摘要:

The Compton Gamma Ray Observatory and three of its four experiment packages continue to function in a nearly flawless manner now well into the eighth year of mission operations. Only the EGRET instrument is operating with reduced capability due mainly to the depleted spark-chamber gas, but it is nonetheless still expected to make significant contributions, notably in the area of Solar flares and AGN variability. We discuss the status of the mission as of mid-1999 as well as the prospects of an extended mission lasting well into the first decade of the next century. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303165

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The Compton Observatory instruments have measured &ggr;-ray lines from several individual sources and from the diffuse interstellar medium. At this late phase of CGRO’s mission, we review the astrophysical achievements by these observations of solar flare spectra, supernova lines from Co and44Tiisotopes, 511 keV annihilation radiation from Galactic plane and bulge, and diffuse 1809 keV radioactivity emission in the Galaxy from26Al.We briefly address other candidate lines from7Beand22Nanova radioactivities, and nuclear12Cand16Ode-excitation lines from Orion or the inner Galaxy. An astronomy with &ggr;-ray lines has been established, the derived lessons suggest specific observations with the INTEGRAL observatory and other experiments of the future. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303166

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

By combining OSSE, SMM and TGRS observations of the galactic center region, Purcell &etal; (1997) and Cheng &etal; (1997) produced the first maps of galactic positron annihilation. That data-set has been augmented with additional data, both recent and archival, and re-analyzed to improve the spectral fitting. The improved spectral fitting has enabled the first maps of positronium continuum emission and the most extensive maps of 511 keV line emission. Bulge and disk combinations have been compared with the 511 keV line data, demonstrating that extended bulges are favored over a GC point source for every disk model tested. This result is independent of whether OSSE-only, OSSE/SMM, or OSSE/SMM/TGRS data-sets are used. The estimated bulge to disk ratio (and to a lesser extent the total flux) is shown to be dependent upon the assumption of bulge shape. A positive latitude enhancement is shown to have an effect upon the B/D ratio, but this effect is secondary to the choice of bulge shape. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303167

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The TGRS experiment on board theWindspacecraft includes a Ge detector with very high resolution (3–4 keV FWHM) at energies around 511 keV. To take advantage ofWIND’s fixed pointing at the south ecliptic pole and its 3 s rotation, TGRS also includes a Pb occulter fixed on the spacecraft body subtending an arc of 90° along the ecliptic plane. Spectra of the Galactic center region, identified by this occultation method, have been accumulated since 1994 November. In this paper we present updated results for the Galactic center positron annihilation line from these occulted spectra. From the results prior to fall 1997 we obtained the intensity, width, energy and variability of the line, the positronium (Ps) fraction, and limited information about the spatial distribution of the line, all of which have been published. Since the fall of 1997, degradation of the instrument performance has limited us to improving our results for the spatial distribution. These updated results are in marginal disagreement (∼2.5&sgr;) with a model based on earlier OSSE measurements. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303168

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We present an updated version of COMPTEL’s 1.809 MeV sky survey. Based on eight years of observations we compare results from different imaging techniques using background from adjacent energy bands. We confirm the previously reported characteristics of the galactic 1.809 MeV emission, specifically an extended galactic ridge emission, mainly concentrated towards the inner galaxy, a peculiar emission feature in the Cygnus region, and a low-intensity ridge extending towards Carina and Vela. Because this gamma ray line is due to the decay of radioactive26Al,predominantly synthesized in massive stars, one anticipates flux enhancements aligned with regions of recent star formation. This is born out by the observations. In particular the Cygnus feature, first presented in 1996 based on three years of COMPTEL data, is confirmed. Based on the stellar population we distinguish three prominent areas in this region, for which we separately derive fluxes, and discuss interpretations. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303169

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

OB associations and young open clusters constitute the most prolific nucleosynthesis sites in our Galaxy. The combined activity of stellar winds and core-collapse supernovae ejects significant amounts of freshly synthesised nuclei into the interstellar medium. Radioactive isotopes, such as26Alor60Fe,that have been co-produced in such events may eventually be observed by gamma-ray instruments through their characteristic decay-line signatures. However, due to the sensitivity and angular resolution of current (and even future) &ggr;-ray telescopes, only integrated &ggr;-ray line signatures are expected for massive star associations. In order to study such signatures and to derive constraints on the involved nucleosynthesis processes, we developed a multi-wavelength evolutionary synthesis model for massive star associations. This model combines latest stellar evolutionary tracks and nucleosynthesis calculations with atmosphere models in order to predict the multi-wavelength luminosity of a given association as function of its age. We apply this model to associations and clusters in the well-studied Cygnus region for which we re-determined the stellar census based on photometric and spectroscopic data. In particular we study the relation between 1.809 MeV &ggr;-ray line emission and ionising flux, since the latter has turned out to provide an excellent tracer of the global galactic 1.809 MeV emission. We compare our model to COMPTEL 1.8 MeV &ggr;-ray line observations from which we derive limits on the relative contributions from massive stars and core-collapse supernovae to the actual26Alcontent in this region. Based on our model we make predictions about the expected26Aland60Feline signatures in the Cygnus region. These predictions make the Cygnus region a prime target for the future INTEGRAL mission. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303170

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The COMPTEL map of the 1.809 MeV line, which is attributed to the radioactive decay of26Al,shows significant excess emission in the Cygnus region. We investigate counterparts of this emission, based on COMPTEL data accumulated over 8 years. Previous studies suggested that this flux is due to the integrated, but unresolved, nucleosynthesis from young, massive objects like Wolf Rayet (WR) stars and core collapse supernovae. Beside a static scenario of known point sources-WR stars and SNRs-we consider OB associations in a dynamic scenario to model the observed flux in the Cygnus region. We carry out population synthesis studies to determine the time-dependent production of26Aland also kinetic as well as radiative energy. Furthermore we consider the impact of enhanced26Alyields probably occurring in a fraction of massive close binary systems. We compare the nucleosynthesis results of our OB association model with recent measurements in the Cygnus region. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303171

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The type Ia supernova SN 1998bu in M96 was observed by COMPTEL for a total of 88 days starting 17 days after the detection of the SN. A special mode improving the low-energy sensitivity was invoked. We obtained images in the 847 keV and 1238 keV lines of56Cousing an improved point-spread function for the low-energies. We do not detect SN1998bu. Sensitive upper limits at both energies constrain the standard supernova model for this event. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303172

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Limitations in COMPTEL44Tiline searches arise from uncertainties in different background modelling techniques, and in different event selection criteria to suppress a large part of the background. Therefore, the significance of the reported detections of Cas A and RX J0852-4622/GRO J0852-4642 have been reassessed in great detail. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303173

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Energetic particles accelerated in supernova remnants provide a variety of continuum emission signatures over the entire electromagnetic spectrum. The measured hard X-ray continuum emission from the Cas A supernova remnant indicates in fact the presence of high-energy electrons and makes it an interesting candidate for study at MeV energies. We have analyzed COMPTEL data with respect to continuum emission in addition to the previously detected44Tiline. The results provide useful constraints on models of electron shock acceleration in this object. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303174

出版商:AIP    

年代:1900

数据来源: AIP