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01/28/05 18:17:18 (20 years ago)
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galante
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  • trunk/MagicSoft/GRB-Proposal/Monitor.tex

    r6000 r6102  
    1 \section{The GRB monitor at La Palma}
     1\section{The Burst Alarm System at La Palma}
    22
    3 \subsection{The socket connection to GCN}
    4 \subsection{The GRB webpage}
    5 \subsection{The accoustic alert}
    6 \subsection{The interface to the Central Control}
    7 \subsection{Emails to the GRB-mailing list}
     3{\bf Current status:}
     4
     5\par
     6
     7The Burst Alarm System is installed and working since last summer
     8in La Palma. The duty of the Burst Alarm System
     9is to perform a full-time survey of the GCN (Gamma-Ray Bursts
     10Coordinates Network) alerts. Different satellite experiments perform GRB monitoring
     11in their wide FOV and send immediately the coordinates of the GRBs to the GCN network.
     12The network send the alerts to registered users and allows other satellites as well as
     13ground based observatories to observe the GRBs and their afterglows at different wavelenghts.
     14The Burst Alarm System is composed by a main program -
     15the core of the system - which acts in two ways: on the
     16one hand it manages the monitoring of the GCN, on the other it manages
     17the communication with the Central Control (CC). Then it also manages
     18three communication channels to notice the shifters
     19about a alert situation. The program is called {\it gspot} (Gamma
     20Sources POinting Trigger). It is a C based daemon running 24
     21hours a day onto the {\it www} machine, our external server, in a
     22{\it stand alone} mode. It do not need to be operated and is
     23fully automatically able to manage network diconnections
     24within the external net and/or the internal one.
    825
    926
    10 \ldots {\bf NICOLA } \ldots
     27\subsection{The connection to GCN}
     28
     29The connection to GCN is performed by {\it gspot} through a
     30TCP/IP connection within a computer at Goddard Space Flight
     31Center (GSFC). This computer distributes the informations it is recieving from the satellite
     32experiments through the normal internet socket connection. The {\it gspot} onto our
     33side acts as a server while the client, running at the GSFC,
     34manages the communication of the data concerning the GRBs
     35and concerning the status of the connnection. \\
     36
     37The format of the data distributed through GCN differ between the individual satellites
     38and the kind of package. There are three satellites participating in the GRB survey:
     39HETE-2, INTEGRAL and SWIFT. All are sending alerts which include the
     40UTC, coordinates (not always), error on coordinates
     41(not always) and intensity (photon counts) of the burst.
     42The first notice from HETE-2 and INTEGRAL usually do not include the coordinates.
     43In only few cases coordinates are distibuted delayed in more refined notices.\\
     44
     45In case of an alert {\it gspot} stores the informations and enters into
     46an {\bf Alarm State}. The duration of the alert state depends on the following parameters:
     47
     48\begin{itemize}
     49\item {\bf darkness of the sky}, determined from the distance of the sun
     50to the astronomical horizon of 108$^\circ$ zenith;
     51\item {\bf position of GRB}, the GRB equatorial
     52coordinates are transformed into local horizontal coordinates and comparised whether the
     53GRB zenith angle is smaller than 70$^\circ$; in the case that moon is
     54shining in the sky, we propose to reduce this zenith limith to 60$^\circ$;
     55\item {\bf position of moon}, checking whether the angular
     56distance from the GRB to the moon is at least 30$^\circ$.
     57\end{itemize}
     58
     59If one or more of these conditions failed then {\it gspot}
     60enters into a {\bf Yellow Alarm State}. It means that the GRB is not observable
     61at the moment. Currently the program do not calculate if and when the GRB will
     62become observable at La Palma.
     63If all conditions mentioned above are satisfied,
     64{\it gspot} enters into a {\bf Red Alarm State}, which means that
     65the GRB is considered to be observable at the current time.\\
     66
     67In both cases (in RED and YELLOW alarm state) {\it gspot} assamble the communication
     68with the CC and sends the GRB equatorial coordinates (RA/DEC J2000).
     69For the communication to CC the format defined in \cite{CONTROL} is used. In the same time
     70the shifters and the GRB-MAGIC group is contacted in different ways described in the next sessions.
     71
     72\subsection{The interface to the Central Control}
     73
     74An interface of {\it gspot} sends all the relevant informations about it's status to {\it arehucas}.
     75In the case of {\bf NO Alarm State} the standard packages, containing the main global status
     76of the two subsystems, are continuosly excanged between CC and {\it gspot}.
     77In the alert case {\it gspot} starts to send to CC special alert packages,
     78containg major informations of the GRB and on the ''colour'' of the alert.
     79The exchange of the alert packages continues untill the following steps occur:
     80
     81\begin{itemize}
     82\item {\it gspot} get from {\it arehucas} the confirmation
     83that it recived the alert notice; {\it arehucas} must send the alert back in order to
     84to perform a crosscheck of the relevant data;
     85\item the alarm state expire after {\bf 5 hours}.
     86\end{itemize}
     87
     88At the moment {\it arehucas} informs the shift crew about the alern and undergo
     89further steps only in case of red alerts. In this case a pop-up window
     90appears with all the alert information recived by the burst monitor.
     91The operator has to confirm the notice by closing the pop-up window.
     92He can decide to stop the current scheduled observation and to point the GRB.
     93A new button in the CC will be displayed and allows to point the the telescope to
     94the GRB coordinates by pushing it.
     95
     96\subsection{GRB archive and emails to the GRB-mailing list}
     97
     98In case of an alert, even if it did not contain the necessary coordinates, the
     99informations are translated into ''human language'' and stored into ASCII files.
     100In the same time an e-mail is send to the MAGIC GRB-mailing list.
     101
     102\subsection{The GRB web page}
     103
     104The status of the GRB Alert System and relevant informations from the last
     105alert are displayed on a seperate web page. The page is hosted on the web server in La Palma.
     106The address is the following:\\
     107
     108\qquad \qquad http://www.magic.iac.es/site/grbm/\\
     109
     110The web page automatically updates itself every 10 seconds. In this way
     111the status of the Burst Alarm System can be checked from everywere.
     112
     113\subsection{The acoustic alert}
     114
     115A further CC-indipendent acoustic alarm called {\it phava}
     116(~PHonetic Alarm for Valued Alerts~) will be installed
     117in La Palma very soon. It will provide a loud acoustic signal
     118even if {\it arehucas} is switched off, so that people in the counting house
     119will be noticed about the alert situation. The signal will be on as long as
     120{\it gspot} stays in alarm state, and in any case for a minimum of 1 minute.
     121This device will keep also a display where to fast check the status
     122of the system and of the alert.
     123
     124\subsection{Alerts recived untill now}
     125
     126Since July, 15th 2004 {\it gspot} has been working stable.
     127It recived from HETE-2 and INTEGRAL about 100 alerts, most of them without coordinates.
     128More precisely only 20 of them contained GRB's coordinates. Time delays
     129were in most cases very large - in the order of of several minutes or even
     130tens of minutes. In the beginning the Burst Monitor contained some bugs so that we can not
     131rely on the alerts untill November last year. Since the bugs were fixed we got only one red alert.
     132This alert came from INTEGRAL with a delay of 71 seconds, it happened
     133on December 19th at 1:44 am and the GRB zenith angle was $\sim 60^\circ$. Pitty that the weather
     134conditions were very bad durnig this night.
     135
     136
     137\subsection{Tasks to be arranged}
     138
     139The Burst Alarm System is currently able to provide the minimum
     140features needed to point and to observe a GRB. Anyway several
     141things must be defined in order to improve our efficiency
     142to point and observe GRBs.
     143
     144\begin{itemize}
     145\item {\bf Yellow Alarm strategy}
     146First of all the strategy to follow in case of a yellow
     147alarm, i.e. in case of a not observable GRB, is not defined yet.
     148In such a case the CC does not undertake any steps,
     149except confirming the alarm notice to the Burst Monitor. We do not
     150calculate if and when the GRB will become observable.
     151It would make sense to check if during the period of 5 hours we could point to the burst.
     152Then the Alarm System would change to {\bf Red Alarm State}
     153at that time and allow the observation.
     154
     155\item {\bf sequence of alerts}
     156Another procedure that needs to be defined is how to deal with new alerts
     157that are distributed during the time that {\it gspot} stands
     158in alarm state. The status of the system now is that {\it gspot}
     159locks its alert status untill it exits
     160the alarm state. This feature was implemented in order not to
     161loose GRB informations due to nasty events.
     162Such situation can appear ONLY when the CC is switched off so
     163that it cannot recive the alert. Indeed such situation can
     164occour when more than one alert happens in the late afternoon or
     165in the 5 hours before the beginning of the night-shift.
     166In such a case we propose
     167to implement into {\it gspot} a list in which every
     168item is a GRB's alert that expires after:
     169
     170\begin{itemize}
     171\item having been noticed to the CC;
     172\item the canonical 5 hours.
     173\end{itemize}
     174
     175If more than one alert is present in the list then the program
     176gives a mark to the GRB based on the total time of observability
     177within the canonical 5 hours, on the intensity of the
     178burst itself and on the time to wait to get the GRB observable.
     179Such a mark should reflect our estimation in the chances that
     180we have to observe that GRB.
     181The GRB with the highest mark will be noticed to the Central Control.
     182
     183\end{itemize}
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