Search for gamma emission from 12 nearby AGNs


Report on the search for TeV gamma emission from 12 nearby AGNs in the AIROBICC 92/93 data (internal report)

By J.L. Contreras, A. Moralejo. Last updated July 2 1996.

Search for gamma emission in the energy range 50 - 100 TeV from 12 nearby AGNs in AIROBICC March 92 - March 93 data. No evidence has been found. A 1.8 sigma excess is observed in a high quality sample with no gamma/hadron separation cut. In a sample with somewhat relaxed quality cuts (although with similar angular resolution) containing 35% more events, the excess is of only 1.6 sigma. The excess vanishes when a gamma/hadron separation cut is applied in the parameter log10(Ns/L90). Flux upper limits on the gamma flux from these sources are presented.

*WARNING*WARNING*WARNING: there are two important changes with respect to previous versions (before July 96). The most important one is a new energy cut, which sets the gamma energy window more precisely in the range 50 - 100 TeV. Then we have included two more sources which were missing in the previous versions. Both things made numbers change significantly!

Click HERE to get the postscript file.

ADITTIONAL PLOTS: (last updated 17 Jul 96)

Here is a 2d-map (2 deg x 2 deg) of the significances around the 12 AGNS (superimposed) for the 92-93 AIROBICC sample. The energy range (gammas) is 50 - 100 TeV. No gamma/hadron separation cut has been applied. The circle is the ON region (0.24 degrees radius) which has been used in the search (see report). Click here to see a larger region of sky (3 deg x 3 deg around the AGNs). The projection of the events is done in celestial coordinates centered in each AGN and then the 12 AGNs are superimposed.

The separation parameter log10(Ns/L90) is plotted versus the light radius. The quality cuts are the same specified in the report. PS1 contains 2 such plots for MC gammas and hadrons (spectral weights included) at 10 and 25 degrees zenith angle incidence. PS2 contains the comparison between MC hadrons and real data. The third plot, PS3 shows the distribution for the events in the environment of the 12 AGNs (OFF region) compared with that of the ON events.


Comparison of reconstructed AIROBICC and Scintillator directions in the March 92 - March 93 data (on request from the Kiel group).

For each run number we have calculated the angle X such that 63% of the (reconstructed) events in the run show a discrepancy between the AIROBICC and scintillator directions lower than X. We require that the core has been reconstructed inside the array boundaries (= excluding the 10 m outer strip). The events we use belong to a subsample of 92-93 data (those events within 3 degrees of 46 selected sources). The plots show the angle "X" defined above versus the run number, first using all reconstructed events, then only those with more than 20 fired AIROBICC huts and more than 30 Scintillator huts.

Click HERE to get the postscript file.


Preliminary search of gamma emission from AGNs in AIROBICC 94 - 95 data (29/09/94 - 12/04/95) + (21/06/95 - 2/08/95).

Only some plots are available. Using the same quality cuts as in the 92/93 sample (see report above). No gamma/hadron separation available yet. With no adittional energy cut, no significant excess is seen (less than 1 sigma) in the superposition of the 11 AGNs (Mrk421 excluded due to the telescope veto). After a cut in L90 to restrict the gamma energy range to 50-100 TeV, no significant excess is seen either (roughly 0.5 sigma).

Click HERE to get the postscript file containing the 1-d plots.

HERE you can have a look at the effect of the CT-veto around the direction of Mrk 421. The 2-d projection is centered in Mrk421. The cuts we used were the following: distance core-edge greater than 10 m, chi2 of the AIROBICC cone fit lower than 2 and a number of fired AIROBICC huts between 12 and 30.


A 2-d map (Egamma > 50 TeV) around the CRAB for the same 94 - 95 data is also available. No excess is seen within 0.4 degrees of the Crab's direction.


Preliminary search of gamma emission from AGNs in 94 - 95 Scintillator data (29/09/94 - 12/04/95) + (21/06/95 - 2/08/95).

Only some plots are available. Using the same quality cuts (those concerning scintillator quantities only) as in the 92/93 airobicc sample (see report above). Data containing airobicc info are also included, but also for those runs only scintillator information has been used (direction, NKG, etc). With no energy cut, no significant excess is seen in the superposition of the 12 AGNs. After a cut in Ns (reconstructed shower size) to restrict the gamma energy range to 50-100 TeV (click here to get the ps file showing Ns vs energy for MC gammas), no significant excess is seen either. Nevertheless, this is still preliminar. The background estimate method is different from the simple 'ring' method (in the plots of the 12 sources together it is very obvious that there is a systematic effect due to acceptance: the number of events in the rings decreases for increasing distance to the center). Hence the background has been calculated independently in each ring by generating 10 "artificial" events per every true event in the sample (using the event time and 10 random directions whose distribution in theta and phi follows the one observed in the total sample).

Click HERE to get the postscript file containing the events plots.

Another plot: the distribution of log10(Ns) for the real data (from a smaller period contained in the total sample). Click here to get the ps file.


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