[en] M. S. P. Kelley, University of Maryland; T. Lister, Las Cumbres Observatory (LCO); K. Sharma, H. Kumar, and V. Bhalerao, Indian Institute of Technology, Bombay; and G. C. Anupama and S. Barway, Indian Institute of Astrophysics -- on behalf of the "Zwicky Transient Facility (ZTF) Collaboration", the "Las Cumbres Observatory Outbursting Objects Key (LOOK) Project", and the "GROWTH India Collaboration -- report that ZTF data taken with the 1.2-m Schmidt telescope at Palomar Observatory indicate that comet C/2020 R4 brightened between two g-band images taken on June 2.254 and 4.224 UT. The brightening appears as a compact source, with a radial extent up to 7"; within a 7" radius aperture, the comet brightened by -0.73 +/- 0.05 mag. Follow-up imaging with LCO 1-m telescopes at McDonald Observatory confirm the event. Over the next 22 to 46 hr, the comet continued to brighten by up to -1.39 +/- 0.07 mag in the g-band with the same aperture size, as compared to the June 2 data. However, the cadence of the photometry cannot discriminate between a single prolonged brightening event or a series of small outbursts. Combined photometry with the 0.7-m GROWTH India Telescope, LCO, and ZTF indicate a shallow decrease in brightness thereafter. Photometric g-band magnitudes from all telescopes on the PS1 magnitude system are as follows: June 2.254, 17.31 +/- 0.04; 4.224, 16.58 +/- 0.03; 5.151, 16.01 +/- 0.02; 6.149, 15.92 +/- 0.06. Also from this monitoring are the following r-band magnitudes: June 2.208, 16.93 +/- 0.03; 5.150, 15.67 +/- 0.03; 6.149, 15.483 +/- 0.05; 6.225, 15.54 +/- 0.03; 7.632, 16.00 +/- 0.04; 8.218, 16.10 +/- 0.03; 8.630, 16.19 +/- 0.03; 8.707, 16.22 +/- 0.02; 9.142, 16.17 +/- 0.02; 9.630, 16.34 +/- 0.02; 9.714, 16.33 +/- 0.02; 10.227, 16.45 +/- 0.03. Over this time period, the comet's heliocentric and geocentric distances ranged from r = 1.78-1.88 AU and Delta = 1.52-1.78 AU. <P />C. S. Morris, Fillmore, CA, USA, reports the following total unfiltered CCD magnitudes, coma diameters, and tail lengths for comet C/2020 R4: May 2.26 UT, 10.7, 6'.2, --; 20.23, 15.0, 1'.2, 4'.7 long in p.a. 120 deg; 29.24, 15.8, 1'.3, 10'.4 long in p.a. 109 deg; June 10.23, 16.0, 0'.8, 2'.8 long in p.a. 102 deg; 11.24, 16.1, 0'.8, 3'.5 long in p.a. 102 deg; 12.22, 15.8, 0'.8, 5'.0 long in p.a. 102 deg; 13.21, 16.0, 0'.8, 7'.7 long in p.a. 104 deg; 15.22, 16.3, 0'.7, 9'.7 long in p.a. 99 deg; 26.19, 17.2, 0'.6, 9'.6 long in p.a. 98 deg. <P />W. Hasubick, Buchloe, Germany, reports that he was unable to detect comet C/2020 R4 visually with a 44-cm reflector (limiting mag 13.0) on June 1.88 UT. Further to CBET 4964, J. J. Gonzalez, Leon, Spain, reports the following visual total-magnitude and coma-diameter estimates (unconfirmed by any other visual observations): June 4.94, 11.7, 6'; 9.94, 11.5, 6'. <P />E. Jehin, Y. Moulane, J. Manfroid, F. Pozuelos, M. Ferrais, and D. Hutsemekers, STAR Institute, University of Liege, report that they obtained the following preliminary production rates for comet C/2020 R4 from photometry undertaken using the narrowband HB comet filters on the 0.6-m TRAPPIST-South and TRAPPIST-North telescopes (cf. CBET 4729, 4840) on May 7 and 12, using a Haser model (with V_p = V_d = 1 km/s, for 10000 km and correcting for the phase angle), with the comet at r = 1.56 AU and Delta = 0.89 AU (75 days past perihelion): May 7, Q(OH) = (3.72 +/- 0.25) x 10**27 molecules/s; May 7, Q(NH) = (2.32 +/- 0.15) x 10**25 molecules/s; May 12, Q(CN) = (4.38 +/- 0.10) x 10**24 molecules/s; May 12, Q(C2) = (3.45 +/- 0.11) x 10**24 molecules/s; May 12, Q(C3) = (1.95 +/- 0.18) x 10**24 molecules/s. The dust-production rate proxy was A(0)f[rho](R) = 61 +/- 6 cm.
