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VII. About the Poster

One of the most amazing things about gamma-ray bursts is their enormous power. Power is defined as the amount of energy emitted per unit time. Shown on the poster is a bar graph which compares the power emitted by several different radiant objects or events. The values given represent the peak power output of each. In other words, it is a snapshot in time at the instant each object or event is emitting the greatest amount of power it will ever emit. Some things — like the light bulb — emit constant power over time. Other things like a supernova explosion or a gamma-ray burst can emit enormous amounts of power one second and thousands or hundreds of thousands of times less power the next second. By showing peak power, we allow ourselves to compare very different things like light bulbs and supernovae in a meaningful way. Simply put, we display on our graph the following information: in the one second (whenever it occurred) that they each emitted their maximum power, what was it?

It may be interesting to consider the total energy (or power x time) emitted as well. This takes into account the amount of time that each object or event emitted energy and how much energy they emitted as a function of time. Consider this, the total energy emitted by a supernova is only about a factor of 10 to 1000 less than that emitted by a gamma-ray burst. Given the values you see on the peak power graph on the poster, what does this tell us about the amounts of time over which these events occur?

Running down the left side of the poster is a series of images which illustrate how the light curve of a GRB (i.e., a plot of its intensity as a function of time) would appear as an image on the sky. While based on real data, these images are only meant to be illustrative; you cannot, in fact, create an all-sky image in gamma-rays on the brief timescales of a GRB. What the illustration shows is that a burst can become so bright that it overwelms the elements of the detector which are imaging the burst location. Those detector elements become overloaded and begin to "spill over" into the nearby detector elements. So in a way, the size of a spot on the image is proportional to the intensity of the source (of course, so is the color of the spot). What you will notice is that at the maximum of the GRB, the event is brighter than the whole rest of the sky and temporarily blinds the detector to seeing anything else.

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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