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IAUC 6156: X-RAY SOURCES IN M31; 1995D

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                                                  Circular No. 6156
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
Phone 617-495-7244/7440/7444     TWX 710-320-6842 ASTROGRAM CAM

     G. L. Israel and A. Treves, International School for Advanced
Studies (SISSA-ISAS), Trieste; L. Stella and G. Tagliaferri,
Osservatorio Astronomico di Brera, Merate; and T. Belloni, Anton
Pannekoek Astronomical Institute, Amsterdam, communicate:  "We
performed a power-spectrum analysis of the archival ROSAT High
Resolution Imager (HRI) light curves of the thirteen brightest x-
ray sources detected in M31 during a long (48000-s) exposure on
1990 July 25-28 (cf. Primini et al. 1993, Ap.J. 410, 615).  Coherent
pulsations at a barycentric period of 76.92(3) s are detected
in about 600 photons from ROSAT source 58 (= Einstein source 69; cf.
Trinchieri and Fabbiano 1991, Ap.J. 382, 82) with a significance >
3.4 sigma; the modulation is nearly sinusoidal in shape, with a 40-
percent pulsed fraction (i.e., semiamplitude modulation divided by
the mean source count rates).  We find also some evidence for
3.01856(5)-s periodic modulation in about 300 photons from ROSAT
source 60 (Einstein source 71), with a 50-percent pulsed fraction
and a significance > 2.7 sigma.  We also searched for periodicities
in PSPC data of the two sources obtained on 1991 July 27 (30000 s),
1992 Aug. 6-9 (10000 s), and 1993 Jan. 2-7 (17000 s).  No significant
pulsations were found; the corresponding upper limits to the
amplitude were in all cases consistent with the HRI results.  Both
sources have luminosities close to 10**38 erg/s, such that large
period derivatives are expected.  If confirmed, these would be the
first x-ray pulsators detected beyond the Magellanic Clouds.
Follow-up x-ray and optical observations are encouraged."

     R. W. Argyle and L. V. Morrison, Royal Greenwich Observatory,
report an accurate optical position for SN 1995D obtained with the
Carlsberg Automatic Meridian Circle on La Palma, operated by P. S.
Herridge and F. Belizon:  R.A. = 9h40m54s.753 +/- 0s.005, Decl. =
+5o08'26".16 +/- 0".08 from 8 observations (equinox J2000.0, FK5
reference frame, epoch 1995.16).  The following V magnitudes have
also been obtained (+/- 0.13 mag):  Feb. 23.03 UT, 13.46; 24.03,
13.42; 25.03, 13.39; 26.02, 13.54.
     Visual magnitude estimates (cf. IAUC 6137):  Mar. 21.793 UT,
14.2 (L. Szentasko, Veresegyhaz, Hungary); 24.82, 14.6 (K.
Sarneczky, Raktanya, Hungary); 28.83, 14.6 (Szentasko); Apr. 2.79,
15.0 (Sarneczky).

1995 April 6                   (6156)            Daniel W. E. Green

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