(cba:news) ASASSN-18ey = MAXI J1820+070

[Joe Patterson]

Hi CBAers,

We're accumulating a great several-month light curve of this black-hole 
transient.  It was hard to discern a period - lots of wiggles appearing, 
showing promise, and then disappearing - for ~2 months.  Over the last 9 
days the star got its act together and showed an impressive 
large-amplitude wave with a period of 17 hours.  Exactly what kind of 
period it is - orbital? superhump? precession? outburst? - is still 
unclear.  And for an equatorial star that's a really awkward period, 
since no one can get long runs and the pitfalls of daily aliasing are 
severe.

Stephen Brincat, Josch Hambsch, and Geoff Stone have been carrying most 
of the water in recent weeks.  Malta, Chile, and California have pretty 
great climates in June!  But the upcoming 1-2 weeks are critical in 
assessing the coherence (the stability) of this signal... and I hope 
that other observers will pay special attention to this star now!

Observations from AU/NZ are of special value since that is a nearly 
unrepresented longitude in our coverage.  Nights are decently long down 
there, the star is still mag 13.4, and the star transits near midnight. 
No need for fast data - 30 s or even 60 s is just fine.  The table is set!

joe p

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