EVLA L-Band Spectral-Line Science Below 1200 MHz

Emmanuel MomjianNRAO-Socorro

The VLA @ L-band

• The VLA L-band system has:– OMT bandwidth of 1200-1800 MHz.– LNA bandwidth of 1200-1800 MHz.– Post-Amp bandwidth of 1200-1800 MHz.

• VLA antennas can tune between 1225 and 1900 MHz.

The VLA @ L-band

Perley & Hayward 2008

The poor sensitivity windows are caused by resonances within VLA’s dielectricphase shifter and/or microwave lens.

• The VLA can also tune between 1100 and 1225 MHz, but with limited capability.

The EVLA @ L-band

• EVLA antennas will tune between 930-2000 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 (960-1200 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=0.2467 (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 1413+135

PKS 1413+135RFI

Short baseline Intermediate baseline Long 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 1413+135

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

RFI: D-configuration

Baseline 16-17~ 60 m

PKS 1413+135

B-conf.

D-conf.

• z=0.3127 (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 1127-145

PKS 1127-145

rms = 10 mJy/bm/chHardly any RFI.

RFI: D-configuration

D-conf.B-conf.

PKS 1127-145

• z=0.3941 (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 0248+430

QSO 0248+430

rms = 20 mJy/bm/chRFI-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 (zHI~0.53).