ALMA CO Observations of the Mixed-Morphology Supernova Remnant W49B: Efficient Production of Recombining Plasma and Hadronic Gamma-rays via Shock-Cloud Interactions

Abstract

We carried out new CO(J = 2-1) observations toward the mixed-morphology supernova remnant (SNR) W49B with the Atacama Large Millimeter/submillimeter Array (ALMA). We found that CO clouds at ∼10 km s −1 show a good spatial correspondence with synchrotron radio continuum as well as an X-ray deformed shell. The bulk mass of molecular clouds accounts for the western part of the shell, not for the eastern shell where near-infrared H 2 emission is detected. The molecular clouds at ∼10 km s −1 show higher kinetic temperature of ∼20-60 K, suggesting that modest shock-heating occurred. The expanding motion of the clouds with ∆V ∼6 km s −1 was formed by strong winds from the progenitor system. We argue that the barrel-like structure of Fe rich ejecta was possibly formed not only by an asymmetric explosion, but also by interactions with dense molecular clouds. We also found a negative correlation between the CO intensity and the electron temperature of recombining plasma, implying that the origin of the high-temperature recombining plasma in W49B can be understood as the thermal conduction model. The total energy of accelerated cosmic-ray protons W p is estimated to be ∼2 × 10 49 erg by adopting an averaged gas density of ∼650 ± 200 cm −3 . The SNR age-W p diagram indicates that W49B shows one of the highest in-situ values of W p in the gamma-ray bright SNRs.

Discovery of a Wind-Blown Bubble Associated with the Supernova Remnant G346.6-0.2: A Hint for the Origin of Recombining Plasma

“…Figure 6c shows the scatter plot between the electron temperature kT e and the peak integrated intensity of 12 CO(J = 2-1) line emission for the regions 1-6 which were defined by Auchettl et al (2017). Although a negative correlation between the CO intensity and kT e will be expected for the thermal conduction scenario (Matsumura et al 2017;Okon et al 2018Okon et al , 2020Sano et al 2021), we could not find such a correlation (correlation coefficient ∼ −0.09). It is noteworthy that the regions containing the shocked molecular clouds do not always exhibit the lower kT e values.…”

“…Although the conventional value of total energy of accelerated cosmic rays W p is thought to be ∼ 10 49 -10 50 erg per a single supernova explosion, the observational constraint for W p was insufficient because of lack of unified identification and/or quantification for shock interacting clouds using the CO/H I radio line emission. Most recently, Sano et al (2021) presented the first reliable results of an SNR age-W p relation for eleven gamma-ray SNRs. The authors discovered a positive correlation between the SNR age and W p with ages below ∼ 6 kyr, suggesting that in-situ values of W p for young SNRs are limited by the short duration time of cosmic-ray acceleration, also known as the age-limited acceleration (cf.…”

“…For the thermal conduction scenario, on the other hand, rapid electron cooling is caused by shock-interactions with cold/dense molecular clouds via thermal conduction (e.g., Kawasaki et al 2002Kawasaki et al , 2005. In fact, the lower electron temperature of recombining plasma is found toward the shocked molecular clouds in the SNRs IC443, W28, W44, and W49B (Matsumura et al 2017;Okon et al 2018Okon et al , 2020Sano et al 2021). To distinguish the two primary scenarios, therefore, it is essential to investigate the spatial distribution of plasma conditions and their relation to the ISM.…”

Investigation of the Physical Origin of Overionized Recombining Plasma in the Supernova Remnant IC 443 with XMM-Newton

“…Observational results on W49B preferring this scenario are reported by some authors, e.g., Miceli et al (2010), Lopez et al (2013), andHolland-Ashford et al (2020), although they are questioned by Sano et al (2021) based on recent ALMA data. Yamaguchi et al (2018), who performed spatially resolved spectroscopy of the remnant with NuS-TAR, revealed obvious spatial variations of RP parameters, which are naturally explained by the rarefaction scenario.…”

Imprints of the jittering jets explosion mechanism in the morphology of the supernova remnant SNR 0540-69.3

“…Core collapse supernova (CCSN) remnants (SNRs) have inhomogeneous structures of filaments, arcs, clumps, and 'Ears' (two opposite protrusions from the main SNR). Examples include the SNRs Vela (images by, e.g., Aschenbach et al 1995;García et al 2017), SNR G292.0 + 1.8 (e.g., Park et al 2002Park et al , 2007, and SNR W49B (e.g., Lopez et al 2013;Sano et al 2021). This holds for the inner ejecta of CCSNe that have inhomogeneous structures of filaments, clumps, and rings of the different heavy elements such as oxygen, silicon, sulfur, argon and iron.…”