Possible Fragmentation of Comet 29P/Schwassmann-Wachmann 1

ATel #13164; Michael S. P. Kelley (U. Maryland), Dennis Bodewits (Auburn U.), Quanzhi Ye (U. Maryland), Tony L. Farnham (U. Maryland), and James Bauer (U. Maryland) on behalf of the Zwicky Transient Facility Collaboration
on 3 Oct 2019; 18:53 UT
Distributed as an Instant Email Notice Comets
Credential Certification: Michael Kelley (msk@astro.umd.edu)

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We report the discovery of an apparent fragment or swarm of fragments at comet 29P/Schwassmann-Wachmann 1 in images taken with the Zwicky Transient Facility (ZTF) survey (Bellm et al. 2019, PASP, 131, a8002) and the Lowell 31" robotic telescope. Observations between 2019 Oct 01.32 and 03.29 UTC consistently show an extension to the East of the comet. Previous images, taken 2019 Sep 25.37 UTC and earlier have a more compact and azimuthally symmetric inner coma. A preliminary analysis of 60-second R-band images taken with the Discovery Channel Telescope (DCT) at Oct 25.2 UTC confirm the lack of the extended feature at that time.

We combined ZTF images taken 2019 Sep 23 to 25, scaled and subtracted the result from the 2019 Oct images to examine the feature more clearly. The center of the feature is 7 to 9 arcsec away from the nucleus at a position angle of ~70 deg (E of N). A centered 5 arcsec radius aperture encloses most of the feature, and has an apparent r-band magnitude of 18.4 ± 0.1 on Oct 2, compared to 16.04 ± 0.04 mag for 29P itself (AB mag system). The feature does not appear to have a distinct central condensation. We suggest it may be a swarm of mini-comets, similar to those seen at comet 73P-B (e.g., Fuse et al. 2007, PASJ, 59, 381). Motion of the feature is less than 2 arcsec from Oct 1 to 3, but we acknowledge that this interpretation is subjective and relies on processed images.

The ZTF has observed 29P many times, often daily, since the reported outburst of 2019 Sep 12 (ATEL #13110). However, there are substantial gaps from 2019 Sep 14 to 17 and 26 to 30 UTC. Photometry throughout this period from other observers may help determine the origin of the apparent fragments, i.e., if they were ejected recently or during a previous outburst.

This work makes use of observations obtained with the Samuel Oschin Telescope 48-inch at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW.

These results also made use of the Lowell 31" and the Discovery Channel Telescope at Lowell Observatory. Lowell is a private, non-profit institution dedicated to astrophysical research and public appreciation of astronomy and operates the DCT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University and Yale University. We thank Brian Skiff and Larry Wasserman for assistance with the 31" observing queue.