Hubble captures rare 'light echo' from star explosion ucddublin AAS_Office
1. IntroductionLight echoes are produced when photons emitted by a transient source scatter off interstellar dust clouds . Often appearing as arcs or wisps of light, LEs were first detected in Galactic and extragalactic novae over a hundred years ago and successfully explained as scattering phenomena by Couderc . Later, LEs were found around variable stars , while more recently, LEs associated with historical supernovae have been documented .
2. HST Observations of SN 2016adjHST observed SN 2016adj over eight epochs extending from 2016 February 22 to 2021 July 28 with the Wide Field Camera 3 . Drizzled HST frames were retrieved from the Mikulski Archive for Space Telescopes, consisting of eight, six, and five epochs taken with the F438W, F547M, and F814W filters, respectively, and a single epoch with the F555W filter. A summary of the HST images used in this study is provided in Table 1.
3.3. Foreground Distance of the Scattering Dust SheetsFollowing the single-scattering formalism , the distance between a transient light source and a foreground LE-producing dust sheet can be inferred from the geometric relationship Patat ) relates the observed LE color LE to the intrinsic color of the SN at the peak following: . Given the high and uncertain reddening parameters associated with SN 2016adj , we adopt mag , which implies values of 1.0 ± 1.0 to 2.8 ± 0.2 .
Within this scheme, LE1 is formed by a dense, clumpy layer of CSM located along the LoS extending over an area perpendicular to the isodelay surfaces of at least ∼28 ± 10 pc. LE3 and LE4 are formed by distinct dust sheets characterized by rather extensive holes relative to our LoS and first encountered by the scattering ellipsoid between +578 days and +1991 days.