<p>Did you check this page? <a href="http://arxiv.org/help/trackback/" rel="nofollow">http://arxiv.org/help/trackback/</a></p>

<p>arXiv does support trackbacks but only on pages with a url of the form <code>http://arxiv.org/abs/{paper_id}</code></p>
Submit a trackback to arXiv - User-Agent issues
<p>I would like to submit a trackback to <a href="http://arxiv.org" rel="nofollow">arXiv</a> using the only php script available I found, <a href="http://sourceforge.net/projects/phptrackback/" rel="nofollow">PHP Trackback</a>.
However it seems like I am not able to proceed since I get a "HTTP 403 Forbidden" error. It further states:</p>

<blockquote>
  <p>Sadly, your client does not supply a proper User-Agent, and is consequently excluded.</p>
</blockquote>

<p>So, how can I include a User-Agent? As a guess I tried</p>

<pre><code>fputs($tb_sock, "User-Agent: " . $_SERVER['HTTP_USER_AGENT'] . "\r\n");
</code></pre>

<p>inside the corresponding function in the above mentioned script. 
Hence my question:</p>

<p><strong>Is there a way to supply a User-Agent sending a trackback?</strong></p>

<p>Please note that I do not have any blogging software on webspace. Thanks in advance!</p>