Status of GRB Scaler Analysis David Williams Taylor Aune.
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Transcript of Status of GRB Scaler Analysis David Williams Taylor Aune.
Status of GRB Scaler AnalysisStatus of GRB Scaler Analysis
David WilliamsDavid Williams
Taylor AuneTaylor Aune
April 21, 2007GRB Scaler Analysis — Milagro Collaboration Meeting 2
ContributorsContributors
Work of Eitan Anzenberg – Senior Thesis (on Memo’s page)
– Memo on pressure and temperature corrections
Monte Carlo data for low energy (500MeV – 5GeV) generated by Vlasios Vasileiou
GRB Catalog from Pablo Saz Parkinson
April 21, 2007GRB Scaler Analysis — Milagro Collaboration Meeting 3
Scaler AnalysisScaler Analysis
Nothing fancy - no individual events are reconstructed
Record aggregate counts from each PMT each second
Increased sensitivity to lower energy events (< 100 GeV)
Spatial and spectral resolution of a source is impossible
Check for an increase in counting rates above background coincident with satellite-detected GRBs
April 21, 2007GRB Scaler Analysis — Milagro Collaboration Meeting 4
Time ResolutionTime Resolution
Whether two hits on same channel overlap depends on ToT– At threshold: ≥35 ns separation needed for low; ≥53 ns separation for high
– Longer separations needed for larger pulses
• E.g at high threshold, ≥188 ns separation needed for two low threshold hits
– Multiple hits on same channel not a bit effect
– Only consider 0 or 1 hits per channel at each threshold
• Small underestimate of Aeff –> higher flux limit
Whether two hits on different channels in an OR’d group overlap is pulse height independent– ≥25 ns separation needed for low– ≥46 ns separation needed for high– Hits with less separation overlap and extend OR’d pulse– Sort list of hits within each group and determine number of resolved
counts based on minimum separation
April 21, 2007GRB Scaler Analysis — Milagro Collaboration Meeting 5
Effective Area CalculationEffective Area Calculation
Two Monte Carlo data sets:– Standard 5 GeV – 500 TeV, E-2 gamma-ray files– Special 500 MeV – 5 GeV, E-2 gamma-ray files
Basically just counting hits– Modified version of CalibrateMC2.c
Calculate effective area assuming all PMTs are live and usedCalculate effective area in bins of and interpolate linearly in
log Aeff vs. sec for each burstScale effective area down by fraction of PMTs which actually
are live and used for a given burstTubes excluded are both those known to be dead from the
EMS data, and those that are members of the OR groups that were excluded earlier because of bad behavior
April 21, 2007GRB Scaler Analysis — Milagro Collaboration Meeting 6
Fluence Upper LimitsFluence Upper Limits
Assume an unabsorbed spectrum of dN/dE ~ E-2 from the sourceCalculate limits on the fluence (5 - 50 GeV):
– For sources with estimated z, use that.
– Otherwise use four generic redshifts:
• 0.1, 0.5, 1, 2
Take into account the absorption from the EBL (Primack ‘05)
unabsorbedz = 0.1z = 0.5z = 1.0z = 2.0
April 21, 2007GRB Scaler Analysis — Milagro Collaboration Meeting 7
Fluence Upper LimitsFluence Upper Limits
In the current GRB catalog, we have 17 bursts with “known” z. Of those, 11 have z<3.
Fluence upper limits range from 6.9 x 10-6 to 0.2 ergs/cm2
These limits are comparable to those of ARGO-YBJ and those predicted to be obtained with Auger
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
April 21, 2007GRB Scaler Analysis — Milagro Collaboration Meeting 8
Work to be done…Work to be done…
Incorporate the low energy (500 MeV - 5 GeV) monte carlo data
Clean up the code, potentially add a scaler specific histogram function to milinda
Add the GRBs from the last few months
Recalculate fluences using the low threshold muon layer - currently seems to have comparable sensitivity to the air shower