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Using X-ray to TeV Instruments to Probe Blazars, GRBs, and Cosmological Parameters

Using X-ray to TeV Instruments to Probe Blazars, GRBs, and Cosmological Parameters. Abe Falcone (Penn State University). Outline of Talk. Ground based gamma-ray astronomy described (briefly) VHE blazars & GRBs: Observed multiwavelength characteristics Source studies

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Using X-ray to TeV Instruments to Probe Blazars, GRBs, and Cosmological Parameters

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  1. Using X-ray to TeV Instruments to Probe Blazars, GRBs, and Cosmological Parameters Abe Falcone (Penn State University) SCIPP seminar (26 Jan 2007)

  2. Outline of Talk • Ground based gamma-ray astronomy described (briefly) • VHE blazars & GRBs: • Observed multiwavelength characteristics • Source studies • Implications for Universe • Present status • The future SCIPP seminar (26 Jan 2007)

  3. Source emits g-ray g-ray interacts Imaging Air Cherenkov Technique Effective area is size of light pool ~ 105 m2 SCIPP seminar (26 Jan 2007)

  4. Cosmic Ray Rejection Technique g-ray proton • g-ray images: - narrow, short, smooth • Hadronic images: - broad, long - local muons, patchy • hadron rejection: 99.7% (10-3) 5o Crab Nebula with Whipple 10 m ~7sin 1hour SCIPP seminar (26 Jan 2007)

  5. Stereo Reconstruction • Exclude muon background • Determine source from intersection of shower axis • Crab nebula ~35σ in 1 hour with VERITAS 80 m SCIPP seminar (26 Jan 2007)

  6. GeV/TeV Observatories HEGRA CAT MAGIC Whipple 10m CANGAROO STACEE H.E.S.S. CELESTE Milagro VERITAS Tibet AS MAGIC Tibet Solar Two SCIPP seminar (26 Jan 2007)

  7. Blazar Categories • FSRQ Vs. BL Lac • Low Peaked Vs. High Peaked Fossati et al. 1998, Ghisselini et al. 1998 SCIPP seminar (26 Jan 2007)

  8. Swift GLAST VERITAS Broadband Coverage X-ray Spectrum: Swift,... 0.2 keV – 150 keV Gamma ray: GLAST, AGILE,... 30 MeV – 300 GeV all sky (~103 AGNs) VHE: VERITAS, HESS,... 50 GeV – 50 TeV (5 mCrab, 50 hours) Pointed (~ 50 AGNs) Mrk501 SED taken from Catanese & Weekes 1999 SCIPP seminar (26 Jan 2007)

  9. Why Study Blazars at VHE? • Need to understand acceleration mechanisms capable of producing large luminosity at very high energies: • SSC? (Maraschi et al. 92, Tavecchio et al 98, …) • External IC? (Dermer & Schlickeiser 2002, …) • Proton cascades? (Mannheim 93, …) • Proton synchrotron? (Muecke & Protheroe 2000, Aharonian 2000, …) • Constrain local environment characteristics: Doppler factor, seed populations, photon vs. magnetic energy density, accel. and cooling timescales, … • Potential sources of cosmic ray acceleration • Need to understand blazar development and evolution • Constrain models of extragalactic infrared background Figure from J.Buckley 1998 SCIPP seminar (26 Jan 2007)

  10. 03 96 97 98 99 00 01 02 TeV Blazars - RXTE ASM Overview Mrk421 Mrk501 1ES2344 1ES1959 PKS2155 H1426 2-12 keV Krawczynski et al. 2003 SCIPP seminar (26 Jan 2007)

  11. Mrk 421 Spectral Variability • Power law spectral index varies from 1.89 ± 0.04 in the high flux state to 2.72 ± 0.11 in the low flux state based on 2001/02 Whipple data (Krennrich et al. 2002) HEGRA sees of ~0.75 during Mrk421 flaring (Aharonian et al. 2002) (0.75-1.5 TeV) /(1.5-4 TeV) SCIPP seminar (26 Jan 2007)

  12. >350 GeV Optical (U) 2-10 keV >350 GeV Correlated TeV - X-ray emission of a bright Mrk 421 flare on 19 Mar 2001 Correlated Lightcurves Multiwavelength lightcurve of Mrk501 from 2-20 Apr 1999 (Catanese et al. 1997) 50-150 keV 2-10 keV SCIPP seminar (26 Jan 2007)

  13. 1ES1959: Overall Lightcurves & Orphan Flare SCIPP seminar (26 Jan 2007)

  14. Doppler Factors of TeV Emitters • SSC mechanisms require a large Doppler factor in the blazar jet • Edwards and Piner (and independently, Marscher) have used the VLBA to show that the Doppler factors are surprisingly low for TeV gamma-ray emitting blazars (however, there is wiggle room since TeV emission may originate much deeper in jet than ~5 pc) • Furthermore, they find no new components emerging after periods of high energy flaring, in contrast to observations of GeV blazars Edwards and Piner 2004 SCIPP seminar (26 Jan 2007)

  15. Mrk 421 • Exhibited shortest observed TeV flaring timescale for any blazar at <15 minutes (Gaidos et al. 1996, Nature) • VHE emission seems to be dominated by flaring episodes Mrk421 lightcurve from 28 Oct 2002 to 11 Mar 2003 based on 28.4 hours of Whipple data SCIPP seminar (26 Jan 2007)

  16. Blazars: Short Timescale Flaring • Lower flux sources and more sources will enhance characterization of catalog • Improved Spectra between ~0.1-10 TeV • Well sampled lightcurves From Gaidos et al. 1996, Nature SCIPP seminar (26 Jan 2007)

  17. PKS 2155 on 2006 Jul 27 • A previously low flux (~0.05 Crab) source • HESS observes: • >10 Crab flux!!! • < 5minute doubling time!!! • During huge TeV flares, the X-ray flux was also variable, but to a significantly lower degree • ~2x flux variability • little/no shifting of 1st Epeak HESS (>200GeV) time bins = 2min Costamante et al. 2006, Aharonian et al. 2007, Falcone et al. 2007 (analysis ongoing) SCIPP seminar (26 Jan 2007)

  18. H1426+428 Extreme BL-Lac type active galactic nuclei (AGN) Known TeV emitter Displays characteristic double humped spectral energy distribution (SED) in a F representation High peaked: Perhaps the highest peak of any known AGN. Its first peak in the SED is in excess of 100 keV during a quiescent state! Relatively distant TeV emitting object at a redshift of z=0.129  excellent target for studies of IR background Steep measured TeV spectrum SCIPP seminar (26 Jan 2007)

  19. H1426: X-ray Variability TeV Flux (Whipple) X-ray Spectral variability is evident and it does not directly track the flux level. No TeV flaring evident. X-Ray Flux X-Ray Index SCIPP seminar (26 Jan 2007)

  20. Blazar H 1426+428: HIDs • X-ray HID diagrams from different observations exhibit varying orientation • We need high-statistics hardness-intensity diagrams at TeV energies, contemporaneous with wavelengths spanning the first peak in the SED. New instruments should achieve this, thus constraining acceleration and cooling timescales at different regions of spectra. Falcone, Cui, Finley 2003, ApJ SCIPP seminar (26 Jan 2007)

  21. Extragalactic Background • Broad multiwavelength spectra are required to ascertain the existence of a VHE cutoff in the observed blazar spectrum • The following factors will contribute to the ability of this generation of VHE instruments to measure the EBL: • Increased source count by more than an order of magnitude will improve statistics and knowledge of intrinsic source spectrum • Increased sensitivity results in sources at higher redshifts, thus allowing us to study more severely attenuated sources • Improved spectral resolution will allow for a more accurate determination of cutoff energy • Aharonian et al. (2006) have used new distant blazar 1ES 1101 (along with a small handful of others) and an assumed intrinsic spectrum to constrain EBL lower limits to values close to the minimum predicted values (Primack et al. 2004) • Contemporaneous multiwavelength campaigns are crucial. GLAST and X-ray instruments, such as Swift and RXTE are needed to measure full SED! SCIPP seminar (26 Jan 2007)

  22. Fossati et al. 1998, Ghisselini et al. 1998 Potential New Source Types • LBLs • FSRQs (Falcone et al. 2004, and Perlman et al.) • Use VHE along with longer wavelengths to characterize complete blazar main sequence and/or to characterize blazar evolution • Explore potential of AGN acceleration mechanisms in the presence of different ambient medium, including potentially higher electron densities and increased scattering • Search for cosmic ray acceleration signatures SCIPP seminar (26 Jan 2007)

  23. VERITAS • Array of f/1.0 imaging air Cherenkov telescopes with 12 m diameters • Located at Kitt Peak in Southern Arizona, USA • Sensitivity: <0.005 Crab at 200 GeV (50hr, 5) • Slewing Speed: 1 deg/sec • Angular Resolution: < 0.05o • Energy Resolution: E/E = 0.15 to 0.20 SCIPP seminar (26 Jan 2007)

  24. Active Galactic Nuclei Extragalactic Background Light Gamma Ray Bursts Shell-type Supernova Remnants Galactic Diffuse Emission Gamma-ray Pulsars Plerions Unidentified Sources Dark Matter (Neutralino Annihilation) * Cosmic Ray Origin Lorentz symmetry violation Science with VERITAS SCIPP seminar (26 Jan 2007)

  25. VERITAS Camera and Electronics • 499 pixels per camera • Each pixel is a 28mm Photonis XP2970/02 PMT • Pixel spacing = 0.15o FOV = 3.5o • Each PMT has a pre-amplifier located in the camera • Readout of each PMT through dual-gain 8-bit FADC boards • Trigger: • CFD for single channel • Pattern trigger for coincidence between multiplicities of neighboring channels • Array trigger for multiple telescopes operating stereoscopically SCIPP seminar (26 Jan 2007)

  26. Shower Timing: The Movie SCIPP seminar (26 Jan 2007)

  27. Differential Flux Sensitivity Whipple 10-m VERITAS - 4 Expected Performance (3, 50 hours) SCIPP seminar (26 Jan 2007)

  28. Relative Sensitivity GLAST and next generation VHE instruments complement one another well SCIPP seminar (26 Jan 2007)

  29. VERITAS Status • During Winter/Spring 2004, we completed the operation of the VERITAS prototype. • While not intended to provide competitive sensitivity, the prototype was intended to provide a test bed for VERITAS systems. Many important lessons were learned. • The prototype was converted into a complete telescope, T1 of the array. • VERITAS-4 construction is complete. Engineering/comissioning data is being taken. Science quality data has been obtained with 3 telescope array. • Sources are being detected and studied (stay tuned)! SCIPP seminar (26 Jan 2007)

  30. VERITAS Multiwavelength Observing Strategies • ToO observations from initiated by space-based instruments (ASM, Swift, GLAST, …) • Scheduled multiwavelength campaigns (RXTE, Integral, Swift, GLAST, …) • Ground-based monitoring of VHE sources generating ToO’s for satellite instruments • It is very important to have: • All-sky X-ray and gamma-ray monitoring (and notification) by space based instruments • ToO and monitoring programs in place at all wavelengths from GeV down to radio SCIPP seminar (26 Jan 2007)

  31. What Has Been Learned about blazars? • Very short TeV emission timescales  small regions for TeV gamma-ray acceleration • One flare is not the same as another flare. Some TeV flares have correlated X-ray emission, while others do not (and vice versa). • Simple one-component SSC does not explain all TeV emission, while it seems to work for some cases • Cooling electrons in the jet are certainly related to the TeV emission at some times, but the coupling may be either directly or indirectly • Much work to be done by applying more robust and diverse models and much work to be done to obtain full contemporaneous multiwavelength coverage for more flares! SCIPP seminar (26 Jan 2007)

  32. Why Study GRBs at VHE? • Need to understand acceleration mechanisms in jets, energetics, and therefore constrain the progenitor and jet feeding mechanism • Constrain local environment characteristics: Doppler factor, seed populations, photon vs. magnetic energy density, accel. and cooling timescales, … • Potential sources of UHE cosmic ray acceleration SCIPP seminar (26 Jan 2007)

  33. VHE GRB Observations • At this time, there are no firm detections of >100 GeV photons from GRBs (There are a few low significance potential detections at the ~3σ level; e.g. Atkins et al. and Amenomori et al.) • There are several reported upper limits (e.g. Saz-Parkinson et al. 2006, Atkins et al., Albert et al, Horan et al. 2007) • This is not surprising since the predictions for emission are just barely obtainable by the most sensitive current instruments such as VERITAS • Detection of VHE photons from GRBs would be very constraining to jet parameters. In particular, it could help to determine the hadronic component of the jet and the bulk Lorentz factor of jet plasma. (Could solve mysery of UHECRs!) • X-ray flares may provide another mechanism for detecting inverse Compton scattering from GRBs Zhang & Meszaros 2001 At Least VERITAS/HESS/MAGIC-2 sensitivity is needed, along with fast slewing OR all-sky coverage SCIPP seminar (26 Jan 2007)

  34. Cosmic Ray Source • While most GeV/TeV emission is expected to be IC, there is some component from p+ synchrotron, p+γ initiated cascades, and inelastic n+p initiated cascades. The latter is thought to be dominant. • If there is significant UHECR acceleration, then we could detect these • BUT, like blazars, it will be difficult to break degeneracy between IC and hadronic • Have the advantage of better constraints on Lorentz factor and smaller timescales/regions SCIPP seminar (26 Jan 2007)

  35. Cosmology with GRBs Multiple Methods: Use high redshift GRBs (4 < z < 20) to probe star formation history and epoch of reionization (see Woosley 2006, Lamb & Reichart 2000) (requires ability to obtain accurate redshifts from follow-up, which is tricky when redshifted into deep IR) Use GRBs as a back-illuminating light to map WHIM dark matter by means of its absorption features on the GRB spectra (see Nicastro et al.) (requires XMM/Chandra level of spectral resolution) Use GRB as a standard candle (after correcting Eiso toEγ) and then measure cosmological expansion parameters, similar to SNe methods (see Ghirlanda et al. 2005) (even with the correction factors on Eiso,still unclear if GRBs can be treated as standard candles) (need to measure Epeak and redshift) Use above method to constrain Ωm vs ΩΛand w0 vs w1 (see Firmani et al. 2006) (however, contraints may not compete with SNe at low redshifts without many more observations) SCIPP seminar (26 Jan 2007)

  36. GRB 050904: z = 6.29 High redshift, extremely bright (J=17.5, possibly as bright as 12 very early) => good cosmological probe; as predicted by Lamb and Reichart (2000) GRB survey is very efficient at finding high z objects (1/14 Swift redshifts) Near reionization time Limits on earliest star / galaxy formation Massive star implied by early collapse time; This GRB may be the first of many that can be used to probe >100Msolar stars that formed in the early universe and collapsed to GRBs, as predicted by Woosley et al. (2006). Eiso ~ 1054 ergs, Ejet ~ 1051 ergs => very similar to other bursts at lower z SCIPP seminar (26 Jan 2007)

  37. Lorentz Invariance Violation • Energy dependent delays of simultaneously emitted photons can limit (or measure) Lorentz invariance • Best lower limits to-date are from GRBs at keV/MeV energies; • 0.0066Epl ~ 0.66×1017 GeV • Our major disadvantage: we can't see the distant GRBs due to IR absorption • Our major advantage: High and broad energy range, especially if we measure a delay between GLAST - TeV • Everyone's disadvantage: Inherent energy dependent delays • With a detection of ~1 TeV photons by a >10x V/H/M sensitivity instrument and a detection by GLAST, the limit could be increased by ~100x (to ~Epl), asumming a GRB like 050502B at z=0.5 !!! • Need a very sensitive (>10x VERITAS) instrument to create light curves SCIPP seminar (26 Jan 2007)

  38. UnIdentified Objects (an aside) • TeV counterparts to unidentified objects from surveys at other wavelengths can provide strict constraints • Superior sensitivity of VERITAS will define the high energy spectrum of many EGRET UnIDs • With the upcoming launch of GLAST, SWIFT, … many new UnID objects are expected. TeV instruments are creating their own UnID catalog, as well! SCIPP seminar (26 Jan 2007)

  39. The Future • On the Ground: • There is an initiative within VERITAS to expand the current array with 3 enhanced telescopes • There are multiple "Beyond VERITAS" ideas to be proposed. Short term plans include MRI proposals to build small telescopes on a wide baseline (--> addressing >10 TeV region very cheaply) • Larger "Beyond VERITAS" plans are being developed (a white paper is being written) • From Space: • There will be a paucity of X-ray telescopes in about 6 years; this void will need to be filled • In the long term, there are several large X-ray missions planned (Con-X, EDGE, ...) to address blazars, GRBs, and cosmological questions SCIPP seminar (26 Jan 2007)

  40. Conclusions: What the future holds • Bigger source catalogs (diverse, deep, & distant) should be created by this generation of IACTs, as well as GLAST and Swift-BAT • Increased source count will allow population studies • Better energy resolution and many sources, some at higher redshift  Better EBL determination • Better sensitivity  better time resolution • Flaring timescales may further limit size of emission region • More detailed correlation studies and more accurate time lag studies • Detailed HID diagrams can be created at VHE and compared to lower energies as a function of time! More modeling will be necessary to interpret these data, and it may severely constrain tcool & taccel • Well-defined campaigns with guaranteed contemporaneous multiwavelength data are required! Plan now. • New source detections, particularly high-peaked FSRQs, may provide some of the most exciting upcoming results • We don’t yet understand the acceleration mechanism for VHE gamma rays in blazars (in spite of SSC popularity). The new data has the potential to put the nail in the coffin for many models • At this time, it is unwise to rule out blazar models involving proton acceleration! • There is scientific motivation and room for future TeV instruments on the ground and X-ray to γ-ray missions in space (although funding will certainly be tight) SCIPP seminar (26 Jan 2007)

  41. The VERITAS Prototype • 87 mirrors (~1/4 full) • 240 chs, using old recycled PMTs (~1/2 full camera) • VERITAS DAQ system SCIPP seminar (26 Jan 2007)

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