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

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)
Abe Falcone, Penn State

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

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
~7 s in 1hour
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

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)
Abe Falcone, Penn State

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)
Abe Falcone, Penn State

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)
Abe Falcone, Penn State

8. Broadband Coverage X-ray Spectrum: Swift,... Gamma ray:
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)
GLAST
VERITAS
Swift
Mrk501 SED taken from Catanese & Weekes 1999
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

9. Why Study Blazars at VHE?
Figure from J.Buckley 1998
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
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

10. TeV Blazars - RXTE ASM Overview01 97 99 02 98 96 00 03
Mrk421
Mrk501
1ES2344
1ES1959
2155: 96/97 DETECTION
PKS2155
H1426
2-12 keV
Krawczynski et al. 2003
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

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)
( TeV) / (1.5-4 TeV)
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

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

13. 1ES1959: Overall Lightcurves & Orphan Flare
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

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)
Abe Falcone, Penn State

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)
Abe Falcone, Penn State

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

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)
Abe Falcone, Penn State

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=  excellent target for studies of IR background
Steep measured TeV spectrum
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

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

20. Blazar H : 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)
Abe Falcone, Penn State

21. H1426 TeV Spectrum
Very steep TeV spectrum found by both Whipple (Petry et al. 2002) and HEGRA (Aharonian et al. 2002)
HEGRA results coupled with measurements of the EBL lead to an intrinsic spectral index of ~1.9
Figure from Aharonian et al. 2002
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

22. 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)
Abe Falcone, Penn State

23. Potential New Source Types
LBLs
FSRQs
Fossati et al. 1998, Ghisselini et al. 1998
(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)
Abe Falcone, Penn State

24. 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)
Abe Falcone, Penn State

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

26. 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)
Abe Falcone, Penn State

27. Shower Timing: The Movie
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

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

29. Relative Sensitivity
GLAST and next generation VHE instruments complement one another well
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

30. 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)
Abe Falcone, Penn State

31. 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)
Abe Falcone, Penn State

32. 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)
Abe Falcone, Penn State

33. 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)
Abe Falcone, Penn State

34. 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)
Abe Falcone, Penn State

35. 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)
Abe Falcone, Penn State

36. 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 to Eγ) 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 ΩΛ and 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)
Abe Falcone, Penn State

37. GRB : 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)
Abe Falcone, Penn State

38. 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 B at z=0.5 !!!
Need a very sensitive (>10x VERITAS) instrument to create light curves
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

39. 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)
Abe Falcone, Penn State

40. 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)
Abe Falcone, Penn State

41. 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)
Abe Falcone, Penn State

42. 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)
Abe Falcone, Penn State

43. Detailed 1ES1959 Lightcurves
TeV X
10 keV
X-ray index
optical
Orphan TeV Flare
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State

44. Expected Performance of VERITAS-4 and VERITAS-7
Double exposure
Single exposure
Sky survey
3% lower
10% lower
30% lower
3.7x10-12 erg cm-2 s-1
1.4x10-12 erg cm-2 s-1
1.4x10-11 erg cm-2 s-1
Flux sensitivity (50h)
10 TeV
1 TeV
100 GeV
+ 20%
+ 90%
3x109 cm2
2.2x109 cm2
3.3x108 cm2
Collecting Area
50 g/min
35 g/min
Crab Nebula Rate
90 GeV
110 GeV
Peak Energy
VERITAS-7
VERITAS-4
Characteristic
SCIPP seminar (26 Jan 2007)
Abe Falcone, Penn State