Interstellar Comet 2I/Borisov is Single Again

ATel #13618; Qicheng Zhang (Caltech), Quanzhi Ye (U. Maryland), Ludmilla Kolokolova (U. Maryland)

on 6 Apr 2020; 00:31 UT

Distributed as an Instant Email Notice Comets

Credential Certification: Quanzhi Ye (qye@umd.edu)

Subjects: Optical, Comet

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We report the development of the apparent fragmentation event of interstellar object 2I/Borisov, initially reported in ATel #13611 and #13613. Hubble Space Telescope ACS/WFC images on 2020 April 3.2 UT (HST GO 16044, PI Zhang) showed only one remaining component, possibly corresponding to the sunward component shown in the March 30 images (HST GO 16089, PI Jewitt). The other component, located 0.1 arcsec north of the sunward component in the March 30 images, has disappeared. Instead, a diffuse, blob-like feature is visible in its place, extending from the remaining component towards P.A. 0 deg. Individual cropped frames and a composite stacked frame can be found here.

Preliminary photometric measurements of the comet from the GO 16044 data show a pause in fading between the two HST visits of 2020 March 2 and April 3 while heliocentric distance increased from 2.74 to 3.25 au and geocentric distance increased from 2.34 to 2.69 au, consistent with the outburst in activity reported by ATel #13549. The F606W ST magnitude measured inside a fixed 1,000 km radius aperture over the past four epochs is tabulated below.

Date (UT) Mag +/- 2020 Jan 6.9 19.04 0.05 2020 Jan 28.4 19.26 0.05 2020 Mar 2.9 19.85 0.05 2020 Apr 3.2 19.94 0.05

This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program HST GO 16044.