1. Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
2. Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8568, Japan
3. Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan
4. SUBARU Telescope, National Astronomical Observatory of Japan, 650 North A'ohoku Place, Hilo, Hawaii, USA
5. European Space Agency, Space Science Department, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands

Correspondence to: Oliver Krause¹Ken'ichi Nomoto^2,3 Correspondence and requests for materials should be addressed to O.K. (Email: krause@mpia.de) or K.N. (Email: nomoto@astron.s.u-tokyo.ac.jp).

Abstract

Type Ia supernovae are thermonuclear explosions of white dwarf stars in close binary systems¹. They play an important role as cosmological distance indicators and have led to the discovery of the accelerated expansion of the Universe^{2, 3}. Among the most important unsolved questions⁴ about supernovae are how the explosion actually proceeds and whether accretion occurs from a companion or by the merging of two white dwarfs. Tycho Brahe's supernova of 1572 (SN 1572) is thought to be one of the best candidates for a type Ia supernova in the Milky Way⁵. The proximity of the SN 1572 remnant has allowed detailed studies, such as the possible identification of the binary companion⁶, and provides a unique opportunity to test theories of the explosion mechanism and the nature of the progenitor. The determination of the hitherto unknown^{7, 8, 9} spectroscopic type of this supernova is crucial in relating these results to the diverse population of type Ia supernovae¹⁰. Here we report an optical spectrum of Tycho's supernova near maximum brightness, obtained from a scattered-light echo more than four centuries after the direct light from the explosion swept past the Earth. We find that SN 1572 belongs to the majority class of normal type Ia supernovae.

1. Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
2. Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8568, Japan
3. Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan
4. SUBARU Telescope, National Astronomical Observatory of Japan, 650 North A'ohoku Place, Hilo, Hawaii, USA
5. European Space Agency, Space Science Department, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands

Correspondence to: Oliver Krause¹Ken'ichi Nomoto^2,3 Correspondence and requests for materials should be addressed to O.K. (Email: krause@mpia.de) or K.N. (Email: nomoto@astron.s.u-tokyo.ac.jp).

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