[vsnet-chat 5385] (fwd) [vsnet-campaign-v4641sgr 142] observation of sgrv4641

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

(fwd) [vsnet-campaign-v4641sgr 142] observation of sgrv4641

From: "Toni Scarmato" <toniscarmato@hotmail.com>
Date: Sun, 14 Jul 2002 11:20:33 +0200

Dear all,

those are my observation on 2002 July 13.

Observations made with a 203 mm SCT, f/10, 140x.  Good conditions of the
sky.Magnitude limite 13.0v. Object about 20 degrees above the horizon.

I think that the source SGRV4641 appear in quiescence state at <13.0v, but
your acitivity continue.

Data

20020713.839 11.3v 1 second
20020713.842 12.0v 1 second
20020713.847 11.3v 1 second
20020713.847 11.5v 2 seconds
20020713.854 11.9v 2 seconds
20020713.865 12.0v 1 second
20020713.868 12.3v 2 second
20020713.882 12.3v 1 second
20020713.885 12.2v 1 second
20020713.887 12.3v 1 second
20020713.911 12.8v 2 seconds


Concern mine observations and Taichi Kato comment

........The data and Scarmato's last part of the observation was
simultaneous.The CCD data again disproves the reality
of Scarmato's "flares"..........

I must to say that I am completely in agreement with Mike Linnolt's
comment......

...........Note that visual observation or video recording is the only way
to monitor the full rangeof the brightness variations.
CCD would be limited by the integration times
and thus yield only a mean value, unless one
has sufficient aperture to do sub-second
integrations............

..........Beware of drawing conclusions from "short term" variations in this
star using CCD. The fluctuations are so rapid that even fast photometry with
1sec exposures and 2.5sec integrations wont catch them faithfully. Visual
observations show the true behavior here. To compare favorably, CCD would
need somewhere around 0.1-0.2sec integration times, and continuous
monitoring without gaps. Essentially you need video recording equipment.
I would recommend someone just hook up a DV camera or camcorder to a good
size observatory class instrument and record several minutes of the stars
behavior for a true reference of its variability........


I want to add, as I sayd on previous reports, that the events reported are
very random and sometime seem not regarding all the stellar surface but
appear as little point of light very intense. Instead, the events less
intense have a larger surface emission.
I think that in CCD data this event are added at the total brightness.  This
can explain the low modulation observed or "small flares".
Instead, only "prolonged intense flares" can to be detected compltely by
CCD.
I think that visual observers must to observ the microquasar for at least
30-60 minutes and to do attention at all the "apparent ligth flashes"
observed around
the source.


Regards,
Toni Scarmato

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