[vsnet-alert 3743] (fwd) SAX pointing of BLLac

[Taichi Kato <tkato>]

(fwd) SAX pointing of BLLac

Date: Sat, 27 Nov 1999 10:15:57 +0100 (GMT+0100)
From: Roberto Nesci <nesci@astro.uniroma1.it>
Subject: SAX pointing of BLLac

Dear collegues,


The campaign of June 99 on BL Lac has given good results, the optical and
Xray data are reduced and I soon start to write down the 'optical' part of
a draft, while Gianpiero Tagliaferri and Paolo Giommi will care the Xray side.
There is however something puzzling, a strong and fast Xray flare without 
optical counterpart.

Our group has the right of a second ToO pointing on BL Lac, which is still
rather active, so BeppoSAX will observe the source from Dec 5 10:50 UT, to
Dec 7 17:30 UT. 

Given the result of the first run, we feel that it will be better to put
the results of both pointings in a single paper. Clearly an optical coverage
of the second pointing would be extremely valuable, so that I think that
a new effort might be done by the WEBT people to follow also this (shorter) 
BeppoSAX pointing.

I asked John Mattox about his opinion in activating again the WEBT, and he
agrees.


>From the previous observation experience, the time resolution of BeppoSAX
with a good S/N is expected to be about 1 hour, and spectral variations in 
the soft (1-3 KeV) and hard (3-10 KeV) bands will be looked for.

I think the optical observations should be capable to detect spectral
variations as well, not just flux variations, so I propose that the
participating groups will observe in at least two bands (V and I); at
least 4 observations/hour for each filter should be obtained, to be well
comparable to the expected X-ray data. 

Comparison stars B,C,H and K should used, taken from the list by Bertaud et al.
1969 (Astron. Astrophys. 3, 436). The finding chart may also be found at
http://vsnet.lsw.uni-heidelberg.de/projects/extragalactic/charts/2200+420.html

I suggest to use the same procedure we have already tested for the first
BeppoSAX observation of BL Lac. So, after the Beppo SAX pointing is over, 
please send me via e-mail for each frame 
date, exposure time, filter, start time (or center of exposure time)
instrumental magnitudes for comparison stars and for BL Lac itself.
I will take care to obtain the final magnitudes.

Good sky to all

Roberto Nesci

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