{
  "email": "peter.woods@msfc.nasa.gov",
  "circularId": 1394,
  "editedOn": 1777052630796,
  "version": 2,
  "bibcode": "2002GCN..1394....1F",
  "createdOn": 1022267761000,
  "submitter": "Peter Woods at UAH/MSFC  <peter.woods@msfc.nasa.gov>",
  "editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov>",
  "subject": "XRF 020427: Sudden Ionospheric Disturbance (SID)",
  "eventId": "XRF 020427",
  "body": "G.J. Fishman, P.M.. Woods, C. Hossfield and L. Anderson report that the\nX-ray rich event of April 27, 2002 was detected as a Sudden Ionospheric\nDisturbance (SID) by Len Anderson in South Perth Australia, indicating\nthat XRF 020427 (GCN 1383), produced a prodigious amount of ionizing\nx-ray flux.   The disturbance is clearly seen, lasting about one minute,\nin a low-resolution all-day strip chart recording from a Very Low\nFrequency (VLF) radio receiver near Perth.  Although a quantitative\nmeasure of the flux of this event could not be determined by this\nmethod, the SID magnitude (and thus the ionizing flux) is comparable to\nthat observed from the Aug. 27, 1998 super-flare from SGR 1900+14 (Inan,\net al., Geophys. Res. Lett., v.26, p.3357, 1999).  A large flux of\nx-rays below ~15 keV was deduced from that flare (op. cit.).  One\nintense gamma-ray burst, GRB830801, was also observed to produce a SID\nbut at a much weaker level (Fishman and Inan, Nature v.331, p.418,\n1988).  The strong ionizing present in this burst confirms that this is\na long, x-ray rich event of unknown origin, as suggested by in't Zand et\nal. (GCN 1383).\n\nNote: SIDs have been used to study solar flares since the 1950s.  In\nthis case, the SID was observed as a major change in the propagation of\na continuous VLF radio transmission at 19.8 kHz from Northwest Cape,\nAustralia.  The VLF radio receiver trace can be seen at:\n\nhttp://gammaray.nsstc.nasa.gov/~woods/xrf020427.html\n\nThis message may be cited."
}