Central Bureau for Astronomical Telegrams
IAUC 4889: EXTRAGALACTIC N2H+; GALACTIC CENTER ANNIHILATION RADIATION
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Circular No. 4889
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
EXTRAGALACTIC N2H+
R. Mauersberger and C. Henkel, Max-Planck-Institut fuer
Radioastronomie, Bonn, report: "We have detected extragalactic
N2H+ from NGC 253, Maffei 2, IC 342, M82, and NGC 6946. This is
the third molecular ion detected outside the Galaxy. The measurements
were carried out with the Theiy 30-m telescope in Spain. A
preliminary comparison of N2H+ and CS data from the five galaxies
and from dense cores in our Galaxy suggests that relative abundances
and excitation of N2H+ may be similar in both groups of sources."
GALACTIC CENTER ANNIHILATION RADIATION
The U.S.-France collaboration in gamma-ray spectroscopy (J.
Matteson, M. Pelling, B. Bowman, M. Briggs, D. Gruber, R. Lingenfelter,
and L. Peterson, University of California at San Diego; R. Lin,
P. Feffer, D. Smith, and K. Hurley, University of California at
Berkeley; C. Cork, D. Landis, P. Luke, N. Madden, D. Malone, R.
Pehl, and M. Pollard, Lawrence Berkeley Laboratory; P. von Ballmoos,
M. Niel, and G. Vedrenne, Centre d'Etudes Spatiales des Rayonnements;
and P. Durouchoux, Centre d'Etudes Nucleaires de Saclay) reports:
"We have detected a low flux of very narrow 511-keV electron-positron
annihilation radiation from the galactic center (GC) region, indicating
that the luminosity of the compact source of annihilation radiation
has decreased below the level observed 7 months earlier. The
GC was observed on May 22 with a new high-resolution gamma-ray
spectrometer that has a 20-deg FWHM field-of-view, twelve 130-cm3
Ge detectors, and an energy resolution of 2.1 keV FWHM. The 6-hr
observation was from a high-altitude balloon launched from Alice
Springs, Australia. Results from multi-parameter Gaussian fits to
the data are: flux = (6.49 +/- 1.93) x 10E-4 photons cmE-2 sE-1
and width < 1.8 keV (95 percent confidence). If the flux is
interpreted as diffuse galactic emission, the instrument's 24-deg
effective aperture gives a flux of (1.55 +/- 0.46) x 10E-3 photons
cmE-2 sE-1 radE-1, in agreement with the results of Share et al.
1988 (Ap.J. 326, 717). The line-width limit is consistent with
annihilation in the warm (10E4 K) phase of the interstellar medium.
The flux and line-width limit are each 0.5 of the measurements by
Leventhal et al. 1989 (Nature 339, 36) with a 17-deg field-of-view
in 1988 Oct., when the compact source was active, implying that
the broader width is associated with the compact source."
1989 November 2 (4889) Daniel W. E. Green
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