Electronic Telegram No. 5717 Central Bureau for Astronomical Telegrams Mailing address: Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network COMET C/2026 M3 (MASTER) Y. Kechin and V. Lipunov, Sternberg Astronomical Institute, Lomonosov, Moscow State University, reported a new asteroidal object that was found with an auto-detection system on numerous 180-s unfiltered CCD images (limiting mag 21.2) obtained with the twin MASTER 0.4-cm f/2.5 robotic telescopes located at the Guillermo Haro Astrophysics Observatory at Cananea, Sonora, Mexico, on June 19 (astrometry tabulated below) while looking for an optical counterpart to the gamma-ray burst EP260618A. 2026 UT R.A. (2000) Decl. Mag. June 19.30148 18 30 22.46 +23 14 51.0 20.3 19.31031 18 30 22.22 +23 14 52.7 20.6 19.31914 18 30 22.06 +23 14 53.9 20.8 19.32797 18 30 21.83 +23 14 54.7 20.3 19.33682 18 30 21.61 +23 14 56.0 20.3 26.39219 18 27 35.79 +23 31 02.5 20.3 26.42473 18 27 35.01 +23 31 06.5 20.5 26.45792 18 27 34.20 +23 31 10.0 20.6 The object was reported to the Minor Planet Center's NEOCP webpage and then moved by the MPC to its PCCP webpage based on its nearly parabolic orbit. Two stacked sets of seventy-five 30-s CMOS exposures taken by A. Aletti and L. Buzzi (Varese, Italy) with a 0.84-m f/3.5 Newtonian reflector on July 5.02- 5.05 UT show a softer aspect with respect to field stars, with a 6" coma and a faint tail 6" long in p.a. 185 degrees. R. Weryk, Department of Physics and Astronomy, University of Western Ontario, writes that four 45-s w-band survey images taken on July 6.5 UT with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala, HI, USA, in 2".2-2".3 seeing show a diffuse coma of size 2".8 (full-width-at-half-maximum) with a hint of a short tail toward p.a. 175 degrees. Three 60-s gri-band follow-up images obtained by Weryk and R. Wainscoat with the 3.6-m Canada- France-Hawaii Telescope at Mauna Kea (queue observer L. Wells; queue coordinator H. Flewelling) in 0".7 seeing on July 8.44 show a condensed head of size 1".5 (FWHM) with a broad tail 18" long spanning p.a. 155-190 degrees. Twenty-five stacked unfiltered CCD images obtained by E. Bryssinck (Kruibeke, Belgium) during July 8.98-9.03 UT with a 0.4-m f/3.8 reflector show a diffuse coma 8" in diameter with no tail; the magnitude was 20.1 within a circular aperture of radius 5".0. Thirty additional 120-s stacked images obtained during July 12.98-13.03 show a diffuse coma 7".8 in diameter with a central condensation and no tail; the magnitude was 19.8 within a circular aperture of radius 5".0. Thirty-two stacked 90-s CMOS exposures taken on July 11.6 UT by K. Yoshimoto (Kumage, Yumaguchi, Japan) with a 0.3-m f/4 reflector show a faint coma 13" in diameter of total mag 19.8. Fourteen stacked 60-s CCD images obtained remotely by H. Sato (Tokyo, Japan) on July 12.6 with a 0.51-m f/6.8 astrograph at Siding Spring, NSW, Australia, show a strongly condensed coma of diameter 8" with no tail; the magnitude was 19.6 as measured within a circular aperture of radius 4".3. The available astrometry appears on MPEC 2026-N90. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 173 observations spanning 2026 June 19-July 15 (mean residual 0".4). There are no close approaches to major planets. T = 2027 Jan. 21.42619 TT Peri. = 50.30632 Node = 282.35742 2000.0 q = 12.0610922 AU Incl. = 93.88598 The following ephemeris by Nakano from the above orbital elements uses photometric power-law parameters H = 4.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2026 06 09 18 34.27 +22 45.6 11.440 12.113 129.7 3.7 18.5 2026 06 19 18 30.49 +23 14.1 11.402 12.109 132.3 3.6 18.4 2026 06 29 18 26.57 +23 36.2 11.387 12.104 133.1 3.5 18.4 2026 07 09 18 22.63 +23 51.6 11.394 12.100 132.2 3.6 18.4 2026 07 19 18 18.82 +24 00.5 11.423 12.096 129.7 3.7 18.5 2026 07 29 18 15.25 +24 03.2 11.472 12.093 125.7 3.9 18.5 2026 08 08 18 12.06 +24 00.4 11.540 12.089 120.7 4.1 18.5 2026 08 18 18 09.32 +23 52.8 11.624 12.086 114.9 4.4 18.5 2026 08 28 18 07.13 +23 41.6 11.722 12.083 108.7 4.5 18.5 2026 09 07 18 05.52 +23 27.6 11.829 12.080 102.1 4.7 18.5 2026 09 17 18 04.53 +23 12.2 11.943 12.077 95.3 4.8 18.5 2026 09 27 18 04.15 +22 56.3 12.059 12.075 88.5 4.8 18.6 2026 10 07 18 04.39 +22 41.0 12.175 12.073 81.8 4.7 18.6 2026 10 17 18 05.20 +22 27.3 12.287 12.071 75.2 4.6 18.6 2026 10 27 18 06.54 +22 16.1 12.391 12.069 68.9 4.4 18.6 2026 11 06 18 08.36 +22 08.1 12.485 12.067 63.0 4.2 18.6 2026 11 16 18 10.60 +22 04.2 12.566 12.066 57.6 4.0 18.6 2026 11 26 18 13.19 +22 04.7 12.632 12.064 53.0 3.7 18.7 2026 12 06 18 16.04 +22 10.2 12.681 12.063 49.4 3.6 18.7 2026 12 16 18 19.09 +22 21.0 12.712 12.062 47.0 3.4 18.7 2026 12 26 18 22.25 +22 37.4 12.724 12.062 46.0 3.4 18.7 2027 01 05 18 25.43 +22 59.5 12.717 12.061 46.5 3.4 18.7 2027 01 15 18 28.56 +23 27.3 12.692 12.061 48.4 3.5 18.7 2027 01 25 18 31.54 +24 00.7 12.649 12.061 51.5 3.7 18.7 2027 02 04 18 34.30 +24 39.4 12.590 12.061 55.6 3.9 18.7 2027 02 14 18 36.75 +25 23.1 12.517 12.062 60.5 4.1 18.6 2027 02 24 18 38.82 +26 11.3 12.432 12.062 65.9 4.3 18.6 2027 03 06 18 40.43 +27 03.5 12.338 12.063 71.7 4.5 18.6 2027 03 16 18 41.51 +27 58.7 12.237 12.064 77.7 4.6 18.6 2027 03 26 18 42.01 +28 56.2 12.134 12.065 83.7 4.7 18.6 2027 04 05 18 41.88 +29 54.8 12.030 12.067 89.7 4.8 18.6 2027 04 15 18 41.09 +30 53.5 11.930 12.068 95.5 4.7 18.5 2027 04 25 18 39.63 +31 51.0 11.836 12.070 101.1 4.7 18.5 2027 05 05 18 37.50 +32 46.0 11.751 12.072 106.3 4.6 18.5 2027 05 15 18 34.74 +33 37.2 11.677 12.074 110.9 4.5 18.5 2027 05 25 18 31.42 +34 23.4 11.618 12.077 114.7 4.4 18.5 2027 06 04 18 27.62 +35 03.5 11.574 12.079 117.7 4.3 18.5 2027 06 14 18 23.46 +35 36.6 11.547 12.082 119.7 4.2 18.5 2027 06 24 18 19.08 +36 02.1 11.538 12.085 120.5 4.2 18.5 2027 07 04 18 14.62 +36 19.7 11.546 12.088 120.1 4.2 18.5 2027 07 14 18 10.26 +36 29.3 11.571 12.092 118.7 4.2 18.5 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2026 CBAT 2026 July 16 (CBET 5717) Daniel W. E. Green