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(cba:news) ASASSN-18ey = MAXI j1820-070 (Joe Patterson) [2018-05-10T10:01:01Z]


Hi CBAers,

Some great data on this star rolling in. It's declining VERY slowly - still about V-12.8 - and showing some waves suggestive of a period near 3.5 or 7 hours. Promises to be a great target for the next month or more.

While a few runs showed some quasi-periodic oscillations with a timescale near 12 s, this is a REALLY awkward timescale for us to investigate. The readout ("dead") time is a mighty big price to pay, and I suggest we abandon this (high-speed) observing style. We'll get much better sensitivity if we adopt integration times appropriate for the brightness - maybe 20 sec in clear light, or ~40 s in V (still bright enough for V, if you like your V filter).

The equatorial location and short northern nights are also somewhat problematic, since we thrive on LONG nightly time series. We can overcome this with an even-more-than-usually-extensive spread in terrestrial longitude. And let's do it! This ia the brightest black-hole transient in many years, and we already have a nice supply of X-ray and Hubble data to accompany the optical time series.

The most prolific observers so far are Michael Richmond in Rochester, NY, John Rock in England, Tonny Vanmunster in Belgium, and Stephen Brincat in Malta. The first three are in famously cloudy and certainly northern locations, so their luck can't continue long. There's not much data yet from the western USA, so that would help a lot. Also AU/NZ, Africa, and southern Europe (except Brincat) have been quiet.

Oops, I forgot Josch Hambsch from Chile. His data, nearly every night and well-calibrated, will eventually have a big impact. But the lower time resolution makes it less suitable for *defining* the features (eclipses?) in the light curve. So I hope that the USA observers will keep a close watch on this fascinating star - which seems ready to surrender a few secrets, but is making us work hard for them!

joe p

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