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Status of GRB Scaler Status of GRB Scaler Analysis Analysis David Williams David Williams Taylor Aune Taylor Aune

Status of GRB Scaler Analysis

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Status of GRB Scaler Analysis. David Williams Taylor Aune. Contributors. 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. - PowerPoint PPT Presentation

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Page 1: Status of GRB Scaler Analysis

Status of GRB Scaler AnalysisStatus of GRB Scaler Analysis

David WilliamsDavid Williams

Taylor AuneTaylor Aune

Page 2: Status of GRB Scaler Analysis

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

Page 3: Status of GRB Scaler Analysis

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

Page 4: Status of GRB Scaler Analysis

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

Page 5: Status of GRB Scaler Analysis

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

Page 6: Status of GRB Scaler Analysis

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

Page 7: Status of GRB Scaler Analysis

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.

Page 8: Status of GRB Scaler Analysis

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