Publication Date


Journal or Book Title

The Astronomical Journal


We discovered a large-scale shell G53.9+0.2 around the Crab-like pulsar wind nebula (PWN) G54.1+0.3 with 1420 MHz continuum Very Large Array observations. This is confirmed by a new infrared (IR) image at 8 μm from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire project, which reveals an intriguing IR shell just surrounding the large radio shell. We analyze the 21 cm H I absorption spectra and 13CO emission spectra toward PWN G54.1+0.3 and bright sources on both radio and IR shells. Continuous H I absorption up to the tangent point and absence of negative H I absorption features imply that PWN G54.1+0.3 has a distance beyond the tangent point but within the solar circle, i.e., 4.5-9 kpc. G54.1+0.3 is likely at a distance of 6.2 kpc due to the morphological association of the PWN with a CO molecular cloud at a velocity of 53 km s–1, as revealed by high-resolution 13CO images. Based on the H I absorption spectrum and recombination line velocity (40 km s–1) of the bright H II region G54.09–0.06, which is on the IR shell, the IR shell is likely located at a distance of 7.3 kpc, which is also the distance of the associated large-scale radio shell. At this distance, the radio shell has a radius of ~30 pc. The radio shell may be thermal and lack IR emission due to dust destruction, or it may be nonthermal and part of a newly found old supernova remnant. In either case, it is located at a distance different from PWN G54.1+0.3.


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