SN2001cn in IC4758 ( 18h 46mn18.26ss -65°45'23.9" ) CTIO Nick Suntzef
offset 2.6" W 17.9" S magnitude 14.8 http://www.ctio.noao.edu/~nick/sn/sn2001cn/sn2001cn.html
Telescope LX200 12" f/d 2.7 ST7E UAI173 Ste Clotilde REUNION ISLAND CTIO Pablo Candia
2001/06/11.95 unflated binning 2x 60s
2001/04/29.03 unflated limiting mag 19 binning 2x 60s
confirmation image 2001/06/12.85 mag 14.8 180s
referenced image DSS UK Schmidt 1976/04/04.75 limiting mag 21
SUPERNOVA 2001cn IN IC 4758
R. Chassagne, Ste. Clotilde, Ile de Reunion, reports the
discovery of an apparent supernova (mag about 14.8) on unfiltered
CCD images taken on June 11.95 and 12.85 UT with a 0.30-m
reflector. SN 2001cn is located at R.A. = 18h46m17s.84, Decl. =
-65o45'41".8 (equinox 2000.0), which is 2".6 west and 17".9 south
of the nucleus of IC 4758. The new object does not appear on a
Digital Sky Survey image (U.K. Schmidt 1.2-m telescope) taken on
1976 May 4.75 (limiting mag about 21.0). R. Santallo, Faaa,
Tahiti, French Polynesia, reports a confirmation of SN 2001cn at
mag about 14.8 on unfiltered CCD images taken on June 13.531 with a
0.2-m reflector, and he provides the following position end
figures: 17s.88, 41".8 (or 1".8 west and 17".4 of the galaxy
SUPERNOVA 2001cn IN IC 4758
P. Candia, R. C. Smith, and N. Suntzeff, Cerro Tololo
Interamerican Observatory (CTIO), report: "A spectrum taken by D.
Norman and K. Olsen (CTIO) on June 14.3 UT with the Cerro Tololo
1.5-m telescope (+ Cassegrain Spectrograph) shows SN 2001cn (cf.
IAUC 7643) to be a type-Ia supernova near maximum light. The
supernova photospheric expansion velocity with respect to the host
galaxy is 11000 km/s, based on the difference between the NASA/IPAC
Extragalactic Database recession velocity for IC 4758 of 4647 km/s
and the measured Si II absorption trough (rest 635.5 nm)."
Dear SN watchers,
R. Chassagne discovered his 8th SN 2001cn in the southern galaxy.
It is now around mag 15.0. Congratulations, Robin!
SN 2001cn was discovered on June 11.95 at mag about 14.8, and
remains at nearly the same magnitude until June 13.531 when R.
Sanrallo confirmed it. The SN position is: R.A. = 18h46m17s.84, Decl.
= -65o45'41".8 (2000.0), which is about 2" west and 18" south of the
nucleus of the face-on spiral (Sc) galaxy IC 4758. There are several
foreground stars around this galaxy nearly the same angular distance
from the nucleus as SN, so the identification needs care.
The reported magnitude is somewhat brighter than the expected
maximum (V magnitude 15.4) of typical SN Ia for this galaxy's
recession velocity (4647 km/s). It would possibly be caused that the
discoverer (and also confirmer) used ST-7E, which is sensitive for
blue light, and USNO-A2.0 r magnitude for the comparison stars.
SNe in the early stage is usually bluer than the surrounding
comparison stars, so the blue-sensitive CCD (without filter) will
catch more photons from the young SN than stars whose r magnitude is
comparable with that of SN. It is possible, however, that this SN is
intrinsically bright; further follow-up photometry (and of course the
spectral classification) will make it clear.
Hitoshi Yamaoka, Kyushu Univ., Japan