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All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Search for the Identification of 3EG J1835+5918: Evidence for a New Type of High-Energy Gamma-Ray Source

The EGRET source 3EG J1835+5918 is the brightest and most accurately positioned of the as-yet unidentified high-energy gamma-ray sources at high Galactic latitude (l, b = 89 deg, 25 deg). We present a multiwavelength study of the region around it, including X-ray, radio, and optical imaging surveys, as well as optical spectroscopic classification of most of the active objects in this area. Identifications are made of all but one of the ROSAT and ASCA sources in this region to a flux limit of approximately 5 x 10(exp -14) erg/sq cm s, which is 10(exp -4) of the gamma-ray flux. The identified X-ray sources in or near the EGRET error ellipse are radio-quiet QSOs, a galaxy cluster, and coronal emitting stars. We also find eight quasars using purely optical color selection, and we have monitored the entire field for variable optical objects on short and long time scales without any notable discoveries. The radio sources inside the error ellipse are all fainter than 4 mJy at 1.4 GHz. There are no flat-spectrum radio sources in the vicinity; the brightest neighboring radio sources are steep-spectrum radio galaxies or quasars. Since no blazar-like or pulsar-like candidate has been found as a result of these searches, 3EG J1835+5918 must be lacking one or more of the physically essential attributes of these known classes of gamma-ray emitters. If it is an AGN it lacks the beamed emission radio of blazars by at least a factor of 100 relative to identified EGRET blazars. If it is an isolated neutron star, it lacks the steady thermal X-rays from a cooling surface and the magnetospheric non-thermal X-ray emission that is characteristic of all EGRET pulsars. If a pulsar, 3EG J1835+5918 must be either older or more distant than Geminga, and probably an even more efficient or beamed gamma-ray engine. One intermittent ROSA T source falls on a blank optical field to a limit of B greater than 23.4, V greater than 23.3, and R greater than 22.5. In view of this conspicuous absence, RX J1836-2+5925 should be examined further as a candidate for identification with 3EG J1835+5918 and possibly the prototype of a new class of high-energy gamma-ray source.

Mirabal, N.↗
DOE OSTI2024

The Dependence of Gamma-Ray Burst Jet Collimation on Black Hole Spin

Gamma-ray bursts (GRBs) are the most luminous events in the Universe and are excellent laboratories to study extreme physical phenomena in the cosmos. Despite a long trajectory of progress in understanding these highly energetic events, there are still many observed features that are yet to be fully explained. Observations of the jet opening angle of long gamma-ray bursts (LGRBs) suggest that LGRB jets are narrower for those GRBs at higher redshift. This phenomenon has been explained in the context of collimation by the stellar envelope, with denser (lower metallicity) stars at higher redshifts able to collimate the jet more effectively. However, until now, the dependence of the jet opening angle on the properties of the central engine has not been explored. We investigate the effect of black hole spin on the jet collimation angle for a magnetically launched jet, using the general relativistic radiation magnetohydrodynamical code ν bhlight . We present 3D results for a range of spin values. The simulations show that higher-spinning black holes tend to create narrower jets. If indeed LGRB progenitors in the early Universe are able to produce black hole central engines with higher spin, this could account for at least some of the observed jet opening angle-redshift correlation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1982

Upper limits to pulsed gamma ray emission from PSR 0833-45, 1747-46, and 1818-04

Pulsed gamma ray emission from three pulsars (PSR 0833-45, 1747-46, and 1818-04) have been sought on a balloon flight of the University of New Hampshire Large Gamma Ray Telescope, which incorporates a shielded sodium iodide scintillator array, and was launched from Alice Springs, Australia. Over the energy range 0.1 - 10 MeV, no evidence is found for pulsed gamma rays, and upper limits are set for Vela which are comparable to, or below, the extrapolation to lower energies of the pulsed emission reported by SAS-2 and COS-B.

Cherry, M. L.↗
DOE OSTI2023

Creating a High Energy Alert System for the HAWC Gamma Ray Observatory [Slides]

One of the greatest mysteries in astrophysics is exactly how Cosmic Rays (CRs) are accelerated up to extremely high energies within our galaxy. Hadronic models of possible CR accelerators, including supernova remnants and pulsars, require the production of both gamma rays and neutrinos at these sources. Searching for coincidences between neutrino and the highest energy gamma ray observations can help confirm these theories. The High Altitude Water Cherenkov (HAWC) observatory is a ground based gamma ray observatory located at 4100m in Puebla, Mexico. HAWC is able to detect gamma rays with energies greater than 100 TeV, has a wide field of view, and a 95% duty cycle, making it ideal for these types of coincidence searches. This work aims to create a high energy alert system for HAWC, sending out an alert to other experiments for gamma ray events it sees above 56 TeV.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2010

Intense Gamma-Ray Flashes Above Thunderstorms on the Earth and Other Planets

Intense millisecond flashes of MeV photons have been observed with space-borne detectors in Earth orbit. They are expected to be present on other planets that exhibit lightning. The terrestrial gamma-ray flashes (TGFs) were discovered with the Burst and Transient Source Experiment (BATSE) aboard the Compton Gamma-Ray Observatory (CGRO) in the early 1990s. They are now being observed with several other instruments, including the Gamma-ray Burst Monitor (GBM) detectors on the Fermi Gamma-ray Space Telescope. Although Fermi- GBM was designed and optimized for the observation of cosmic gamma-ray bursts (GRBs), it has unprecedented capabilities for TGF observations. The TGFs usually have extremely hard continuous spectra, typical of highly- Comptonized bremsstrahlung radiation. These spectral are harder than those of GRBs, with photons extending to over 40 MeV. The most likely origin of these high-energy photons is bremsstrahlung radiation produced by a relativistic "runaway avalanche" electron beam. Such a beam is expected to be produced in an extended, intense electric field in or above thunderstorm regions. The altitude of origin and beaming characteristics of the radiation are quite uncertain. They have generated considerable observational and theoretical interest in recent years. This talk will give an overview of the all of the space-borne observations of TGFs that have been made thus far. Instruments are being designed specifically for TGF observations from new spacecraft as well as from airborne platforms

Fishman, Gerald J.↗
NASA NTRS1994

A search for the radio counterpart to the 1994 March 1 gamma-ray burst

We report on the results of a search for the radio counterpart to the bright gamma-ray burst of 1994 March 1. Using the Dominion Radio Astrophysical Observatory Synthesis Telescope sensitive, wide-field radio images at 1.4 GHz and 0.4 GHz were made of a region around GRB 940301. A total of 15 separate radio images were obtained at each frequency, sampling a near-continuous range of post-burst timescales between 3 and 15 days, as well as 26, 47, and 99 days. We place an upper limit of 3.5 mJy on a fading/flaring radio counterpart at 1.4 GHz and 55 mJy at 0.4 GHz. Unlike past efforts our counterpart search maintains high sensitivity over two decades of post-burst time durations. Time-variable radio emission after the initial gamma-ray burst is a prediction of all fireball models, currently the most popular model for gamma-ray bursts. Our observations allow us to put significant constraints on the fireball parameters for cosmological models of gamma-ray bursts.

Frail, D. A.↗
NASA NTRS1980

The use of an active coded aperture for improved directional measurements in high energy gamma-ray astronomy

The coded aperture, a refinement of the scatter-hole camera, offers a method for the improved measurement of gamma-ray direction in gamma-ray astronomy. Two prototype coded apertures have been built and tested. The more recent of these has 128 active elements of the heavy scintillator BGO. Results of tests for gamma-rays in the range 50-500 MeV are reported and future application in space discussed.

Johansson, A.↗
NASA NTRS1975

Apollo 17 mission Report. Supplement 6: Calibration results for gamma ray spectrometer sodium iodide crystal

A major difficulty in medium energy gamma-ray remote sensing spectroscopy and astronomy measurements was the high rate of unwanted background resulting from the following major sources: (1) prompt secondary gamma-rays produced by cosmic-ray interactions in satellite materials; (2) direct charged-particle counts; (3) radioactivity induced in the detector materials by cosmic-ray and trapped protons; (4) radioactivity induced in detector materials by the planetary (e.g., earth or moon) albedo neutron flux; (5) radioactivity induced in the detector materials by the interaction of secondary neutrons produced throughout the spacecraft by cosmic-ray and trapped proton interactions; (6) radioactivity induced in spacecraft materials by the mechanisms outlined in 3, 4, and 5; and (7) natural radioactivity in spacecraft and detector materials. The purpose of this experiment was to obtain information on effects 3, 4, and 5, and from this information start developing calculational methods for predicting the background induced in the crystal detector in order to correct the Apollo gamma-ray spectrometer data for this interference.

Dyer, C.↗
DOE OSTI2025

COCOA: A compact Compton camera for astrophysical observation of MeV-scale gamma rays

COCOA (COmpact COmpton cAmera) is a next-generation gamma-ray telescope designed for astrophysical observations in the MeV energy range. The detector comprises a scatterer volume employing the LiquidO detection technology and an array of scintillating crystals acting as absorber. Surrounding plastic scintillator panels serve as a veto system for charged particles. The detector's compact, scalable design enables flexible deployment on microsatellites or high-altitude balloons. Gamma rays at MeV energies have not been well explored historically (the so-called "MeV gap") and COCOA has the potential to improve the sensitivity in this energy band.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Threshold effects on V/V(max) for gamma-ray bursts

The interpretation of the observed gamma-ray burst V/V(max) statistic in terms of spatial distributions is model-dependent. Detection of gamma-ray bursts requires the counting rate in one or more detectors to exceed a threshold C(lim) determined from a time-dependent background rate B(t). The sampling depth of the burst detector is thus time-dependent, and, if burst sources are nonuniform in space, the observed V/V(max) distribution will be affected by B(t). We demonstrate this effect with a simple geometric distribution of standard candles and argue that V/V(max) statistic without information on threshold variations is insufficient for rigorous data analysis. Peak count rates and threshold values must be given separately for all events in order to facilitate a meaningful comparison of observations with theoretical distribution models.

Hartmann, D. H.↗
NASA NTRS2001

Gamma Ray Large Area Space Telescope (GLAST) Balloon Flight Engineering Model: Overview

The Gamma Ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) is a pair-production high-energy (greater than 20 MeV) gamma-ray telescope being built by an international partnership of astrophysicists and particle physicists for a satellite launch in 2006, designed to study a wide variety of high-energy astrophysical phenomena. As part of the development effort, the collaboration has built a Balloon Flight Engineering Model (BFEM) for flight on a high-altitude scientific balloon. The BFEM is approximately the size of one of the 16 GLAST-LAT towers and contains all the components of the full instrument: plastic scintillator anticoincidence system (ACD), high-Z foil/Si strip pair-conversion tracker (TKR), CsI hodoscopic calorimeter (CAL), triggering and data acquisition electronics (DAQ), commanding system, power distribution, telemetry, real-time data display, and ground data processing system. The principal goal of the balloon flight was to demonstrate the performance of this instrument configuration under conditions similar to those expected in orbit. Results from a balloon flight from Palestine, Texas, on August 4, 2001, show that the BFEM successfully obtained gamma-ray data in this high-background environment.

Thompson, D. J.↗
DOE OSTI2021

International Workshop on Next Generation Gamma-Ray Source

A workshop on The Next Generation Gamma-Ray Sources , sponsored by the Office of Nuclear Physics at the Department of Energy, was held November 17--19, 2016 in Bethesda, Maryland. The goals of the workshop were to identify basic and applied research opportunities at the frontiers of nuclear physics that would be made possible by the beam capabilities of an advanced laser Compton beam facility. To anchor the scientific vision to realistically achievable beam specifications using proven technologies, the workshop brought together experts in the fields of electron accelerators, lasers, and optics to examine the technical options for achieving the beam specifications required by the most compelling parts of the proposed research programs. An international assembly of participants included current and prospective $\gamma$-ray beam users, accelerator and light-source physicists, and federal agency program managers. Sessions were organized to foster interactions between the beam users and facility developers, allowing for information sharing and mutual feedback between the two groups. The workshop findings and recommendations are summarized in this report.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1991

The transient gamma-ray spectrometer

The authors describe the Transient Gamma-Ray Spectrometer (TGRS) to be flown onboard the WIND spacecraft. This instrument is designed to detect cosmic gamma-ray bursts over the energy range of 20 keV to 10 MeV with an expected spectroscopic resolution of 2 keV at 1 MeV (E/Delta-E = 500). The active detection element is a 215-cu cm high-purity n-type Ge crystal cooled to cryogenic temperatures by a passive radiative cooler. The geometric field of view (FOV) defined by the cooler is 170 deg FWFM. Burst data are stored directly in an onboard 2.75-Mb burst memory with an absolute timing accuracy of +/-1.5 ms. This capacity is sufficient to store the entire spectral data set of all but the largest bursts. In addition to burst measurements, the instrument will also study solar flares, search for possible diffuse background lines, and monitor the 511-keV positron annihilation radiation from the galactic center. The experiment is scheduled to be launched on a Delta II launch vehicle from Cape Canaveral on December 31, 1992.

Owens, A.↗
NASA NTRS1992

Spectral evolution during a complex gamma ray burst observed with BATSE

More than 270 gamma ray bursts have been observed to date with the BATSE (Burst and Transient Source Experiment) aboard the Compton Gamma Ray Observatory. Many have a duration of 10 seconds or more and complex structure with multiple peaks or spikes. Complex bursts in the energy range 30 keV to 1 MeV were systematically analyzed to determine the relations between intensity and spectral shape, or hardness. The burst hardness rises and falls in during spikes, but somewhat earlier than the intensity. A simple correlation between intensity and hardness is, therefore, not observed: the intensity lags instead. Results from one burst which shows evidence for longer lags in longer spikes are reported.

Gruber, D. E.↗
NASA NTRS1990

Large-scale anisotropy in the extragalactic gamma-ray background as a probe for cosmological antimatter

Intrinsic anisotropies in the extragalactic gamma-ray background (EGB), which should be detectable with the forthcoming Gamma Ray Observatory, can be used to examine some of the mechanisms proposed to explain its origin, one of which, the baryon-symmetric big bang (BSBB) model, is investigated here. In this simulation, large domains containing matter and antimatter galaxies produce gamma rays by annihilation at the domain boundaries. This mechanism can produce mountain-chain-shaped angular fluctuations in the EGB flux.

Gao, Yi-Tian↗
NASA NTRS1985

1000 GeV gamma rays from Cygnus X-3: An update

Measurements of 1000 GeV gamma-rays from Cygnus X-3 made with the University of Durham facility at Dugway, Utah in 1981/82 are reviewed. The light curve of the 4.8 hour modulated emission is updated and shows evidence significant at the 4.4 sigma level for strong emission (9% of the cosmic ray rate) at phase 0.625 and less significant (1.4 sigma level) indications of weaker emission (3% of the cosmic ray rate) at phase 0.125. The effect constituting the excess on the few nights showing the strongest emission appears to arise from the smallest Cerenkov light signals suggesting a steep gamma-ray spectrum. The 1982 data have been searched unsuccessfully for evidence of emission at phase 0.2, in coincidence with the results from the ultra-high energy (extensive Air Showers (EAS) measurements in 1979-1982. A systematic investigation of a long term variation in the strength of the peak of the 4.8 hr modulated 1000 GeV gamma-ray emission has been made. We find that in addition to the approximately 34 d variation reported by us previously, a stronger effect exists at around 19d.

Chadwick, P. M.↗
NASA NTRS1994

The 1993 multiwavelength campaign on 3C 279: The radio to gamma-ray energy distribution inlow state

Simultaneous observations of 3C 279 at radio, millimeter, near-infrared, optical, ultraviolet (with IUE) and X-ray (with ROSAT) wavelengths were obtained in 1992 December-1993 January, during a three week pointing at the source by the Compton Gamma Ray Observatory. The blazar was in a quiescent or 'low' state during this period. Comparing the multiwavelength energy distribution to that from 1991 June, when 3C 279 was in its brightest recorded gamma-ray state, we find the following: (1) 3C 279 faded dramatically at all frequencies above 10(exp 14) Hz, while the flux variations at low frequencies (radio to millimeter wavelengths) were minor. (2) The near-infrared-optical-ultraviolet spectral shape was softer (steeper) in the quiescent state, and the X-ray spectra also appear softer, although the spectral indix measured by ROSAT refer to a lower energy band than that measured earlier with Ginga. (3) The ratio of the gamma-ray luminosity to that across all other frequencies decreased from a value of approximately equal to 10 in the flaring state to a value approximately equal to 1 in the quiescent state. These findings imply that the production of gamma-rays is closely related to the optical-ultraviolet continuum, in agreement with models where gamma-rays are produced through inverse Compton (IC) scattering by relativistic electrons emitting the synchrotron continuum. The observed nonlinear relation between the synchrotron and IC requires both a change in the electron spectrum and an associated change in the seed photons.

Maraschi, L.↗