# Comparison of switching modes

Figure: Integrated intensities of seven lines in the E230 setup for the three switching modes position-switching (PSW, shown as squares), wobbler-switching (WSW; triangles) and frequency-switching (FSW, circles), for calibration with MIRA (black) and MRTCAL (blue) with default settings. The integrated intensities are normalized to those measured for position switching. Bars indicate the 1 standard deviation over all scans of the according line. The three leftmost lines 1–3 are bright (peak temperature 6–10 K). Lines 4–7 are weaker ( 1 K).

All three switching modes available for spectral line observations were observed with the same EMIR 1 mm band setup in order to check the consistency of the line intensities between the different switching mode. To our knowledge, this is the first time this kind of study is done at the 30m-Telescope.

Figures compares the integrated line intensities for seven lines in position, wobbler, and frequency switching mode. In all cases, the individual scans were corrected for the gain-elevation curve as the source is barely resolved. Moreover, both polarizations were averaged. Integrated line intensities from the frequency-switched spectra may suffer from a higher uncertainty due to strong baseline ripples that are associated with this switching mode. This is especially true for the weaker lines.

The integrated line intensities in position-switching are consistent between both calibration software, with MRTCAL intensities reaching 991% (mean over the seven lines and its 1 standard deviation) of the MIRA intensities.

For wobbler-switching, the integrated line intensities amounts to 931% of the intensities in position-switching for both MIRA- and MRTCAL-calibrated spectra. This reduction of line intensity is expected because of the reduced anntena gain when tilting the subreflector. For a tilt of 90 , the antenna main beam gain at 230 GHz is reduced to 0.93 (see report by Peñalver 2016), in agreement with the observed value.

For frequency-switching, the integrated intensities reach 941% of the position-switching intensities for the MRTCAL-, and 891% for MIRA-calibrated spectra. MRTCAL delivers integrated intensities that better match the position switching ones, probably because the frequency calibration and folding of the two phases is done in a different way than in the usual combination of MIRA and CLASS. Indeed, Winkel et al. (2012) indicate that the usual approach underestimates line intensities when the line strengths is not negligible compared to the system temperature.

The remaining difference of 61% between frequency-switching and position-switching when the data is calibrated by MRTCAL could be related to a lost of receiver efficiency when the frequency throw is large. In our case, it was set to the maximum value of 23.4 MHz because IRC+10216 lines are relatively broad. This effect will be further explored in new observations.