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Unexpected visitor next to supernova SN2023BEE

The supernova SN2023BEE, discovered on 1 February 2023, has been extensively photographed and measured, most notably by the Supernova Observers Group (ObSN) https://www.obsn.es/


But during the observing campaign we have had an unexpected and stealthy visitor leaving its mark next to its host galaxy, NGC 2708 in Hydra.


On different nights of the campaign, at a different time each time, this visitor left subtle marks in our pictures that were mistaken for the stars surrounding the galaxy and the supernova. You had to be very observant to spot it, but the marks were there.


This is a 300" capture with R filter on 7/4/2023 at 21:41 UTC, apparently normal, and yet in this photo there are "stars" that are not stars.




The following image shows 3 "stars" that should not be there, and the position of a fourth one that appears in the next capture. The false stars have an almost Gaussian profile, cannot be mistaken for artefacts, and are equidistant and aligned, which seems to indicate that it is something in motion. In fact, the position of the fourth false star in the following capture indicates the direction of the movement, which is marked with an arrow.




It is not uncommon for traces of satellites to appear in our photos, which is a problem because of the uncontrolled growth of the constellation of artificial objects that often make observations difficult. In this case, the visitor was also a satellite, specifically a geostationary (GEO) satellite, but why do we see very star-like markings instead of traces?


GEO satellites orbit synchronously in a circular orbit at about 36,000 km. These satellites can be observed at the same position in altitude and azimuth in the sky, they do not move with the stars. When we take a picture of the sky with sidereal tracking, we see them as a trace.


Our visitor is the Telecom 1B satellite, an old 700 kg communications satellite, launched in 1985 and operated by France Telecom, which is in uncontrolled mode and does not behave like a normal GEO, hence the anomalous behavior we observed.




Telecom 1B is currently spinning uncontrollably on its 3 axes. It does not follow a perfect geostationary orbit, so if we stop the sidereal tracking of our mount, we will not see it stationary, as happens with operational GEOs, but it will move.


A very interesting aspect of the Telecom 1B's gyro is that it produces glints from the reflections of its various elements, such as the panels or reflective surfaces of its structure. And it is precisely these sparkles that we can see as stars in the photos shown above.


The following picture is taken without tracking, the stars appear as traces, and Telecom 1B, instead of being a point (as a normal GEO would behave) is a discontinuous trace with strong variations in brightness, in the region of 5 magnitudes.




A first photometric analysis reveals that the satellite has a spin period of 0.8 revolutions per minute. From here, in the Photometry Group of the AAM (Agrupación Astronómica de Madrid), we propose to make an in-depth study of the light curve of this satellite, analyzing both the fundamental frequency and all its harmonics and, if possible, to deduce how it is spinning.

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