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IAUC 6749: 1997dg; V2116 Oph

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                                                 Circular No. 6749
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html
Phone 617-495-7244/7440/7444 (for emergency use only)

     Q.-y. Qiao, Y.-l. Qiu, and J.-y. Hu, Beijing Astronomical
Observatory (BAO); A. Esamdin, Urmqi Astronomical Station; and Y.
Zhang, Beijing Normal University, on behalf of the BAO Supernova
Survey, report their discovery of an apparent supernova found on
unfiltered CCD images taken on Sept. 27.72 (mag about 16.7) and
28.60 UT (mag 16.4) with the BAO 0.60-m reflector.  SN 1997dg is
located near the center of the host galaxy, at R.A. = 23h40m14s.21,
Decl. = +26o12'11".8 (equinox 2000.0).  Images of the same field
taken on Sept. 4 (limiting mag about 19.0) show no star at this
     S. Jha, P. Garnavich, P. Challis, and R. Kirshner, Center for
Astrophysics, report that a spectrum of SN 1997dg taken by J. Luu
on Sept. 30.3 UT at the Multiple Mirror Telescope reveals that it
is a type-Ia supernova near maximum light.  The approximate
redshift is 0.03, derived from the strong Si II 615-nm feature.
Images taken by N. Grogin on Sept. 29.4 at the Whipple Observatory
1.2-m telescope yield magnitudes B = 17.2, R = 16.9 (measured
relative to nearby USNO-A1.0 star 1125.20187894).

     M. G. Pereira, F. Jablonski, and J. Braga, Instituto Nacional
de Pesquisas Espaciais; and D. Chakrabarty, Massachusetts Institute
of Technology, write:  "Following the detection of optical
pulsations close to the rotational period of the neutron star in
V2116 Oph = GX 1+4 (IAUC 6489; Jablonski et al. 1997, Ap.J. 482,
L171), we made additional optical-period measurements during 1997
with a 0.6-m telescope (+ CCD photometer; 20-30-s time resolution
in the R band).  Fourteen different determinations yield a
barycentric period ranging from 126.36 +/- 0.19 s on May 18.25 UT
to 127.50 +/- 0.16 s on Aug. 20.08.  Although V2116 Oph was in a
bright optical state (R = 15.5-15.9) during most of July, no
optical pulsations were detected in the interval July 24-29, to a
detection limit of about 0.3 percent in modulation amplitude.  The
optical measurements for the interval May-Aug. indicate a spin-down
rate of +4.0 +/- 0.6 s/yr.  Preliminary analysis of 20-60-keV x-ray
timing data from the CGRO/BATSE all-sky monitor shows that the x-
ray pulse period of GX 1+4 was 126.438 +/- 0.008 s on May 18.5 and
126.986 +/- 0.008 s on July 11.5.  The pulsar was rapidly spinning
down at a relatively steady rate of +3.9 s/yr from early May
through early July, and then abruptly decreased its spin-down rate
to +2.0 s/yr in early July.  At present, it continues to spin down
at this rate.  The May-July rate is consistent with the value
indicated by the optical measurements."

                      (C) Copyright 1997 CBAT
1997 September 30              (6749)            Daniel W. E. Green

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