This direct numerical approach marks a considerable quantitative advance by incorporating important aspects of the relevant physics not included in previous treatments.
123517774
THE GRAVITON PROPAGATOR IN HOMOGENEOUS AND ISOTROPIC SPACETIMES
We find the propagator for gravitons in spacetimes with homogeneous and isotropic flat (k =0) spatial sections. The method also appfies to the k = +1 and k = -1 cases. The vacuum state is assumed to be homogeneous and isotropic in the same way as the spacetime. In the four most interesting physical cases, which are de Sitter space, the radiation and dust dominated models, and flat space, we obtain the graviton propagator in closed form for the adiabatic vacuum state.