4 research outputs found
The Locations of Gamma-Ray Bursts Measured by COMPTEL
The COMPTEL instrument on the Compton Gamma Ray Observatory is used to
measure the locations of gamma-ray bursts through direct imaging of MeV
photons. In a comprehensive search, we have detected and localized 29 bursts
observed between 1991 April 19 and 1995 May 31. The average location accuracy
of these events is 1.25\arcdeg (1), including a systematic error of
\sim0.5\arcdeg, which is verified through comparison with Interplanetary
Network (IPN) timing annuli. The combination of COMPTEL and IPN measurements
results in locations for 26 of the bursts with an average ``error box'' area of
only 0.3 deg (1). We find that the angular distribution of
COMPTEL burst locations is consistent with large-scale isotropy and that there
is no statistically significant evidence of small-angle auto-correlations. We
conclude that there is no compelling evidence for burst repetition since no
more than two of the events (or 7% of the 29 bursts) could possibly have
come from the same source. We also find that there is no significant
correlation between the burst locations and either Abell clusters of galaxies
or radio-quiet quasars. Agreement between individual COMPTEL locations and IPN
annuli places a lower limit of 100~AU (95% confidence) on the distance to
the stronger bursts.Comment: Accepted for publication in the Astrophysical Journal, 1998 Jan. 1,
Vol. 492. 33 pages, 9 figures, 5 table
A combined model for the X-ray to gamma-ray emission of Cyg X-1
We use recent data obtained by three (OSSE, BATSE, and COMPTEL) of four
instruments on board the Compton Gamma Ray Observatory, to construct a model of
Cyg X-1 which describes its emission in a broad energy range from soft X-rays
to MeV gamma-rays self-consistently. The gamma-ray emission is interpreted to
be the result of Comptonization, bremsstrahlung, and positron annihilation in a
hot optically thin and spatially extended region surrounding the whole
accretion disk. For the X-ray emission a standard corona-disk model is applied.
We show that the Cyg X-1 spectrum accumulated by the CGRO instruments during a
~4 year time period between 1991 and 1995, as well as the HEAO-3 gamma1 and
gamma2 spectra can be well represented by our model. The derived parameters
match the observational results obtained from X-ray measurements.Comment: 11 pages including 6 ps-figures and 2 tables, latex2e, uses
emulateapj.sty (ver. of 18 Sep 96, enclosed), epsfig.sty, times.sty. To
appear in July 20, 1998 issue of ApJ (v.502