[vsnet-chat 685] the international campaign of Markarian 421

[Katsura Matsumoto <katsura>]

Dear VSNETers,

I would like to inform you the international campaign of Markarian 421 
organized by Dr. Mattox as the coordinator of the WEBT (Whole Earth 
Blazar Telescope). I forward the following message of the WEBT with 
permission of forwarding by Dr. Mattox.

Best regards,

Katsura Matsumoto (Kyoto University, Japan)
e-mail: katsura@kusastro.kyoto-u.ac.jp

==============================================================================
>From mattox@bu.edu Wed Nov 26 08:15 JST 1997
Subject: WEBT update #8

Dear WEBT Collaborators,
 
Good news! Our proposal for a very long ASCA observation of Markarian 421
next spring has been approved. The ASCA PI is Tadayuki Takahashi from ISAS.
The observation is tentatively scheduled from April 26 to May ~4, 1998. 
The ASCA observation will be continuous (when the source is not occulted by
the Earth) within this interval - an unprecedented 300,000 seconds of ASCA
time!

In addition to ASCA, extensive observations will be made by RXTE and 
TeV observatories. We have also applied for a EUVE observation. And 
Stefan Wagner has requested that his approved CGRO observation also
take place at this time.

It will be very valuable to get ~1 week of continuous optical monitoring
during this campaign. Please let me know if I can help in any way with
your observing proposals.

I have created a Web page for this campaign at 
http://gamma.bu.edu/webt/mrk421.html
It includes a link to Stefan's finding chart, a tentative WEBT visibility
plot, and a link to a discussion of Mrk 421 photometry (posting
initially 1995 e-mail from Mark Kidger and Stefan Wagner on this topic).

Mrk 421 photometry is difficult because the magnitude ~13 blazar is embedded
in a host galaxy which is of comparable brightness. There are 2 very bright
stars nearby (magnitudes 6.5 and 7.5 at 2.1 and 3.9 arc-minutes respectively).
There is also a magnitude ~14 galaxy ~16'' away. And, there are  no 
well-positioned, nearby stars of similar brightness for differential
photometry. 

I suggest that we begin now to prepare for this campaign.

Step one. At some convenient time before the end of 1997, obtain a CCD 
frame through an R filter using the telescope and camera you tentatively 
plan to use next spring (obtain dark and flat field frames). Produce a 
frame corrected for dark current, read bias, and flat field, and take a 
shot at photometry. I would like to collect these frames, and your 
photometry. I expect that we may identify severe problems in our initial 
attempts which hopefully can be overcome by April through changes in 
technique, and perhaps some equipment upgrades.
A PSF fit may be appropriate for photometry in conjunction with a detailed
model of the galactic emission. A CCD chip with bloom mitigation may help.

Step two. After we have an initial strategy, I would like to do a 24 hour
WEBT run on Mrk 421. The purpose of this run will be WEBT calibration
through simultaneous exposure from adjacent sites. We will not try to get 
continuous coverage. Thus, each participant will be expected to take only 
a few frames at the beginning and ending of the night.

More new business.

Tom reports a possible high optical state of 3C 279 - see 
http://gamma.bu.edu/webt/3c279.text -
linked from the "Here are recent blazar flux measurements:"
line of the WEBT home page.

Just saw IAUC 6776 reporting strong and variable X-ray flux for
PKS 2155-304 from SAX observations.

Old business.

I do not expect to schedule a 2nd WEBT observation of 0235+164
this Fall. We are still very far from completing the reduction of
the data from our first run. In fact, there are a number of open issues
regarding WEBT photometry. See 
http://gamma.bu.edu/webt/webt_reduce.text

I am keenly interested in achieving a complete reduction of
the 0235+164 data that we have. Please provide your final frames (corrected 
for dark current, read bias, and flat field) in FITS format, and your
photometry results. Gino expects to finish a paper on 0235+164 photometry
for publication in PASP next week. If possible, I will  provide a link
to it from 
http://bu-ast.bu.edu/~mattox/multiwavelength/0235.html

Cheers,
John

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp