L. M. Barbier

The First Swift BAT Gamma-Ray Burst Catalog

We present the first Swift Burst Alert Telescope (BAT) catalog of gamma-ray bursts (GRBs), which contains bursts detected by the BAT between 2004 December 19 and 2007 June 16. This catalog (hereafter the BAT1 catalog) contains burst trigger time, location, 90% error radius, duration, fluence, peak flux, and time-averaged spectral parameters for each of 237 GRBs, as measured by the BAT. The BAT-determined position reported here is within 1.75 --> of the Swift X-Ray Telescope (XRT)-determined position for 90% of these GRBs. The BAT T90 and T50 durations peak at 80 and 20 s, respectively. From the fluence-fluence correlation, we conclude that about 60% of the observed peak energies, -->Epeakobs, of BAT GRBs could be less than 100 keV. We confirm that GRB fluence to hardness and GRB peak flux to hardness are correlated for BAT bursts in analogous ways to previous missions results. The correlation between the photon index in a simple power-law model and -->Epeakobs is also confirmed. We also report the current status for the on-orbit BAT calibrations based on observations of the Crab Nebula.

Epeak estimator for gamma-ray bursts observed by the swift burst alert telescope

We report a correlation based on a spectral simulation study of the prompt emission spectra of gamma-ray bursts (GRBs) detected by the Swift Burst Alert Telescope (BAT). The correlation is between the E peak energy, which is the peak energy in the νFν spectrum, and the photon index (Γ) derived from a simple power-law (PL) model. The E peak-Γ relation, assuming the typical smoothly broken PL spectrum of GRBs, is log E peak = 3.258 – 0.829 Γ (1.3 ≤ Γ ≤ 2.3). We take into account not only a range of E peak energies and fluences, but also distributions for both the low-energy photon index and the high-energy photon index in the smoothly broken PL model. The distribution of burst durations in the BAT GRB sample is also included in the simulation. Our correlation is consistent with the index observed by BAT and E peak measured by the BAT, and by other GRB instruments. Since about 85% of GRBs observed by the BAT are acceptably fit with the simple PL model because of the relatively narrow energy range of the BAT, this relationship can be used to estimate E peak when it is located within the BAT energy range.

CdZnTe and CdTe detector arrays for hard X-ray and gamma-ray astronomy

Abstract A variety of CdZnTe and CdTe detector arrays were fabricated at NASA/GSFC for use in hard X-ray and gamma-ray astronomy. Mosaic, pixel, and 3-D position-sensitive detector arrays were built to demonstrate the capabilities for high-resolution imaging and spectroscopy for 10 to 2xa0MeV. This paper will summarize the different arrays and their applications for instruments being developed at NASA/GSFC. Specific topics to be addressed include materials characterization, fabrication of detectors, ASIC readout electronics, and imaging and spectroscopy tests.

XA readout chip characteristics and CdZnTe spectral measurements

The authors report on the performance of a CdZnTe (CZT) array readout by an XA (X-ray imaging chip produced at the AMS foundry) application specific readout chip (ASIC). The array was designed and fabricated at NASA/Goddard Space Flight Center (GSFC) as a prototype for the Burst Arc-Second Imaging and Spectroscopy gamma-ray instrument. The XA ASIC was obtained from Integrated Detector and Electronics (IDE), in Norway. Performance characteristics and spectral data for /sup 241/Am are presented both at room temperature and at -20/spl deg/C. The measured noise (/spl sigma/) was 2.5 keV at 60 keV at room temperature. This paper represents a progress report on work with the XA ASIC and CZT detectors. Work is continuing and in particular, larger arrays are planned for future NASA missions.

A measurement of cosmic ray deuterium from 0.5–2.9 GeV/nucleon

The rare isotopes ^(2)H and ^(3)He in cosmic rays are believed to originate mainly from the interaction of high energy protons and helium with the galactic interstellar medium. The unique propagation history of these rare isotopes provides important constraints on galactic cosmic ray source spectra and on models for their propagation within the Galaxy. Hydrogen and helium isotopes were measured with the balloon-borne experiment, IMAX, which flew from Lynn Lake, Manitoba in 1992. The energy spectrum of deuterium between 0.5 and 3.2 GeV/nucleon measured by the IMAX experiment as well as previously published results of ^(3)He from the same instrument will be compared with predictions of cosmic ray galactic propagation models. The observed composition of the light isotopes is found to be generally consistent with the predictions of the standard Leaky Box Model derived to fit observations of heavier nuclei

Confirmation of the [FORMULA][F]E[SUP][RM]src[/RM][/SUP][INF][RM]peak[/RM][/INF]-E[INF][RM]iso[/RM][/INF][/F][/FORMULA] (Amati) Relation from the X-Ray Flash XRF 050416AObserved by theSwiftBurst Alert Telescope

We report Swift Burst Alert Telescope (BAT) observations of the X-ray flash (XRF) XRF 050416A. The fluence ratio between the 15-25 and 25-50 keV energy bands of this event is 1.1, thus making it the softest gamma-ray burst (GRB) observed by BAT so far. The spectrum is well fitted by a Band function with E of 15.0 keV. Assuming the redshift of the host galaxy (z = 0.6535), the isotropic equivalent radiated energy Eiso and the peak energy at the GRB rest frame (E) of XRF 050416A are not only consistent with the correlation found by Amati et al. and extended to XRFs by Sakamoto et al. but also fill in the gap of this relation around the 30-80 keV range of E. This result tightens the validity of the E-Eiso relation from XRFs to GRBs. We also find that the jet break time estimated using the empirical relation between E and the collimation corrected energy Eγ is inconsistent with the afterglow observation by the Swift X-Ray Telescope. This could be due to the extra external shock emission overlaid around the jet break time or to the nonexistence of a jet break feature for XRFs, which might be a further challenge for GRB jet emission models and XRF/GRB unification scenarios.

Performance of Prototype Segmented CdZnTe Arrays

The Burst and All Sky Imaging Survey (BASIS) is a proposed mission to provide {approximately}3 arc second locations of approximately 90 Gamma-Ray Bursts (GRBs) per year. The BASIS coded aperture imaging system requires a segmented detector plane able to detect the interaction position of (10--150 keV) photons to less than 100 {micro}m. To develop prototype detector arrays with such fine position resolution the authors have fabricated many 15 mm x 15 mm x 2 mm 100 {micro}m pitch CdZnTe strip detectors. They have assembled these fine pitch CdZnTe strip detectors into prototype 2 x 2 and 6 x 6 element arrays read out by ASIC electronics. The assembly and electronics readout of the 6 x 6 flight prototype array will be discussed, and preliminary data illustrating the uniformity and efficiency of the array will be presented.

CZT strip detectors for imaging and spectroscopy: collimated beam and ASIC readout experiments

We report the status of ongoing investigations into Cadmium Zinc Telluride (CZT) strip detectors for application in hard X-ray astronomy. We have instrumented a nine strip by nine strip region of a two sided strip detector made in our detector fabrication facility. In order to measure the position resolution of our detectors, we have implemented a collimated beam that concentrates radiation to a spot size less than the strip width of our detector. We have also performed charge collection studies as a function of incident photon energy and bias voltage with a single sided, 100 /spl mu/m pitch CZT strip detector wire bonded to an SVX ASIC charge amplifier. The detectors exhibited excellent strip uniformity in terms of photon count rate and spectroscopic information.

Neutron imaging camera

We describe the Neutron Imaging Camera (NIC) being developed for the detection of special nuclear materials by NASA/GSFC and NSWC/Carderock. The NIC is a self-contained, robust, omni-directional and 3He-independent neutron detector based on the Three-Dimensional Track Imager (3-DTI) technology developed at GSFC for gamma-ray astrophysics applications. The 3-DTI is a large volume time-projection chamber that provides ∼ 0.4 mm resolution for the 3-D tracking of a charged particle. The incident direction of fast neutrons, 0.1 MeV < En < 10 MeV, are reconstructed from the momenta and energies of protons resulting from single and double scatters on methane (CH4). We present angular and energy resolution of the NIC derived from laboratory and accelerator testing.

Probing the Nature of Short Swift Bursts via Deep INTEGRAL Monitoring of GRB 050925

Abstract We present results from Swift, XMM-Newton, and deep INTEGRAL monitoring in the region of GRB 050925. This short Swift burst is a candidate for a newly discovered soft gamma-ray repeater (SGR) with the following observational burst properties: (1) galactic plane (bxa0=xa0−0.1°) localization, (2) 150xa0ms duration, and (3) a blackbody rather than a simple power-law spectral shape (with a significance level of 97%). We found two possible X-ray counterparts of GRB 050925 by comparing the X-ray images from Swift XRT and XMM-Newton. Both X-ray sources show the transient behavior with a power-law decay index shallower than −1. We found no hard X-ray emission nor any additional burst from the location of GRB 050925 in ∼5xa0ms of INTEGRAL data. We discuss about the three BATSE short bursts which might be associated with GRB 050925, based on their location and the duration. Assuming GRB 050925 is associated with the HII regions (W 58) at the galactic longitude of lxa0=xa070°, we also discuss the source frame properties of GRB 050925.