High energy flare physics group summary

The contributions of the High Energy Flare Physics Special Session in the American Astronomical Society Solar Physics Division Meeting are reviewed. Oral and poster papers were presented on observatories and instruments available for the upcoming solar maximum. Among these are the space-based Gamma Ray Observatory, the Solar Flare and Cosmic Burst Gamma Ray Experiment on the Ulysses spacecraft, the Soft X Ray Telescope on the spacecraft Solar-A, and the balloon-based Gamma Ray Imaging Device. Ground based observatories with new capabilities include the BIMA mm-wave interferometer (Univ. of California, Berkeley; Univ. of Illinois; Univ. of Maryland), Owens Valley Radio Observatory and the Very Large Array. The highlights of the various instrument performances are reported and potential data correlations and collaborations are suggested

Report of the x ray and gamma ray sensors panel

Overall five major areas of technology are recommended for development in order to meet the science requirements of the Astrotech 21 mission set. These are: detectors for high resolution gamma ray spectroscopy, cryogenic detectors for improved x ray spectral and spatial resolution, advanced x ray charge coupled devices (CCDs) for higher energy resolution and larger format, extension to higher energies, liquid and solid position sensitive detectors for improving stopping power in the energy range 5 to 500 keV and 0.2 to 2 MeV. Development plans designed to achieve the desired capabilities on the time scales required by the technology freeze dates have been recommended in each of these areas

Capabilities of GRO/OSSE for observing solar flares

The launch of the Gamma Ray Observatory (GRO) near solar maximum makes solar flare studies early in the mission particularly advantageous. The Oriented Scintillation Spectrometer Experiment (OSSE) on GRO, covering the energy range 0.05 to 150 MeV, has some significant advantages over the previous generation of satellite-borne gamma-ray detectors for solar observations. The OSSE detectors will have about 10 times the effective area of the Gamma-Ray Spectrometer (GRS) on Solar Maximum Mission (SMM) for both photons and high-energy neutrons. The OSSE also has the added capability of distinguishing between high-energy neutrons and photons directly. The OSSE spectral accumulation time (approx. 4s) is four times faster than that of the SMM/GRS; much better time resolution is available in selected energy ranges. These characteristics will allow the investigation of particle acceleration in flares based on the evolution of the continuum and nuclear line components of flare spectra, nuclear emission in small flares, the anisotropy of continuum emission in small flares, and the relative intensities of different nuclear lines. The OSSE observational program will be devoted primarily to non-solar sources. Therefore, solar observations require planning and special configurations. The instrumental and operational characteristics of OSSE are discussed in the context of undertaking solar observations. The opportunities for guest investigators to participate in solar flare studies with OSSE is also presented

Comparative Studies of Line and Contiuum Positron Annihilation Radiation

Positron annihilation radiation from the Galaxy has been observed by the OSSE, SMM and TGRS instruments. Improved spectral modeling of OSSE observa-tions has allowed studies of the distribution of both positron annihilation radiation components, the narrow line emission at 511 keV and the positronium continuum emission. The results derived for each individual annihilation component are then compared with each other. These comparisons reveal approximate agreement between the distribution of these two emissions. In certain regions of the sky (notably in the vicinity of the previously reported positive latitude enhancement), the distribution of the emissions differ. We discuss these differences and the methods currently being employed to understand whether the differences are physical or a systematic error in the present analysis

Supernovae and Positron Annihilation Radiation

Radioactive nuclei, especially those created in SN explosion, have long been sug-gested to be important contributors of galactic positrons. In this paper we describe the findings of three independent OSSE/SMM/TGRS studies of positron annihi-lation radiation, demonstrating that the three studies are largely in agreement as to the distribution of galactic annihilation radiation. We then assess the predicted yields and distributions of SN-synthesized radionuclei, determining that they are marginally compatible with the findings of the annihilation radiation studies

Comparative Studies of Line and Continuum Positron Annihilation Radiation

Positron annihilation radiation from the Galaxy has been observed by the OSSE, SMM and TGRS instruments. Improved spectral modeling of OSSE observations has allowed studies of the distribution of both positron annihilation radiation components, the narrow line emission at 511 keV and the positronium continuum emission. The results derived for each individual annihilation component are then compared with each other. These comparisons reveal approximate agreement between the distribution of these two emissions. In certain regions of the sky (notably in the vicinity of the previously reported positive latitude enhancement), the distribution of the emissions differ. We discuss these differences and the methods currently being employed to understand whether the differences are physical or a systematic error in the present analysis.Comment: 5 pages, to appear in the proceedings of the Gamma 2001 Symposium (Baltimore, April 2001

Hard X-Rays From Supernova 1993J

The OSSE experiment on the Compton Observatory observed SN 1993J during three intervals, approximately 9--15, 23--36, and 93--121 days after outburst. There is evidence for continuum emission below 200 keV in the first two of these periods. Power-law fits yield intensities at 100 keV of (1.82+/-0.39)*E(-3) photons cm(-2) s(-1) MeV(-1) and (0.89+/-0.35)*E(-3) photons cm(-2) s(-1) MeV(-1) , and photon indices of -2.3+/-0.5 and -2.2+/-0.9, respectively. There is no evidence for any emission in the longer, more sensitive, third observation. These continua are too bright and too steep to be entirely due to Comptonized gamma-rays from radioactive (56) Ni and (56) Co alone. A thermal bremsstrahlung spectrum, for example, also adequately describes the OSSE data, with kT =~ 75 keV. These continua extrapolate well above nearly contemporaneous measurements at lower energies. Instead, a power-law of fixed photon index -1.2 fit to the first OSSE observation extrapolates approximately to the total luminosity measured by ASCA (Tanaka IAU Circ. 5753) from 1--10 keV, one day earlier. For a thermal spectrum a higher temperature, near 200 keV, can also fit both data sets---but only marginally. This emission cannot be unambiguously attributed to SN 1993J. Because of the large OSSE field of view, SN 1993J cannot be separated from other sources such as the nucleus of M81 or even M82. However, OSSE did observe this region twice earlier, 597 and 443 days before SN 1993J and no continuum emission was detected at either time. The apparent decline of the emission does seem to correlate well with those of SN 1993J as seen by ASCA and ROSAT. No evidence for line emission is seen in any observation. This work is supported by NASA DPR S-10987C

The Co-57 Abundance in SN 1987A

Astrophysical implications of the detection by OSSE of Co-57 gamma radiation from SN 1987A are discussed. By burying the alpha-rich-freezeout portion at deeper gamma depths than in published models, it is shown that it remains barely possible that the bolometric luminosity during days 1200-1800 could derive from Co-57 power without requiring 57/56 production ratios greater than twice solar. Alternative mechanisms which may contribute to the bolometric power at late times are proposed

The 57Co Abundance in SN 1987A

We discuss several astrophysical consequences of the detection by OSSE (Kurfess et al. 1992) of 57Co gamma radiation from supernova 1987A. Models with low photoelectric absorption cannot account for both OSSE data and the bolometric luminosity. By burying the alpha-rich-freezeout portion at deeper gamma depths than in published models, we show that it remains barely possible that the bolometric luminosity during days 1200-1800 could derive from 57Co power without requiring 57/56 production ratios greater than twice solar. We illustrate this by slowing the expansion within the inner four solar masses of ejecta in model 10HMM

Hard X-ray Emission from Cassiopeia A SNR

We report the results of extracting the hard X-ray continuum spectrum of Cas A SNR from RXTE/PCA Target of Opportunity (TOO) observations and CGRO/OSSE observations. The data can rule out the single thermal bremsstrahlung model for Cas A continuum between 2 and 150 keV. The single power law model gives a mediocre fit (~5%) to the data with a power-law index, $\Gamma$ = 2.94$\pm$0.02. A model with two component (bremsstrahlung + bremsstrahlung or bremsstrahlung + power law) gives a good fit. The power law index is quite constrained suggesting that this continuum might not be the X-ray thermal bremmstrahlung from accelerated MeV electrons at shock fronts (Asvarov et al. 1989) which would have $\Gamma\simeq$2.26. With several SNRs detected by ASCA showing a hard power-law nonthermal X-ray continuum, we expect a similar situation for Cas A SNR which has $\Gamma$=2.98$\pm$0.09. We discuss the implication of the hardest nonthermal X-rays detected from Cas A to the synchrotron radiation model.Comment: 5 pages, 2 postscript figures, 1 postscript table, latex uses epsfig.sty, aipproc.sty, to appear in the proc. of the 4th COMPTON symposium, held in Williamsburg, VA, April 27-30, 1997. Minor correction for SN1006's power-law index in Table