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4. A Sensitive Situation

In order to study a cosmic phenomenon, there are several factors to consider when designing your detector system. One is how bright the phenomena are that you will be studying. Related to this is how often an event of a given brightness occurs. If you don’t understand these things, you could look for a very long time and see nothing...or you could be blown away by the first event!

Examine the plot below. Note that it is a Log-Log plot, so think carefully in trying to answer the questions below. On the X-axis you see the number of photons per square centimeter per sec detected from a GRB (this is merely a measure of its brightness) and on the Y-axis you see the number of bursts each year which are that bright or brighter. These bursts can occur anywhere in the sky. So we will assume that our detector is located far from Earth and can continuously view the entire celestial sphere.

Log N vs. Log photons

1.) If your detector can measure bursts which are 100 photons per cm2 per sec or brighter, how many GRBs would you detect each year?

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2.) If you are designing a new detector and want to be able to detect about two GRBs per week, what are the dimmest bursts that you would detect? What does this mean about how sensitive a detector you must design?

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3.) If your detector is 100 times more sensitive than what you found in (1), how many GRBs would you detect each week?

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Imagine the Universe! is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

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This page last updated: Thursday, 21-Nov-2002 12:11:31 EST