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IAUC 6810: 1997ff, 1997fg; NGC 2060

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                                                 Circular No. 6810
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVAE 1997ff AND 1997fg
     R. L. Gilliland, Space Telescope Science Institute; and M. M.
Phillips, Cerro Tololo Interamerican Observatory, report their
discovery of two apparent supernovae in the Hubble Deep Field (HDF).
The objects were detected in second-epoch exposures of the HDF
obtained with WFPC2 on the Hubble Space Telescope (+ F814W filter)
between 1997 Dec. 23.6 and 27.0 UT; they were not present in images
taken on 1995 Dec. 25.  SN 1997ff is located 0".11 west and 0".11
south of the center of a galaxy designated by Williams et al. (1996,
A.J. 112, 1335) as 4-403.0, whose position is given as R.A. =
12h36m44s.11, Decl. = +62o12'44".8 (equinox 2000.0).  SN 1997fg is
located 0".31 east and 0".31 south of the center of 3-221.0, which
has position end figures 57s.67, 13'15".3 (and redshift 0.952).
Magnitudes were obtained by breaking the new series of HDF
observations into three sets (each of total exposure 21~000 s) and
were derived with reference to the I-band magnitudes of stars in
the HDF from Flynn et al. (1996, Ap.J. 466, L55):  SN 1997ff, Dec.
23.83 UT, I = 26.77 +/- 0.14; 25.78, 27.20 +/- 0.21; 26.74, 26.85
+/- 0.15.  SN 1997fg, Dec. 23.83, I = 25.93 +/- 0.07; 25.78, 26.04
+/- 0.07; 26.74, 26.02 +/- 0.07.  SN 1997ff is a 9-sigma detection,
while SN 1997fg is > 20 sigma.

NGC 2060
     F. E. Marshall, Goddard Space Flight Center (GSFC); J.
Middleditch, Los Alamos National Laboratory; W. Zhang, GSFC; and E.
V. Gotthelf, GSFC and Universities Space Research Association,
report the discovery of pulsations from NGC 2060 = N157B, a Crab-
like supernova remnant in the Large Magellanic Cloud (cf. Henize
1956, Ap.J. Suppl. 2, 331; Mathewson et al. 1983, ibid. 51, 345):
"An observation with the Rossi X-ray Timing Explorer on 1996 Oct.
12 revealed pulsations in the band 2-10 keV with a period of
16.114712 +/- 0.000003 ms.  Pulsations were also seen in the band
10-25 keV.  Analysis of archival data acquired with the ASCA X-ray
Observatory confirms the RXTE detection and the identification with
N157B.  Using a subsequent RXTE detection of the pulsar on 1996
Dec. 22, and ASCA detections on 1993 June 13, Aug. 29, Sept. 23,
and 1995 Nov. 6, we derive a period derivative of (5.124 +/- 0.003)
x 10E-14 s/s.  This appears to be the most rapidly rotating pulsar
yet seen that has not been spun up since its birth.  The pulsar is
likely associated with the compact x-ray source in N157B (Wang and
Gotthelf 1998, Ap.J., in press; preprint available at
http://xxx.lanl.gov/abs/astro-ph/?9708087).  Observations at other
wavelengths are encouraged."

                      (C) Copyright 1998 CBAT
1998 January 22                (6810)            Daniel W. E. Green

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