Central Bureau for Astronomical Telegrams
IAUC 5541: GEMINGA
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Circular No. 5541
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@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
GEMINGA
W. Hermsen and B. N. Swanenburg, Laboratory for Space
Research, Leiden; R. Buccheri, L. Scarsi, and B. Sacco, Istituto di
Fisica Cosmica ed Applicazioni dell'Informatica, Consiglio Nazionale
delle Ricerche, Palermo; K. Brazier, G. Kanbach, G. G. Lichti,
H. A. Mayer-Hasselwander, and A. W. Strong, Max-Planck-Institut fur
Extraterrestrische Physik, Garching; I. Grenier, Service
d'Astrophysique, Centre d'Etudes Nucleaires de Saclay; K. Bennett and M.
Busetta, Space Science Department, European Space Agency, ESTEC,
Noordwijk; and J. Mattox, Goddard Space Flight Center, report:
"The EGRET and ROSAT telescopes have recently revealed the presence
of a periodicity of 237 ms in the emission from the gamma-ray
source Geminga (Bertsch et al. 1992, Nature 357, 306) and its soft
x-ray counterpart 1E 0630+178 (Halpern and Holt 1992, Nature 357,
222). We have analyzed the COS-B data of five observations (those
numbered 0, 14, 39, 54, and 64, performed between 1975 Aug. and
1982 Apr.) with Geminga in the field of view for gamma-ray energies
above 100 MeV. Using the Einstein HRI position, we find an
extremely stable law of variation of the pulsation frequency, valid
for the whole COS-B lifetime, with parameters given by t0 = 1979
Mar. 14.0 UT, f0 = 4.217 750 122 77 +/- 0.000 000 000 24 Hz,
f0(dot) = (-0.195 237 9 +/- 0.000 002 4) x 10E-12 Hz sE-1,
f0(double dot) = (0.28 +/- 0.16) x 10E-24 Hz sE-2. The accuracy of
these parameters is significantly greater than that reported by
Bignami and Caraveo (1992, Nature 357, 287) and now allows the
detection of pulsations also in the data from COS-B observation No.
54. The stability of the absolute phases of the peaks is within 5
ms for the five COS-B observations. Therefore we recommend use of
these parameters for archival searches. When we perform the analysis
using the position of G", the proposed optical counterpart for
Geminga (Halpern and Tyler 1988, Ap.J. 330, 201; Bignami et al.
1987, Ap.J. 319, 358), the timing solution changes slightly (mainly
in the value of f0(double dot)) but remains statistically consistent
with that reported above. The COS-B light curve shows, as in
the EGRET case, two main peaks separated by 0.5 in phase with a
significant bridge of emission between them. Detailed analysis on
the variability of the light curve shape and spectra is in progress."
1992 June 10 (5541) Daniel W. E. Green
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