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The following is a reply to a request-for-permission I received 2005-01-18. --fvw* 22:56, 2005 Feb 6 (UTC) 

Dear Sir,

You get hereby permission to use the text of the attached HTML file
as a basis for the intended Wikipedia article (under the GNU FDL).

Since I have very little experience with Wikipedia and consider
myself biased with respect to HEGRA, I'd like to thank you for
your willingness to write an article about HEGRA instead of trying
to do this myself.

The attached HTML file is a minor modification of the original web
page by me to which you referred. In particular, I got rid of links
to maps of unknown origin now and replaced GIF format images with PNG.
The text itself is not substantially affected. It's just that
MAGIC is no longer 'being built up' but is now operational.

For your convenience, I uploaded three images (taken or drawn by me)
to Wikipedia Commons, which you might want to consider for the article:
   Hegra.jpg
   Hegra_scint_and_air.png
   Shower_detection.png
The third one is a more general version of the drawing that you get
when you click onto the thumbnail to the right of the title in the
web page (hegra_shower_detection.png). The other two are identical to
images used in the HEGRA.html web page.

   Kind regards,
     Konrad Bernlöhr

> ---------- Forwarded message ----------
> Date: Sat, 15 Jan 2005 00:57:26 +0100
> From: Frank v Waveren <fvw@var.cx>
> To: werner.hofmann@mpi-hd.mpg.de
> Subject: HEGRA experiment webpage
> 
> Dear Sir,
> 
> In the process of writing an article on HEGRA for Wikipedia I came
> across your webpage at http://www.mpi-hd.mpg.de/hfm/HEGRA/HEGRA.html;
> I would like to use the text of this page if I may.
> 
> Wikipedia (http://en.wiki.x.io) is a free encyclopaedia that is
> collaboratively-edited by volunteers from around the world.
> 
> To be included in Wikipedia the text has to be licensed under the GNU
> Free Documentation License. This means anybody will have the right to
> share your materials and update them: for example, to keep up with new
> information. You can read this license in full at:
> http://www.wiki.x.io/wiki/Wikipedia:Text_of_the_GFDL
> 
> The license also expressly protects authors "from being considered
> responsible for modifications made by others" while ensuring that
> authors get credit for their work. There is more information on our
> copyright policy at:
> http://www.wiki.x.io/wiki/Wikipedia:Copyrights
> 
> If you are the copyright owner of this piece of text and would be
> willing to license it under the GFDL, we would be most grateful.
> 
> Thank you for your time, I look forward to your reply.
> 
-- 
Konrad Bernlöhr <Konrad.Bernloehr@mpi-hd.mpg.de>

--=-Ukm75GbPaKhvSc/l0IVq
Content-Disposition: attachment; filename=HEGRA.html
Content-Type: text/html; name=HEGRA.html; charset=ISO-8859-15
Content-Transfer-Encoding: 7bit

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>High Energy Gamma Ray Astronomy (HEGRA)</title>

<link rel="stylesheet" media="screen" type="text/css" 
      href="http://www.mpi-hd.mpg.de/hfm/MPI/mpi.css">
<link rel="stylesheet" media="print" type="text/css" 
      href="http://www.mpi-hd.mpg.de/hfm/MPI/mpi.css">
<meta name="description" content="The High Energy Gamma Ray Astronomy 
   (HEGRA) experiment on the island La Palma measured very energetic 
   particles (cosmic rays) and gamma rays from cosmic sources. 
   This page serves as a link to descriptions of the various measuring 
   devices.">
<meta name="keywords" content="HEGRA, cosmic ray, gamma ray,
   astrophysics, experiment, space radiation, air shower, airshower">
</head>


<body alink="#ff0033" bgcolor="#ffffff" link="#479088" text="#000000" 
      vlink="#2e90b4">

<h1>
<a href="http://www.mpi-hd.mpg.de/hfm/HEGRA/hegra.jpg">
<img src="http://www.mpi-hd.mpg.de/hfm/HEGRA/hegra-tiny.jpg" 
     alt="[Picture of HEGRA array]" align="middle"></a>
 The HEGRA experiment 
<a href="http://www.mpi-hd.mpg.de/hfm/HEGRA/hegra_shower_detection.png">
<img src="http://www.mpi-hd.mpg.de/hfm/HEGRA/hegra_shower_detection_tiny.png" 
     alt="[Air shower detection]" align="middle"></a>
</h1>

<!--
  Related images in Wikipedia commons:
     [[Image:Hegra.jpg]]
     [[Image:Hegra_scint_and_air.png]]
     [[Image:Shower_detection.png]]
-->

The High Energy Gamma Ray Astronomy (HEGRA) experiment was located on
La Palma (Canary Islands) at a height of 2200 m a.s.l. (at the site of the
<a href="http://www.iac.es/orm/indice.html">Observatory</a>
operated by the <a href="http://www.iac.es/home.html">IAC</a>).
It consisted of several
detector types for observing secondary particles or light from
particle cascades in the atmosphere 
(<A href="http://www.mpi-hd.mpg.de/hfm/CosmicRay/Showers.html">
Extensive Air Showers</A>, EAS).
The EAS detected by HEGRA are produced by cosmic ray
particles in the energy range 10<sup>12</sup> to 10<sup>16</sup> eV.
With its various types of detectors HEGRA was taking data between
1987 and 2002.
<p>

The detectors with the lowest energy threshold were the
<a href="http://www.mpi-hd.mpg.de/hfm/CT/CT.html">Atmospheric Cherenkov Telescopes</a>
with 'cameras' of photomultiplier tubes.
They were sensitive to showers above 10<sup>12</sup> eV (1 TeV) but had
to look towards possible sources and could be operated only during clear,
moonless nights. They detected 
<a href="http://www.mpi-hd.mpg.de/hfm/ChLight/Cherenkov.html">Cherenkov light</a> 
from relativistic
secondary particles in the air showers. The field of view was about
4.6 degrees. There were a total of six of these telescopes in operation.
They were dismantled in September 2002.
</p><p>

Another detector type for the Cherenkov light was 
<a href="http://www.mpi-hd.mpg.de/hfm/HEGRA/hegra_scint_and_air.png">AIROBICC</a>
(AIrshower Observation By Angle Integrating Cherenkov Counters) with
one large photomultiplier looking at the sky above it.
49 of these detectors were spread in a 7-by-7 grid to observe the
amplitude and the time of arrival of the front of Cherenkov light.
Another 48 were added later on.
These counters had a wide field of view but could be operated also
only during clear, moonless nights. Their energy threshold was a few
10<sup>13</sup> eV. The AIROBICC array has been dismantled.</p><p>

The first detector type of HEGRA was the array of 1 m<sup>2</sup> 
<a href="http://www.mpi-hd.mpg.de/hfm/HEGRA/hegra_scint_and_air.png">
scintillation counters</a>
which were used to measure the numbers and arrival times of secondary
particles in air showers arriving at ground level. More than 250 of these
counters were in operation, spread over a 180-by-180 m<sup>2</sup> area.
These detectors were operated day and night at any weather. The energy
threshold of the scintillator array was between 40 and 100 TeV,
depending on the kind of primary cosmic ray particle.
The scintillator array has been dismantled as well.</p><p>

The scintillator array was sensistive to all types of charged secondary particles.
To be able to select secondary muons in air showers there were the 
Muon 'Towers' with 16 m<sup>2</sup> area each. 
Seventeen of these detectors were installed on La Palma.</p><p>

There were two more types of detectors at the HEGRA site: the
<a href="http://www.mpi-hd.mpg.de/hfm/CRT/CRT.html">CRT (Cosmic Ray Tracking)</a> 
detectors and the 
<a href="http://www.pi.infn.it/clue/">CLUE</a> 
(Cherenkov Light Ultraviolet Experiment).

A successor to the HEGRA Cherenkov telescopes is operational since 2004
at the HEGRA site: <a href="http://hegra1.mppmu.mpg.de/">MAGIC</a>.
A direct successor to the stereoscopic system of Cherenkov telescopes
is the <a href="http://www.mpi-hd.mpg.de/HESS">H.E.S.S.</a> experiment.
</p><hr>

The main 
<a href="http://www-hegra.desy.de/hegra/">HEGRA server</a> is now in Hamburg. 

 <hr>

For pointers to various cosmic ray and neutrino experiments 
worldwide see 
<a href="http://www.mpi-hd.mpg.de/hfm/CosmicRay/CosmicRaySites.html">here</a>.

</body></html>
--=-Ukm75GbPaKhvSc/l0IVq--

HEGRA Page Comments

[edit]

I have been trying to write a document on cosmic-ray "telescopes" and one of the topics I was having trouble tracking down was HEGRA. There is a website but it is a pain to get much useful information out of it.

So I was very pleased to find that Wikipedia had a page on it. There is quite a bit of useful detail on this page.

However, although I applaud the efforts of the author and wish to encourage him/her in the work ... this is a confusing article to read.

May I politely suggest a more structured approach to the description of the HEGRA array? Try to create a chronological list of the evolution of the array, giving the elements created at each time and a description of each. Another curious item is what, if any, elements of the old HEGRA array survived to accompany the new MAGIC Cerenkov telescope. Doesn't sound like any ...

These are no more than suggestions, and again I applaud the efforts of the author. I just would like to give some hopefully useful feedback.

Since the author is obviously interested in cosmic-ray telescopes, I will be glad to share my (incomplete) document for feedback of my own. Cosmic ray telescope technology is not very well documented and it's a bit of a scavenger hunt to track things down.

MrG mister_g_n000p@earthlink.net / valid to 1 jan 06

[edit]

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