[vsnet-alert 23474] ATLAS19shr: bright (14.2m) large amplitude dwarf nova in Ophiuchus

[Denis Denisenko d.v.denisenko@gmail.com via vsnet-alert]

ATLAS team (J. Tonry et al.) has reported a bright transient in
Ophiuchus ATLAS19shr = AT 2019nex on August 11:

ATLAS19shr
  20190807.292  <192c  ATLAS  last non-detection
  20190811.330    14.17c ATLAS  Outburst!
https://wis-tns.weizmann.ac.il/object/2019nex

Last non-detection by ASAS-SN does not further constrain the time of
outburst start:
  20190807.023  <169g  ASAS-SN (Shappee et al., Kochanek et al.)

There were no outbursts in ASAS-SN data since February 2013, no
outbursts in CRTS data from September 2005 to June 2015, and no
outbursts in 111 SkyMorph/NEAT images from August 1997 to July 2006.

There was a possible past outburst on two DASCH plates obtained in
Bloemfontein on 1935 June 05/06:

DASCH_J163947.8-083938
  19350605.972  16.14B
  19350606.041  16.35B

The object at quiescence is identical to SDSS J163947.73-083935.8 with
the following magnitudes:
u=21.98(20) g=22.29(9) r=21.69(8) i=21.74(13) z=21.59(46)
Pan-STARRS: g=21.84(14) r=21.70(7) i=21.70(5) z=21.47(22)

The current outburst amplitude is at least 7.5 magnitudes. The object
is most likely a dwarf nova of WZ Sge type. Time-resolved photometry
is encouraged.

Denis Denisenko