[vsnet-alert 23964] AT 2019zhd = ZTF19adakuot outburst

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

Something unusual has exploded in Andromeda galaxy M31 (or in our own Milky
Way in front of M31). The object was originally discovered by ZTF on 2019
Dec. 14 at 20.35r magnitude. After two months of "pumping-up" it has
suddenly brightened by 4m in less than 4 days:
https://lasair.roe.ac.uk/object/ZTF19adakuot/

ZTF19adakuot
  20200208.112   18.72r  ZTF Lasair
  20200208.178   19.18g  ZTF Lasair
  20200212.113   15.44r  ZTF Lasair
  20200212.159   15.39g  ZTF Lasair

Object has been also reported to CBAT TOCP by somebody from Japan, judging
from the observing time:
http://www.cbat.eps.harvard.edu/unconf/followups/J00403785+4034529.html

PNV J00403785+4034529
  20200213.4600  14.9U   CBAT TOCP
Offset from M31 nucleus: 1441" West, 2476" South

For M31 distance modulus of m-M=24.4, ZTF magnitude corresponds to M=-9 and
TOCP magnitude to M=-9.5. The brightest "nova" in M31 (2008-11b at 14.7)
was not a classical Nova, but a foreground dwarf nova.

By the coincidence, there was a gravitational wave signal S200213t at
04:12:39 UTC with the 90% confidence level localization area including M31:
https://gracedb.ligo.org/superevents/S200213t/

M110 was mentioned by P. Evans among 20 most possible host galaxies of
S200213t in GCN 27045: https://gcn.gsfc.nasa.gov/gcn3/27045.gcn3

Spectroscopy and follow-up multi-color photometry are urgently needed.

Denis Denisenko