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Spitzer mid-IR detection of optical transient in NGC 3344 and candidate progenitor

ATel #4502; J. L. Prieto (Princeton)
on 20 Oct 2012; 17:49 UT
Credential Certification: Jose L. Prieto (jose@obs.carnegiescience.edu)

Subjects: Infra-Red, Optical, Supernovae, Transient

Referred to by ATel #: 4507, 4544

We report on analysis of archival Spitzer data of the recent optical transient discovered and reported in the CBAT TOCP by M. Tsuboi at RA = 10:43:34.05 and DEC = +24:53:29.0 in the nearby galaxy NGC 3344 at 6.4 Mpc (from Virgo-corrected recession velocity via NED). The host galaxy has been observed with Spitzer IRAC (Apr. 2004 and Jul. 2012) and MIPS (Jan. 2008) instruments by different programs: 69 (PI: Fazio), 40204 (PI: Kennicutt), and 80025 (PI: van Zee). We detect a bright mid-IR source at the position of the optical transient in the IRAC 3.6 and 4.5 micron images obtained on July 9 and July 14, 2012 (UT). The Vega magnitudes of the source are: [3.6] = 12.31 +/- 0.05 mag, [4.5] = 12.03 +/- 0.05 (July 9, 2012), and [3.5] = 12.18 +/- 0.05, [4.5] = 11.96 +/- 0.05 (July 14, 2012). In the IRAC images obtained in 2004 this source is much fainter (~4 mag at 4.5 micron), with estimated preliminary magnitudes: [3.6] < 16.6, [4.5] = 16.4, [5.8] = 15.9, [8.0] = 15.3 (+/- 0.3 mag).

The detection of a bright mid-IR source with absolute magnitude M_4.5 = -17 (nu*Lnu = 2.4x10^6 Lsun) in the Spitzer/IRAC images obtained July 9-14 2012 most likely indicates that the outburst of the transient in NGC 3344 had already started. The candidate progenitor detected in Spitzer/IRAC images in 2004 with M_4.5 = -12.6 mag implies that it had a mid-IR luminosity nu*Lnu = 4x10^4 Lsun (4.5 micron), consistent with a massive star origin. The mid-IR properties of the transient/progenitor and its low optical luminosity compared to normal core-collapse SNe (V=15 mag, MV ~ -14) make it consistent with the properties of SN 2008S-like transients (e.g., Thompson et al. 2009, ApJ, 705, 1364; Kochanek et al. 2011, ApJ, 741, 37). It could also be a low-luminosity Type IIP supernova.

Spitzer detection of optical transient in NGC 3344