Description of a subset of single events from the BATSE gamma ray burst data

About 15 percent of the gamma ray bursts in the Burst and Transient Source Experiment (BATSE) data exhibit a simple light curve consisting mainly of a single pulse without fine substructures. In 12 of the burst profiles, the pulse shapes show a linear rise and decay. Three events have a distinct sharp rise followed by a long, almost exponential decay. Searches based on only a sharp rise selection criterion resulted in five more grbs with different profile complexities. In one case, we identify an envelope of fast oscillations with a long, softer tail lasting about 100 seconds. The majority of events were detectable at energies above 300 keV, with tentative estimates for fluences that vary between 4.0 x 10(exp -8) and 5.4 x 10(exp -6) ergs/sq cm. We describe here their general characteristics (durations, rise-decay times) and their hardness ratios

\u3cem\u3eIn vivo\u3c/em\u3e Imaging of Human Cone Photoreceptor Inner Segments

Purpose. An often overlooked prerequisite to cone photoreceptor gene therapy development is residual photoreceptor structure that can be rescued. While advances in adaptive optics (AO) retinal imaging have recently enabled direct visualization of individual cone and rod photoreceptors in the living human retina, these techniques largely detect strongly directionally-backscattered (waveguided) light from normal intact photoreceptors. This represents a major limitation in using existing AO imaging to quantify structure of remnant cones in degenerating retina. Methods. Photoreceptor inner segment structure was assessed with a novel AO scanning light ophthalmoscopy (AOSLO) differential phase technique, that we termed nonconfocal split-detector, in two healthy subjects and four subjects with achromatopsia. Ex vivo preparations of five healthy donor eyes were analyzed for comparison of inner segment diameter to that measured in vivo with split-detector AOSLO. Results. Nonconfocal split-detector AOSLO reveals the photoreceptor inner segment with or without the presence of a waveguiding outer segment. The diameter of inner segments measured in vivo is in good agreement with histology. A substantial number of foveal and parafoveal cone photoreceptors with apparently intact inner segments were identified in patients with the inherited disease achromatopsia. Conclusions. The application of nonconfocal split-detector to emerging human gene therapy trials will improve the potential of therapeutic success, by identifying patients with sufficient retained photoreceptor structure to benefit the most from intervention. Additionally, split-detector imaging may be useful for studies of other retinal degenerations such as AMD, retinitis pigmentosa, and choroideremia where the outer segment is lost before the remainder of the photoreceptor cell

Gamma-Ray Lines from Young Supernova Remnants

The gamma-ray luminosity of a typical type I supernova remnant has been calculated by assuming that the origin of the optical luminosity is due to the energy of the radioactive decay of Ni56. Tt is ex- pected that Ni56 is the most abundant nucleus resulting from silicon burning in the supernova shock conditions. The requisite mass of Ni56 (0.14 Mo) gives rise to gamma-ray lines with energies near 1 MeV that should be detectable in young supernova remnants at distances up to a few Mpc. Future detectors aboard satellites should be able to detect events at the rate of about two observable events per year. A few supernova remnants in the Galaxy should be observable at all times in lines following the decay of Ti44

Monitoring Cen X-3 with BATSE

The eight uncollimated BATSE Large Area Detectors (LAD's) provide the ability to monitor pulsed hard x ray sources on a nearly continuous basis. Using data from the LAD's, the pulse timing and pulsed flux of the 4.8 second period binary x ray pulsar Centaurus X-3 was analyzed over a two month period. The methods and initial results of this analysis, which includes both data folded onboard GRO and 1.024 second resolution discriminator rates folded on the ground, are presented

Multifocal ERG findings in carriers of X-linked retinoschisis

Purpose To determine whether retinal dysfunction in obligate carriers of X-linked retinoschisis (XLRS) could be observed in local electroretinographic responses obtained with the multifocal electroretinogram (mfERG). Methods Nine obligate carriers of XLRS (mean age, 46.2 years) were examined for the study. Examination of each carrier included an ocular examination and mfERG testing. For the mfERG, we used a 103-scaled hexagonal stimulus array that subtended a retinal area of approximately 40° in diameter. The amplitudes and implicit times in each location for the mfERG were compared with the corresponding values determined for a group of 34 normally-sighted, age-similar control subjects. Results Mapping of 103 local electroretinographic response amplitudes and implicit times within a central 40° area with the mfERG showed regions of reduced mfERG amplitudes and delayed implicit times in two of nine carriers. Conclusions The mfERG demonstrated areas of retinal dysfunction in two carriers of XLRS. When present, retinal dysfunction was evident in the presence of a normal-appearing fundus. Multifocal ERG testing can be useful for identifying some carriers of XLRS

Multimodal Imaging of Photoreceptor Structure in Choroideremia

Purpose Choroideremia is a progressive X-linked recessive dystrophy, characterized by degeneration of the retinal pigment epithelium (RPE), choroid, choriocapillaris, and photoreceptors. We examined photoreceptor structure in a series of subjects with choroideremia with particular attention to areas bordering atrophic lesions. Methods Twelve males with clinically-diagnosed choroideremia and confirmed hemizygous mutations in the CHM gene were examined. High-resolution images of the retina were obtained using spectral domain optical coherence tomography (SD-OCT) and both confocal and non-confocal split-detector adaptive optics scanning light ophthalmoscope (AOSLO) techniques. Results Eleven CHM gene mutations (3 novel) were identified; three subjects had the same mutation and one subject had two mutations. SD-OCT findings included interdigitation zone (IZ) attenuation or loss in 10/12 subjects, often in areas with intact ellipsoid zones; RPE thinning in all subjects; interlaminar bridges in the imaged areas of 10/12 subjects; and outer retinal tubulations (ORTs) in 10/12 subjects. Only split-detector AOSLO could reliably resolve cones near lesion borders, and such cones were abnormally heterogeneous in morphology, diameter and density. On split-detector imaging, the cone mosaic terminated sharply at lesion borders in 5/5 cases examined. Split-detector imaging detected remnant cone inner segments within ORTs, which were generally contiguous with a central patch of preserved retina. Conclusions Early IZ dropout and RPE thinning on SD-OCT are consistent with previously published results. Evidence of remnant cone inner segments within ORTs and the continuity of the ORTs with preserved retina suggests that these may represent an intermediate state of retinal degeneration prior to complete atrophy. Taken together, these results supports a model of choroideremia in which the RPE degenerates before photoreceptors

Do Gamma-Ray Burst Sources Repeat?

The demonstration of repeated gamma-ray bursts from an individual source would severely constrain burst source models. Recent reports (Quashnock and Lamb 1993; Wang and Lingenfelter 1993) of evidence for repetition in the first BATSE burst catalog have generated renewed interest in this issue. Here, we analyze the angular distribution of 585 bursts of the second BATSE catalog (Meegan et al. 1994). We search for evidence of burst recurrence using the nearest and farthest neighbor statistic and the two-point angular correlation function. We find the data to be consistent with the hypothesis that burst sources do not repeat; however, a repeater fraction of up to about 20% of the observed bursts cannot be excluded.Comment: ApJ Letters, in press, 13 pages, including three embedded figures. uuencoded Unix-compressed PostScrip

Discovery of the Orbit of the X-Ray Pulsar OAO 1657-415

Timing observations of the 38 s accreting X-ray pulsar OAO 1657-415 made with the BATSE large-area detectors on the Compton Gamma Ray Observatory have revealed a binary orbit with an X-ray eclipse by the stellar companion. Arrival time analysis of 20-60 keV data yielded the following best-fit orbital elements: P_(orb) = 10^d.4436 ± 0^d.0038, a_x sin i = 106.0 ± 0.5 lt-sec, e = 0.104 ± 0.005, ω = 93° ± 5°, T_(π/2) = JD 2,448,516.49 ± 0.05 TDB. From the pulsar mass function f_x(M) = 11.7 ± 0.2 M_⊙ and the measured eclipse half-angle θ_e = 29.7 ± 1.3 deg, we infer that the stellar companion is a supergiant of spectral class B0-B6. If the companion can be identified and its orbital velocity measured, the neutron star mass can be constrained. Both intrinsic spin-up and spin-down of the pulsar were measured during our observation

FiberGLAST: a scintillating fiber approach to the GLAST mission

FiberGLAST is a scintillating fiber gamma-ray detector designed for the GLAST mission. The system described below provides superior effective area and field of view for modest cost and risk. An overview of the FiberGLAST instrument is presented, as well as a more detailed description of the principle elements of the primary detector volume. The triggering and readout electronics are described, and Monte Carlo Simulations of the instrument performance are presented

Assessing Retinal Structure In Complete Congenital Stationary Night Blindness and Oguchi Disease

Purpose To examine retinal structure and changes in photoreceptor intensity after dark adaptation in patients with complete congenital stationary night blindness and Oguchi disease. Design Prospective, observational case series. Methods We recruited 3 patients with complete congenital stationary night blindness caused by mutations in GRM6, 2 brothers with Oguchi disease caused by mutations in GRK1, and 1 normal control. Retinal thickness was measured from optical coherence tomography images. Integrity of the rod and cone mosaic was assessed using adaptive optics scanning light ophthalmoscopy. We imaged 5 of the patients after a period of dark adaptation and examined layer reflectivity on optical coherence tomography in a patient with Oguchi disease under light- and dark-adapted conditions. Results Retinal thickness was reduced in the parafoveal region in patients with GRM6 mutations as a result of decreased thickness of the inner retinal layers. All patients had normal photoreceptor density at all locations analyzed. On removal from dark adaptation, the intensity of the rods (but not cones) in the patients with Oguchi disease gradually and significantly increased. In 1 Oguchi disease patient, the outer segment layer contrast on optical coherence tomography was 4-fold higher under dark-adapted versus light-adapted conditions. Conclusions The selective thinning of the inner retinal layers in patients with GRM6 mutations suggests either reduced bipolar or ganglion cell numbers or altered synaptic structure in the inner retina. Our finding that rods, but not cones, change intensity after dark adaptation suggests that fundus changes in Oguchi disease are the result of changes within the rods as opposed to changes at a different retinal locus