Discovery of a Light Echo from SN 2003gd

Abstract

Archival HST/ACS data reveal details of a light echo around SN 2003gd in the galaxy M74, only the fifth supernova around which resolved echoes have been reported. An echo is detected 0Љ .3 from the supernova between position angles of 250Њ and 360Њ, with a fainter signal present at a few other position angles. This material lies ∼180 pc in front of the supernova, with a thickness of 60-120 pc, and may delineate the disk of M74. This structure has a gas density of 1-2 cm Ϫ3 , typical of the interstellar medium; however, the dust grains are smaller than those found in our Galaxy, with maximum grain sizes around 0.25 mm. Since only one epoch of data exists, in two wave bands and with a low signal-to-noise ratio, deeper annual visits should be made with HST and ground-based adaptive optics telescopes.

Observation of light echoes around very young stars

“…Each image was reduced in the standard manner (e.g. bias subtraction, flat fielding), then geometrically registered to a common orientation using field stars as described in Sugerman (2005). rms residuals of geometric registration are less than 0.1 pixel for all images.…”

“…2), and are slightly more apparent when the point-spread function (PSF) of S CrA has been removed (Stetson 1987), as shown in the middle column. Since light echoes are transient phenomena, we employed the PSF-matching and difference-imaging techniques of Tomaney & Crotts (1996) and Sugerman (2005), combined with the NN2 algorithm of Newman & Rest (2006), to remove all sources of constant flux and produce echo-only images for each epoch. These are shown in the right column of Fig.…”

“…We identified the angular distance of each echo from S CrA (see Table 1), by iteratively fitting Gaussian functions to radial surface-brightness profiles taken at various position angles (Sugerman 2005), avoiding an "ear"-like filament which shows brightness variations over time. This "ear" feature is stationary and can be explained as an isolated knot with thickness smaller than cΔt, where Δt is a typical pulse duration.…”

“…All those conditions are not usually met. In fact, light echoes are impressive and very rare phenomena that have been witnessed in only a handful of events (Couderc 1939;Suntzeff et al 1988;Bode & Evans 1985;Rest et al 2005;Krause et al 2005;Bond et al 2003;Sugerman 2005;Quinn et al 2006;Sugerman 2003;Crotts & Yourdon 2008;Liu et al 2003;Rest et al 2008a,b;Cappellaro et al 2001;Sparks et al 1999Sparks et al , 2008Bond & Sparks 2009, and references therein). Such events are mostly explosive or nearly explosive (supernovae, novae, novae-like, a Cepheid variable, and a planetary nebula) from stellar objects in their latest stages of evolution.…”

A Light Echo from Type Ia SN 1995E?

“…Important clues to the distribution and properties of the dust in their vicinity may be found by studying the brightness and geometry of SN Ia light echoes. The distance between the dusty region and light source is readily calculable with a few simplifying assumptions about the dust distribution (Couderc 1939;Sugerman 2003). Further information such as polarization measurements could even provide independent distance measurements between the observer and the explosive event (Sparks et al 1999).…”