Central Bureau for Astronomical Telegrams
IAUC 2929: X-RAY BURSTS FROM GALACTIC CENTER REGION; HR 1099
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Circular No. 2929
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Cable Address: SATELLITES, NEWYORK
Western Union: RAPID SATELLITE CAMBMASS
X-RAY BURSTS FROM GALACTIC CENTER REGION
The Ariel 5 Group, University of Birmingham, reports that the
Ariel 5 rotation modulation collimator experiment has detected flux
from within the error boxes of MXB1730-335 and MXB 1728-34 (IAUC
2922, 2925). Although bursts have been detected, the flux integrated
over one orbit (93 min) is higher than expected from the observed
burst occurrence rates. Positions for the burst sources were
determined to be R.A. = 17h30m14s, Decl. = -33o21' and R.A. = 17h28m29s,
Decl. = -33o48' (equinox 1950.0), respectively. The radius of the
error circle was 2' in each case.
J. Heise, Astronomical Institute, Laboratory for Space Research,
Utrecht; and J. Grindlay, Center for Astrophysics, report
that the x-ray detectors on ANS detected 19 bursts from the repetitive
burst source MXB1730-335 during 8 min of observations on Mar.
14.640 and 15.239 UT. The bursts were typically one-quarter of the
Crab intensity and of a few seconds duration. From the ratio of
total counts detected in the bursts in the two HXX detectors with
fields of view 3o x 10', Decl. was determined (90-percent confidence
level) to be 2'.5 +/- 1' north of the pointing position used (IAUC
2925). The ratio of counts seen in the HXX and SXX detectors confines
the source to the central portion of the field in R.A.. The
region of intersection of the ANS and SAS-3 positions is then at
R.A. = 17h30m12s +/- 10s, Decl. = -33o22'.5 +/- 1' (equinox 1950.0).
W. Liller, Center for Astrophysics, reports that a near-infrared
plate (7000-9000 A) taken in 1" seeing with the 400-cm telescope
at Cerro Tololo Interamerican Observatory reveals a faint
star cluster, probably globular, with coordinates R.A. =l7h30m08s +/- 1s,
Decl. = -33o21'25" +/- 10" (equinox 1950.0). The position is in excellent
agreement with those given above for MXB1730-335. Deep B and V
plates also taken with the 400-cm telescope do not show the cluster,
but it appears as a faint, diffuse patch on a red plate (6100-6800 A)
at magnitude R ~ 21. These data are consistent with a globular
cluster 30 kpc from the earth with absorption A_V 15 magnitudes.
HR 1099
F. N. Owen, National Radio Astronomy Observatory, reports
detection of this RS CVn-type binary with the NRAO interferometer on
four separate days during Feb. 29-Mar. 11. Observed flux densities
varied over 9-136 mJy at 2695 MHz and over 10-179 mJy at 8085 MHz.
1976 March 19 (2929) Brian G. Marsden
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