IC59+40 Point Source Analysis Mike Baker, Juan A Aguilar, Jon Dumm, Chad Finley, Naoko Kurahashi, Teresa Montaruli 12 May 2011 http://wiki.icecube.wisc.edu/index.php/ic59+40_point_source_analysis
Goals We would like to unblind the IC59 dataset and perform searches from IC40 by UW PS group on the combined IC40+59 dataset: Time-integrated: all-sky scan & source list - Remove IC22 hotspot from the list, add Tycho SNR also discussion of re-adding several microquasars. Time-dependent: triggered flare search with Fermi lightcurves & untriggered flare all-sky scan Still in progress, unblinding requests to come: Stacking and extended source searches, microquasars & IACT triggered flare search. Also of interest is a plan for an all-sky scan for extended sources. 2
IC59 Data Sample - May 20, 2009 to May 31, 2010-348 days of livetime out of 375 days running - 93% of data used in analysis For comparison, IC40 had 375 days of livetime with 92% of data used in analysis. Level 3 3
Intro to PS analysis Use an unbinned maximum-likelihood analysis to test for a clustering of events in space. Energy information is also used to give more weight to high-energy events. A sample of atmospheric neutrinos in the upgoing region and high-energy atmospheric muons in the downgoing region are obtained from the method of event selection. P-values for all analyses are obtained by comparing the data to samples scrambled in azimuth and time. 4
Upgoing region Two sets of cuts were tested: A machine learning algorithm (BDT), trained using the data as the background sample. We also tested a manual event selection based on simple cuts (Straight Cuts) on reconstruction quality parameters, similar to that used in IC40. 5
Boosted Decision Tree In order to improve signal efficiency at lower energies, we have trained BDTs with both an E-2 and an E-2.7 signal spectrum (bdtlow and bdthigh, respectively). The training is performed in the same way in both cases, taking two trees with different variables and combining the results. We require: bdtlow > 1.45 or bdthigh>1.4. http://wiki.icecube.wisc.edu/index.php/ic-59_ps_bdt 6
Boosted Decision Tree We find the machine learning algorithm gives an effective area (right, all up-going zeniths) which is above that achieved from the manual selection at all energies. Below right is the angular error distribution. For E-2 spectrum events 50% are reconstructed within 0.7 degrees of the true angle. Dashed SC Solid BDT Red E^-3 Blue E^-2 7
IceTop veto In the downgoing region, we can use information from IceTop to reject atmospheric muons that hit IceTop. Follow the InIce track to the surface, and calculate the time residual of the IceTop hits from a shower from the track. Then count the number of hits in IceTop compatible with being from the shower. 8
IceTop veto The veto becomes more effective at vertical angles. IceTop information from data events is used to simulate uncorrelated noise for signal simulation. Requiring 2 or more SLC hits in IceTop retains 99% of neutrino downgoing signal. 9
IceTop veto No Veto In the downgoing region we use an zenithdependent energy cut to select a constant number of muons per unit solid angle. The IT veto allows us to loosen this energy cut in the region from vertically downgoing to a zenith of 30 degrees. Use Veto 10
Comparison of BDT to Manual Selection BDT Straight Cuts E-2 nu efficiency (wrt L3 up-going) 58% 48% Atm nu eff. (wrt L3 up-going) 27% 20% Events per Day (up-going) 120 90 Events per Day (down-going) 170 150 Atm. Muon Contamination (up-going) 4.7% 4.5% Total Events (up-going) 43339 29856 Total Events (down-going) 64230 57471 11
Systematic Errors We will estimate the signal selection efficiency using dedicated simulation with variations of the ice scattering and absorption and DOM efficiency in a plausible range. 12
Combining Datasets The challenge in combining datasets is how to split up the signal fraction. The spectrum is the same in all combined samples. Ratio of effective areas isn't constant, so the relative contribution varies depending on the spectral index. At left is an example of relative of contributions of IC40 and IC59 at +16o dec versus spectrum. 13
Combining Datasets The result of combining datasets gives us a roughly 50% improvement in the sensitivity compared to only using IC59 for an E-2 spectrum signal. IT Veto 14
40 String all-sky result Atmospheric Neutrinos E-2 Signal Atmospheric Muons ApJ. 732:18,2011 Hottest location in the all sky search is: Ra=113.75, Dec=15.15 Hotter spot seen in 18% of scrambled maps. 15
40+59 Strings Scrambled Map Atmospheric Neutrinos E-2 Signal Atmospheric Muons Propose to run the all-sky search on the combined sample, and over the same source list as with IC40, excluding the IC22 hottest spot, and adding the Tycho SNR. 16
Add Tycho SNR to the candidate source list Recently observed by VERITAS [1] with spectral index of -1.9 and no cutoff observed to 10 TeV. Also there are hints for non-linear shock acceleration and high B-fields (230 ug from VERITAS fits to hadronic models) [2], consistent with object transiting into the Sedov phase. Volk et al. [3] claim inconvertible evidence of nuclear particle acceleration. Tycho is not in the EGRET or first Fermi catalogue, no clear evidence of TeV before VERITAS: 1.7% of Crab at 1 TeV, > 1 TeV 0.9% of Crab. Young: 438 yrs old, electrons up to 10 TeV, Distance: 4.5 ± 0.5 kpc Radio: spectral index 0.65 and flux at 1.4 GHz of 40.5 Jy [1] arxiv:1102.3871 [2] arxiv:1101.1454 [3] arxiv:0803.1403
Time-dependent analyses As in IC40, we propose to use lightcurves from Fermi to test for flaring behavior. The lightcurve is used to test for neutrino emission in coincidence with photon flares. We propose to use the lightcurves from both IC40 and IC59 to test for flaring behavior from 23 sources. The blazar 3C 454.3 lightcurve is shown below. IC40 IC59 18
We tested the discovery potential for different true levels of emission, and find a similar behavior in the combined sample as in only IC40. Objects with Fermi lightcurves: 23 5 objects with flares in both sets 11 objects with flares in only IC59 7 objects with flares in only IC40 Lots of info and links here: http://wiki.icecube.wisc.edu/index.php/ic59_time_dependent_analysis/mwl 19
Untriggered Flare Search We are interested in performing a search for transient sources which doesn't rely on information from other experiments, such as the flare search mentioned previously or GRB searches. This search only searches for only the most significant flare from a particular direction. Here background events are in blue, with 5 injected signal events in red. The height of the line corresponds to S/B ratio of the event in the time-integrated analysis. 20
Untriggered Flare Search This search is capable of finding clusters from GRB to AGN flare timescales. For flares of one second this is a factor of four improvement in discovery potential with respect to the time-integrated method. We propose to perform the search on IC59 sample only since it was already applied to IC40. http://wiki.icecube.wisc.edu/index.php/ic59_time_dependent_analysis/untriggered
Review of IC40 untriggered results We found a hottest flare from two events on Feb. 12, 2009 at (254.75, 36.25). The best-fit gamma was 2.15, the best-fit width was 15 seconds. A more significant flare was seen in 56% of scrambled maps, so it is compatible with background. The two events found also triggered the Optical Follow Up program, but no afterglow was seen. 22
Unblinding Summary We would like to unblind: A skymap and source list using the combined IC40+59 for presentation at the ICRC and a combined paper. This will use the IC40 PS sample and the IC59 BDT-selected sample. A time-dependent search using multiwavelength data from the IC40+59 period. A list of interesting sources is available on the wiki. An untriggered flare search providing the most significant flare of the IC59 data taking period. http://wiki.icecube.wisc.edu/index.php/ic59+40_point_source_analysis 23
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Upgoing (straight) Cuts: http://wiki.icecube.wisc.edu/index.php/ic-59_ps_event_selection (From L3): require largest Topologically split track to be upgoing. MPE Rlogl < 8.3 MPE Paraboloid Sigma < 2.5 deg MPE Direct Length > 150 MPE Direct NCh > 5 Bayes Llh ratio > 30 At least one time- or geo-split reconstruction must succeed, and all split recos must have a Zenith > 80 deg 25
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Data/MC comparisons Paraboloid Sigma MPEFit rlogl 27
BDT vs Straight Cuts We find that the BDT keeps more neutrinos and yields a somewhat better sensitivity than the straight cuts. 28
Likelihood Method: Probability Density Functions for Background Likelihood Function Individual event probability Background PDF from scrambled data: J. Braun et al. Astrop. Phys. 33 (2010) 175.; J. Braun et al. Astropart. Phys. 29 (2008) 299 and arxiv:0801.1604 29
Local Coordinate Effects We have the local coordinate functions for IC40 and IC59. IC40 The effect of the 'long end' vs the 'short end' from IC40 is mostly smoothed out. Effects from events reconstructed along lines of strings is still evident. IC59 30
The hottest flare in IC40 corresponded to two events 22 seconds apart. There is a spatial separation of 2.01 degrees between the events. Paraboloid sigma = 0.60 deg Nch 65 Energy = ~30 TeV Paraboloid sigma = 1.96 deg Nch 17 Energy = ~3TeV 31