Herschel SPIRE fourier transform spectrometer: calibration of its bright-source mode
Valtchanov, Ivan; Hopwood, Rosalind; Naylor, David A.; Lu, Nanyao; Polehampton, Edward T.; Swinyard, Bruce M.; Benielli, Dominique; Fulton, Trevor; Imhof, Peter; Lim, Tanya; Marchili, Nicola; Schulz, Bernhard; Sidher, Sunil
United States, United Kingdom, Canada, France, Italy, Spain
Abstract
The Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) on board the ESA Herschel Space Observatory has two detector setting modes: (a) a nominal mode, which is optimized for observing moderately bright to faint astronomical targets, and (b) a bright-source mode recommended for sources significantly brighter than 500 Jy, within the SPIRE FTS bandwidth of 446.7-1544 GHz (or 194-671 microns in wavelength), which employs a reduced detector responsivity and out-of-phase analog signal amplifier/demodulator. We address in detail the calibration issues unique to the bright-source mode, describe the integration of the bright-mode data processing into the existing pipeline for the nominal mode, and show that the flux calibration accuracy of the bright-source mode is generally within 2 % of that of the nominal mode, and that the bright-source mode is 3 to 4 times less sensitive than the nominal mode.