Richard,

That's a very interesting analysis.

Updated plot attached. A very sudden jump between May 7.9 and May 8.9
and then a rather precipitous drop from May 11.9 though to last night.
I'm hoping to get one more image of it tonight although around half the
aperture of the scope will be cut off by my observatory shed. At the
rate it is fading there might be not much left.

Nick.

On 16/05/2020 18:26, Richard Miles - rmiles.btee at btinternet.com (via
baa-comet list) wrote:
> Nick,
>
> Can you update your plot?
>
> It looks like another disruption event occurred on 2020 May 08.1±0.3
> that ejected a cloud of debris sunwards at speeds of about 50-100 m/s.
> Such an energetic event must have involved considerable force / internal
> pressure so the nucleus may very well have broken up. Eight days later,
> the nuclear magnitude has faded by about 60%.
>
> Images attached.
>
> The timing fits in perfectly with your attached email from a week ago!
>
> Richard
>
> ----- Original Message ----- From: "Nick James" <ndj@nickdjames.com>
> To: <baa-comet@simplelists.com>
> Sent: Saturday, May 09, 2020 8:35 AM
> Subject: [BAA Comets] C/2019 Y4 (ATLAS) sudden brightening
>
>
>> Morning everyone,
>>
>> Up until yesterday the central region (11 arcsec radius) of C/2019 Y4
>> has been brightening at around 0.05 mag per day but last night it had
>> jumped by a whole magnitude compared to the night before (May 7.9 vs May
>> 8.9). The attached plot is from my astrometry with a 0.28-m, f/10 SCT in
>> Chelmsford.
>>
>> Terry Lovejoy, via the CometWatch FB group, reports a similar sudden
>> increase between May 8.12 and May 9.12 using the iTelescope T11 system
>> in New Mexico.
>>
>> With all the excitement over C/2020 F8 (SWAN) please remember to keep
>> observing Y4 for as long as you can.
>>
>> Nick.
>>
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