Electronic Telegram No. 724
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html


SUPERNOVAE 2006mp AND 2006mq
     L. Watson, D. DePoy, and J. L. Prieto, Ohio State University; and P. M.
Garnavich, University of Notre Dame, report that optical spectra (range
380-730 nm) of 2006mp (cf. CBET 720) and 2006mq (cf. CBET 721) were obtained
with the Hiltner 2.4-m telescope (+ CCDS spectrograph) at MDM Observatory on
Nov. 6.1 and 6.5 UT.  The spectrum of 2006mp is blue and shows features
typical of a type-Ia supernova before or at maximum light, although the Si II
(635.5 nm at rest) and S II "W" (546.8 and 563.3 nm at rest) features are
weak compared with normal type-Ia supernovae at early phases.  After
comparing it with library spectra from the literature, the spectrum is found
to be very similar to that of the overluminous type-Ia supernova 1991T
(Phillips et al. 1992, A.J. 103, 1632) at maximum light.  The best match is
found to occur when the spectrum of 1991T is redshifted by (1+z) = 1.023,
which implies an approximate recession velocity for the host galaxy (MCG
+08-31-29) of 6900 km/s.
     The spectrum of 2006mq shows conspicuous absorption/emission P-Cyg
features with broad absorption minima at 442, 479, 506, 569, 603, 628, and
698 nm (rest wavelength), assuming a recession velocity for the host galaxy,
ESO 494-G26, of 968 km/s (Theureau et al. 1998, A.Ap. Suppl. 130, 333).  The
spectrum resembles the spectra of type-I supernovae around two weeks after
maximum.  A type-Ia supernova matches well the overall shape of the spectrum,
with the main difference being the presence of a strong double absorption in
2006mq at 603 and 628 nm (rest) instead of the single absorption typically
present in type-Ia supernovae at these epochs.  Some type-Ib/c supernovae
show the double feature at 1-2 weeks after maximum, which has been
potentially identified with H_alpha and He I at high velocity (e.g.,
Elmhamdi et al. 2006, A.Ap. 450, 305; Branch et al. 2006, PASP 118, 791).
In particular, the spectrum of the type-Ic supernova 1990B (Matheson et al.
2001, A.J. 121, 1648) at 13 days after maximum is a reasonable match to that
of 2006mq.  Thus, 2006mq is most likely a type-Ia supernova around two weeks
after maximum, but the possibility of this object being a type-Ib/c supernova
cannot be completely ruled out.  The interstellar absorption feature Na I D
is also detected, and an equivalent width of 0.2 nm is measured, implying a
very high Galactic extinction in the line-of-sight of E(B-V)_Gal > 0.4
magnitude (Munari and Zwitter 1997, A.Ap. 318, 269), consistent with the
value given by the reddening maps of Schlegel et al. (1998, Ap.J. 500, 525):
E(B-V)_Gal = 0.42 mag.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2006 CBAT
2006 November 6                  (CBET 724)               Daniel W. E. Green