IRAM 30 m CO-line Observation toward PeVatron Candidate G106.3+2.7: Direct Interaction between the Shock and the Molecular Cloud Remains Uncertain

Abstract

Supernova remnant (SNR) G106.3+2.7 was recently found to be one of the few potential Galactic hadronic PeVatrons. Aiming to test how solid the SNR is associated with the molecular clouds (MCs) that are thought to be responsible for hadronic interaction, we performed a new CO observation with the IRAM 30m telescope toward its "belly" region, which is coincident with the centroid of the $\gamma$-ray emission. There is a filament structure in the local-standard-of-rest velocity interval $-8$ to $-5$ km/s that nicely follows the northern radio boundary of the SNR. We have seen asymmetric broad profiles of ${}^{12}$CO lines, with widths of a few km/s along the northern boundary and in the "belly" region of G106.3+2.7, but similar ${}^{12}$CO line profiles are also found outside the SNR boundary. Further, the low ${}^{12}$CO J=2-1/J=1-0 line ratios suggest the MCs are cool. Therefore, it is still uncertain whether the MCs are directly disturbed by the SNR shocks, but we do find some clues that the MCs are nearby and thus can still be illuminated by the escaped protons from the SNR. Notably, we find an expanding molecular structure with a velocity of $\sim$3.5 km/s and a velocity gradient of the MCs across the SNR from $\sim -3$ to $-7$ km/s, which could be explained as the effect of the wind blown by the SNR's progenitor star.

arXiv comment16 pages, 9 figures. Accepted by the Astrophysical Journal

References in corpus (28)

• The CO-to-H2 Conversion Factor
• The Milky Way in Molecular Clouds: A New Complete CO Survey
• TeV Gamma-Ray Sources from a Survey of the Galactic Plane with Milagro
• PSR J2229+6114: Discovery of an Energetic Young Pulsar in the Error Box of the EGRET Source 3EG J2227+6122
• Cavity of Molecular Gas Associated with Supernova Remnant 3C 397
• Probing X-ray Absorption and Optical Extinction in the Interstellar Medium Using Chandra Observations of Supernova Remnants
• Particle acceleration in winds of star clusters
• Potential PeVatron supernova remnant G106.3+2.7 seen in the highest-energy gamma rays
• The SNR G106.3+2.7 and its Pulsar Wind Nebula: relics of triggered star formation in a complex environment
• Detection of Extended VHE Gamma Ray Emission from G106.3+2.7 with VERITAS
• HAWC J2227+610 and its association with G106.3+2.7, a new potential Galactic PeVatron
• Expanding molecular bubble surrounding Tycho's supernova remnant (SN 1572) observed with IRAM 30 m telescope: evidence for a single-degenerate progenitor
• Linear relation for wind-blown bubble sizes of main-sequence OB stars in a molecular environment and implication for supernova progenitors
• A Possible X-ray and Radio Counterpart of the High-Energy Gamma-ray Source 3EG J2227+6122
• Fermi LAT detection of pulsed gamma-rays from the Vela-like pulsars PSR J1048-5832 and PSR J2229+6114
• VER J2227+608: A Hadronic PeVatron Pulsar Wind Nebula?
• Discovery of molecular shells associated with supernova remnants. (II) Kesteven 75
• Molecular Environment and an X-ray Spectroscopy of Supernova Remnant Kesteven 78
• Hadronic vs leptonic models for $\gamma$-ray emission from VER J2227+608
• X-Ray Emission from the PeVatron-candidate Supernova Remnant G106.3+2.7
• ALMA CO Observations of Gamma-Ray Supernova Remnant N132D in the Large Magellanic Cloud: Possible Evidence for Shocked Molecular Clouds Illuminated by Cosmic-Ray Protons
• Revealing a peculiar supernova remnant G106.3+2.7 as a petaelectronvolt proton accelerator with X-ray observations
• An Investigation of the Interstellar Environment of Supernova Remnant CTB 87
• Discovery of Shocked Molecular Clouds Associated with the Shell-Type Supernova Remnant RX J0046.5$-$7308 in the Small Magellanic Cloud
• Large-field CO(1--0) observations toward the Galactic historical supernova remnants: a large cavity around Tycho's supernova remnant
• The environment of supernova remnant VRO 42.05.01 as probed with IRAM 30m molecular line observations
• A Small-Scale Investigation of Molecular Emission toward the Tip of the Western Lobe of W50/SS433
• Discovery of Broad Molecular lines and of Shocked Molecular Hydrogen from the Supernova Remnant G357.7+0.3: HHSMT, APEX, Spitzer and SOFIA Observations