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We search for fast-expanding Hi shells associated with Galactic supernovaremnants (SNRs) in the longitude range l \approx 32\arcdeg to 77\arcdeg using21-cm line data from the Inner-Galaxy Arecibo L-band Feed Array (I-GALFA) Hisurvey. Among the 39 known Galactic SNRs in this region, we find such Hi shellsin four SNRs: W44, G54.4-0.3, W51C, and CTB 80. All four were previouslyidentified in low-resolution surveys, and three of those (excluding G54.4-0.3)were previously studied with the Arecibo telescope. A remarkable new result,however, is the detection of Hi emission at both very high positive andnegative velocities in W44 from the receding and approaching parts of the Hiexpanding shell, respectively. This is the first detection of both sides of anexpanding shell associated with an SNR in Hi 21-cm emission. Thehigh-resolution I-GALFA survey data also reveal a prominent expanding Hi shellwith high circular symmetry associated with G54.4-0.3. We explore the physicalcharacteristics of four SNRs and discuss what differentiates them from otherSNRs in the survey area. We conclude that these four SNRs are likely theremnants of core-collapse supernovae interacting with a relatively dense (>~1cm^-3) ambient medium, and we discuss the visibility of SNRs in the Hi 21-cmline.

Hi Shells and Supershells in the I-GALFA Hi 21-cm Line Survey: I. Fast-Expanding Hi Shells Associated with Supernova Remnants