The VLA Low-band Ionospheric and Transient Experiment (VLITE)

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1 The VLA Low-band Ionospheric and Transient Experiment (VLITE) Walter Brisken (NRAO/UMN) Tracy Clarke (NRL) DiFX Workshop November 2014 Bologna, Italy

2 National Radio Astronomy Observatory s Very Large Array 330 MHz dipoles installed on VLA in 1990, and in regular use until MHz dipoles partially deployed in 1991, complete system in use from 1998 to 2009 Both the systems were developed through cooperation between NRAO and NRL code 7213 Systems were decommissioned by the VLA upgrade in 2009 Hicks et al. (2006) 2

3 NRL-Developed Wideband Low Frequency Receivers NRL-developed broadband low frequency receiver. NRL worked with NRAO to develop a new broadband low frequency receiver to replace the old narrow-band system Full system first light was May 2012 and system has been in operation on the VLA since that date In May 2013 Code 7213 proposed to develop a commensal low frequency software correlator backend for nearly continuous monitoring of ionospheric and transient events tapping into the new low frequency receivers VLITE: VLA Low Band Ionosperic and Transient Experiment Hicks et al. (2006) 3

4 VLITE: Overview VLITE is a new commensal backend on the NRAO VLA MHz It74 uses dedicated samplers, fiber transmission, and a dedicated backend software correlator to tap into the low band receivers on 10 VLA antennas VLITE samples a bandwidth of 64 MHz, centered on 352 MHz and provides a temporal resolution of 2s 330 and MHz spectral resolution of 100 khz VLITE will operate on all PI-driven observations at 1 GHz and above and is expected to produce several thousand hours of commensal P band data per year of operation VLASS will cover entire sky > -40d Right: One year of VLA pointings (>3000 hr) shown for the 330 MHz primary beam. This would cover 25% of the VLA sky. Total: >3000 hr 1 hr Hicks et al. (2006) 4 10 hr 100 hr

5 VLITE: Scientific Drivers Ionosphere: high resolution remote sensing of the Earth s ionosphere to 74 MHzcoupling mechanisms of fine, medium and large scale ionospheric study dynamics Transients (slow): searches of large (2.5 ) FoV for transients on time scales of 2s to 1 hour in real-time 330 MHzplus off-line searches for longer term transients Astrophysics: off-line process will provide sensitive simultaneous imaging for spectral studies, source size, extended emission properties etc for nearly all PI-driven science programs VLITE image of a 6 field around 3C286 showing VLITE in red, NVSS in blue and VLSS in green. Note the large number of sources seen well outside the 5 primary beam. This shows the power of VLITE for transient searches. VLITE image of the Tycho SNR made from a PI-driven observation.

6 VLITE: Current Status VLITE has undergone rapid deployment: 74 MHz System Requirements Review November 2013 Preliminary Design Review December 2013 Critical Design Review April 2014 MHzin June 2014 First system deployed on330 the VLA First light fringes: July 17, 2014 Single target field image: July 29, 2014 (5 antennas) Multi-target field image: August 8, 2014 (5 antennas) Full 10 antennas outfitted on the VLA September 1, 2014 Scientific and Technical Commissioning June November 2014 Full operations anticipated at end of commissioning For more information on VLITE contact: Namir Kassim (VLITE PI and transient pipeline) Tracy Clarke (VLITE Commissioning and astrophysics pipeline) Joseph Helmboldt (Ionospheric science) 6. Above: VLITE First Light Fringes on a QSO. VLITE image (red) of Crab nebula with Chandra in blue.

7 . VLITE Images 74 MHz 330 MHz VLITE module in VLA antenna. 3 Degrees Blue circle shows FWHM of VLITE PB. Note the large number of sources imaged well outside the beam. 7 First multi-source image of targets separated by 1.5. VLITE FoV is 2.5.

8 VLITE Technical Details 10 Antennas Dual pol: X/Y (really H/V!) 64 MHz bandwidth (320 to 384 MHz) Pointing / scan definitions based on VLA observing

9 VLITE Design Decisions Send data as UDP packets to correlator but receive them as raw packets Allows other software (e.g., transient search) to get another copy without any userspace interaction libevent is at the core of the vlite-executor application Found to be an excellent base for event-driven (packets, timers, interrupts, file i/o, ) software

10 DiFX changes required for VLITE Raw socket datastream input Vex2difx notation (example): networkport=eth2 # physical ethernet port WindowSize=42 # number of bytes to strip from beginning of each packet (42 for UDP) Datastream processes must run as root! sudo inside mpifxcorr wrapper does this Currently VDIF only X/Y polarization support Just a couple trivial changes needed This is not support for translation to R/L or for correlation of R/L with X/Y. It is just propagation of the labels through the system!

11 VLITE Correlator quirks Cleanly killing mpifxcorr quickly, cleanly is not reliable: using drastic measures now Sometimes one antenna gets weird patterns in weights (image courtesy Wendy Peters)

12 VLITE DiFX Correlator Overview vlite-difx1 40 Gbps Infiniband network Antenna V0 Each signal is up to 128 MB/s on 10 GbE Antenna V1 Output data: 600 kb/s on 10 GbE vlite-master To post-processor Antenna V8 Antenna V9 vlite-difx5

13 Low-Band Observatory (LOBO) DiFX Correlator The logical conclusion of the VLITE development path RCP LCP Subband 0 RCP Subband 1 LCP Node 0 A pair of 56 Gbps Infiniband networks Node 1 Antenna 1 RCP LCP Antenna 2 Subband 0 RCP Subband 1 LCP Node 2 Output data: 150 MB/s each subband on 10 GbE Node 3 Each signal is up to 512 MB/s on 10 GbE Node 54 (RCP+LCP could share a fiber if needed) Node 55 To post-processor RCP LCP Antenna 27 Subband 0 RCP Subband 1 LCP Node 52 Node 53 VFASTR Processor