Dave Kieda* for the VERITAS Collaboration *University of Utah Department of Physics & Astronomy

☞ Square Array of Four 12m Ø optical reflectors (Amado, AZ) ☞ Each Telescope: 499 Pixel PMT camera, 500 Mhz FADC readout ☞ Detects Very High Energy (VHE) gamma-rays ( eV) ☞ Fully operational since May 2007

132 known Sources (doubled since 2007) VERITAS has discovered a large fraction of the new VHE sources New Source discovery requires continually increasing VERITAS sensitivity => Reduction in threshold energy can allow access to new science

A.McCann, 2012 ICRC Sensitivity < 100 GeV can help connection to FERMI pulsars… 120 GeV Gap

✪ ✪ ✪ ✪ ✩ Rearrange Telescopes to Better Geometry (SAO, U. Utah + collaboration) ✩ Higher sensitivity Photomultiplier Tubes (Purdue, U Delaware, U. Utah, Wash U, UCSC) ✩ Faster Pattern (Level 2) Trigger (Iowa State U, Argonne NL) ✩ Communication (Fiber Optic) Network Upgrade (SAO, U. Utah) 2.1 M$ MRI-R2 funded project (National Science Foundation, University of Utah) Main cost is the new photomultiplier tubes (1.2 M$)

Current: Photonis PMT XP2970 ~18-22% peak QE New: Hamamatsu PMT R10560 ~34-40% peak QE $495 each (x 2200) = $1M

Nepomuk Otte 2012 ICRC Talk XP2970 Photonis

VERITAS Upgrade results in increases in effective detection area. Largest gains are at the lowest energies (E< 100 GeV) Conservative estimate

Use E -2.5 source spectrum Peak energy: 95 GeV before upgrade 70 GeV after upgrade Conservative estimate

L2 Hardware Overview and Timetable J. T. Anderson – VERITAS Collaboration Meeting – January 22 nd, L2 Pattern Design Concept Camera trigger processing is done in custom 9U VME Crate –Camera pixels (discriminated bits) received by I/O cards –Pixels of camera face mapped into regions using custom backplane –Pixels at boundaries between regions duplicated to insure no gaps in logic Divide 499 channel camera into 3 regions –~166 pixels per region + ~15 overlap pixels/region Each region processed independently by its own “L1.5” region processor –Potential gamma events identified by 3-fold coincidence of neighboring pixels sampled at 400MHz –All such coincidences occurring are reported to telescope- wide L2 processor (timestamp + list of hits) L2 processor combines data from L1.5 processors –All L1.5 data sets within selected time window are merged together –Any coincidence generates trigger to L3 –Capable of performing calculations required to feed a topological trigger algorithm –System controller 3-Fold Coincidence; center plus any two of surrounding 6 PMT Afterpulsing: Need 4-fold Coincidence

L2 Hardware Overview and Timetable J. T. Anderson – VERITAS Collaboration Meeting – January 22 nd, 2010 Trigger performance – Test Stand Timing Alignment 12 This shows the timing variation in the test stand system before timing is aligned (log scale, +/-5ns). Color indicates relative delay. Green is “median”. Blue is “early”. Red is “late”. Note: each pixel has multiple measurements taking into account every coincidence equation in the logic. All raw data is saved. Color displays are average of all measurements for that pixel.

L2 Hardware Overview and Timetable J. T. Anderson – VERITAS Collaboration Meeting – January 22 nd, 2010 Trigger performance – Test Stand Timing Alignment 13 This shows the timing variation in the test stand after timing is aligned (log scale). Color indicates relative delay. Green is “median”. Blue is “early”. Red is “late”. The two gray pixels were manually disabled (cable issue).

Factor of ~2 reduction in time to see 10 mCrab source since 2007 (48 hr -> 26 hr) New Hi-QE PMT (>34%), faster pattern trigger system: 2012 (26 hr -> < 20 hr for a 10 mCrab source) Increased Sensitivity, especially < 100 GeV: Bridge E gap to FERMI Pixel design/testing complete, fabrication underway Pattern Trigger testing nearing completion: all tests passed Upgrade Project is on time, under budget September/October 2011: Pattern Trigger Installation Summer 2012: High-QE PMT Installation (all 4 telescopes) September 2012: VERITAS – II begins operations

Total Upgrade Cost $2.1 M (Funded by NSF MRI-R2 grant) Major cost item is Photomultipliers ($1.1 M)