TCP J21040470+4631129 (UG:)

https://www.aavso.org/vsx/index.php?view=detail.top&oid=838181

Spectroscopy, precise astrometry, and multiband as well as time-resolved photometry are urgently required (I renamed the transient, as it is probably a dwarf nova outburst and not a "possible supernova").

Discovery details:

R.A. 21h04m04.70s, Decl. +46°31'12.9" (J2000.0)

2019 July 12.490 UT, 9.2 mag (CCD, unfiltered)

Discoverer: Hideo Nishimura (Shizuoka-ken, Japan)

2019 07 12.490 UT

Discovered by Hideo Nishimura, Shizuoka-ken, Japan, on three frames using Canon EOS 6D Digital camera + 200-mm f/3.2 lens under the limiting mag = 14.5, who writes nothing is visible at this location on a frame taken on 2019 July 10.502 UT with the limit mag.= 15s and there is a candidate star (mag = 17) on DSS. An image will be provided later.

2019 07 12.490 UT

A discovery image at http://www.oaa.gr.jp/~oaacs/image/PSNinCyg2019.jpg

2019 07 12.61 UT

This transient does not look like a "possible supernova", but is likely a nearby dwarf nova outburst. I strongly recommend to use the designation TCP J21040470+4631129 instead of PSN J21040470+4631129. --- Patrick Schmeer (Saarbrücken-Bischmisheim, Germany)

2019 07 12.61 UT

The likely (blue) progenitor (supposedly Nishimura-san's mag. 17 candidate star) is USNO-A2.0 1350-13375367 (Bmag. 17.7, Rmag. 17.2) with Gaia DR2 position end figures 04.688s, 13.75" (equinox J2000.0, epoch 2015.5, Gmag. 17.77, parallax 9.1337 ± 0.1156 mas (distance 109.2 ± 1.4 pc)). Other designations are USNO-B1.0 1365-0394214, GSC2.3 N31X108363 (Fmag. 15.71, Bjmag. 17.76, Vmag. 18.34), PSO J210404.693+463113.906 (gmag. 18.20, rmag. 18.01), IPHAS J210404.68+463114.0. No outbursts were recorded by the ASAS-SN Sky Patrol (Shappee et al. 2014ApJ...788...48S and Kochanek et al. 2017PASP..129j4502K) between 2015 March 20 and 2019 July 9; complete light curve at https://asas-sn.osu.edu/light_curves/56580af1-4b5a-4270-b96b-b77ef1ea8739. The transient is probably a dwarf nova outburst with an amplitude of at least 9 magnitudes (WZ Sge type?). Spectroscopy as well as multiband and time-resolved photometry are strongly recommended. --- Patrick Schmeer (Saarbrücken-Bischmisheim, Germany)

http://www.cbat.eps.harvard.edu/unconf/followups/J21040470+4631129.html

Clear skies,

Patrick