Date of Award

12-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Physics

Advisor

Dr. Mark D. Leising

Committee Member

Dr. Dieter Hartmann

Committee Member

Dr. Jeremy King

Committee Member

Dr. Catalina Marinescu

Abstract

Type Ia supernovae are widely studied for their uniform properties, which make them ideal candidates for cosmological surveys. Although these exploding stars are popular targets, key funda-mental questions about their nature remain, and new techniques need to be developed to investigate the progenitor system and explosion mechanisms. Light echoes are created by light scattering off dust that reaches the observer after the direct path light from the explosion arrived and have been studied for the past 100 years. Light echoes from Type Ia supernovae are rare, with only a few cases being discovered in the past decades. Because light echoes are ten magnitudes fainter than maximum light, the high intrinsic luminosity of Type Ia supernovae make them prime candidates for the search for light echoes. From these studies, the surroundings can be probed, which is critical for understanding supernovae.

We present the discovery of a light echo from SN 2007af in NGC 5584. Hubble Space Telescope images taken three years after explosion reveal the existence of two separate echoes; an outer echo and smeared central region, which we propose as an unresolved inner echo. The sequence of images, spanning four months, shows the growth of the outer ring, which is consistent with the expected growth of an echo in that time span with the estimated dust sheet distance. In total, a dozen images were obtained from the cosmological campaign that focused on observing Cepheid variable stars for calibration purposes in the F160W, F350LP. F555W, and F814W filters with the Wide Field Camera 3, and we focus on the latter two filters for our analysis.

Analysis performed on all of the images gives key insight into the environment around SN 2007af. The interstellar material dust sheet that created the outer echo is located ∼800 pc in front of the supernova. Exploring the color of the echoes gives implications on the dust type. The change in magnitude between the light echo and the supernova at peak is used to estimate the optical depth of the dust. A background star or galaxy in the precise spot of the supernova causing the inner echo is deemed improbable by our investigation. We will present arguments supporting and opposing the suggestion that the inner echo was produced from circumstellar dust. Finally, the light echo from SN 2007af is compared with other echoes from Type Ia supernovae.

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Physics Commons

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