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Share, G. H.

Publications and source records attributed to Share, G. H..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

A 154-day periodicity in the occurrence of hard solar flares?

An analysis of the temporal distribution of 139 solar flares monitored by the Gamma Ray Spectrometer aboard the Solar Maximum Mission is reported. It is found that, instead of being randomly distributed in time, these events have a tendency to occur in groups with a mean spacing of about 154 days (75 nHz) over the observing interval. A larger sample of flares with an X-ray classification of M 2.5 or larger recorded by the GOES satellite showed a similar regularity.

Rieger, E.↗
NASA NTRS1984

Spectral feature of 31 December 1981 gamma-ray burst not confirmed

Measurements of a gamma ray burst at 01:37 UT on December 31, 1981 using the SMM gamma ray spectrometer (GRS) are compared with those made by the Konus instruments on Veneras 11-14. Burst time profiles, photon spectra, and detector energy loss spectra for three time intervals are compared for the GRS and the Konus instruments. It is concluded that the SMM spectra exhibit no evidence for the presence of emission features reported by the Konus group.

Nolan, P. L.↗
NASA NTRS1983

Gamma-ray observational constraints on the origin of the optical continuum emission from the white-light flare of 1980 July 1

Results are presented for the flare of July 1, 1980, which started at approximately 1627 UT and in which simultaneous measurements were made of X-ray, gamma-ray, and optical continuum emission for the entire duration of the flare. The X-ray and gamma-ray observations were made by the Gamma-Ray Spectrometer on the Solar Maximum Mission satellite. The optical measurements were taken at the Sacramento Peak Observatory and the Big Bear Solar Observatory (Zirin and Neidig, 1981). It is found that the major white-light emission that occurs in the late phase of the flare could not have been due to heating by electron or ion precipitation. This conclusion derives from the fact that the X-ray and gamma-ray flux peaks approximately 1 minute before the maximum of the optical continuum mission emission. It is also found that approximately 73 percent of the optical continuum emission, representing a spatially and temporally distinct bright point, follows this maximum with little or no X-ray or gamma-ray emission in the same period.

Ryan, J. M.↗
NASA NTRS1983

Solar neutrons from the impulsive flare on 1982 June 3 at 1143 UT

A transient flux of high energy solar neutrons from 50 MeV to about 1 GeV has been detected by the Gamma Ray Spectrometer (GRS) on the Solar Maximum Mission (SMM) satellite following an intense burst of high energy photons (less than 100 MeV) peaking at 1143:29 UT. The neutrons were also detected by the IGY neutron monitor on Jungfraujoch (Switzerland). In this paper the SMM GRS observations are summarized and compared with the Jungfraujoch neutron monitor data, and both the time dependent neutron flux at the earth and the neutron emission spectrum at the sun are estimated.

Chupp, E. L.↗
NASA NTRS1983

Positron annihilation radiation from solar flares

Positron-annihilation radiation has been observed from the June 21, 1980 and June 3, 1982 flares by the gamma-ray spectrometer on the Solar Maximum Mission satellite. The observed 0.511-MeV line fluences from the flares were 14.6 + or - 3.3 gamma/sq cm and 103 + or - 8 gamma/sq cm, respectively. Measurement of the line width establishes an upper limit to the temperature in the annihilation region of 3 x 10 to the 6th K. The time dependence of the 0.511-MeV line during the 1980 flare is consistent with the calculations of Ramaty et al. (1983) for positrons created in the decay of radioactive nuclei. The time dependence of the 0.511-MeV line for the 1982 flare is more complex and requires more detailed study.

Share, G. H.↗
NASA NTRS1983

Upper limits of narrow annihilation lines in gamma-ray bursts

The SMM gamma-ray experiment has observed 60 gamma-ray bursts from March 1980 to August 1982. Details of one burst are illustrated. There is weak evidence for a broadened spectral feature early in the burst, which was also detected by the Konus experiment. The present detailed search is limitd to narrow lines (less than 70 keV FWHM) near 500 keV; none is found in any of the bursts. This absence contrasts with the reported detection of several broader features (Mazets et al., 1981). The implications for the physical conditions in the annihilation region are discussed.

Nolan, P. L.↗
NASA NTRS1982

A direct observation of solar neutrons following the 0118 UT flare on 1980 June 21

The Gamma Ray Spectrometer on the Solar Maximum Mission satellite has observed energetic solar neutrons (greater than 50 MeV) at the earth following a solar flare that occurred on the west limb on June 21, 1980 at 01:18:20 UT. Impulsive photon emission from 10 keV to greater than 65 MeV lasting over a period of about 66 s was followed by a transient flux of 50-600 MeV neutrons incident over a 17 minute period. The peak counting rate corresponds to an average flux at the earth of (3.8 + or - 0.6) x 10 to the -2nd neutrons/sq cm s at 130 MeV. These observations indicate the emission of 3 x 10 to the 28th neutrons/sr with energies greater than 50 MeV, requiring the rapid acceleration (much less than 60 s) of protons to GeV energies during the impulsive phase of the flare.

Chupp, E. L.↗
NASA NTRS1982

Observation of gamma-ray bursts with the SMM gamma-ray spectrometer

The gamma-ray spectrometer on SMM is sensitive to bursts within its field of view with intensities greater than 0.000005 erg/sq cm above 100 keV. It has detected 17 events between February 1980 and March 1981 with the characteristics of cosmic gamma-ray bursts. The most intense burst, on 19 April 1980, had a photon spectrum consistent with a power law with spectral index - 2.5 from 300 keV to approximately 7 MeV. It is not possible at present to exclude the sun as the source of this burst. Spectra of 11 of the bursts have been studied for line features with no clear evidence for line emission greater than 300 keV. The continuum radiation from about half of these events have hard emission extending to approximately equal to or greater than 2 MeV.

Share, G. H.↗
NASA NTRS1982

Frequency of gamma-ray bursts greater than 3 x 10 to the -6th erg/sq cm

Results are presented for gamma-ray burst observations with the Large Area Sky Survey instrument on HEAO-1. It is noted that during the time HEAO-1 was operational, the instrument detected at least 12 confirmed gamma-ray bursts with intensities greater than 3 microerg/sq cm and identified six additional unconfirmed bursts. The rates of gamma-ray bursts are estimated to be about 125 per yr for intensities greater than 3 microerg/sq cm and approximately 50 per yr for intensities greater than 10 microerg/yr. The data are shown to yield a log N - log S relation for gamma-ray bursts that is consistent with a spherical distribution of sources within the Galaxy and having a broad range of intrinsic luminosities.

Share, G. H.↗
NASA NTRS1982

Observation of gamma-ray bursts from 10 keV to 9 MeV

Time histories and count-rate spectra of some of the gamma-ray bursts detected by the spectrometer on the Solar Maximum Mission between Feb. 20, 1980, and May 1981 are presented. Individual peaks observed in some of the bursts are found to differ significantly in hardness from one another. The similarity in the time profiles in the different energy bands is seen as suggesting that photons spanning two decades in energy are produced by the same mechanism. It is noted that all of the bursts are detected to energies greater than approximately 1 MeV. Two of the spectra presented are seen as being well fit by single power laws; the indices, however, are strikingly different. The other two sepctra require either two power laws or an exponential function. No clear evidence is found for the existence of narrow line features in any of the bursts.

Share, G. H.↗
NASA NTRS1982

Spatial variation for flares observed with the gamma ray spectrometer aboard the SMM satellite

A search is made for anisotropic X-ray bremsstrahlung photon production from relativistic electrons by studying the heliocentric angular dependence of 53 flares detected at energies above 300 keV. No evidence is found for a higher rate of detectable flares near the limb at the 80 percent confidence level. This result implies that the X-ray directivity as defined by the ratio of photon intensity at 75 deg and 0 deg of heliocentric angle is less than 1.5 above 300 keV and strongly rejects any flare model predicting X-ray production from a radial 'beam' of energetic electrons.

Zolcinski, M. C.↗
NASA NTRS1981

Observations with the SMM gamma-ray spectrometer - The impulsive solar flares of 1980 March 29

Gamma-ray continuum emission from 0.3 to 1 MeV was observed with the gamma-ray spectrometer on the Solar Maximum Mission satellite during two impulsive solar flares on 1980 March 29, from active region 2363 at 0918 UT and from active region 2357 at 0955 UT. Evidence is presented for a hardening of the spectrum during the impulsive phase of the flares. The photon intensity greater than 100 keV appears to decay at a slower rate than that at lower energies. Time-integrated photon spectra for both flares are incompatible with a single-temperature thermal-bremsstrahlung model. Upper limits for prompt and delayed gamma-ray lines are presented.

Ryan, J. M.↗
NASA NTRS1980

An X-ray survey of distant rich clusters of galaxies with HEAO 1

The paper presents a 1-10-keV survey of distance class 4, 5, and 6 Abell clusters using the HEAO 1 NRL large area survey experiment. The survey is a little less than 1/30 of the Abell catalog. Eleven clusters are identified with X-ray sources, and X-ray upper limits are provided for 60 others.

Ulmer, M. P.↗
NASA NTRS1980

Identification of a faint X-ray source with the W Ursae Majoris star VW Cephei

The NRL instrument aboard the HEAO 1 satellite has detected a faint X-ray source, which has been identified tentatively with the contact binary star (W UMa variable) VW Cephei. Its luminosity is between 3 x 10 to the 30th and 4 x 10 to the 31st ergs/sec (0.1-10 keV), and the results suggest some variation of the X-ray flux with phase.

Carroll, R. W.↗
NASA NTRS1979

X-ray emission from gamma-ray sources in the galactic anticentre region

An X-ray survey of three high energy gamma-ray sources in the galactic anticenter region conducted using the large area sky survey instrument on HEAO 1 is presented. The sensitivity of this survey is highest reported, and two, and possibly three, X-ray sources were detected in the vicinity of gamma 195+5. Three new X-ray sources have been discovered within a few degrees of CG176-7, but none overlaps the gamma-ray error box. These results demonstrate that gamma-ray sources like CG195+4 and CG176-7 have emission characteristics different from the Crab pulsar, but may be similar to the Vela pulsar. Alternatively, the lack of detectable X-ray flux suggests that the gamma-ray emission arises from cosmic-ray interactions in dense interstellar clouds. An interesting feature of the new X-ray sources is that four of them may be associated with early-type stars which exhibit emission lines.

Share, G. H.↗
NASA NTRS1979

HEAO 1 observation of a type I burst from MXB 1728-34

Results are presented for an analysis of data on a type I X-ray burst from MXB 1728-34 observed by three large-area instruments on HEAO 1. The measurements cover the energy range from 2 to 150 keV and provide the capability of resolving significant intensity variations on a time scale of milliseconds and spectral changes on a scale of tenths of seconds. The initial rise of the burst is discussed, millisecond intensity variations are examined, and the spectral evolution of the burst is described. Physical parameters are estimated for various source models, and the total X-ray flux at energies of 85 to 180 keV during the burst is shown to have been no more than about 6% of the total observed X-ray flux at energies below 25 keV.

Hoffman, J. A.↗