ALMA CO Observations of Supernova Remnant N63A in the Large Magellanic Cloud: Discovery of Dense Molecular Clouds Embedded within Shock-ionized and Photoionized Nebulae

Abstract

We carried out new 12 CO(J = 1-0, 3-2) observations of a N63A supernova remnant (SNR) from the LMC using ALMA and ASTE. We find three giant molecular clouds toward the northeast, east, and near the center of the SNR. Using the ALMA data, we spatially resolved clumpy molecular clouds embedded within the optical nebulae in both the shock-ionized and photoionized lobes discovered by previous Hα and [S ii] observations. The total mass of the molecular clouds is ∼800 M ⊙ for the shockionized region and ∼1700 M ⊙ for the photoionized region. Spatially resolved X-ray spectroscopy reveals that the absorbing column densities toward the molecular clouds are ∼1.5-6.0 × 10 21 cm −2 , which are ∼1.5-15 times less than the averaged interstellar proton column densities for each region. This means that the X-rays are produced not only behind the molecular clouds, but also in front of them. We conclude that the dense molecular clouds have been completely engulfed by the shock waves, but have still survived erosion owing to their high-density and short interacting time. The X-ray spectrum toward the gas clumps is well explained by an absorbed power-law or high-temperature plasma models in addition to the thermal plasma components, implying that the shock-cloud interaction is efficiently working for both the cases through the shock ionization and magnetic field amplification. If the hadronic gamma-ray is dominant in the GeV band, the total energy of cosmic-ray protons is calculated to be ∼0.3-1.4 × 10 49 erg with the estimated ISM proton density of ∼190 ± 90 cm −3 , containing both the shock-ionized gas and neutral atomic hydrogen.

Radio emission from interstellar shocks: Young type Ia supernova remnants and the case of N 103B in the Large Magellanic Cloud

“…1, contrary to the usual expectations that involve simple compression (amplification) of magnetic field. This is somewhat similar to what we observed in the case of Galactic SNR Vela Jr. (Maxted et al 2018) and LMC SNR N 63A (Sano et al 2019a). However, both of these SNRs are most likely result of CC explosion.…”

High energy gamma-ray detection of supernova remnants in the Large Magellanic Cloud

“…This is a bright core-collapse SNR embedded within the large HII region N63, associated with dense molecular clouds, shockionised gas, and photoionised gas. Its age is estimated to be about 3500 years (Sano et al 2019) or within the range 2000 − 5000 yr (e.g., Hughes et al 1998;Warren et al 2003). This source is the second brightest SNR in LMC and was observed from radio to Xrays (Warren et al 2003;Williams et al 2006a;Caulet & Williams 2012;Sano et al 2019).…”

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

“…Following the proposed scenario, the forward shock was freely expanded in the low-density medium at the beginning, and then suddenly encountered with the dense gaseous materials traced by 13 CO line emission and/or cool plasma component. Since the shock-cloud interaction generates multiple reflected (or inward) shocks, the Fe-rich ejecta is efficiently heated up at higher densities toward the center of the SNR (see also Sano et al 2019b). The X-Ray Imaging and Spectroscopy Mission (XRISM, XRISM Science Team 2020) will provide us with further understanding of shockinteractions through a detailed spatial comparison between the X-ray derived ionic properties and CO clouds.…”