On 18/04/2019 10:55, wrote:
Am Donnerstag, 18. April 2019 09:27:08 UTC+2 schrieb Martin Brown:
On 18/04/2019 08:03, wrote:

Katie Bouman's image is sharper and includes more details.

They are not necessarily "details" so much as imaging artefacts
that haven't quite been fully calibrated out yet.

The image in Paper is more blurred and also darkened on the edge.
The good word "Calibrate" I would not use for this kind of editing


But it is pretty much what happens when the phase calibration of VLBI
baseline data is fine tuned by self calibration on the initial result.
Basically you can use the known property of the sky brightness being
everywhere positive to detect and fix residual systematic errors.

A brief introduction to VLBI is online here.

http://www.phys.unm.edu/~gbtaylor/as.../vlbi_apr4.pdf

I would refer you to page 45 of it which shows the result of VLBI on a
fairly typical source without phase calibration, with first cut
reference only and then the final image after full self calibration.

Note that some of the junk on the intermediate image has coalesced into
real source structure and the resulting background is much flatter.

FWIW M87 jets observed by VLBI at 43GHz on a 10mas image size are on
page 11 although a nicer video at several epochs is online he

http://www.aoc.nrao.edu/~cwalker/M87...vies_only.html

--
Regards,
Martin Brown