1. 5th Science AGILE Workshop, June 2008 1 Observations of pulsars with MAGIC Marcos López (INFN/Padova) on behalf of the MAGIC collaboration

2. MAGIC 5th Science AGILE Workshop, June 20082 Outline Importance of detecting pulsars with CTs Results from first MAGIC observations A new trigger concept Crab pulsar detection !

3. MAGIC 5th Science AGILE Workshop, June 20083 What we learnt from EGRET Typically 2 peaks, and interpulse emission. Typically 2 peaks, and interpulse emission. Crab only pulsar which same behaviour at all wavelengths ! Crab only pulsar which same behaviour at all wavelengths ! ~2000 pulsars known, but only 7(+3) at -rays ! ~2000 pulsars known, but only 7(+3) at -rays !

4. MAGIC 5th Science AGILE Workshop, June 20084 Crab pulsar as seen by EGRET above 100 MeV: Two peaks, broad structures above 5 GeV: First peak seems to disaperar Two 100  50 GeV photons!

5. MAGIC 5th Science AGILE Workshop, June 20085 EGRET pulsars: Multi-wavelength spectra Maximum of emission in the hard X- and - ray range Maximum of emission in the hard X- and - ray range Spectra are very different above 1 GeV Spectra are very different above 1 GeV Cherenkov Telescopes High energy spectral cutoffs High energy spectral cutoffs

6. MAGIC 5th Science AGILE Workshop, June 20086 Acceleration of electrons Cooling mechanisms a) Curvature radiation b) Synchrotron, I.C. of X-rays  -rays interact with magnetic field, via Magnetic pair production Polar Cap Model Sturrock (1971); Ruderman & Sutherland (1975); Harding (1981); Daugherty & Harding (1982) Polar Cap model predicts super-exponential cutoff in high energy  -ray spectra ! Models of  -ray emission in Pulsars

7. MAGIC 5th Science AGILE Workshop, June 20087  -ray emission occurs near LC Charges accelerated in vacuum gap   -rays via Curv. rad. B not strong enough for pair-production. But, curvature photons interact with non-thermal X- rays Outer Gap model Cheng, Ho & Ruderman (1986); Romani (1996) Electrons may up scatter IR photons to TeV Gamma-rays ! Softer exponential cutoff in the high energy  -ray spectra ! Models of  -ray emission in Pulsars

8. MAGIC 5th Science AGILE Workshop, June 20088 Discrimination between models Different models predict different spectral cutoff. Measuring the spectral tail is possible to distinguish between models. Where do  -rays come from? Outer gap or polar cap? MAGIC SumTrig CherenkovTelescope(originalMAGIC)

9. MAGIC 5th Science AGILE Workshop, June 20089 First Crab observations Data taken in Oct-Dec 2005. 16 hours of optimal quality A hint of a signal found –2.9  in phase with EGRET Derived upper limits –Eo<27 GeV (exp. case) –Eo<60 GeV (super-exp case) J. Albert et al., Astrophys. J. 674,1037 (2008)

10. MAGIC 5th Science AGILE Workshop, June 200810 PSR B1951+32 31 hours taken in July-Sept. 2006 No signal found Constrained cutoff energy to: Eo<32 GeV J. Albert et al., Astrophys. J. 669,1143 (2007)

11. MAGIC Part III: Gamma-ray Pulsars with MAGIC. Optical Crab observations11 MAGIC PMTs designed to detect fast Cherenkov pulses  2ns  Need to be adapted to low frequency observations A PMT was modified to be set at the camera center for optical observations Electronic Chain Cpix signal is split in 2:  To 16 bits ADC, rate 2-20 kHz  MAGIC FADC Allows  and optical simultaneous observations simultaneous observations Motivation: Check that MAGIC electronic+software are reliable for  -ray pulsar searches Optical observations of Crab F. Lucarelli et al., NIM A 589, 415 (2008)

12. MAGIC 5th Science AGILE Workshop, June 200812 MAGIC Crab campaign observed in optical and  simultaneously Optical observations of Crab  Made Crab result robust !

13. MAGIC 5th Science AGILE Workshop, June 200813 Summary first MAGIC pulsar campaign No pulsed signal found from any of the observed pulsars But obtained the lowest upper limit so far Conclusion: –Even the low energy threshold of MAGIC (50-60 GeV) was not enough for catching pulsars –Solution: Develop a new trigger threshold concept  The MAGIC SumTrigger

14. MAGIC 5th Science AGILE Workshop, June 200814 PULSED SPECTRUM (EGRET) A  (E) NO EGRET CUTOFFS: POLAR CAP = FAST OUTER GAP = SLOW FLUX or COLLECTION AREA ENERGY YES Difficulty of triggering pulsars with CTs New trigger

15. MAGIC 5th Science AGILE Workshop, June 200815 A new trigger concept Idea –clusters of several pixels –sum up analog signals from individual pixels –discriminate on the summed signal –Built at MPI (Munich) in summer 2007 Advantages: –Small signals contribute to the trigger signal  Lower threshold –Improved signal/noise ratio.

16. MAGIC 5th Science AGILE Workshop, June 200816 A new trigger concept Improvements Size distribution peak shifts to lower energies Higher coll. area at low energies Sum- & std trigger data taken in parallel Improvement Trigger threshold decreased in a factor ~2

17. MAGIC 5th Science AGILE Workshop, June 200817 Crab pulsar detection !!! Data sample –Observations with new trigger between Oct07 and Feb08 –24 h. of optimal data at low zenith angle Analysis 3 different analysis show clear signal > 5  –2 independent timing software: barycenter correction+folding+periodicity tests –4 different image cleaning algorithms

18. MAGIC 5th Science AGILE Workshop, June 200818 Results –Clear signal above 25 GeV at 6.3  in phase with EGRET –Observed 8500 pulsed  -ray events Crab pulsar detection !!! Astronomical Telegram #1491 (28th April 2008) A publication is being prepared, which details about the cutoff energy P1 clearly visible, conversely to EGRET  First Surprise ! Sorry, wait until the publication for getting the plots

19. MAGIC 5th Science AGILE Workshop, June 200819 Conclusions Pulsars seemed impossible to detect with current CTs, due to low spectral cutoffs, but we insisted… First MAGIC pulsar observation campaign already show a hint of Crab pulsar. New trigger built to confirm it. First detection of Crab pulsar with a CT after 20 years chasing it –Both peaks visible ! –Cutoff higher than expected ! MAGIC opens the road to new discoveries…

20. MAGIC 5th Science AGILE Workshop, June 200820 Outlook: The coming future HESSII under constructionHESSII under construction MAGIC II nearly ready…MAGIC II nearly ready… first light in Sept. 2008 first light in Sept. 2008 AGILE successfully in space since more than 1 yearAGILE successfully in space since more than 1 year GLAST just launchedGLAST just launched  More than 100 new  –ray pulsars could be discovered ! Full coverage of the  -sky from 100 MeV to 10 TeV