Flashing satellite, 3 min period

From: Caleb Vorwaller (c.vorwaller@gmail.com)
Date: Sun Aug 26 2012 - 11:21:09 UTC

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    I'm a recreational backyard astronomer (past 6 years).
    
    I'm trying to figure out what this object is.  Maybe you can help:
    
    Location: 30°11'24.96"N  81°36'13.92"W (10263 Whispering Forest Drive,
    Jacksonville, FL, USA 32257)
    
    Date and time: Friday, August 24, 2012, 10:24pm Eastern Daylight Time
    
    Time of sunset: 7:58pm Eastern Daylight Time
    
    End civil twilight: 8:23pm Eastern Daylight Time
    
    Limiting magnitude in area of observation: 4
    
    Description of observation: I was out re-learning the stars in the
    constellation Aquarius and saw a stationary, white, magnitude -3 flash
    (conservative estimate), with a duration of ˝ second, located ˝ degree
    east of Epsilon Aquarii.  It was not a blink, but a quick gradual fade
    in-and-out.  Here are times and locations of each identical flash:
    
    10:24pm (˝ degree east of Epsilon Aquarii (Albali))
    10:27pm (same location)
    -I was sketching the constellation Capricornus and looking at my star
    chart during this time, not paying attention to the area of the
    observations-
    10:37pm (a little east of Mu Aquarii)
    10:40pm (seemed to be closer to Beta Aquarii (Sadalsuud))
    10:43pm (perhaps east ˝ degree)
    -I decided to go inside at this point as the mosquitoes were getting
    bad, but before I stepped into the house, I made two more
    observations-
    10:58pm (˝ degree southeast of Beta Aquarii)
    11:01pm (same location)
    11:49pm – 11:53pm (searched for the object in the area of Alpha to
    Beta Aquarii, where it should have been relative to my other
    observations, but it was gone)
    
    The object may have been in some kind of geosynchronous orbit, or
    moving extremely slowly from west to east (but not fast enough to be
    in semisynchronous orbit).  The flashes occurred with regularity every
    3 minutes.  The time gaps greater than 3 minutes exist because I was
    not looking.  I was not using a timer, just the clock on my phone.
    
    Notes: At first I thought it may have been a dim Iridium flare, but
    the stationary and slow repetitive nature of the flash rules that out.
     Then I thought it may be in geostationary orbit, but my understanding
    is that the brightest of the geostationary satellites has only reached
    magnitude +3, so that option is out.  However, it was located between
    the ecliptic and the celestial equator, so it is a good candidate for
    an  object in some sort of geosynchronous orbit. Due to its bright
    magnitude, I believe it is in a geosynchronous orbit closer to the
    earth than the geostationary orbit.  The fact that it was gone at
    11:49pm leads me to believe that it was reflecting the sun; it
    couldn’t have been an object close to earth producing its own light –
    the light was far too bright, and the object was in the same spot, as
    far as I observed it, for over half an hour.  The first observation at
    10:24pm was only about 2 hours after the end of civil twilight (not
    too late to reflect the sun), and by 3 hours after the end of civil
    twilight, it was gone.  The flash was probably due to the object
    spinning with a rotational period of 3 minutes.  This is the best
    description I can give, and beyond that I have no further ideas.
    
    All of my guesses were based off of searches on the internet.  I did
    find some flashing satellites, but none with a period of 3 minutes,
    and none at magnitude -3 or brighter that were in geosynchronous
    orbit.
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