Q&A: X-ray Astronomy

Q:
I was speaking to someone on the Chandra project and they mentioned something about an X-ray anomaly comming from somewhere in the Atlantic Ocean. Is that accurate? If so then I would like to learn more about this.

A:
You are probably referring to the South Atlantic Anomaly.

The South Atlantic Anomaly (SAA), is the name for an area that exhibits a local minimum in the magnetic field. Due to the lower field, the trapped particles of the lower Van Allen belt, at this location penetrates to lower altitudes. Hence, spacecrafts that otherwise are flying below the Van Allen belts, experience a somewhat increased radiation level while passing the SAA.

The centre of the South Atlantic Anomaly is located at approximately latitude -30 and longitude -45. It extends some 25 in latitude and 30 in longitude from the centre.

The increased radiation level in the SAA is characterized by an increased level of high energetic protons. At the centre, the flux of protons with an energy above 50MeV is increased 1000 relative to the flux, at the same altitude, outside the SAA.