5th Science AGILE Workshop, June 2008

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Observations of pulsars with MAGIC

Observations of pulsars with MAGIC

Marcos López (INFN/Padova)

on behalf of the MAGIC collaboration

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OutlineOutline

Importance of detecting pulsars with CTs

Results from first MAGIC observations

A new trigger concept

Crab pulsar detection !QuickTime™ and a

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What we learnt from EGRETWhat 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 !

~2000~2000 pulsars known, but only pulsars known, but only 77(+3)(+3) at at -rays !-rays !

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Crab pulsar as seen by EGRETCrab pulsar as seen by EGRET

above 100 MeV: Two peaks,

broad structures

above 5 GeV: First peak seems to

disaperarTwo 100Two 10050 50

GeVGeVphotons!photons!

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EGRET pulsars: Multi-wavelength spectraEGRET pulsars: Multi-wavelength spectra

Maximum of emission Maximum of emission in the hard X- and in the hard X- and --ray rangeray range

Spectra are very Spectra are very different above 1 GeV different above 1 GeV

Che

renk

ov T

eles

cope

sC

here

nkov

Tel

esco

pes

High energy spectral High energy spectral cutoffscutoffs

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Acceleration of electronsCooling mechanisms

a) Curvature radiation

b) Synchrotron, I.C. of X-rays

-rays interact with magnetic field, via Magnetic pair production

−+ +→+ eeBr

γ

Polar Cap ModelPolar 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

)/1exp( pp BEB κ −⋅∝

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-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 Outer Gap model Cheng, Ho & Ruderman (1986); Romani (1996)

€

→ e+e−

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

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Discrimination between models Different models predict different spectral cutoff. Measuring the spectral tail is possible to distinguish between

models.

Where do Where do -rays come from? Outer gap or polar cap?-rays come from? Outer gap or polar cap?

MA

GIC

Sum

Trig

MA

GIC

Sum

Trig CherenkovCherenkov

TelescopeTelescope(original (original MAGIC)MAGIC)

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First Crab observationsFirst 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)

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J. Albert et al., Astrophys. J. 674,1037 (2008)

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PSR B1951+32PSR 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)

Part III: Gamma-ray Pulsars with MAGIC. Optical Crab observations 11

MAGIC

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 Allows and optical and optical

simultaneous observationssimultaneous observations

Motivation:Motivation: Check that MAGIC electronic+software are Check that MAGIC electronic+software are reliable for reliable for -ray pulsar searches-ray pulsar searches

Optical observations of CrabOptical observations of Crab

F. Lucarelli et al., NIM A 589, 415 (2008)

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MAGIC Crab campaign observed in optical and simultaneously

Optical observations of CrabOptical observations of Crab

Made Crab result robust !

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Summary first MAGIC pulsar campaignSummary first MAGIC pulsar campaign

No pulsed signal found from any of the observed pulsars

But obtained the lowest upper limit so farConclusion:

– 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

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PULSED SPECTRUM (EGRET)

A(E)

NO

EGRET CUTOFFS: POLAR CAP = FAST OUTER GAP = SLOW

FL

UX

or

CO

LL

EC

TIO

N A

RE

A

ENERGY

YESYES

Difficulty of triggering pulsars with CTsDifficulty of triggering pulsars with CTs

New trigger

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A new trigger conceptA 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.

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A new trigger conceptA 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

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Crab pulsar detection !!!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

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Results– Clear signal above 25 GeV at 6.3 in phase with EGRET– Observed 8500 pulsed -ray events

Crab pulsar detection !!!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

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ConclusionsConclusions

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…

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Outlook: The coming futureOutlook: The coming future

•HESSII under constructionHESSII under construction

•MAGIC II nearly ready…MAGIC II nearly ready… first light in Sept. 2008first light in Sept. 2008

•AGILE successfully in space AGILE successfully in space since more than 1 year since more than 1 year

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•GLAST just launchedGLAST just launchedMore than 100 new More than 100 new –ray pulsars –ray pulsars could be discovered !could be discovered !

Full coverage of the Full coverage of the -sky from -sky from 100 MeV to 10 TeV100 MeV to 10 TeV

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