[en] E. Jehin, Y. Moulane, F. Pozuelos, M. Ferrais, J. Manfroid, and D. Hutsemekers, Universite de Liege, report an outburst of comet 2I/Borisov between Mar. 7.4 and 10.4 UT using the TRAPPIST-South 0.6-m telescope at La Silla (Jehin et al. 2011, Messenger 145, 2). A series of ten 240-s R_c-band exposures (1".3/pixel) are taken routinely about every two nights in the course of a concerted monitoring of this interstellar comet that was started in Oct. 2019. A small circular-aperture radius of only 2 pixels (5".2 diameter) was used to mitigate star contamination, as the comet has been crossing very crowded star fields for several weeks. They report a constant R magnitude of 18.0 +/- 0.1 between Feb. 26.4 and Mar. 7.4 UT on six different nights after selecting carefully the best images (only a few images are not contaminated on each night). On Mar. 10.4, the magnitude was 17.1 +/- 0.1, showing an increase of 0.8 +/- 0.1 mag with respect to Mar. 7 and previous nights. Three nights later, on Mar. 13.4, the comet had faded by 0.3 mag (to 17.4 +/- 0.1). No peculiar features were observed. R_c magnitudes measured are as follows: Feb. 26.39, 17.9; Mar. 1.37, 18.2; 2.37, 18.0; 5.34, 18.0; 6.39, 18.1; 7.37, 17.8; 10.41, 17.1; 13.38, 17.4. There is no indication of an outburst on Mar. 4 or 5 as reported by Drahus et al. (who reported a brightening of about 0.3 mag betwen Mar. 4.3 and 5.3, approximately constant brightness between Mar. 5.3 and 8.3, and another brightening of about 0.4 mag between Mar. 8.3 and 9.3; cf. website URL http://www.astronomerstelegram.org/?read=13549). <P />H. Sato, Tokyo, Japan, reports that CCD images taken remotely with a 0.51-m f/6.8 astrograph at Siding Spring on Feb. 3.73 UT show a strongly condensed coma 15" in diameter with a magnitude 17.0 as measured within a circular aperture of radius 8".2; images taken on Feb. 27.73 show a strongly condensed coma 12" in diameter with a magnitude 17.9 as measured within a circular aperture of radius 6".5. <P />S. Nakano, Sumoto, Japan, provides the following revised hyperbolic orbital elements for comet 2I/2019 Q4 from 2625 observations spanning 2018 Dec. 13-2020 Mar. 13 (mean residual 0".74). <P />Epoch = 2019 Dec. 23.0 TT <P />T = 2019 Dec. 8.55260 TT Peri. = 209.12348 <P />e = 3.3570561 Node = 308.14887 2000.0 <P />q = 2.0065881 AU Incl. = 44.05303 These elements use non-gravitational parameters Y1 = +0.97 +/- 0.26, Y2 = +3.5633 +/- 0.3569, Y3 = -2.29 +/- 0.12, with sublimating molecule CO or N_2 using Yabushita's theory (1996 MN 283, 347). The original value of original 1/a is -1.174851, and the original value of future 1/a is -1.174635 (+/- 0.000020). A purely gravitational solution gives residuals of -3" mainly in Decl. around the first available observations and -3" mainly in R.A. around the most recent observations. A non-gravitational water/ice solution gives A1 = +1.46, A2 = +16.3000, A3 = -11.7011. Nakano adds that when the solution's original value of 1/a converges within 0.0000001 at r = 923 AU from the solar-system barycenter (in the year AD 1885), the barycentric eccentricity = 3.367112; when the future value of 1/a converges at r = 996 AU from the solar-system barycenter (in the year AD 2165), the barycentric eccentricity will be 3.364014; and the osculating barycentric eccentricity is 3.370990, with the mean error in e being +/- 0.000040.
