using x-ray to tev instruments to probe blazars, grbs, and cosmological parameters

Abe Falcone, Penn StateSCIPP seminar (26 Jan 2007)

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

– Implications for Universe

• Present status

• The future


Imaging Air Cherenkov Technique

ray interacts ray interacts

Source emits Source emits rayray

Effective area is size of light pool ~ 105

m2


-ray images:

- narrow, short, smooth

• Hadronic images:

- broad, long

- local muons, patchy

• hadron rejection: 99.7% (10-3)

-ray proton

Crab Nebula with Whipple 10 m

~7 in 1hour

Cosmic Ray Rejection Technique

5o


80 m

Stereo Reconstruction

• Exclude muon background

• Determine source from intersection of shower axis

• Crab nebula ~35σ in 1 hour with VERITAS


GeV/TeV Observatories

MAGIC

H.E.S.S.

CANGAROO

CELESTE

STACEE

Tibet

Milagro

Whipple 10m

HEGRA

Solar Two

Tibet AS

VERITAS

CAT

MAGIC


Blazar Categories

• FSRQ Vs. BL Lac• Low Peaked Vs. High Peaked

Fossati et al. 1998, Ghisselini et al. 1998


Broadband Coverage

GLAST

VERITAS

Swift X-ray Spectrum:Swift,...0.2 keV – 150 keV

Gamma ray: GLAST, AGILE,...30 MeV – 300 GeVall sky (~103 AGNs)

VHE: VERITAS, HESS,...50 GeV – 50 TeV(5 mCrab, 50 hours)Pointed (~ 50 AGNs)

Mrk501 SED taken from Catanese & Weekes 1999


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


TeV Blazars - RXTE ASM Overview0197 99 029896 00 03

Mrk421

Mrk501

1ES2344

1ES1959

PKS2155

H14262-12 keV

Krawczynski et al. 2003


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)

(0.75-1.5 TeV) /(1.5-4 TeV)

HEGRA sees of ~0.75 during Mrk421 flaring (Aharonian et al. 2002)


Correlated LightcurvesMultiwavelength lightcurve of Mrk501 from 2-20 Apr 1999 (Catanese et al. 1997)

>350 GeV

50-150 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


1ES1959: Overall Lightcurves & Orphan Flare


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


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


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


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

time bins = 2min

Costamante et al. 2006, Aharonian et al. 2007, Falcone et al. 2007 (analysis ongoing)

HESS(>200GeV)


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


H1426: X-ray Variability

X-ray Spectral variability is evident and it does not directly track the flux level. No TeV flaring evident.

TeV Flux

(Whipple)

X-Ray Flux

X-Ray Index


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


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!


Potential New Source Types

• LBLs

• FSRQs

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

Fossati et al. 1998, Ghisselini et al. 1998

(Falcone et al. 2004, and Perlman et al.)


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


Science with VERITAS

Active Galactic NucleiExtragalactic Background Light

Shell-type Supernova Remnants

Gamma-ray PulsarsPlerions

Gamma Ray Bursts

Dark Matter (Neutralino Annihilation) *

Galactic Diffuse Emission

Unidentified Sources

Lorentz symmetry violationCosmic Ray Origin


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


Shower Timing: The Movie


Expected Performance

(3, 50 hours)

Whipple 10-m

VERITAS - 4

Differential Flux Sensitivity


Relative Sensitivity

GLAST and next generation VHE instruments complement one another well


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)!


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:

1) All-sky X-ray and gamma-ray monitoring (and notification) by space based instruments

2) ToO and monitoring programs in place at all wavelengths from GeV down to radio


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!


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


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

At Least VERITAS/HESS/MAGIC-2 sensitivity is needed, along with fast slewing OR all-sky coverage

Zhang & Meszaros 2001


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


Cosmology with GRBsMultiple 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)


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


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


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!


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


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)


The VERITAS Prototype• 87 mirrors (~1/4 full)• 240 chs, using old recycled PMTs (~1/2 full camera)• VERITAS DAQ system

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