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

Joe Patterson jop at astro.columbia.edu
Sat May 5 15:33:19 EDT 2018

Hi CBAers,

Some of you probably saw the ATEl that Michael Richmond and Stephen 
Brincat sent out, reporting, among other things, a 3.4 hour period in 
the light curve of this still crazy-bright X-ray (presumably black-hole) 
transient.  Origin unknown, but let's jump in and figure it out!  All 
longitudes and latitudes and lassitudes invited.

As usual, long (3+ hours) coverage will have greatest impact.  But all 
the data show a point-to-point scatter far greater than the error of 
measurement.  This means that there is considerable source variation on 
timescales of just a few seconds - basically unlike CVs, which are 
considerably fonder of timescales around *minutes*, not *seconds*.  We 
found a similar thing years ago: a 6-second QPO in our study of 1118+48, 
another black-hole transient.  So as long as the source is bright (now 
12.5) and assuming your measurement error can tolerate it, keep the 
integrations short!  (Can't be any more quantitative than that, since we 
don't actually know the timescale).

I certainly recommend this guy as #1 priority.  Some of you are doing a 
great job with AM CVn, and our many-month coverage of it will have great 
impact.  But old Maxie has highest priority whenever it's above 2 
airmasses - certainly at non-USA longitudes, and I'd say at USA also.

joe p

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