We present the calibration and background model for the Proportional Counter Array on board the Rossi X-Ray Timing Explorer. The energy calibration is systematics-limited below 10 keV, with deviations from a power-law fit to the Crab Nebula plus pulsar of less than 1%. Unmodeled variations in the instrumental background amount to less than 2% of the observed background below 10 keV and less than 1% between 10 and 20 keV. Individual photon arrival times are accurate to 4.4 s at all times during the mission and to 2.5 s after 1997 April 29. The peak pointing direction of the five collimators is known to a precision of a few arcseconds.

Is Mars actively releasing organic and other minor gases into the atmosphere? We present a comprehensive search for trace species on Mars, targeting multiple volatile organic species (CH 4 , CH 3 OH, H 2 CO, C 2 H 6 , C 2 H 2 , C 2 H 4), hydroperoxyl (HO 2), several nitrogen compounds (N 2 O, NH 3 , HCN), and two chlorine species (HCl, CH 3 Cl) through their rovibrational spectra in the 2.8-3.7 lm spectral region. The data were acquired over a period of 4 years (2006-2010) using powerful infrared high-resolution spectrometers (CRIRES, NIRSPEC, CSHELL) at high-altitude observatories (VLT, Keck-2, NASA-IRTF), and span a broad range of seasons, Doppler shifts and spatial coverage. Here, we present results from a selection of high-quality spectra obtained on four separate dates, representing a fraction of our search space. For most of these species we derived the most stringent upper limits ever obtained, and because the targeted gases have substantially different resident lifetimes in the Martian atmosphere (from hours to centuries), our measurements not only test for current release but also provide stringent limits on the quiescent levels. In particular, we sampled the same regions where plumes of methane have been recently observed (e.g., Syrtis Major and Valles Marineris), allowing us to test for seasonal and temporal variability.