Status of GRB Scaler Analysis

1. Status of GRB Scaler Analysis David Williams Taylor Aune

2. 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 GRB Scaler Analysis — Milagro Collaboration Meeting

3. Scaler 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 GRB Scaler Analysis — Milagro Collaboration Meeting

4. Time 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 GRB Scaler Analysis — Milagro Collaboration Meeting

5. Effective 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 used • Calculate effective area in bins of and interpolate linearly in log Aeff vs. sec  for each burst • Scale effective area down by fraction of PMTs which actually are live and used for a given burst • Tubes 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 GRB Scaler Analysis — Milagro Collaboration Meeting

6. Fluence Upper Limits • Assume an unabsorbed spectrum of dN/dE ~ E-2 from the source • Calculate 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) unabsorbed z = 0.1 z = 0.5 z = 1.0 z = 2.0 GRB Scaler Analysis — Milagro Collaboration Meeting

7. Fluence 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 GRB Scaler Analysis — Milagro Collaboration Meeting

8. 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 GRB Scaler Analysis — Milagro Collaboration Meeting