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If you want to learn more, we suggest the following videos by Khan Academy about the electric and magnetic fields, as well as the electromagnetic field, respectively: https://bit.ly/2DnXRYl, https://bit.ly/2mrkGjR and https://bit.ly/2q7CSou.
Note that the noun and adjective of gamma rays are spelled differently. The noun is spelled as gamma rays (for example, “gamma rays are very energetic”), while the adjective is written as gamma-ray (for example, “gamma-ray astronomy is a young field”).
Given that cosmic rays are charged particles (such as electrons and protons), they get randomly deflected in their travel through space by the IGMF and ISMF. That is why by observing cosmic rays, scientists are not able to identify the source from which they originate. To understand cosmic-ray sources, we need to study non-charged particles from the source’s cosmic rays, such as neutrinos and, of course, gamma rays! Nevertheless, the study of cosmic rays can lead to important information, such as their abundance in our Universe.
One of the most famous microquasars is Cygnus X-1, which caused Stephen Hawking to lose a bet with Kip Thorne. Do you know the story? Have a look in https://bit.ly/2SrDG6u.
The smaller the PSF of an instrument the better. This is because with a smaller PSF, an instrument can disentangle smaller and finer details in the sky… so more information!
The lower the sensitivity’s value, the better the instrument! For example, if we have two instruments, one with a sensitivity of 0.6 C.U. (have a look to the definition of Crab Units) and another with 0.4 C.U. for a certain energy range, it means that the first instrument will be able to detect sources whose flux is above 0.6 C.U., while the second will do so for sources with flux already above 0.4 C.U. So the second can detect even weaker sources, which is definitely better.
An example of variability in astrophysical sources? In binary systems, there is the so-called orbital variability produced when the star eclipses the companion and the light cannot reach us in the same way. This is a constant variability because the flux (amount of light) increases and decreases according to the orbital movement.
(Last Updated: October 2019)