A First Look At VERITAS Data Stephen Fegan Vladimir Vassiliev UCLA

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Data Analysis Flowchart Image conditioning. Geometry reconstruction. Event parameterization. Energy reconstruction. Data Selection.  Independent telescope parameters.  Array. Results. Standard approach. Picture/boundary cleaning. Has not been optimized. Has not been investigated. Array cuts, based on combining the various parameters from all images have not been investigated. To be investigated… Methods 1&2 from reconstruction memo of December. Parameterization from memo also. Cuts based on individual telescope images using parameters from memo. Simple “box” shaped cuts and multi- dimensional cuts using “NSpace”

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Geometry reconstruction Method1: fit arrival direction and core from individual image axes, weighted “appropriately”. Method 2: Fit single shower axis to all images simultaneously. This axis is projected onto focal plane of each telescope. Method 3: Fit single shower axis to all images simultaneously. This axis is defined in real 3D space. Methods 1 and 2 give comparable results with two telescopes. Method 3 has not been investigated.

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Event parameterization Once the shower axis has been reconstructed each image can be mapped into “physical space”, giving: 1)Mean emission height and track length. 2)Depth s of mean emission in atmosphere in g/cm 2. 3)Mean angle of emission with respect to trajectory. 4)Physical width of emission region. 5)Dispersion s in photon arrival times assuming emission along primary trajectory.

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Data selection Simple cuts on parameters in Dec. memo:  Log 10 (size) > 2.5  Emission region width< 15m  Emission height> 5000m  Emission length> 750m Simulations suggest cuts should be energy dependent. Studies using n-dimensional cutting system NSpace 1 is ongoing. Preliminary results discussed here. 1 See T. Nagai’s thesis for write up of NSpace methodology

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Results: Mrk 421 – 9 pairs Background rate of 16.4/min/deg 2 based on θ<0.2° (SIMPLE CUTS) Significance 29σ, rate 5.76/min

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Results: table of Mrk421 pairs RunDurationONOFFRateSignificance TOTAL (SIMPLE CUTS)

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Results: Mrk 421 – 10 wobble at 0.3° Theta 2 distribution with respect to source position Theta 2 distribution with respect to symmetric wobble position Source counts as they appear from off source location. No obvious spill over to theta=0 area. Wobble offset of 0.3º seems to be sufficient. (SIMPLE CUTS)

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Results: table of Mrk421 wobble runs RunDurationONOFFRateSignificance TOTAL (SIMPLE CUTS)

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Results: strong source optimization Photon dominated regime: For strong source, optimize theta cut for significance. Peak is quite broad. Theta cut from 0.15° to 0.25° gives high significance. We chose 0.2° for high rate. 9 Mrk421 pairs (SIMPLE CUTS)

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Results: weak source optimization Background dominated regime: For weak source optimize theta cut for excess/sqrt(background) – Q- value. Shown is Q-value, normalized to 1 at theta=1. Peak is much narrower. Theta cut from 0.12° to 0.16° gives best significance on weak sources. 9 Mrk421 pairs (SIMPLE CUTS)

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Results: Mrk421comparison with Whipple VERITAS Run VERITAS Rate VERITAS Significance Whipple Run Whipple Rate Whipple Significance Whipple results from J. Kildea 2 VERITAS and Whipple run numbers are similar after 40 years of Whipple operation (SIMPLE CUTS)

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Results: Mrk501comparison with Whipple VERITAS Run VERITAS Rate VERITAS Significance Whipple Run Whipple Rate Whipple Significance Whipple results from J. Kildea (SIMPLE CUTS)

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Results: aperture function Cosmic-ray acceptance as a function of off-axis angle, after cuts. These events are the most gamma-ray like CRs. Gamma-ray response will likely be somewhat similar. Quite flat to 0.8 degrees. Fast decline at 1.75 degrees (SIMPLE CUTS)

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev NSpace: basic ideas Form multi-dimensional histogram in space defined by event parameters. Fill two histograms: from ON & OFF runs or from SIM & OFF data. Order cells “according to significance (likelihood,…)” (many ordering schemes possible). Make “filter” by picking cells from ordering to maximize total significance (likelihood,…). Repeat all steps above varying bin sizes of the histogram until significance (likelihood,…) is maximized. Bin sizes and histogram dimension are your optimization parameters. Final filter is an effective volume in multidimensional space. Cut ON events according to whether they are inside or outside the filter.

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev NSpace: example in two dimensions log(size) width ON counts OFF counts Highest single cell significance(4.7 sigma) Two cell set with highest overall significance (6.5 sigma) Seven cell set with highest overall significance (9.9 sigma). Thereafter adding any more cells decreases significance.

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev NSpace: single telescope space Space based on three single telescope parameters:  Log 10 (λ c )*12 bins no 4 – 8  Emission width20 bins no 0 – 40 m  Emission depth10 bins no 0 – 1000 g/cm 2 ON histogram: 9 Mrk421 runs – theta<0.2 OFF histogram: 9 Mrk421 runs – theta<1.0 Optimize filter on T1 parameters Apply to both T1 & T2 when cutting * λ c : density of emitters in coherent regime [m -1 ], see December memo for details

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev NSpace: optimization results Filter with 70 cells gives close to the peak Q-value and gives good rate For comparison, straight cuts have Qmax=6 (with theta cut of 0.16°)

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev NSpace: optimization results Filter with 70 cells gives close to the peak Q-value and gives good rate For comparison, straight cuts have Qmax=6 (with theta cut of 0.16°)

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev Straight CutsNSpace Cuts Data SetONOFFRateSigmaONOFFRateSigma 9 Mrk421 Pairs Mrk421 Wobble Mrk501 Wobble Faint source improvement not as large as indicated from optimization ( =1.76 vs =1.51). This reflects some degree of “tuning” of space to specific runs used in optimization. NSpace: comparison with straight cuts (NSpace with theta cut of 0.15°) (Straight with theta cut of 0.14°) 1 Optimization done on these runs Bright source significance is approximately equal with this NSpace filter but rate is lower. A theta cut of 0.2 gives better significance and rate for both sets of cuts.

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev NSpace: 10 Mrk421 wobble runs Background rate of 5.0/min/deg 2

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev

RunDurationONOFFRateSignificance TOTAL NSpace: results for Mrk501 wobble 1 Using traditional Gaussian significance formula (somewhat inaccurately) If Crab is 5  /min then 4% Crab in 5  or 18% Crab in 5  HESS claimed 11% Crab in 5 

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev NSpace: 501 comparison with Whipple VERITAS Run VERITAS Significance VERITAS Rate Whipple Run Whipple Significance 1 Whipple Rate Whipple results from J. Kildea (NSpace)

VERITAS Collaboration Meeting June 29, 2006, Leeds, UK A First Look At VERITAS Data Stephen Fegan & Vladimir Vassiliev NSpace: future work Preliminary optimization done quickly for meeting, need to look in detail at:  Ordering strategy  Array/Energy parameters  Bin size optimization  Parameter choice/Dimension Optimization 9 runs are not enough to do filter selection properly. Need lots of CRAB data and/or simulations. NSpace provides flexible and robust frame of work for data analysis including detailed spectrum analysis. Optimistic about success of this method!