Re: Superbird A flash phase shift

Mike McCants (mikem@freeside.fc.net)
Thu, 12 Mar 1998 00:34:40 -0600 (CST)

Ron Lee wrote:

>> The phase shift that Rob mentions below is visible in binoculars.

Yes, I easily saw it last night with 7x50 binoculars even though
a bright moon was not very far away.

Rob Matson wrote:

> Let's define the midpoint as the approximate time of the phase shift (i.e.
> the point at which odd and even flashes are of equal brightness, but
> probably not quite peak brightness).

Seems reasonable to me.  I estimate this time was about 2:57:00 UT
plus or minus 20 seconds on March 11 UT.  I used 7x50 binoculars
from Austin, Tx.

I wrote about observations made on Monday evening:

>> There was also a minor maximum about 3:11 UT.  Brightest
>> flashes were to about magnitude 7.5.

Let me call the "first" series of flashes "series A".  This
series started some time before 2:51 UT March 10.  I believe
this series peaked about 2:54:30 UT.

Let me call the series of flashes "in between" the flashes
of series A "series B".  The first flash of series A was timed
at 2:51:37.0 UT and the first flash of series B was timed 11.7
seconds later.  But series A was much brighter than series B
at this time.  I estimated that series B was equal to series A
about 2:55:30 and series B probably peaked about 2:56:30.
At 2:58:15 I estimated that series B was magnitude 4 and
series A was magnitude 9.  A last "very faint" flash from
series A was recorded at 2:58:59.1 UT.  The last flash from
series B was recorded as 3:01:07.0 UT.  The series A and B
were uniformly separated by 11.6 seconds.

So I believe that the difference between the brightest flashes
of series A and the phase shift time was only about 1 minute.

A new "series C" of flashes was timed from 3:09:26.8 UT until
3:15:39.0 UT.  The maximum was probably about 3:11 UT.  This
series was "in phase" with series A.  Taking the time of its
last flash and subtracting the time of the first flash of
series A gives 62 cycles in 1442.0 seconds for a period
of 23.258 seconds.

There were no recorded times in this series C that were not
multiples of 23.26 seconds.

I (and Ed) saw this series C the previous evening from about 3:13
until they faded out about 3:17 March 9 UT.  Only 6 timings
were made and they were all multiples of 23.26 seconds.

----

There were measurements last year of a pair of overlapping
series that were not an even split of time.  On August 29, 1997
(all dates/times UT) I recorded times starting at 3:33:21.6 UT.
Of the first 11 times, 10 of these showed alternating differences
of 11.3 and 12.0 seconds.  One time was apparently in error.
One series was labeled 9th magnitude and the other was labeled
10th magnitude.  The brighter of the pair was after the 12.0
second interval. (3:33:21.6 to 3:35:18.8)

The timings resumed at 3:40:20.1 UT.  (Insert comment here
about allowing Ed to take a look for a while. :-)
Another 9 timings were recorded, all showing the 12.0/11.3
split, but the brighter (magnitude 8) was now 11.3 seconds
after the fainter (magnitude 9).  (3:40:20.1 to 3:41:52.2)

Further timings from 3:45:22.5 to 3:45:57.0 and 3:51:22.7
to 3:51:45.9 also showed the same split.  The last entry
has the comment "entry into the Earth's shadow".  So apparently
we watched this behavior for over 18 minutes before shadow
entry occurred.

The total time for 47 cycles was 1093.1 seconds, giving
a period of 23.257.  This is the same period that I measured
two nights ago.

A message from Ed to the list indicates that we saw this same
behavior for 11 minutes before shadow entry the previous night.

My record file indicates that we saw this same behavior for
19 minutes the following night before shadow entry at 3:58.

Of course these faint flashes could be from relatively
small flat areas.

2:53 UT last August, but we were not looking at that time.

----

I see that Kurt has 2 "uneven" flash period entries in PPAS7.
One says 11.1 + 12.1 and the other says 6.1 + 17.2!

----

Oh dear.  Now I have found notes from observations that Ed and
I made 13 months ago on Feb. 17, 1997.  All times UT.  Most
of the observations were made using the AAS 12 1/2 inch telescope.
I "promised" a more detailed report 13 months ago, so I guess
I'm a little late.  Better late than never?

My report a year ago indicated that we started watching at 2:06 UT.

2:21 "brighter tumbles now - magnitude 11.5 or so"
     18 cycles in 105.2 seconds.  Period 5.84 seconds.
     Drawing showing a regular tumble with 5.8 indicated from
     primary maximum to secondary maximum.

2:26:30 flashes to magnitude 10 and 11 alternating
    Drawing with a regular tumble and a flash on top of it.

2:28:25.8 - stopwatch is started at this time.
Comment "Flashes to magnitude 8 or 9".  "Br" notation
for relative time entries 1:45.6, 2:32.3, 2:55.7, 3:42.5.
Comment for 2:31:20 - "2:55.7 magnitude 5?!"
Comment for 2:38:10 - "magnitude 8 and 10 alternate"
This refers to flashes every 11.7 seconds.

514.4 seconds divided by 22 cycles = 23.38 second period.

2:41 "maxima around magnitude 11 - 5.8 second period still there"

2:47:43.8 to 2:54:44.6 - timings - 420.8 seconds / 18 = 23.38 seconds

2:49 "magnitude 7 or 8 flashes"

2:52 "magnitude 9 flashes"

2:53:40 "magnitude 10.5 flashes - 11.5 to invisible in background -
         5.8 second period"

2:55:10 "magnitude 9.5 flash"

3:00 to 3:11 "regular tumbles to 12 or 13 every 5.85 seconds"

3:24 "same - one flash to 11.5 every once in a while"

3:25:59 "flash to 10.5!"

[timings lost] "flash to 9.5"

[timings lost] "alternate flash to 9 and 11 period 11.7"

[timings lost] "8th 11th 7.5"

3:35:17.2 "mag 6.5?"

3:36:50.9 "mag 5.5"

3:37:37.6 "mag 5.5"
3:37:49.1 "mag 11.5"

3:39:34.7 "mag 4.5"
3:42:18.3 "mag 4.0 using 3 inch finder scope"
3:44:15.3 "mag 4.5 using 3 inch"
3:45:13.8 "mag 10.5"
3:45:25.4 "mag 5.0?"
3:47:34.6 "mag 9.0?"
3:47:45.7 "mag 5.0 - secondary max 11th"
3:49:42.6 "mag 4.0?"
[Note that there was not a "phase reversal" here.]
[3:49:42.6 - 3:39:34.7 = 607.9 / 26 = 23.38 seconds]
3:51:27.5 "mag 10.0"
3:55:10.2 "mag 6.5 or 7?"
3:55:56.9 "mag 7.5?"
3:56:08.3 "mag 9.5 (secondary)"
3:56:55.0 to 3:58:17.7 "mag 9" on timings separated by 11.7 or 23.4 seconds
shadow entry

So if the phase reversal was happening here, it was 13 minutes
after a series A maximum.  This does not match what I saw the
last two nights.

Taking timing 1:26:44.4 - timing 1:06:51.4 = 1193.0 / 51 = 23.39 seconds.

Mike McCants