G11.2−0.3: THE YOUNG REMNANT OF A STRIPPED-ENVELOPE SUPERNOVA

Abstract

We present results of a 400 ks Chandra observation of the young shell supernova remnant (SNR) G11.2−0.3, containing a pulsar and pulsar-wind nebula (PWN). We measure a mean expansion rate for the shell since 2000 of 0.0277 ± 0.0018% yr −1 , implying an age between 1400 and 2400 yr, and making G11.2−0.3 one of the youngest core-collapse SNRs in the Galaxy. However, we find very high absorption ( A V  ∼ 16 m  ± 2 m ), confirming near-IR determinations and ruling out a claimed association with the possible historical SN of 386 CE. The PWN shows strong jets and a faint torus within a larger, more diffuse region of radio emission and nonthermal X-rays. Central soft thermal X-ray emission is anticorrelated with the PWN; that, and more detailed morphological evidence, indicates that the reverse shock has already reheated all ejecta and compressed the PWN. The pulsar characteristic energy-loss timescale is well in excess of the remnant age, and we suggest that the bright jets have been produced since the recompression. The relatively pronounced shell and diffuse hard X-ray emission in the interior, enhanced at the inner edge of the shell, indicate that the immediate circumstellar medium into which G11.2−0.3 is expanding was quite anisotropic. We propose a possible origin for G11.2−0.3 in a stripped-envelope progenitor that had lost almost all its envelope mass, in an anisotropic wind or due to binary interaction, leaving a compact core whose fast winds swept previously lost mass into a dense irregular shell, and which exploded as a SN cIIb or Ibc.