Bright Infrared Progenitor of Luminous Transient in NGC300 implies Explosion of a Massive Star
ATel #1550; Jose L. Prieto (Ohio State University)
on 29 May 2008; 15:57 UT
Credential Certification: Jose Prieto (prieto@astronomy.ohio-state.edu)
Subjects: Infra-Red, Transient
We report analysis of pre-explosion, archival Spitzer images of NGC300
obtained in Dec. 28, 2007 (PI: R. Kennicutt). We detect an infrared
source at RA=00:54:34.53, DEC=-37:38:31.71 (J2000), which is within 1
sigma (0.25") of the position of the luminous transient discovered by
Monard (IAUC # 8946 ), and reported by Berger & Soderberg (ATEL #1544). The
source is detected in all four IRAC bands at 3.6, 4.5, 5.8 and 8 micron,
and in the MIPS 24 micron band. The flux densities of the source are (in
micro Jy, errors approx. 10%): 6.7 (3.6 micron), 76.6 (4.5 micron),
324.8 (5.8 micron), 877.2 (8.0 micron) and 2523.0 (24 micron). The
spectral energy distribution of the Spitzer source suggests radiation
from warm dust (see "http://www.astronomy.ohio-state.edu/~prieto/ngc300_sed.gif").
A black-body fit to the SED gives an integrated luminosity of L=9x10^4
Lsun (using a distance to NGC300 of 1.9 Mpc) and dust temperature of 300
K. The luminosity of the source implies a massive star with 15-20 Msun.
The properties of this SED are remarkably similar to the properties of the
progenitor of SN2008S in NGC6946 detected in Spitzer images and undetected in
deep optical imaging (Prieto et al. 2008, ApJL accepted, http://arxiv.org/abs/0803.0324).
Furthermore, the luminosity of the optical transient (relatively faint
compared to typical core-collapse supernovae, too bright for novae) and
spectrum reported in IAUC # 8946 also have striking similarities. We propose
that the luminous transient in NGC300 and SN2008S share the same origin:
they are most likely the energetic explosion of a massive star enshrouded in
its own dust. It is still not clear if they are the result of core-collapse
or something like the super-outburst of an LBV.
