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IAUC 2819: A0621-00 AND Prob. OPTICAL Id; N Sgr 1975; Cyg X-3

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                                                  Circular No. 2819
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.

     T. Matilsky, Massachusetts Institute of Technology, reports
that the SAS-3 X-Ray Astronomy Group has observed the transient x-ray
source A0621-00 in Orion (IAUC 2814, 2817) from Aug. 8.5 to
15.5 UT.  When first observed the source was as bright as Sco X-1
in the energy range 1.5 to 5 keV.  In two days the source increased
dramatically in intensity to four times brighter than Sco X-1, and
it has subsequently remained at that level.  However, the source is
only about half as bright as Sco X-1 in the 5 to 13 keV range, thus
indicating its relative softness.  No periodic pulsing has been
observed to a limit of 1 percent in the range 1 to 500 seconds.  Data
obtained with the rotating modulation collimators on SAS-3 yield
the position as R.A. = 6h20m06s.4, Decl. = -0o19'04" (equinox 1950.0) with
a 90-percent confidence error radius of 2'.

     F. Boley and R. Wolfson, Dartmouth College, report an optical
object about 1' from the above x-ray location, namely at R.A. =
6h20m11s, Decl. = -0o19'10" (equinox 1950.0).  On Aug. 15, 16 and 17 it
appeared at magnitude 12 or brighter, which is at least five
magnitudes brighter than on the Palomar Sky Atlas.  Identification was
made using image-tube photography on the 130-cm telescope at
McGraw-Hill Observatory, operated on Kitt Peak by the University of
Michigan, Dartmouth and M.I.T.  Spectra obtained at 120 A/mm dispersion
show no emission or absorption features.  T. Gull and D. York
obtained three spectra on Aug. 17 at 5 A/mm using the 400-cm Mayall
telescope at Kitt Peak; these also show no stellar lines, but sharp
interstellar absorption lines were observed.

     K. Osawa, Tokyo Observatory, reports the following precise
position, measured by H. Kosai from a plate taken by N. Kojima, Ishiki:
R.A. = 17h55m11s.74, Decl. = -28o21'36".6 (equinox 1950.0).

     K. Locher, Grut-Wetzikon, Switzerland, sends magnitude
estimates: Aug. 3.87 UT, 12.6; 4.86, 12.6; 5.88, 12.7; 8.87, 13.5.

     N. Kawajiri, Radio Research Laboratories, Kashima Branch,
reports that the intensity of this source at 4.2 GHz was 16.3 +/- 1 Jy
on Aug. l6d15h20m UT and 15.8 +/- 1 Jy on Aug. 16d19h30m UT.

1975 August 19                 (2819)              Brian G. Marsden

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