Notes from the discussion period of the GLAST GeV-TeV Symposium, held
on 30 September 2004 at SLAC.

Dave Thompson (DJT) and Rene Ong (RAO) led the discussion by posing 
a number of questions to the group.  The questions are listed below, 
and following each question is an approximate representation of the 
discussion that followed, as recorded by RAO.


1.  We can plan cross-calibration in the overlapping energy range. 
    Not an easy task.  Maybe get a small group together for planning?

This question was favorably received - everyone agrees that it is an 
important thing to do.  Dirk Petry of the GSSC has investigated 
some of the requirements associated with doing cross-calibration - he 
concluded that it could take up to several years of Crab data to do 
a good job.  There was a fair bit discussion on whether the Crab 
should be used exclusively or whether sources other than the Crab, such 
as flaring AGN (e.g. W Comae) would be useful.  The main argument for 
the Crab is that it is a steady source and this would reduce systematics 
associated with the knowing the flux level.  Advantages for a strong 
AGN are that the gamma-ray flux could be much higher than the Crab 
for certain time periods, allowing the calibration to be done quicker.  
The point was also made that it might be easier to calibrate using 
a spectrum with a cutoff feature than with a featureless power law.
It was pointed out that a major problem associated with Cherenkov
telescopes is understanding the throughput of the atmosphere and
thus flux normalization is important as energy calibration.  The
action item was that DJT would contact each instrument to find out
who would be interested in working in a small group.


2.  The GLAST Project is committed to immediate public release of 
    data for transients, both bursts and flares.  TeV telescopes can 
    follow up with observations, then work with the GRB and LAT teams 
    on joint analysis. Should LAT also consider announcements to the 
    TeV community of sources that have particularly flat spectra (that 
    might extend to higher energies)?  Should the reverse also be true -
    TeV telescopes tell LAT when they find a source that is flaring or 
    has a steep spectrum?  How would we exchange such information, and 
    what would we do with it on both sides?
    
First, there was some discussion of the extensive planning already
underway by the GLAST team to define what transients are and to provide
ways to alert the community in a prompt manner.  A list of ~20 sources
to be monitored on a continual basis (with light curves being reported
in semi-real time) is being developed by Peter Michelson, with input 
from members of the LAT team and from the community.  The general 
response from the TeV community was that this work is really important 
and useful and the more information that could be disseminated rapidly, 
the better in making quick follow-up observations.

In regards to the second question (whether TeV telescopes should "alert"
the LAT), it was generally acknowledged that it was unlikely for a
TeV alert to substantially alter the GLAST observing program, as the
entire sky is visible to GLAST over its 90 minute scanning cycle.
(By contrast, a dedicated re-point would take typically ~6 hours). What
became more apparent in the discussion was that more coordination
is really needed in the TeV community.  Right now each experiment works
rather independently and general policies and procedures for alerts
are not well established and publicized.  Ideally, each TeV telescope
could publish on its web page a reasonable summary of its upcoming
observing schedule (night by night) and also detected light curves on 
a number of key sources that it observed.  No action item came out of
this question, but it was pointed out that there have been several
multi-wavelength (MW) meetings sponsored by VERITAS and that hopefully 
such meetings will continue in the U.S. and overseas.


3.  GLAST will have a Guest Investigator program.  TeV U.S. team members 
    should propose correlative observations. $$'s are involved.

Steve Ritz and Peter Michelson discussed the workings of the GLAST 
Scientific Working Group (SWG) and the GLAST User's Committee (GUC).  
It is through these forums that the interests of the broader community 
are represented.  Planning and discussions are being carried out
regarding the make-up of the GI program.  The GI program is a way
to award research funds and to shape the observing program after the
first year.  Funds are available only to U.S. scientists.  Another
key point is that there will be no data rights awarded to successful
GI proposals.  The conclusion from the discussion is that the TeV
community (and other communities) will need to prepare for the
GI program and should provide feedback to members of the SWG and the
GUC.  Steve Ritz made the point that he is always willing to listen
to suggestions at any time.


4.  The TeV community can join in promoting development of a more 
    complete blazar catalog.  Are there complementary contacts in 
    radio, optical and X-rays who could be enlisted?

There was interest from the community in helping develop better
catalogs.  There was some sentiment that the broader community does
not fully understand how important this effort is (i.e. how limited
the current catalogs are).  It was suggested that the GLAST work
and planning in this area be presented at a future meeting for
response.   No names of possible contacts to other wavelengths came
out of the discussion.


5.  Both communities can help maintain MW information sharing, i.e. 
    Web pages. The GLAST MW Web page (next chart) includes information 
    about a MW mail exploder with a public archive.  Do the TeV groups 
    have an interest in using this?

The TeV telescopes are making increasing use of MW pages.  The HESS
page (coordinated by S. Wagner) is used for general organization of MW
activities and includes both a public and private area.  The VERITAS
page (coordinated by J. Buckley, L Fortson, and H. Krawczynski) will
include the observation program, along with light curves in the
future.  The policies for joint observations and proposals with
the VERITAS instrument (and deadlines for VERITAS TAC submissions)
are listed on the web page. MAGIC (M. Merck) presented their MW effort 
at the workshop at the Adler Planetarium (Gamma 2002). There was no report 
at this meeting from the CANGAROO group.  It was generally acknowledged 
that these pages are very useful and should be expanded.  Regarding 
the mail exploder, people were in general interested, but it was pointed 
out that this will be much more useful as we get closer to the GLAST 
launch and when we have GLAST data.

HESS MW page:	
     http://www.lsw.uni-heidelberg.de/projects/hess/HESS/hessmultnu.phtml

VERITAS MW page:	
     http://jelley.wustl.edu/multiwave/

No information available about the MAGIC and CANGAROO pages.


6.  We have a common interest in having access to broad spectral 
    coverage.  Should we combine our efforts to line up MW observers 
    at longer wavelengths?

There was a strong consensus that combining efforts would be a useful
thing to do.  The action item is to organize a mini-workshop focused
on this.


7.  Would it be useful to initiate a regular workshop to discuss MW 
    issues of importance to the gamma-ray community?  

As in 6, there was agreement that this was a useful thing to do.  Of
course the real question is the time associated with setting up
and attending workshops.  It was proposed that a MW workshop could
be part of another meeting (e.g. ICRC, HEAD, etc.), but there was a
contrary view that this can be problematic (too many things going
on at once or the MW portion diluted or overshadowed).  In fact,
the upcoming "Cherenkov workshop" to be help at Palaiseau will have
a broader focus, with some emphasis on coordination in the TeV 
community and on MW efforts.  No action item or conclusion came from
the discussion on this question.


8.  Could the TeV community develop GI programs (possibly without $$$, 
    but with access to data)?

There was general consensus that this would be important to do in principle,
but in practice there are difficulties.  There are questions of data
rights to consider and there is the issue that ground-based telescope data
(Cherenkov or air shower) is not trivial to analyze. VERITAS currently 
has a mechanism for outside investigators to use VERITAS data as associate
members, and the group is interested in developing a broader program
beyond this - it is difficult to see how to do this without additional
resources.  Perhaps a segment of the community could come together to 
propose for some added funding. VERITAS does plan to make public its 
observing schedule and light curves on a number of key sources. The
possibility of outside investigators using HESS data will be discussed
in the future by the HESS collaboration.  


9.  Is there is need for coordination between the theoretical and 
    experimental communities, e.g. source modeling?

There was relatively lukewarm interest in this idea.


10. Would a common effort to build a useful Website to coordinate 
    scientific and outreach efforts in the GeV/TeV community be valuable?

In general, this suggestion got a positive response.  Several people
mentioned that it would be useful for both scientific coordination and
for outreach.  The HE gamma-ray community is dispersed and somewhat
weakly coordinated now and so such a site could be quite useful.  There
was concern that it could take significant effort (and possibly $$) 
from the individual instrument teams to make this work well, and so
that issue needs to be considered.