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Supernova 2006X
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Title: VLT Spectropolarimetry of the fast expanding Type Ia SN2006X
Authors: F. Patat, D. Baade, P. Hoeflich, J. R. Maund, L. Wang, J. C. Wheeler

Using VLT-FORS1 we performed optical spectropolarimetric observations of the Type Ia SN2006X on 7 pre-maximum epochs (day -10 to day -1) and one post-maximum epoch (+39 days). The SN shows strong continuum interstellar polarisation reaching about 8% at 4000A, characterised by a wavelength dependency that is substantially different from that of the Milky-Way dust mixture. Several SN features, like SiII 6355A and the CaII IR triplet, present a marked evolution. The CaII near-IR triplet shows a pronounced polarisation (~1.4%) already on day -10 in correspondence with a strong high-velocity feature (HVF). The SiII polarisation peaks on day -6 at about 1.1% and decreases to 0.8% on day -1. By day +39 no polarisation signal is detected for the SiII line, while the CaII IR triplet shows a marked re-polarisation at the level of 1.2%. As in the case of another strongly polarised SN (2004dt), no polarisation was detected across the OI 7774A absorption. The fast-expanding SN2006X lies on the upper edge of the relation between peak polarisation and decline rate, and it confirms previous speculations about a correlation between degree of polarisation, expansion velocity, and HVF strength. The polarisation of CaII detected in our last epoch, the most advanced ever obtained for a Type Ia SN, coincides in velocity with the outer boundary of the Ca synthesised during the explosion (15,000-17,000 km/s) in delayed-detonation models. This suggests a large scale chemical inhomogeneity as produced by off-center detonations, a rather small amount of mixing, or a combination of both effects. In contrast, the absence of polarisation at the inner edge of the Ca-rich layer (8000-10,000 km/s) implies a substantial amount of mixing in these deeper regions.

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RE: Supernova 2006X
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Title: A Second Case of Variable Na I D Lines in a Highly-Reddened Type Ia Supernova
Authors: S. Blondin (1,2), J. L. Prieto (3), F. Patat (1), P. Challis (2), M. Hicken (2), R. P. Kirshner (2), T. Matheson (4), M. Modjaz (5) ((1) ESO, (2) Harvard-Smithsonian CfA, (3) Ohio State University, (4) NOAO, (5) UC Berkeley)

Recent high-resolution spectra of the Type Ia SN 2006X have revealed the presence of time-variable and blueshifted Na I D features, interpreted by Patat et al. as originating in circumstellar material within the progenitor system. The variation seen in SN 2006X induces relatively large changes in the total Na I D equivalent width (\Delta EW ~ 0.5 A in just over two weeks), that would be detectable at lower resolutions. We have used a large data set comprising 2400 low-resolution spectra of 450 Type Ia supernovae (SNe Ia) obtained by the CfA Supernova Program to search for variable Na I D features. Out of the 31 SNe Ia (including SN 2006X) in which we could have detected similar EW variations, only one other (SN 1999cl) shows variable Na I D features, with an even larger change over a similar ~10-day timescale (\Delta EW = 1.66 0.21 A). Interestingly, both SN 1999cl and SN 2006X are the two most highly-reddened objects in our sample, raising the possibility that the variability is connected to dusty environments.

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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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A team of European and American astronomers has announced the discovery of the best evidence yet for the nature of the star systems that explode as type Ia supernovae. The team obtained a unique set of observations with the European Southern Observatory's Very Large Telescope and the Keck I 10-meter telescope in Hawaii.

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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.

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Magnitude 13.8 and rising

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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.

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Magnitude 14.9 and rising..
Type Ia supernova.

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A magnitude 15.3 Supernova, 2006X, was discovered on the 7th February by Shoji Suzuki; M. Migliardi (CROSS) in the Spiral Galaxy Messier 100 (NGC 4321) in the constellation Coma Bernices.
It is located 12" west and 48" south of the nucleus.

M100 lies approximately 65-70 million light years away

Position(2000): R.A. = 12h22m53s.99, Dec. = +1548'33".1

As yet the Type is unknown.

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