EVLA L-Band Spectral-Line Science Below 1200 MHz Emmanuel Momjian NRAO-Socorro

The L-band The VLA L-band system has: –OMT bandwidth of MHz. –LNA bandwidth of MHz. –Post-Amp bandwidth of MHz. VLA antennas can tune between 1225 and 1900 MHz.

The L-band Perley & Hayward 2008 The poor sensitivity windows are caused by resonances within VLA’s dielectric phase shifter and/or microwave lens. The VLA can also tune between 1100 and 1225 MHz, but with limited capability.

The L-band EVLA antennas will tune between MHz. Currently, all EVLA antennas, except for one, use the OMTs of the VLA. However, –these EVLA antennas do not have the microwave lens of the VLA, and –the dielectic phase shifter is replaced with a quadrature hybrid.

Interim EVLA L-Band Sensitivity EVLA ? Interim EVLA

RFI at L-band B. Hesman

RFI ( MHz) B. Hesman

RFI The RFI below 1150 MHz is primarily due to radar transponders used for aeronautical navigation. The strongest are at 1090 (air to ground) and 1030 (ground to air). The others are due to civilian DMEs and Military TACAN systems located every 500 kHz between 1025 and 1150 MHz.

Science Below 1200 MHz To test whether radio astronomical science can be delivered at the lowest frequencies of the L-band, we observed HI absorption lines at: –1139 MHz; a frequency that the whole array can observe. –1082 MHz; a frequency that only EVLA antennas can observe. –1019 MHz; a frequency that only EVLA antennas can observe.

z= (HI frequency at ~1139 MHz). Total time 1 hours (~75% on target) in B- configuration starting at ~7 am MST. Bandwidth 3.1 MHz with 127 spectral channels. PKS

RFI Short baselineIntermediate baselineLong baseline Short baselines are clearly affected by the navigation transponders. The pulses are 3.5 microsecond long (1.1 km) separated by 12 microsecond.

PKS rms = 4.7 mJy/bm/ch Theoretical value = 2.5 mJy/bm/ch

RFI: D-configuration Baseline 16-17~ 60 m PKS B-conf. D-conf.

z= (HI frequency at ~1082 MHz). Total time 1 hours (~75% on target) in B- configuration starting at ~2 am MST. Bandwidth 3.1 MHz with 127 spectral channels. PKS

rms = 10 mJy/bm/ch Hardly any RFI.

RFI: D-configuration D-conf.B-conf. PKS

z= (HI frequency at ~1019 MHz). Total time 1.5 hours (~75% on target) in C- configuration starting at ~12 noon MST. Bandwidth 1.56 MHz with 255 spectral channels. QSO

rms = 20 mJy/bm/ch RFI-clean data set.

Summary Successful L-band observations were carried out with the EVLA at frequencies down to 1019 MHz. The RFI environment had a marginal or no effect for night-time observations and/or extended configurations. These results show that the EVLA, with its new L-band capabilities, will become a major player in spectral-line observations down to ~930 MHz (z HI ~0.53).