Molecular Environment and Thermal X-Ray Spectroscopy of the Semicircular Young Composite Supernova Remnant 3c 396

Abstract

We have investigated the molecular environment of the semicircular composite supernova remnant (SNR) 3C 396 and performed a Chandra spatially resolved thermal X-ray spectroscopic study of this young SNR. With our CO millimeter observations, we find that the molecular clouds (MCs) at V LSR ∼ 84 km s −1 can better explain the multiwavelength properties of the remnant than the V LSR = 67-72 km s −1 MCs that are suggested by Lee et al. (2009). At around 84 km s −1 , the western boundary of the SNR is perfectly confined by the western molecular wall. The CO emission fades out from west to east, indicating that the eastern region is of low gas density. In particular, an intruding finger/pillar-like MC, which may be shocked at the tip, can well explain the X-ray and radio enhancement in the southwest and some infrared filaments there. The SNR-MC interaction is also favored by the relatively elevated 12 CO J=2-1/J=1-0 line ratios in the southwestern "pillar tip" and the molecular patch on the northwestern boundary. The redshifted 12 CO (J=1-0 and J=2-1) wings (86-90 km s −1 ) of an eastern 81 km s −1 molecular patch may be the kinematic evidence for shock-MC interaction. We suggest that the 69 km s −1 MCs are in the foreground based on HI self-absorption while the 84 km s −1 MCs at a distance of 6.2 kpc (the tangent point) are in physical contact with SNR 3C 396. The X-ray spectral analysis suggests an SNR age of ∼ 3 kyr. The metal enrichment of the X-ray emitting gas in the north and south implies a 13-15M ⊙ B1-B2 progenitor star.

Linear Relation for Wind-Blown Bubble Sizes of Main-Sequence Ob Stars in a Molecular Environment and Implication for Supernova Progenitors

“…3C 396 is coincident with a molecular cavity at v LSR ∼ 85-87 km s −1 , and the western boundary of the SNR perfectly follows the eastern face of a molecular wall (Su et al 2011). Lee et al (2009) attribute the near-IR [Fe ii] line emission to the SNR shock overtaking the RSG wind of the SN progenitor, and suggest a progenitor mass of 25-35 M .…”

Comparing Neutron Star Kicks to Supernova Remnant Asymmetries

“…3C 396 (G39.2−0.3)-3C 396 is a middle-aged (≈3000-7000 years old), composite SNR (Harrus & Slane 1999;Su et al 2011). ASCA observations of 3C 396 revealed a non-thermal component dominates at the center of 3C 396 (Harrus & Slane 1999), and Chandra observations resolved this emission as a PWN (Olbert et al 2003).…”

“…ASCA observations of 3C 396 revealed a non-thermal component dominates at the center of 3C 396 (Harrus & Slane 1999), and Chandra observations resolved this emission as a PWN (Olbert et al 2003). Su et al (2011) extracted Chandra X-ray spectra from multiple locations around the perimeter of 3C 396, and emission lines from Si, S, Ar, and Ca were evident. They found the data were bestfit by an absorbed, single NEI plasma, with absorbing columns of N H ≈ (4.4 − 5.5) × 10 22 cm −2 , temperatures of kT ≈ 0.7 − 1.3 keV, and ionization timescales of n e t ≈ (0.4 − 2.7) × 10 11 s cm −3 (although the southwest and east of the SNR only had lower-limits on n e t of > 4 × 10 11 s cm −3 and > 0.8 × 10 11 s cm −3 , respectively).…”

Molecular Environments of Supernova Remnants

“…We find that the western edge, bright in radio, IR, and X-rays, is perfectly confined by a molecular wall (of mass ∼ 10 4 M ⊙ ) revealed in 12 CO (J=1-0) line at V LSR ∼ 84 km s −1 (Su et al 2011). The CO emission gradually gets faint from west to east, which is indicative that the eastern region is of low gas density.…”

“…Some of the estimates can be compared with other available independent assessments, which show considerably good consistency. For 3C 396, Su et al (2011), based on Chandra observation, derived a progenitor mass of 13-15M ⊙ from the metal abundances of the X-ray-emitting gas that may be dominated by the SN ejecta. For 3C 397, a recent XMM-Newton X-ray study has analyzed the metal abundances of the SN ejecta and thus assessed the progenitor's mass to be 11-15M ⊙ (Safi-Harb et al in preparation).…”