The Gamma-Ray Light Curves of SN 1987A

Observations of the SN 1987A ejecta in four Co-56-decay gamma-ray lines, obtained using the SMM gamma-ray spectrometer between February 1987 and May 1989, are reported and analyzed. The instrument characteristics and data-reduction procedures are described, and the results are presented in extensive tables and graphs and discussed with reference to theoretical models. Gamma-ray fluxes significantly above possible instrumental levels (as determined from analysis of pre-1987 data) were detected in the second half of 1987 and the first half of 1988. The data are found to favor a model with some Co-56 in regions of low gamma-ray optical depth by 200 d after the SN outburst over models with all Co-56 at one depth within a uniform expanding envelope. Also investigated are the gamma-ray contribution to the total bolometric luminosity and the escape (and potential observability) of Co-57 gamma rays

Gamma-Ray Limits on Galactic Fe-60 and Ti-44 Nucleosynthesis

We have searched nearly 10 years of data from NASA\u27s Solar Maximum Mission (SMM) Gamma-Ray Spectrometer for evidence of gamma-ray line emission from the decay of the shorter lived daughters, Co-60 and Sc-44, of nucleosynthetic Fe-60 and Ti-44. The data are compared with models of the expected signals from the annual scan of the ecliptic by SMM. These models include (1) the extended diffuse emision from the many supernovae which should contribute Fe-60 over its 2.2 Myr lifetime, and (2) point sources at various locations in the Galactic plane which could be previously undiscovered remnants of supernovae which ejected Ti-44. We find no evidence of Galactic emission from either nucleus; upper limits (99% confidence) are near 8 x 10-5 photons/sq cm/s, for both the 1.17 MeV line from Co-60 decay integrated over the central radian of Galactic longitude and for the 1.16 MeV line from Sc-44 from points near the Galactic center. The limits on 1.16 MeV flux from longitudes near + or - 90 deg rise to approximately 2 x 10-4 photons/sq cm/s because the large angular distance to the ecliptic reduces the sensitivity in those directions. The mass of Fe-60 in the interstellar medium today is constrained to be less than 1.7 solar mass. This sets a limit on the current Galactic production rate of Fe-60 and of other isotopes coproduced with it, for example, Ca-48 and Ti-50. Estimating the current production of these stable isotopes from their solar abundances suggests that there should be about 0.9 solar mass of Fe-60 in the interstellar medium and indicates that Fe-60 could soon be detected with a slightly more sensitive instrument. Comparing the estimated production rates of stable isotopes with the gamma-ray limits on those of radioactive isotopes allows us to constrain some models of Galactic chemical evolution. The mass of Ti-44 at the Galactic center, for example, is (99% confidence) less than 8 x 10-5 solar mass. This is a quite improbable result viewed in either of two ways. Employing plausible models of Galactic chemical evolution constrained to produce the solar concentration of Ca-44 in the Galaxy 4.5 Gyr ago suggests that Ca-44 is produced today at the rate (3-4) x 10-4 solar mass per century. This production rate is consistent with our measurement at 5% confidence only for supernova rates less than 1.5 per century, depending slightly on the actual Ti-44 lifetime, and assuming all Ca-44 is ejected as Ti-44. Lower rates are consistent with our data, because the implied interval with no supernovae is not so unlikely, but the required higher yields of Ti-44 begin to strain current supernova nucleosynthesis calculations. Apart from the solar abundance requirement, we can check the consistency of any combination of supernova rate and Ti-44 yield. A Galactic supernova rate of three per century and a yield 10-4 solar mass of Ti-44 per event, both very reasonable estimates, are consistent with our data at only 5% confidence. Perhaps the typical yield of frequent supernovae is significantly smaller than this, and the source of most Ca-44 is a rare type of high-yield of frequent supernovae is significantly smaller than this, and the source of most Ca-44 is a rare type of high-yield event which has not occurred recently. The isotope Ti-44 is probably not a major contributor to interstellar positions

SMM detection of interstellar Al-26 gamma radiation

The gamma ray spectrometer on the Solar Maximum Mission Satellite has detected the interstellar Al-26 line when the Galactic center traversed its aperture. The center of the emission is consistent with the location of the Galactic center, but the spatial distribution is presently not well defined. The total flux in the direction of the Galactic center is 4.3 + or - 0.4) x .0001 gamma/sq cm-s-rad for an assumed population I distribution

A Search for the 478 keV Line from the Decay of Nucleosynthetic 7Be

Unstable Be-7 (half-life 53.28 days) is expected to be present in the ejecta of classical novae. If the frequency of novae in the central Galaxy is high enough, a nearly steady state abundance of Be-7 will be present there. Data accumulated during transits of the Galactic center across the aperture of the Solar Maximum Mission Gamma Ray Spectrometer have been searched for evidence of the 478 keV gamma-ray line resulting from Be-7 decay. A 3-sigma upper limit of 0.00016 gamma/sq cm s has been placed on the emission in this line from the central radian of the Galactic plane. Less stringent limits have been set on the production of Be-7 in Nova Aquilae 1982, Nova Vulpeculae 1984 No. 2, and Nova Centauri 1986 from observations with the same instrument

Monte Carlo calibration of the SMM gamma ray spectrometer for high energy gamma rays and neutrons

The Gamma Ray Spectrometer (GRS) on the Solar Maximum Mission spacecraft was primarily designed and calibrated for nuclear gamma ray line measurements, but also has a high energy mode which allows the detection of gamma rays at energies above 10 MeV and solar neutrons above 20 MeV. The GRS response has been extrapolated until now for high energy gamma rays from an early design study employing Monte Carlo calculations. The response to 50 to 600 MeV solar neutrons was estimated from a simple model which did not consider secondary charged particles escaping into the veto shields. In view of numerous detections by the GRS of solar flares emitting high energy gamma rays, including at least two emitting directly detectable neutrons, the calibration of the high energy mode in the flight model has been recalculated by the use of more sophisticated Monte Carlo computer codes. New results presented show that the GRS response to gamma rays above 20 MeV and to neutrons above 100 MeV is significantly lower than the earlier estimates

SMM Observations of Gamma-Ray Transients. 3: A Search for a Broadened, Redshifted Positron Annihilation Line from the Direction of the Galactic Center

We have searched for 1980-1988 Solar Maximum Mission gamma-ray spectrometer data for transient emission on timescales from hours to approximately 12 days of broad gamma-ray lines at energies approximately 400 keV, which were reported by the High Energy Astronomy Observatory (HEAO) 1 and SIGMA experiments from two sources lying toward the Galactic center. The lines have been interpreted as the product of the annihilation of positrons in pair plasmas surrounding the black hole candidate 1E 1740.7-2942 and the X-ray binary 1H 1822-371. Our results from a combined exposure of approximately 1.5 x 107s provide no convincing evidence for transient emission of this line on any timescale between approximately 9 hr and approximately 1 yr. Our 3 sigma upper limits on the line flux during approximately 12 day intervals are characteristically 4.8 x 10-3 photon/sq cm/s, while for approximately 1 day intervals our 3 sigma upper limits are characteristically 4.9 x 10-3 photon/sq cm/s. These results imply a duty cycle of less than 1.3% for the transient line measured from 1H 1822-371 during a approximately 3 week interval in 1977 by HEAO 1, and a duty cycle of less than or = 0.8% for the transient line detected in 1990 and 1992 from 1E 1740.7-2942 on approximately 1 day timescales by SIGMA

SMM observations of gamma-ray transients. 2: A search for gamma-ray lines between 400 and 600 keV from the Crab Nebula

We have search spectra obtained by the Solar Maximum Mission Gamma-Ray Spectrometer during 1981-1988 for evidence of transient gamma-ray lines from the Crab Nebula which have been reported by previous experiments at energies 400-460 keV and 539 keV. We find no evidence for significant emission in any of these lines on time scales between aproximately 1 day and approximately 1 yr. Our 3 sigma upper limits on the transient flux during 1 d intervals are approximately equal to 2.2 x 10-3 photons/sq cm/s for narrow lines at any energy, and approximately equal to 2.9 x 10-3 photons/sq cm/s for the 539 keV line if it is as broad as 42 keV Full Width at Half Maximum (FWHM). We also searched our data during the approximately 5 hr period on 1981 June 6 during which Owens, Myers, & Thompson (1985) reported a strong line at 405 keV. We detected no line down to a 3 upper sigma limit of 3.3 x 10-3 photons/sq cm/s in disagreement with the flux 7.2 +/- 2.1 x 10-3 photos/sq cm/s measured by Owens et al

Search for gamma ray lines from SS433

Data obtained with the Gamma Ray Spectrometer (0.3 to 9 MeV) aboard the Solar Maximum Mission satellite from 1980 to 1985 for evidence of the reported Doppler shifted lines from SS433 were examined. The data base covers a total of 468 days when SS433 was in the field of view and includes times of quiescent and flaring radio activity. In 9 day integrations of the SMM data no evidence is found for gamma ray line emission from SS433. The 99% confidence upper limits for 9 day integrations of the shifted 1.37 and 6.1 MeV lines are 0.0013 gamma/sq cm-s and 0.0007 gamma/sq cm-s, respectively. The 360 day time averaged upper limits are 0.0002 gamma/sq cm-s x 0.0001 gamma/sq cm-s for both lines

Spatial and Temporal Variability of the Gamma Radiation from Earth\u27s Atmosphere During a Solar Cycle

The Solar Maximum Mission satellite’s Gamma Ray Spectrometer spent much of its 1980–1989 mission pointed at Earth, accumulating spectra of atmospheric albedo γ-rays. Its 28◦ orbit ensured that a range of geomagnetic latitudes was sampled. We measured the variation with time and cutoff rigidity of some key γ-ray lines which are diagnos-tic of the intensity of the Galactic cosmic radiation penetrating the geomagnetic cutoff and of the secondary neutrons produced in the atmosphere. We found that the inten-sities of nuclear lines at 1.6 MeV, 2.3 MeV and 4.4 MeV varied inversely with solar ac-tivity in cycles 21–22 as expected from the theory of solar modulation of cosmic rays. They were found to be strongly anticorrelated with cutoff rigidity, as expected from the theory of the cutoff, falling by a factor ∼ 3.6 between the lowest (\u3c 7 GV) and high-est (\u3e 13 GV) rigidities sampled. The solar cycle modulation was particularly marked at the lowest rigidities, reaching an amplitude of 16%

Neutral pion production in solar flares

The Gamma-Ray Spectrometer (GRS) on SMM has detected more than 130 flares with emission approx 300 keV. More than 10 of these flares were detected at photon energies 10 MeV. Although the majority of the emission at 10 MeV must be from electron bremsstrahlung, at least two of the flares have spectral properties 40 MeV that require gamma rays from the decay of neutral pions. It is found that pion production can occur early in the impulsive phase as defined by hard X-rays near 100 keV. It is also found in one of these flares that a significant portion of this high-energy emission is produced well after the impulsive phase. This extended production phase, most clearly observed at high energies, may be a signature of the acceleration process which produces solar energetic particles (SEP's) in space