2002-2006  SPASE-2  TeV Gamma-Ray Source Search

Data Sample / Processing / Selection
Angular Resolution
Systematics
The Background
Unblinding Proposal


                                 Unblinding

Progress:

We have spent the last week looking for ways to  improve the background fluctuations.
To do that  we have tested different cuts on the data set (2005 only) and weightings:
These include
  - a cut on the X2 in the shower reconstruction.
    The normalized X2 peaks at 1 but has a long tail
    extending to 10. Showers with X2 exceeding
    10 are declared non analyzable. We tested X2
    of 2 and 5.
  - a cut on T2 which is a measure of the direction
    reconstruction quality and is not normalized in
    the reconstruction code. A cut on T2 < 50
    improves the background fluctuations.
  - weighting of the data set sidereal time as
    recommended by Alan Watson. Sidereal time variations
    are quite large in 2005 with a couple of bins (out
    of 60) exceeding 3 sigma.
  - weighting of events by azimuth. Since RA is a
    combination of sidereal time and azimuth we
    decided to correct on the azimuthal anisotropy of
    the detector that may be a function of the
    magnetic field direction at South Pole, that
    spreads the shower front and increases the
    shower threshold energy.
  - a weighting on the rate of showers was also attempted
    but did not improve anything.

  All these cuts and weights were applied separately to
  see what their effects are. Although the effects of cuts
  and weighting are not significant, we decided to
  apply the two quality cuts and weighting on sidereal
  time and azimuth.

  Binning for the background and the signal were changed
  during the last week. We decided to adopt Tom Gaisser's
  idea of using equal solid angle circular bins that
  correspond better to the calculated angular resolution
  that is binned in space angle. The shape of the
  ellipses used in the determination of the background
  are shown for the three zenith angle bands of the
  three sources in the graphics below. Since the angular
  resolution of SPASE 2 does not change much in this
  energy range we will use equal zenith angle bins.
  This changes the shape of the bins - at higher zenith
  angle we can fit more circles in the zenith angle band.
  Small bins are for S30 > 3, large ones for S30 < 3.

  We will use Li & Ma algorithm for calculation of the
  significance of the source fluxes after unblinding.

Ellipse sizes which preserve solid angle
Source
zenith angle
S30>3
1.58x2.1°=3.3°
S30<3
1.58x3.3°=5.2°
ZEN
minor axis
RA
major axis
no. of backgr bins
ZEN
minor axis
RA
major axis
no. of backgr bins
RX J0852-4622 43.8
3.3
3.7
47
5.2
5.9
28
MSH15-58 32.0
3.3
4.2
41
5.2
6.6
25
HESS J1303-63.1 26.9
3.3
5.7
30
5.2
9.0
18



Kory James Analysis