STACEE status report

1
STACEE status report
Presented to SAGENAP panel, April 15, 2004
Washington, DC K. Ragan McGill University,
Montreal for the STACEE collaboration

• Presentation of experiment
• Science issues goals
• Detector status
• Recent results
• Outlook/Conclusions

2
Presentation of Experiment

• STACEE is based at Sandia National Labs,
  Albuquerque NM
• uses 64 heliostats of the National Solar Thermal
  Test Facility (NSTTF) and custom secondary optics
  to capture Cherenkov light on PMT cameras

Size of heliostat field well matched to Cherenkov
footprint on ground
250 m
(HESS diagram)
3
Presentation of Experiment

• NSTTF is a user facility and we incur costs to be
  present and active there. Currently costs are
  approx. 100/hour for heliostat usage
• Heliostats are well maintained time lost to
  malfunctioning is small (although non-zero!)
• Currently retro-fitting heliostats with more
  rapid motors for GRB response.

4
Presentation of Experiment
Three 1.9m secondaries on 260 level have 16-PMT
cameras
tessellated secondary (1.9 m diameter)
PMT camera
Two 1.1m secondaries on 220 level have 8-PMT
cameras
5
Presentation of Experiment

• custom delay trigger electronics designed to
  capture events in programmable window (8-16 ns)
• full FADC waveform digitization on each channel
  at 1 GHz (more later)

custom delay/trigger (8 channels per board)
Commercial (Acqiris) FADC modules (4 channels per
board)
6
Presentation of Experiment

• Also dedicated atmospheric monitoring station,
  with
• PMT-based photometry
• CCD for autoguiding
• infrared radiometers
• weather station
• data stream 64 waveforms containing full timing
  and amplitude information, plus
• GPS timestamp
• PMT currents rates
• Heliostat position data
• Atmospheric monitoring data

7
Presentation of Experiment

• Due to large mirror area, STACEE achieves lower
  energy threshold than imagers is sensitive
  below 100 GeV
• This will continue to be an important niche in
  the early VERITAS/GLAST era

Simulation of response to Crab flux
threshold
8
Presentation of Experiment

• The STACEE Collaboration
• Alberta Gingrich 1 MSc student
• Barnard/Columbia Mukherjee 1 PhD student
• Case Western Covault 2 post-docs (Driscoll,
  Colombo)
• McGill Hanna Ragan post-doc (Kildea) 4
  students (3 PhD, 1 MSc)
• UCLA Ong research scientist (Zweerink) 2 PhD
  students
• UCSC/SCIPP Williams

9
Presentation of Experiment

• STACEE Milestones
• 1997 SAGENAP presentation first STACEE funding
• 2000 detection of Crab nebula with 32-channel
  instrument at 190 GeV threshold (ApJ 547, 949
  (2001))
• 2001 detection of Mrk421 flare with STACEE-48
  (ApJ 579, L5 (2002))
• 2002 full STACEE-64 commissioned
• 2003 WComae upper limit at 130 GeV threshold
  (ApJ in press)
• 2004-2006(7) Continued operations
• Results published in ApJ and ApJL, as well as
  numerous conference proceedings. Three technical
  papers in NIM.
• Four PhDs, four MScs graduated 6 more PhDs
  2 MScs in pipeline numerous undergraduates
  trained.

10
Science Issues and Goals

• STACEE targets are primarily AGNs, pulsars, GRBs
  but also EGRET UnIDs. Some clear questions
• AGN
• nature of primary particles (leptonic or
  hadronic?)

F. Halzen
11
Science Issues and Goals

• exploration of EBL absorption effects, primarily
  through multi-wavelength campaigns

Absorption exp(-tau)
g Energy
12
Science Issues and Goals

• pulsars
• energy of cutoff of pulsed component (polar cap
  vs. outer gap)?
• GRBs
• maximum energy of burst emission
• luminosity and energy evolution during afterglow

13
Science Issues and Goals

• EGRET UNIDs
• most EGRET sources are unidentified
• huge potential here for study for example,
  recent HEGRA observation of TeV2032 may be
  archetype of cosmic ray nursery

STACEE can address all of these issues with its
unique sensitivity at Elt100 GeV !
HEGRA (Astron. Astrophys. 393 (2000) L37
14
Detector Status

• Current status
• STACEE-64 fully constructed by late 2001
• FADCs fully installed in late spring 2002
• first full season with complete detector
  configuration 2002-2003
• large data samples on AGNs, Crab
• Crab optical pulsar observed to confirm timing
• still on learning curve with FADCs
• padding to account for field darkness
  differences
• in-situ gain measurements
• advanced reconstruction techniques

15
Detector Status

• Crab pulsar is an exciting target in STACEE
  energy regime
• we took special data to observe optical pulsar
  and confirm absolute timing

(HST data)
light pollution _at_ 120 Hz
non-Cherenkov data filtered to remove high-freq
components
16
Detector Status

• digitize PMT anode current at 10 kHz, GPS time
  stamp periodically, fold at known ephemeris of
  Crab

STACEE phase diagram
STACEE phase diagram (simulation)
Observation of optical pulsar confirms both
absolute timing and optical throughput
17
Detector Status
FADC information vastly more powerful than
previous TDC ADC combination, and we are still
on learning curve here
One channel
discriminator threshold
nominal trigger position
18
Detector Status
Stars (no excess expected)

• Eg, padding to account for field darkness
  differences
• excess night sky background (due to different
  star fields) in ON or OFF can compromise ON/OFF
  comparison can mimic g signal or hide it, by
  promoting sub-threshold events

Average On-Off current difference
19
Detector Status

• excess light leads to larger current, and to
  larger variance of baseline in AC-coupled PMT
  traces
• critical to correct for this with padding
  adjustment of lower light data by addition of
  noise
• so make library of NSB pulses
• catalogue them as a function of variance (aka
  current)
• use them to pad lower-light-level data to
  variance/current of noisier data
• FADC data are essential
• it works !

20
Detector Status
Schematically
off-source trace

NSB library trace
on-source trace
Do this channel-by-channel then reimpose trigger
and do direct on-off comparison
padded trace

21
Detector Status
Advanced reconstruction techniques using full
waveform information also promise superior
directional and energy reconstruction
Assuming shower core at array center
Using full waveform information to reconstruct
shower core
22
Detector Status
Both 2002-2003 and 2003-2004 seasons concentrated
on detector studies, Crab, and AGN data
23
Detector Status
Details for current 2003-2004 season

1. EGRET source extreme BLL multi-wavelength
   campaign with RXTE VERITAS as well as lower l
   first such comprehensive broadband campaign to
   our knowledge contemporaneous data will provide
   input to modelers higher z, so possible EBL
   information
2. Standard Candle pulsar energy limit spectrum
   both worthy goals
3. EGRET source, with moderate z, CG predictions
   best source available in this RA range
4. Well studied, EGRET source detected by ACT incl.
   STACEE useful for instrument studies if flaring
   and contemporaneous data with VERITAS
5. Hard EGRET spectrum LBL well-measured in X
   detailed predictions for both electronic SSC and
   proton models
6. XBL, not EGRET source TeV flux predicted from
   X-ray data, found by ACT,
7. Similar to Mrk421, likely data if in flaring
   state.
8. Predictions 7 prompt follow-ups per year in
   SWIFT era. GRB _at_ 100 GeV would be seminal !

Active participation in multi-l campaigns, ToOs,
GCN alerts
24
Detector Status
GRB data acquired
GRB UTC Time Spacecraft Notice Delay (minutes) Time until Observable by STACEE (hours) STACEE Observations
021004 120614 HETE 0.8 14.1 None
021112 032816 HETE 81 3.2 Starting 219 minutes after burst 112 minutes on burst position
021211 111834 HETE 0.4 0.0 None bad weather
030115 032234 HETE 71 8.4 None full moon
030227 084216 INTEGRAL 48 17.7 None
030324 031243 HETE 0.4 2.0 Starting 123 minutes after burst 56 minutes on burst position
030328 112058 HETE 53 16.7 None
030329 113715 HETE 73 15.2 None
030417 062420 INTEGRAL 0.2 gt24 None
030418 095919 HETE 3.6 17.2 None
030501A 031019 INTEGRAL 0.3 4.6 Starting 369 minutes after burst 28 minutes on burst position
030519 140454 HETE 0.6 Infinite None
030528 130303 HETE 0.6 17.6 None
030722 110246 INTEGRAL 0.2 gt24 None
030723 062818 HETE 0.8 Infinite None
030824 164735 HETE 60 11.7 None
030913 170658 HETE 0.6 9.9 None full moon
031015 192346 INTEGRAL 0.2 gt24 None
Bursts from 9/01/02 through 10/31/03 with alert
within 90 of burst
25
Detector Status
Other, more speculative sources possible in
future

1. EGRET source with photons gt 30 GeV AGN at
   unknown redshift competes with Crab
2. Most persistent EGRET UnID Chandra X-ray
   position postulated Geminga-like (radio-quiet)
   pulsar
3. EGRET pulsar SNR CTB80
4. Non-EGRET XBL CG TeV flux predictions
5. First TeV-discovered source extended confused
   region possibly OB-association, postulated as
   archetype of cosmic-ray production regions
6. Low z EGRET source IBL 3C66A-like not seen
   by ACTs
7. Non-EGRET AGN, seen by ACTs XBL 421-like
   spectrum measurement desirable.

26
Recent Results

• W Comae (aka ON231)
• z0.102 EGRET blazar with hard spectrum,
  consistent with power law of a1.73 /- 0.18
• undetected by imagers (at Egt300 GeV)
• extensively studied at X-ray energies
• nice test case for leptonic vs hadronic models
  of blazar emission
• leptonic models predict emission cuts off below
  100 GeV
• hadronic models allow emission to significantly
  higher energies

27
Recent Results

• W Comae data
• STACEE acquired data on WComae in Mar-Jun 2003
• 34 ON-OFF pairs, 13.5 ON-source hours
• after quality cuts on heliostat pointing,
  stability of L1 trigger rates, and DAQ
  performance 10.5 hrs ON-source
• raw ON-excess at 4.6s level but typically 1-2
  mA current excess in ON data
• library padding reduces ON excess to 0.88 s,
  consistent with no emission
• derived 95 UL on flux is typically
• 0.5-1.0x10-10cm-2 s-1
• at threshold energy of 130-160 GeV
• result accepted for publication in ApJ, June
  2004

28
Recent Results

• Resulting upper limits

proton synchrotron models, with low and high
EBL absorption
EGRET power-law
STACEE data is starting to constrain models
29
Recent Results

• 1H1426428
• z0.129 BL Lac
• unobserved by EGRET
• detected by imagers (HEGRA, CAT, Whipple) at
  Egt300 GeV, data consistent with power law (a
  3.5)
• STACEE took 22 ON/OFF pairs in Apr-July 2003
• 10 ON-source hours in raw-data
• 7.5 ON-source hours after quality cuts (helios
  L1)
• no padding done (ON-OFF current diff. lt 0.5 mA)
• 2.9 s excess ON-source
• this data will be start of large multi-yr data
  set on 1H1426428

30
Recent Results

• Resulting upper limit (preliminary)

Petry et al. 2002
31
Recent Results
These results already constrain some EBL
absorption models
32
Outlook/Conclusions

• STACEE is fully operational taking data, doing
  science
• We continue to improve our understanding of the
  data and the power of the FADC system
• Many sources still to be investigated in STACEEs
  unique energy regime
• Normal operations will continue until mid-2006 to
  the threshold of the VERITAS/GLAST era
• Further running beyond mid-2006 will be
  contingent on STACEE results and evolution of
  VERITAS/GLAST.