1. Rencontres de Moriond 20091 Detection of the Crab pulsar with MAGIC: First pulsar detected > 25 GeV Marcos López (INFN/Padova) T. Schweizer, N.Otte, M.Rissi, M.Shayduk for the MAGIC collaboration Rencontre de Moriond, 7th February 2009

2. MAGIC Rencontres de Moriond 20092 The MAGIC Collaboration Collaboration: ~ 150 Physicists, 23 Institutes, 12 Countries: Instituto de Astrofisica de Andalucia, IFAE, UABarcelona, UBarcelona, DESY Zeuthen, Instituto de Astrofisca Canarias, INAF Rome, Croatian MAGIC consortium, University C. Davis, University Dortmund, Institut de Ciencies de l’Espai, University Lodz, UCM Madrid, MPI Munich, INFN/ University Padua, INFN/ University Siena/Pisa, Institute for Nuclear Research Sofia, Tuorla Observatory, Yerevan Institute, INFN/University Udine, University Würzburg, ETH Zürich Goal: Achieve the lowest energy threshold in the world Close unexplored gap between space and ground-based gamma telescopes

3. MAGIC Rencontres de Moriond 20093 Cherenkov Technique Satellites Direct detection No background Small Effective Area ~1m 2 Ground Detectors Indirect detection Huge Effective Area ~ 10 5 m 2 Enormous background Basic fact:  -rays absorbed in atmosphere

4. MAGIC Rencontres de Moriond 20094 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

5. MAGIC Rencontres de Moriond 20095 Crab pulsar as seen by EGRET above 100 MeV: Two peaks, broad structures above 5 GeV: First peak seems to disaperar Waiting for FSGT update..

6. MAGIC Rencontres de Moriond 20096 Maximum of emission at hard X- and -ray Maximum of emission at hard X- and -ray Observational challenge since 20 years Instrument with sensitivity well below 100 GeV needed Cherenkov telescopes Crab EGRET pulsars: Multi-wavelength spectra Spectra are very different above 1 GeV Spectra are very different above 1 GeV High energy spectral cutoffs High energy spectral cutoffs PULSED SPECTRUM POLAR CAP = FAST OUTER GAP = SLOW FLUX 5 GeV ? 100 GeV ENERGY

7. MAGIC Rencontres de Moriond 20097 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

8. MAGIC Rencontres de Moriond 20098  -ray emission occurs near LC Charges accelerated in vacuum gap   -rays via Curv. rad. B not strong enough for pair-production. But:  -rays 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

9. MAGIC Rencontres de Moriond 20099 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)

10. MAGIC Rencontres de Moriond 200910 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 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, M.Lopez et al., NIM A 589, 415 (2008)

11. MAGIC Rencontres de Moriond 200911 MAGIC Crab campaign observed in optical and  simultaneously Optical observations of Crab  Made Crab result robust Phase of radio pulse Optical pulse a bit earlier

12. MAGIC Rencontres de Moriond 200912 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)

13. MAGIC Rencontres de Moriond 200913 Summary first MAGIC pulsar campaign No pulsed signal detected but obtained a hint and the lowest upper limit so far Conclusion: –Even the low energy threshold of MAGIC (55 GeV) was not enough for catching pulsars –Next winter campaign in 2006 we tried again with different trigger topology, but still no success –Solution: Develop a new trigger concept  The MAGIC SumTrigger

14. MAGIC Rencontres de Moriond 200914 Difficulty of triggering pulsars with CTs PULSED SPECTRUM (EGRET) A  (E) NO FLUX or COLLECTION AREA ENERGY YES New trigger

15. MAGIC Rencontres de Moriond 200915 NSB Afterpulses Showers Sum of 18 pixels Trigger rate distribution vs threshold A new trigger concept MAGIC SumTrigger 24 Clusters of 18 pixels in a ring area Add analog signals from a cluster & discriminate on summed signal Problem: Afterpulsing –Solution: Clipping signal Built at MPI (Munich) in summer 2007 Idea Summing signal from several pixels to increases signal/noise ratio MPI Seminar, October 7, 2008 Signal Clipper Σ Analog sum of 18 pixels Signal Clipper... Clipped at 6-8 PhE

16. MAGIC Rencontres de Moriond 200916 Improvement in detection efficiency @ 20 GeV: factor 8 A new trigger concept Improvements Size distribution peak shifts to lower energies Higher coll. area at low E Sum- & std trigger data taken in parallel Trigger threshold decreased in a factor ~2 25 GeV sum trigger Event distribution 55 GeV Std trigger Low trigger threshold of 25 GeV: a break-through for ground-based  -ray astronomy

17. MAGIC Rencontres de Moriond 200917 Low energy events: 20-40 PhE

18. MAGIC Rencontres de Moriond 200918 Low energy events: 20-40 PhE

19. MAGIC Rencontres de Moriond 200919 Low energy events: 20-40 PhE Image analysis possible  Some background rejection

20. MAGIC Rencontres de Moriond 200920 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

21. MAGIC Rencontres de Moriond 200921 Detection of the Crab pulsar above 25 GeV at 6.4 sigma Simultaneous observation of optical Pulse   Crosscheck of MAGIC time stamp Definition of signal region from Fierro98 & Albert et al. 8500+-1330 Excess events Astronomical Telegram #1491 (28th April 2008) P1 clearly visible, conversely to EGRET  First Surprise

22. MAGIC Rencontres de Moriond 200922 Test: Cuts excluding the signal Alpha cut excluding signal Alpha cut including signal

23. MAGIC Rencontres de Moriond 200923 Additional periodicity tests Fine frequency scan -2 -1 0 1 2 x 10 -6 Relative frequency -0.2 -0.1 0 0.1 0. 2 x 10 -6 Relative frequency Coarse frequency scan Excess vs total events

24. MAGIC Rencontres de Moriond 200924 Light curve at different energys Fine binning above 25 GeV Pulses in phase with EGRET 3.4 sigma Pulsed emission still visible > 60 GeV ! P2 became dominant

25. MAGIC Rencontres de Moriond 200925 How do we estimate the cutoff ? Method: Combined fit: EGRET and MAGIC data Fold function with eff. area Calculate the Chi 2 between expected excess and measurement Minimize Total Chi 2 F(E)  A E -  exp(-(E/E 0 ))  )    PULSED SPECTRUM (EGRET) A  ( E) FLUX or COLLECTION AREA ENERGY New trigger Collection Area Folding the flux with the cutoff

26. MAGIC Rencontres de Moriond 200926 Model fit to signal event distribution Total P1 + P2 Probability of cutoff energy E0=17.7 ± 2.8 stat ± 5.0 syst GeV for β =1 (exponential) E0=23.2 ± 2.9 stat ± 6.6 syst GeV for β =2 (super-exponential) F(E)  A E -  exp(-(E/E 0 )  ) folded with eff. area

27. MAGIC Rencontres de Moriond 200927 Total spectrum (P1+P2) of cutoff

28. MAGIC Rencontres de Moriond 200928 Our superexponential cutoff: 23.2 GeV+-2.9 stat GeV+-6.6 syst GeV We can calculate the absorption of gamma photons in the magnetic field From which we can put a lower limit on the distance of the emitting region: 6.2 +- 0.2 stat +- 0.4 syst stellar radii The high location of the emission region excludes the classical polar cap model (emission distance < 1 stellar radius) and challenges the slot gap model Baring et al., 2001 Relatively high cutoff >20 GeV ! Comparison with pulsar models Science 322 (2008) 1221

29. MAGIC Rencontres de Moriond 200929 Summary Pulsars seemed impossible to detect with current CTs, due to low spectral cutoffs, but... MAGIC developed a new trigger concept: Eth=25 GeV First detection of Crab pulsar with a CT after 20 years chasing it: –Both peaks visible –Cutoff higher than expected –High cutoff  emission region at high altitudes: 6xR * Excludes polar cap model and challenges the others Review our knowledge of pulsar physics..busy time for theoreticians… we insisted… MAGIC & Fermi complement each other for pulsar studies

30. BACKUP

31. MAGIC Rencontres de Moriond 200931 Outline MAGIC & Gamma-ray pulsars Results from first MAGIC observations A new trigger concept Crab pulsar detection

32. MAGIC Rencontres de Moriond 200932 The MAGIC Telescope 17 m diameter, parabolic mirror (239 m 2 ) Optical analog signal transmission IPE CENET 3-Level Trigger System & 2 Gsample/s FADC Active Mirror control Light carbon fiber frame (Mirror & Frame:17t, Whole Telescope: 65t) Camera with 3.5° FOV 576 PMTs with high QE (QE max = 30% peak)

33. MAGIC Rencontres de Moriond 200933

34. MAGIC Rencontres de Moriond 200934 Cuts optimization Only SIZE ! Energy resolutionOptimized ALPHA cut Maximal Q-Factor SIZE 30 45%