Type Ibn SN2015G: limits on progenitors from pre-explosion HST images
ATel #7563; Dan Maoz, Dovi Poznanski (Tel-Aviv University)
on 26 May 2015; 07:52 UT
Credential Certification: Dan Maoz (Tel-Aviv University) (maoz@astro.tau.ac.il)
Subjects: Optical, Supernovae
We have analyzed pre-explosion
Hubble Space Telescope images of the site of the Type Ibn supernova
SN2015G (CBET#4087) in NGC 6951.
HST WFPC2 images with total 700 s exposure per band were obtained in April 2001
in F814W (I-band) and in May 2001 in F555W (V-band). Using bright stars
near the SN position, we have aligned the HST images to an I-band
image of the supernova obtained on April 29, 2015 with the Wise Observatory
1m telescope using the LAIWO camera in 2.5" seeing.
We have localized the explosion site to about 0.3"
in the HST images (3 WFPC2 pixels). No source is detected to limiting
AB magnitudes I=25.8 and V=25.5. Assuming the Galactic extinction values
in this direction as listed in NED (based on Schlafly and Finkbeiner 2011),
of A_V=1.0 mag and A_I=0.56 mag, and
a SN Ia-based distance modulus to the galaxy of m-M=31.61 mag (20.9 Mpc,
Mandel et al. 2011, ApJ, 731, 120), this limits the absolute magnitudes
of a pre-explosion progenitor to M_I > -6.4 and M_V > -7.1
(ignoring local extinction). Although no candidate progenitor is detected,
there are about 10 point sources in the HST images within 2 arcsec
(300 pc in projection) of the SN location, some with blue colors
(down to V-I~-0.5, after correcting for Galactic extinction) and absolute
magnitudes M_V ~ -7 to -9, corresponding to luminous stars or compact clusters.
The SN thus appears to have exploded in a star-forming region.
