2013 EW90 was discovered by the Tenagra survey (located near Nogales, AZ, U.S.A.) on images taken by M. Schwartz and P. R. Holvorcem with a 0.41-m f/3.75 reflector on 2013, Mar. 3. Its Tj parameter is 2.75, so it was a good T3 candidate.
Hidetaka Sato remotely observed it on 2013 Apr. 30.15 using a 0.51-m f/4.5 reflector from iTelescope, Mayhill (MPC H06), finding a softer aspect respect to stars (FWHM 4.3″ vs 3.3″) and a coma up to 18″ wide on a stack of 10 x 60 seconds images. He observed it again on May 02.17 with the same telescope/site, finding a 12″ coma on a stack of 6 x 120 seconds images, and FWHM of 5.1″ respect to 3.4″ of stars.
Following his alert to the T3 mailing-list, I asked for some confirmations, which came as following.
L. Buzzi, on behalf of the IASC team (P. Miller, P. Roche, A. Tripp, R. Miles, R. Holmes, S. Foglia, L. Buzzi, T. Vorobjov, T. Lister) obtained 6 x 180 seconds images on May. 03.42-43 in good seeing with the 2.0-m f/10 Faulkes Telescope North from Haleakala. All the images were stacked and measured by himself and S. Foglia, finding a clear cometary aspect, with a diffuse coma at least 5″ wide.
L. Buzzi obtained two night of observations from Schiaparelli Observatory (MPC 204) with a 0.60-m f/4.64 reflector. On the first night (May. 04.90-92) a stack of images totalling 43 minutes of exposure time, 2013 EW90 appears clearly softer respect to stars, with a FWHM about 25% larger and a round 11-12″ coma. On the second night (May. 06.85-89) a stack of images totalling 48 minutes of exposure time in slightly better seeing, the object appears again softer respect to stars, with a FWHM 15-20% larger than stars nearby and a 9″ coma with no tail.
T. Lister, Las Cumbres Observatory Global Telescope Network, obtained 9 x 300 seconds images with the 1.0-m f/8 Ritchey-Chretien from LCOGT Node at McDonald Observatory. All the images were stacked and measured by L. Buzzi, S. Foglia and himself, finding a FWHM more than double respect to stars (3.2″ vs 1.4″) and a 5″ coma.
CBAT released CBET 3522 (subscription required) on May 13; all the observations can be found on MPEC 2013-J52.
Below is the first detection made by H. Sato on Apr. 30: