The Gamma-Ray Burst Monitor (GBM) will significantly augment the science return from the Fermi Observatory in the study of gamma-ray bursts (GRBs). The primary objective of GBM is to extend the energy range over which bursts are observed downward from the energy range of the Large Area Telescope (LAT) on Fermi into the hard X-ray range where extensive previous data sets exist. A secondary objective is to compute burst locations onboard to allow re-orienting the spacecraft so that the LAT can observe delayed emission from bright bursts. GBM uses an array of 12 sodium iodide scintillators and two bismuth germanate scintillators to detect gamma rays from ~8 keV to ~40 MeV over the full unocculted sky. The onboard trigger threshold is ~0.7 photons cm–2 s–1 (50-300 keV, 1 s peak). GBM generates onboard triggers for ~250 GRBs per year.

https://iopscience.iop.org/article/10.1088/0004-637X/702/1/791/pdf

THE fermi gamma-ray burst monitor

This is the first in a series of gamma-ray burst spectroscopy catalogs from the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory, each covering a different aspect of burst phenomenology. In this paper, we present time sequences of spectral fit parameters for 156 bursts selected for either their high peak flux or fluence. All bursts have at least eight spectra in excess of 45 σ above background and span burst durations from 1.66 to 278 s. Individual spectral accumulations are typically 128 ms long at the peak of the brightest events but can be as short as 16 ms, depending on the type of data selected. We have used mostly high energy resolution data from the Large Area Detectors, covering an energy range of typically 28-1800 keV. The spectral model chosen is from a small empirically determined set of functions, such as the well-known "GRB" function, that best fits the time-averaged burst spectra. Thus, there are generally three spectral shape parameters available for each of the 5500 total spectra: a low-energy power-law index, a characteristic break energy, and possibly a high-energy power-law index. We present the distributions of the observed sets of these parameters and comment on their implications. The complete set of data that accompanies this paper is necessarily large and thus is archived in the electronic edition of the Astrophysical Journal.

https://iopscience.iop.org/article/10.1086/313289/pdf

The BATSE Gamma-Ray Burst Spectral Catalog. I. High Time Resolution Spectroscopy of Bright Bursts Using High Energy Resolution Data

We present the calibration and background model for the Proportional Counter Array (PCA) aboard the Rossi X-ray Timing Explorer (RXTE). The energy calibration is systematics limited below 10 keV with deviations from a power law fit to the Crab nebula plus pulsar loss than 1%. Unmodelled variations in the instrument background amount to less than 2% of the observed background below 10 keV and less than 1% between 10 and 20 keV. Individual photon arrival times are accurate to 4.4 microseconds at all times during the mission and to 2.5 microseconds after 29 April 1997. The peak pointing direction of the five collimators is known at few arcsecond precision.

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Calibration of the Rossi X-Ray Timing Explorer Proportional Counter Array

The Chandra X-Ray Observatory, the x-ray component of NASA's Great Observatories, was launched early in the morning of 1999, July 23 by the Space Shuttle Columbia. The Shuttle launch was only the first step in placing the observatory in orbit. After release from the cargo bay, the Inertial Upper Stage performed two firings, and separated from the observatory as planned. Finally, after five firings of Chandra's own Integral Propulsion System--the last of which took place 15 days after launch--the observatory was placed in its highly elliptical orbit of approximately 140,000 km apogee and approximately 10,000 km perigee. After activation, the first x-rays focused by the telescope were observed on 1999, August 12. Beginning with these initial observations one could see that the telescope had survived the launch environment and was operating as expected. The month following the opening of the sun-shade door was spent adjusting the focus for each set of instrument configurations, determining the optical axis, calibrating the star camera, establishing the relative response functions, determining energy scales, and taking a series of `publicity' images. Each observation proved to be far more revealing than was expected. Finally, and despite an initial surprise and setback due to the discovery that the Chandra x-ray telescope was far more efficient for concentrating low-energy protons that had been anticipated, the observatory is performing well and is returning superb scientific data. Together with other space observations, most notably the recently activated XMM-Newton, it is clear that we are entering a new era of discovery in high-energy astrophysics.

Chandra X-ray Observatory (CXO): overview

The synchrotron shock model (SSM) for gamma-ray burst emission makes a testable prediction: that the observed low-energy power-law photon number spectral index cannot exceed -2/3 (where the photon model is defined with a positive index: $dN/dE \propto E{alpha}$). We have collected time-resolved spectral fit parameters for over 100 bright bursts observed by the Burst And Transient Source Experiment on board the {\it Compton Gamma Ray Observatory}. Using this database, we find 23 bursts in which the spectral index limit of the SSM is violated, We discuss elements of the analysis methodology that affect the robustness of this result, as well as some of the escape hatches left for the SSM by theory.

The Synchrotron Shock Model Confronts a "Line of Death" in the BATSE Gamma-Ray Burst Data

The light emitted by electron avalanches in a parallel plate chamber can be used to image the tracks of photoelectrons liberated by the interaction of an incident X-ray with the gas filling the chamber. The differing morphologies of photoelectron tracks and high-energy charged particle tracks can be used for background rejection. The initial direction (before scattering) of the liberated photoelectron also contains information about the polarization of the incident radiation. We have built a small test chamber with which we have imaged photoelectron tracks using an intensified CCD camera. Our results show that optical imaging could be used in a hard X-ray imaging polarimeter useful for astronomy.

Optical imaging chamber for X-ray astronomy

In April 2016 Physics Today challenged its readers to write a fictional news story about a discovery made in 2116. Robert Austin’s winning entry describes a huge space telescope fashioned from laser-machined asteroids.

https://physicstoday.scitation.org/doi/pdf/10.1063/PT.3.3395

Megatelescope releases its first image

We are developing high-energy grazing-incidence replicated optics for a balloon-borne hard-x-ray telescope. When completed, the instrument will have 170 cm2 of effective collecting area at 40 keV and 130 square cm at 60 keV with <= 30 arc seconds half power diameter. This payload will offer unprecedented sensitivity in the hard-x-ray region, with around 250 microCrab sensitivity on long-duration flights and 50-100 microCrab on ultra- long-duration balloon missions The payload consists of 16 mirror modules, each with 14 nested mirrors made from a high-strength nickel alloy, and a corresponding array of 16 focal plane detectors. An engineering demonstration flight is scheduled for the Spring of 2000, using just two mirror modules each with 3 shells, above a pair of gas-scintillation-proportional counters. This flight is intended to test a newly designed gondola pointing and aspect system and the stability of the optical bench design. The first scientific flight of the full payload is scheduled for the Fall of 2002. Full details of the payload and its capabilities will be presented together with data from various mirror-module tests. If available data from the first flight will also be presented.

HERO: high-energy replicated optics for a hard-x-ray balloon payload

Next generation neutron science facilities, such as the Spallation Neutron Source, require improved thermal neutron detectors, with high counting rate capability, high spatial resolution, low cost per unit area, and adaptability to unique geometries. We propose a neutron detector technology, based on arrays of boron-lined plastic straws, that satisfies the above requirements. The elemental component of this detector is a B/sub 4/C-lined mylar straw, 4 mm in diameter and 1 m long, and operated as a proportional counter with an Ar/ethane gas mixture. Thermal neutrons captured in /sup 10/B are converted into secondary particles, which ionize the gas contained within the straw. Using a deep stack of such straws, with 20-25 layers, neutron detection efficiencies up to 80% can be achieved in the 1-10 /spl Aring/ neutron wavelength range. In such a highly segmented array, exceedingly high count rates can be achieved, on the order of 200/spl times/10/sup 6/ cps/m/sup 2/. Gamma ray discrimination was on the order of 10/sup 6/ for an energy threshold of 50 keV; position resolution of a 1-m long detector was measured to be 5.5 mm FWHM, and a highly linear readout was achieved using resistive charge division.

/pdf/novel-neutron-detector-for-high-rate-imaging-applications-4p08rn9dj6.pdf

Novel neutron detector for high rate imaging applications

An optical imaging chamber can be used to detect x-rays by imaging the tracks of photoelectrons ejected when the x-rays are absorbed in the detector volume. These tracks contain information about the location of the x-ray interaction point and its polarization. In the lab, we have obtained a modulation factor of 30% for 60 keV polarized x-rays. Here we discuss preliminary work done towards building a large area hard x-ray imaging polarimeter which will be able to measure x-ray polarizations from bright cosmic x-ray sources at energies between 40 keV and 100 keV.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Robert A. Austin

Papers

Optical imaging chamber for X-ray astronomy

Megatelescope releases its first image

HERO: high-energy replicated optics for a hard-x-ray balloon payload

Novel neutron detector for high rate imaging applications

Development of a hard x-ray imaging polarimeter