An Investigation of the Interstellar Environment of Supernova Remnant CTB 87

Abstract

We present a new millimeter CO-line observation towards supernova remnant (SNR) CTB 87, which was regarded purely as a pulsar wind nebula (PWN), and an optical investigation of a coincident surrounding superbubble. The CO observation shows that the SNR delineated by the radio emission is projectively covered by a molecular cloud (MC) complex at V${}_{\mathrm{LSR}}$ = $-60$ to $-54$ km s${}^{-1}$. Both the symmetric axis of the radio emission and the trailing X-ray PWN appear projectively to be along a gap between two molecular gas patches at $-58$ to $-57$ km s${}^{-1}$. Asymmetric broad profiles of ${}^{12}$CO lines peaked at $-58$ km s${}^{-1}$ are found at the eastern and southwestern edges of the radio emission. This represents a kinematic signature consistent with an SNR-MC interaction. We also find that a superbubble, $\sim 37^{\prime }$ in radius, appears to surround the SNR from HI 21cm (V${}_{\mathrm{LSR}}\sim -61$ to $-68$ km s${}^{-1}$), WISE mid-IR, and optical extinction data. We build a multi-band photometric stellar sample of stars within the superbubble region and find 82 OB star candidates. The likely peak distance in the stars' distribution seems consistent with the distance previously suggested for CTB 87. We suggest the arc-like radio emission is mainly the relic of the part of blastwave that propagates into the MC complex and is now in a radiative stage while the other part of blastwave has been expanding into the low-density region in the superbubble. This scenario naturally explains the lack of the X-ray emission related to the ejecta and blastwave. The SNR-MC interaction also favours a hadronic contribution to the γ-ray emission from the CTB 87 region.

arXiv comment25 pages, 9 figures, 2 tables. Accepted to the Astrophysical Journal

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• FAST early pulsar discoveries: Effelsberg follow-up
• A Radio Continuum and Polarisation Study of the pulsar wind nebula CTB87 (G74.9+1.2)
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• A Small-Scale Investigation of Molecular Emission toward the Tip of the Western Lobe of W50/SS433
• Triggering Collapse of the Presolar Dense Cloud Core and Injecting Short-Lived Radioisotopes with a Shock Wave. VI. Protostar and Protoplanetary Disk Formation
• Deciphering the Nature of the Pulsar Wind Nebula CTB 87 with XMM-Newton
• Supernova remnant G46.8-0.3, a new case of interaction with molecular material
• CO Observations of the SMC-N66 Hii Region with ALMA: Properties of Clumps along Filamentary Molecular Clouds and Possible Expansion Motion
• IRAM 30 m CO-line Observation toward PeVatron Candidate G106.3+2.7: Direct Interaction between the Shock and the Molecular Cloud Remains Uncertain