1 / 44

g - ray astrophysics : news from the astronomical frontier

g - ray astrophysics : news from the astronomical frontier. J. Cortina (IFAE Barcelona). Electromagnetic spectrum : astronomical windows. Traditional astronomy was restricted to the “ optical astronomical window ” which is accessible to the naked eye : ~400-700 nm .

gur
Download Presentation

g - ray astrophysics : news from the astronomical frontier

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. g-rayastrophysics: newsfromtheastronomicalfrontier J. Cortina (IFAE Barcelona)

  2. Electromagneticspectrum: astronomicalwindows Traditionalastronomywasrestrictedtothe “opticalastronomicalwindow” whichisaccessibletothenakedeye: ~400-700 nm. J. Cortina, Gamma ray astronomy

  3. Electromagneticspectrum: astronomicalwindows • Starsrange in temperaturefrom ~3000 K to ~40000 K, so theirblack body emissionspansfrom UV to IR. • Conventionalastronomicalwisdomendof 19th century: theskyisdarkbeyondthesewavelengths. J. Cortina, Gamma ray astronomy

  4. Electromagneticspectrum: astronomicalwindows • Radio astronomy: startedactually by engineerspartlybecauseastronomersexpectednothingandpartlybecauseastronomersdidn’t know how todetect radio waves. • Theskyis full of radio sourcesandthey are notmainsequencestars. • In somegalaxies, radio emissiononly comes fromtheverycoreofthegalaxy: supermassiveblackholespowered by accretionandnot by stellarfusion • Cosmicmicrowave background. J. Cortina, Gamma ray astronomy

  5. Electromagneticspectrum: astronomicalwindows • X-rayastronomy: onlypossiblewhendetectorscouldflyonrocketsorsatellites: • Theskyis full of X-raysourcesandthey are notmainsequencestars • Brighestsources are X-raybinaries: systems made of a starand a compact object (pulsar orblackhole), powered by accretion. J. Cortina, Gamma ray astronomy

  6. Electromagneticspectrum: astronomicalwindows Thelastastronomicalwindowto open istheg-raywindow: everythingbeyond 511 keV. Theatmosphereis opaque tog-rays. Let’ssee how we can detectthemand how thesky looks like in thiswindow. J. Cortina, Gamma ray astronomy

  7. Detectiontechniques J. Cortina, Gamma ray astronomy

  8. Space-baseddetectors g-raysinmediatelyinteractwhentheyentertheEarth’satmosphere g e- e+ • Theobvioussolutionistogetthe detector out oftheatmosphere, onboardofballoons, rocketsorsatellites. • Severalsuchdetectorshaveoperatedsincethe 1970’s: SAS-2, COS-B and EGRET. EGRET catalogued ~350 g-raysources. • Currently: ItalianAgile detector and Fermi/LAT J. Cortina, Gamma ray astronomy

  9. Fermi satellite • Fermi Gamma-raySpaceTelescope • Launchedon 11 June 2008. • Joint ventureof NASA, the US DepartmentofEnergy, andfunding agencies in France, Germany, Italy, Japan, andSweden. • Twoscientificinstruments: • TheLargeAreaTelescope (LAT): 30 MeV - 300 GeV • Gamma-rayBurst Monitor (GBM). 8 keVto30MeV. Detects gamma-rayburstsacrossthewholeoftheskynotoccultedby the Earth. J. Cortina, Gamma ray astronomy

  10. Fermi/LAT LAT detects-rays in the 30 MeV - 300 GeVrange. • Tracker: converts-rayinto e-/e+andmeasurestheirtrajectoriesto determine the-rayincidentdirection. • Calorimeter: measuresenergyofelectron & positron. • Veto: external shieldtoeliminatechargedparticle background. J. Cortina, Gamma ray astronomy

  11. Fermi/LAT tracker • High Z tungstenlayerstoconvert-rayinto e+e-pair. • Four-by-four array oftower modules. • In each module, there are 19 pairsof planes of Si - in eachpair, oneplane has thestripsoriented in the "x-direction", whiletheother has thestripsoriented in the perpendicular "y-direction". J. Cortina, Gamma ray astronomy

  12. Fermi/LAT calorimeter • CsI(Tl) scintillator: highlightyield, coupledwithphotodiodestomeasureenergyofthepair. • Bars, arranged in a segmentedmanner, giveboth longitudinal andtransverseinformationabouttheenergydepositionpattern. J. Cortina, Gamma ray astronomy

  13. Fermi/LAT: performance 60° off-axis Angular resolution on-axis Linesrepresent 3 differentcutstoremove background Effectivearea J. Cortina, Gamma ray astronomy

  14. 1-yearsensitivitytog-rays Galacticplane Near plane Highlatitude J. Cortina, Gamma ray astronomy

  15. Fieldofviewandoperation • Fermi/LAT operates in “surveymode”: itimagesthewholeg-rayskyessentiallyevery 1.5 hours. • Data are processedautomaticallyand made freelyavailabletogetherwiththenecessarytoolstoanalyzethem. (1.5h) J. Cortina, Gamma ray astronomy

  16. Limitationsofspace-basedtelescopes Space-baseddetectorssufferfromtwolimitationswhichpreventthemtocovertheenergyrangeabove~100 GeV: • Areacannotexceed ~1 m2whilethestrongestflareeverreportedabove 200 GeVfeatured1 photon / m2 in 8 h. • At such energies, the detection volume is too small to contain the shower developed by the g-ray. ~1 m2 Calorimeter depth  10 X0 J. Cortina, Gamma ray astronomy

  17. primary -ray Ground-based -ray astronomy • Observe particle showers induced in the atmosphere (28 X0 at s.l.) by -rays • Most successful technique: Imaging Atmospheric Cherenkov Telescopes Very High Energy = E > 30 GeV J. Cortina, Gamma ray astronomy

  18. Gamma- ray Particle shower ~ 10 km ~ 1o Cherenkov light ~ 120 m How to detectg-ray showers: with IACTs J. Cortina, Gamma ray astronomy

  19. ArraysofIACTs • Intersection point of major axes allows simple and more precise source position reconstruction, i.e. better discrimination and angular resolution. • More images means better estimation of shower shape, i.e. better discrimination from cosmic ray background. J. Cortina, Gamma ray astronomy Slide from W. Hofmann

  20. TwogenerationsofIACTs • Pioneer IACT: Whipple 10m telescope in Arizona since 1969. • First array ofIACTs: HEGRA in La Palma, Spain (Germangroups + UCM). • Last 10 years: 2nd IACT generationwithlowerenergythresholdsandbetter flux sensitivities: HESS • Array of 4 x 12 meter (100 m2 mirror) IACTs • Mainly German-French collaboration • LocatedinNamibia (Southern Hemisphere) • Fully operational since 2003. V ERITAS - 4x 12m telescopes in operation in Arizona since 2007. - Mainly US-UK coll. J. Cortina, Gamma ray astronomy

  21. MAGIC telescopes • CollaborationofSpain, Germany, Italy… Located in La Palma, Spain. • Spanishgroups: IAA, IAC, IFAE, ICE, UAB, UB, UCM • Single telescope (MAGIC-I): largest IACT yetconstructed (17mØ), i.e. lowestenergythreshold. • Fastestsampling (2GSps), ultralight CF frameandmirrors, fastrepositioning (<20 secs/180º), active mirror control… • MAGICtelescope array: stereoobservationsdownto 50 GeVregularlysinceFall2009. • M-II isanimprovedcopyof M-I. J. Cortina, Gamma rayastronomy

  22. Performance of MAGIC • Energythresholdis 50 GeV, thelowestamongIACTsandoverlappingwith Fermi/LAT. Flux sensitivity= 0.76% crab >300 GeV • Angular resolution: 0.1º at 100 GeV, down to 0.04º at >1 TeV. • Energy resolution: 20% at 100 GeV, down to 15% around 1 TeV. J. Cortina, Gamma rayastronomy

  23. Physics in theg-rayastronomicalwindow J. Cortina, Gamma ray astronomy

  24. J. Cortina, Gamma ray astronomy

  25. Galacticcosmicrays • Maybetooshamefultomention: cosmicrayswerediscovered100 years ago (1912), butwedon’t know wherethey come from. • Theyrepresent a significantfractionoftheenergycontentofourgalaxy. J. Cortina, Gamma ray astronomy

  26. CR/g-ray connection • Galacticcosmicrays (CR) are believedtooriginate in Supernova Remnants (SNR). • E < 1015eV • Accelerated in the sh0ck between SN ejectaandinterestellarmedium. • Eventuallytheydiffuseawayfromthe SNR andfill up thegalaxy. Cosmicraysgenerateg-raysviap0whentheyinteractwithnucleioftheinterestellarmedium. Sincethedensityof CR ishigher in thenearbyof SNR, oneexpects SNR to “shine” in g-rays.

  27. CR/g-ray connection Detecting 10’sto 100’sof SNR wasoneofthephysicsdriversofthe firstgenerationofIACTs (e.g. HEGRA). Howevertheydiscovered no g-ray bright SNR. ThesecondgenerationofIACTshavemanagedtodiscover a few.

  28. g-raysfrom SNR RXJ1713 (HESS): spatialdistributionofTeVspectralindices • Wehavenotonlydetectedthem, butwe can even resolvetheirmorphology. • We can studyspatialcorrelationswithotherwavelengths, and test dependenceonmagneticfieldintensityandmassdensity. • However: • g-rays may alsooriginatethroughInverse-Compton emissionofelectrons/positronsaccelerated in the SNR. • We do nothavespectra up totheKnee (>100 TeV) toprovethatthey can generatethe CR spectrum. RXJ1713:hadronic vs leptonic J. Cortina, Gamma rayastronomy

  29. g-raysfrom SNR Thesituation may improvefor SNR whichseemsto be interactingwithnearby molecular clouds. • Thecloudincreasesthemassdensityandcorrespondinglytheg-rayemissitivity. • Ifg-raysonly come fromthecloud, theymustcome fromprotons, He… andnotfromelectrons. MAGIC: W51 MAGIC: IC-443 Molecular clouds J. Cortina, Gamma rayastronomy

  30. Extragalactic cosmic rays • Above ~1015eVCR are ofextragalacticorigin. Pierre Auger E>1017eV. • Unfortunatelythereis no clearcorrelationwithanysourceorsourcepopulation. • Can g-raytelescopeshelptoestablishtheirorigin? As with SNR, g-rays are always a by-productof CR interactionwithinterstellarorintergalacticmatter. • Unfortunately: VHE<~1014eVverydifferentenergyranges!! PIERRE AUGER (E~1019eV) AGN

  31. Extragalactic cosmic rays Nearby normal galaxies e.gAndromeda=M31: rCR(M31) ~ rCR(MilkyWay) Notluminousenough in CRs. Starburstgalaxies e.g. M82 or NGC253 Extreme starformation: rCR(M82) ~ 500 xrCR(MilkyWay) Radiogalaxies e.g. Cen A or M87 Active galaxies: CR production in jet developingfrom central Supermassive Black Hole Clusters ofgalaxies e.g. Virgo orPerseus Accumulatedemissionofallgalaxiesoracceleration in largescale shocks.

  32. Fermi/LAT: local galaxies • Fermi/LAT has alreadydetectedemissionfromnearby normal galaxiesandstarbursts. • g-rayluminositydoesnotcorrelatewith total massbutwithstarformationrate (SFR). • SFR probablycorrelatedwithrateof SN explosionsand CR density.

  33. Radiogalaxies Flare at VHE • IACTshavediscoveredfourradiogalaxies at VHE: Cen-A, M87, NGC 1275 and IC 310. • Emission comes fromthe jet andisstrongly variable: unclearifenergy in jet istransported by hadronsand CR may produce theg-rays. MAGIC+VERITAS+HESS: Science325 (2009) 444 MAGIC Brightening of radio core J. Cortina, Gamma ray astronomy

  34. J. Cortina, Gamma ray astronomy

  35. Unidentified Fermi Objects (UFOs) • Abouthalfofthesources in the EGRET catalogue wereunidentified. • Even afterimprovement in sensitivityand angular resolution, about 1/3 ofthesources in the Fermi/LAT catalogue remainwithout a counterpart. • Meaning: thereisplentyofroomforsurprises:newsourcesclasses, even darkmatter…. J. Cortina, Gamma ray astronomy

  36. HESS galacticsurvey • HESS has made the 1st complete scanofthegalacticplane at VHE. • About 60 newsources. • Emissiondominated by pulsar windnebulae (PWN). • 1/3 ofthesourcesstillunidentified. HESS, ICRC2011 J. Cortina, Gamma ray astronomy

  37. Surprise: pulsarsand PWN alloverthe place Thelargestpopulationofsources in the HESS survey are Pulsar WindNebula. So what’s a PWN? 3 1 2 CrabNebula Optical+X-rayimages X-ray: Chandra Artist’sview J. Cortina, Gamma ray astronomy

  38. Surprise: pulsarsand PWN alloverthe place • Pulsars are rotating (P~1-1000 ms) neutronstarswithmagneticfields ~108T. • Allphenomena in pulsars are powered by spindownofrotation. • Electric fieldgenerated by star’srotation can accelerateparticles up to 1012eV. • Pulsar alsogenerates a steadywindofparticles+magneticfieldwhichcarriesawaymostofpulsar’spowerLcrab~1031W (Sun’s L=1026 W). • Fermi/LAT has detectedhundredsofpulsars up to ~10 GeV. • MAGIC and VERITAS havedetectedpulsed VHE emission >400 GeV, in contradictiontoallexistingmodels. g-rays may originatefrommagnetosphereorparticlewind. Magnetosphere: size ~1000 km Neutronstar: size ~10 km J. Cortina, Gamma ray astronomy

  39. Surprise: pulsarsand PWN alloverthe place • Theparticlewindexpandsintothesurrounding dense medium. • Eventuallyitgenerates a shock. • Particlesgetisotropizedand are re-acceleratedtoenergies up to ~100 TeV, with a powerlawenergydistribution. • As manyelectrons as positrons: may explainresultsof PAMELA. e- e+ NEBULA WIND ~0.1 pc SHOCK J. Cortina, Gamma ray astronomy

  40. PWN at g-rays synchr • Theemergingparticles produce electromagneticradiation at allwavelengths as theyexpandintotheinterstellarmedium: PWN. • Electronsgeneratesynchrotronemission up to~1 MeVenergiesandInverse Compton emission up to ~100 TeV (VHE). • More mysterious: Agileand Fermi havereportedGeVflareslasting a fewdays in Crab. Fermi+MAGIC IC HESS J. Cortina, Gamma ray astronomy

  41. Totallyunexpected: hugestructure in ourgalaxy Su, Slatyer & Finkbeiner, usingpublic Fermi data: twolarge gamma-raybubbles, extending 50 degreesaboveandbelowtheGalacticcenter, with a widthofabout 40 degrees in longitude. J. Cortina, Gamma ray astronomy

  42. Fermi bubbles Su, Slatyer & Finkbeiner, usingpublic Fermi data: twolarge gamma-raybubbles, extending 50 degreesaboveandbelowtheGalacticcenter, with a widthofabout 40 degrees in longitude. J. Cortina, Gamma ray astronomy

  43. Totallyunexpected: hugestructure in ourgalaxy • g-rayemissionassociatedwiththesebubbles has a significantlyharderspectrum (dN/dE ∼ E−2) than IC emissionfromgalacticelectrons, org-raysproduced by decayofpionsfrom CR-ISM collisions, • Bubbles are spatiallycorrelatedwiththehard-spectrummicrowaveexcessknown as the “WMAP haze”. Edges are correlatedwith X-rayemissiondetected by ROSAT. • May havebeencreated by somelargeepisodeofenergyinjection in theGalacticcenter, such as pastaccretioneventsontothe central massiveblackhole, or a nuclear starburst in thelast∼ 10 Myr. • Otheralternatives: in situ acceleration in shocks at theedgeofthebubble, steadywindofparticlesfromgalacticcenter… J. Cortina, Gamma ray astronomy

  44. Wrap up • g-rays are thelastwindowtotheuniverse so far: space- andground-baseddetectorshaveconsolidatedthefieldduringthelast 10 years. • Space-baseddetectorslikeAgileand Fermi/LAT: highefficiencytoremove background andreconstructg-rayparameters, butlimitedarea. Ground-basedIACTsreplacethemabove 30 GeV. • Wealthofdiscoveries. Justfewexamples: • Studyofcosmicraysthroughdetectionofg-rays in ourgalaxyandbeyond. • Unexpectedobjects: proliferationof pulsar nebulae, Fermi bubbles. J. Cortina, Gamma ray astronomy

More Related