Central Bureau for Astronomical Telegrams
IAUC 7662: 2001dc
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Circular No. 7662
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 2001dc IN NGC 5777
G. M. Hurst, Basingstoke, England, reports the discovery by M.
Armstrong (Rolvenden, Kent) of an apparent supernova at R.A. =
14h51m16s.15, Decl. = +58o59'02".8 (equinox 2000.0; average from
three CCD images obtained with a 0.35-m reflector), said to be 26"
west and 28" north of the center of NGC 5777. Reported magnitudes
for SN 2001dc [unfiltered CCD data unless otherwise noted, and from
Armstrong unless otherwise noted; '--' means not visible; JKT =
Jacobus Kapteyn Telescope (via P. Meikle, Imperial College;
uncertainty +/- 0.1 mag; June 22 data obtained by D. Bramich, R.
Corradi, and P. Erwin)]: 1995 Apr. 4 UT, [20.8 (Palomar Sky Survey
red plate); Apr. 18, [21 (JKT I-band images); Apr. 24, [22.5 (PSS
blue plate); 1997 Apr. 18, -- (PSS infrared plate); 2000 Dec. 3,
--; 2001 Apr. 12, --; May 12, --; 21.977, 18.6 (prediscovery);
30.958, 18.5 (discovery; limiting mag 19.3); June 1.021, 18.5;
2.985, 18.3 (T. Boles, Coddenham, England); 22.93, B = 21.11, V =
19.83, R = 19.15, I = 18.46 (JKT). M. Irwin (Cambridge
Astronomical Survey Unit) adds that a June 22.93 JKT image yields
position end figures 16s.21, 03".0 for SN 2001dc, which is about
14" west and 22" north of the nucleus of NGC 5777. Meikle notes
that JKT data show that the change in brightness of SN 2001dc from
June 22.93 to July 4.92 was < 0.3 mag in B, 0.1 mag in V, and 0.05
mag in R (all 1-sigma confidence); there was marginal evidence of a
brightening in I (by -0.12 +/- 0.04). Meikle and A. Fassia add: "A
spectrum obtained on July 10.97 at the Isaac Newton Telescope shows
a strong but quite narrow P-Cyg profile in H-alpha. Together with
the lack of significant decline in optical brightness between June
22 and July 4, we conclude that this is a type-IIp supernova, still
in its plateau phase during this period. Other lines identified
include Fe II (501.8 and 516.9 nm), Na I D, and the Ca II infrared
triplet. A blueshifted absorption feature due to H-beta may also
be present, but it is close to the blue limit of the spectrum (482
nm). The trough of the H-alpha profile is blueshifted by about
2400 km/s with respect to the emission peak. The corresponding
figure for Na I D is 2300 km/s. The supernova appears to be an
unusually low-energy event. Assuming negligible extinction, the
V-band magnitude corresponds to M_V = -12.6 (adopting 32.4 as the
distance modulus for NGC 5777), compared with more typical values
(M_V = -15 to -16) for a type-IIp event during its plateau phase
(Patat et al. 1994, A.Ap. 282, 731). Moreover, the velocity seen
in H-alpha is only about half of that normally observed during this
era. Further photometric and spectroscopic observations are
strongly encouraged. Of particular interest is the size of the
decline immediately following the end of the plateau phase."
(C) Copyright 2001 CBAT
2001 July 14 (7662) Daniel W. E. Green
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