The following "magnitude (m2) calculator" applet can be used to estimate how bright an afterglow's magnitude might be at a given time. Click on the button to load the applet and fill in known values or estimates as explained below. [The bottom blue box displays the calculated estimate of m2.]
If multiple measurements of an AG have already been taken the value of the decay index (alpha) can be estimated using the following "decay index (alpha) calculator." [The bottom blue box displays the calculated value of alpha.]
| alpha | decay index of AG, usually varies between approximately -0.5 and -2 (AG flux = constant*time^alpha), if actual value is unknown assume alpha = -1.3 (the observed average value) |
| m1 | measured magnitude of the AG at time t1 |
| t1 | time past the GRB when m1 was measured (e.g. 1 hour after the GRB occurred) |
| m2 | measured magnitude of the AG at time t2 [note that m1 and m2 must be measured in the same waveband] |
| t2 | time past the GRB when m2 will be (or was) measured (e.g. m2 will be measured 5 hours post-burst) [note that any unit of time can be input (minutes,hours,days etc.) so long as both t1 and t2 are input in the same units] |
CAUTION: These are merely tools for making estimates and actual AGs may vary greatly from the results produced here!