This note documents the existence of a daily variation in the 30-70 keV background subtracted count rate. This is similar to the daily peak in the SAA dosage history. To determine the exact period, a power spectrum was calculated using the Lomb algorithm (Press et al.). The result was P=84571.4s, and the 30-70 keV light curves were folded on this period, using a common epoch of MJD = 50096.5970138888879, which is the time of a daily peak in the SAA dosage. The peak-to-peak amplitude of the variation ranges from ~0.3 to ~1.0 cts/s/3pcu. Contrary to earlier reports, there is no firm evidence for a variation in the 0-10 keV light curves.
Background subtracted light curves were accumulated in the 30-70 keV band for several observations that have become public (table 1), using the standard selection criteria for faint sources (table 2).
Object | Obsid | 30-70 keV light curve | 30-70 keV light curve folded on period |
NGC7469 | P10315 | 10315_lc.jpg | 10315_fold.jpg |
Coma Cluster | P10368 | 10368_lc.jpg | 10368_fold.jpg |
IRAS18325-5926 | P30229 | 30229_lc.jpg | 30229_fold.jpg |
IRAS18325-5926 | P30405 | 30405_lc.jpg | 30405_fold.jpg |
MCG-6-30-15 | P20310 | 20310_lc.jpg | 20310_fold.jpg |
NGC3516 | P20316 | 20316_lc.jpg | 20316_fold.jpg |
NGC4051 | P20318 | 20318_lc.jpg | 20318_fold.jpg |
NGC4051 | P30225 | 30225_lc.jpg | 30225_fold.jpg |
PDS456 | P30247 | 30247_lc.jpg | 30247_fold.jpg |
4-day background | P30801 | 30801_lc.jpg | 30801_fold.jpg |
Criterion | Description |
(BKGD_THETAa < -70.0 or BKGD_THETA > 150.0) or TIME_SINCE_SAAb > 30.0 or TIME_SINCE_SAA < 0.0 | Outside the South Atlantic Anomaly |
PCUn_ON 0.5 | PCUn fully on |
ELV > 10.0 | Angle between the satellite pointing direction and the Earth's horizon |
OFFSET < 0.01 | Angle between the satellite pointing direction and the nominal field of view |
VpX1L, VpX1R < 6.25 | Veto rate between the propane layer and the left/right halves of the Xenon layer |
(VpX1L+VpX1R)/Q6c < 0.1 | Normalized propane layer veto rate |