* Astronomy

Title: The Detection of a Light Echo from the Type Ia Supernova 2006X in M100
Authors: Xiaofeng Wang (1,2), Weidong Li (1), Alexei V. Filippenko (1), Ryan J. Foley (1), Nathan Smith (1), Lifan Wang (3) ((1) UC Berkeley; (2) Tsinghua University; (3) Texas A&M University)
(Version v3)

We report the discovery of a light echo (LE) from the Type Ia supernova (SN) 2006X in the nearby galaxy M100. The presence of the LE is supported by analysis of both the Advanced Camera for Surveys (ACS) images taken with the {\it Hubble Space Telescope (HST)} at ~300 d after maximum brightness and the Keck optical spectrum obtained at a similar phase. In the image procedure, both the radial-profile analysis and the point-spread-function (PSF) subtraction method resolve significant excess emission at 2--5 ACS pixels (~0.05''-0.13'') from the centre. In particular, the PSF-subtracted ACS images distinctly appear to have an extended, ring-like echo. Due to limitations of the image resolution, we cannot confirm any structure or flux within 2 ACS pixels from the SN. The late-time spectrum of SN 2006X can be reasonably fit with two components: a nebular spectrum of a normal SN Ia and a synthetic LE spectrum. Both image and spectral analysis show a rather blue colour for the emission of the LE, suggestive of a small average grain size for the scattering dust. Using the Cepheid distance to M100 of 15.2 Mpc, we find that the dust illuminated by the resolved LE is ~27--170 pc from the SN. The echo inferred from the nebular spectrum appears to be more luminous than that resolved in the images (at the ~2\sigma level), perhaps suggesting the presence of an inner echo at <2 ACS pixels (~0.05''). It is not clear, however, whether this possible local echo was produced by a distinct dust component (i.e., the local circumstellar dust) or by a continuous, larger distribution of dust as with the outer component. Nevertheless, our detection of a significant echo in SN 2006X confirms that this supernova was produced in a dusty environment having unusual dust properties.

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The Spiral Galaxy Messier 100 was the target of the FORS1 multi-mode instrument on ESO's Very Large Telescope, following the request of ESO astronomers Dietrich Baade and Ferdinando Patat, who, with their colleagues Lifan Wang (Lawrence Berkeley National Laboratory, US) and Craig Wheeler (University of Texas, Austin, US), performed detailed observations of the newly found supernova SN 2006X .


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This image is a composite based on five images taken with FORS1 on Kueyen (VLT) by Dominique Naef, Eric Depagne and Chris Lidman (ESO). The images were taken through different filters: U, V, R, I, and a narrow-band filter centred on the H-alpha line. The exposure time is 60 seconds in the V, R and I filters, 3 minutes in the U-band and 5 minutes in the H-alpha filter. The field of view is 6.8 x 5.1 arcmin2. North is up and East is to the left.
The final processing was done by Kristina Boneva, Haennes Heyer and Henri Boffin (ESO).
Credit ESO

SN 2006X was independently discovered early February by Japanese amateur astronomer Shoji Suzuki and Italian astronomer Marco Migliardi. Found on 4 February as the 24th supernova of the year, it had a magnitude 17, meaning it was 1000 times fainter than the galaxy. It was soon established that this was another example of a Type-Ia supernova, observed before it reached its maximum brightness. The supernova indeed brightened up by a factor 25 in about two weeks.

Magnitude 14.3 and rising

This image was originally captured by John Chumack with a 51 minute exposure on a 12" Takahashi Mewlon & ST8XE CCD in a near Full Moonlit sky.



The LRGB image was composed from:
L= 1260 sec
R= 600 sec
G= 600 sec
B= 600 sec
And processed in Maxim DL, CCDsoft, & Adobe PS.