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IAUC 4587: X-RAY SOURCES; 1987K; N Vul 1987

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                                                  Circular No. 4587
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM    Telephone 617-495-7244/7440/7444

    F. Makino and the Ginga Team, Institute of Space and Astronautical
Science, Sagamihara, Kanagawa, report: "A bright x-ray nova has been
detected at R.A. = 20h01.6m, Decl. = +24.9 deg (equinox 1950.0,
uncertainty +/- 0.3 deg).  It was observed on Apr. 26.04 UT with the
all-sky monitor on Ginga at an intensity of a few times that of the
Crab Nebula.  The intensity on Apr. 27.17 UT was approximately
1.2 x 10**-7 erg cm**-2 s**-1, or about 6 Crab, in the energy range
2-7 keV.  The spectrum is very soft, and kT = 2 keV for a thin
thermal emission.  Since discovery the daily rate of energy increase
has been less than 10 percent, suggesting that the object is near
maximum.  The source was not detectable (intensity less than 0.05
Crab) on  Apr. 22.17 UT."
    They also communicate: "The transient x-ray source reported on
IAUC 4583 has been found to be an x-ray pulsar.  The heliocentric
pulsation period is determined as 29.508 +/- 0.002 s.  The pulse
profile is roughly sinusoidal with a small modulation of about 10
percent (peak-to-peak).  There are also chaotic variations
superimposed on the regular pulses."

     A. V. Filippenko, University of California, Berkeley, reports:
"Spectra (range 610-930 nm, resolution 1-2 nm) obtained on 1987 Dec.
25 and 1988 Feb. 24 with a CCD spectrograph on the 3-m Shane reflector
at the Lick Observatory show that SN 1987K (IAUC 4426) is a type Ib
supernova.  Very broad emission lines of [O I] 630, [Ca II] 730 and Ca
II 860 nm, typical of type Ib supernovae many months past maximum
brightness, are visible.  Balmer emission lines of hydrogen are
absent.  The supernova was earlier classified as type II (IAUC
4427, 4428), based on uncalibrated spectra that appeared to exhibit
weak H alpha and H beta having P Cygni profiles.
    E. M. Schlegel and R. P. Kirshner, Center for Astrophysics,
independently report that a spectrum taken with the MMT grism
spectrograph on 1988 Apr. 11 shows a broad (about 2500 km/s FWHM)
[O I] 630/636-nm emission feature--but no H alpha.  They also
conclude that the appearance closely matches that of a type Ib
supernova several months past maximum.

     The following visual magnitude estimates suggest that this object
has now recovered in brightness (cf. IAUC 4584):  Apr. 24.11 UT, 14.3
(P. Schmeer, Bischmisheim, West Germany); 24.13, 14.5 (S. Lubbock,
Bridgend, Wales); 25.10, 14.3 (Schmeer).

1988 April 28                  (4587)              Brian G. Marsden

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