Recent TeV Observations of Blazars & Connections to GLAST Frank Krennrich Iowa State University VERITAS Collaboration GSFC, October 24, 2002 AGN

VERITAS Collaboration: Frank Krennrich for the VERITAS collaboration Collaboration members: Iowa State U. Leeds U. (U.K.) McGill University (Canada) Purdue U. Smithsonian Astrophysical Observatory UCLA University College, Dublin (Ireland) U. of Chicago U. of Utah Washington U.

Outline Introduction  atmospheric Cherenkov imaging technique  brief overview of TeV blazars Astrophysics results with Whipple 10m telescope  Mrk /2001, Mrk spectra  H , 1ES Next generation instrument: VERITAS VERITAS – GLAST connection Summary

History of the Whipple 10m Imaging Camera 0.01 – 100 TeV Area ~ 100,000 m 2 E ~ 0.2 – 100 TeV  ~ 0.2 o 100 optical photons/m 2 TeV within a few ns

 -ray images: - narrow, short, smooth Hadronic images: - broad, long - local muons, patchy hadron rejection: 99.7% (10 -3 )  -ray proton Cosmic Ray Rejection Technique Crab Nebula 7  in 1hour Courtesy W.Hofmann

Science Highlights: Whipple 10m 1989 Discovery of TeV photons from the Crab 1992 TeV photons from the blazar Mrk 421 z = Flare of Mrk 501 z = Discovery of H (z = 0.129) 2001 Flare Mrk Weekes et al. 1989, ApJ, 342, 379 Punch et al. 1992, Nature, 358, 477 Gaidos et al. 1996, Nature, 383, 319 Catanese et al. 1997, ApJ, 487, L Giant & short flare from Mrk 421 Krennrich et al. 2002, ApJL, 575, L9 Krennrich et al. 2001, ApJL, 560, L45 ~10 Crab Horan et al. 2002, ApJ, 571, 753 Petry et al. 2002, ApJ, in press

> 70 “EGRET” blazars at 1 GeV Redshift z = 0.03 – 2.28 z H Mrk 421 Mrk 501 1ES ES C66 1ES TeV blazar “Whipple” blazars at 300 GeV Mrk Mrk ES ES H

PKS Search for new TeV Blazars: Mrk 501 Mrk 421 H ES ES Costamante, L. & Ghisellini, G. 2001, A&A, 384, 56

Mrk 421 z = X-ray BL Weak GeV > 86  TeV Mrk 501 z = X-ray BL Marginal GeV > 40  TeV

Multiwavelength spectra Peak: 100 keV/200 GeV X-ray/TeV correlation Mrk 501Mrk 421 Peak at 1 keV/~50 GeV X-ray/TeV correlation Catanese et al., ??? Catanese & Weekes, PASP, 111, (1999)

Mrk 421 in 2000/2001:  23,000  -rays at E> 300 GeV Courtesy of J. Holder (see also Holder et al., 2001, Proc. 27 th ICRC, Hamburg)

Mrk 421/Mrk 501 spectra Mrk 501 Mrk 421 dN/dE ~ E -   K  e –(E/ E )   with E 0 = 4.6 K 0.8 TeV  dN/dE ~ E -   K  e –(E/E )   with E 0 = 4.3 K 0.3 TeV  ( TeV ) syst  Samuelson et al. 1998, ApJL, 501, L17 Krennrich et al. 1999, ApJ, 511, 149 Krennrich et al. 2001, ApJL, 560, L45 0 0

Mrk 421  on average,  -ray luminosity peak shifts to larger energies with increasing flux! Krennrich, F. et al. 2002, ApJL, 575, L9

1997 vs. Mrk 421 high state Mrk average Mrk 421 high state (set I)  spectral index varies but cutoff region remains stable!  imagine instrument with 20 times the sensitivity of Whipple  separate constant from variable component  IR-background density

Mrk 421: spectral variability: Property of a specific blazar or emission mechanism? Krennrich et al. 1999, ApJ, 511, 149 Krennrich et al. 2002, ApJL, 575, L9 Fossati et al. 2000, ApJ, 541, 166 X-ray VHE-  -ray

½ Hourly Spectral Variability: Feb. 1 Feb. 2 Feb. 27 March 19 March 25March 27 P = 3.4 x P = 4.0 x P = 8.5 x 10 -4

½ Hourly Spectral Variability VERITAS collaboration (in preparation)

X-ray/TeV correlation: Mrk 421 preliminary TeV lightcurve & TeV spectral variation X-ray/TeV lightcurve Courtesy of G. Fossati, J. Buckley & M. Jordan preliminary VERITAS collaboration (in preparation)

H : weak signal ~ 80 mCrab from Horan et al. 2002, ApJ, 571, 753

H spectrum: Whipple 2001: dN/dE ~ E K 0.35 K 0.05  Petry et al. 2002, ApJ, in press HEGRA 2001: dN/dE ~ E K 0.6 K 0.05  Whipple+HEGRA: dN/dE ~ E K 0.27 K 0.05  Aharonian et al. 2002, A&A, 384, L23 Petry et al. 2002, ApJ, in press

2002 Flares from 1ES : IAU circular 7903 (VERITAS collaboration), 2002 Holder et al. 2002, in preparation

Conclusion from blazar observations Spectral cutoffs for Mrk 421/501 at ~ 4 TeV:  possible evidence for absorption from IR background  or due to internal break due to  KN  ~ E -1 (when  h soft > m e c 2 ) Spectral variability (Mrk 421):   -ray luminosity peak shifts with increase   -flux correlation holds over 5 years! Rapid variability (Mrk421):  t variability ~ 15 min.   ~ 10  emission region pc H :  first detection of blazar with z ~ at E >300 GeV  steep spectrum: dN/dE ~ E K 0.27 K 0.05 Future: source list steadily growing (5 Whipple blazars)  VERITAS

VERITAS: Very Energetic Radiation Imaging Telescope Array System 50 GeV – 50 TeV Area: = 100,000 m 2 (1 TeV) = 40,000 m 2 (300 GeV) = 1,000 m 2 (50 GeV) Angular res.: 0.03 o – 0.14 o Energy resolution: 10-18% Observation strategy: pointed exposures

Arrays of Imaging Telescopes I - 50 GeV – 50 TeV -  ~ 0.03 ~ Flux sensitivity: m VERITAS

DESIGN 7-telescope Array 12 m Reflectors 500 PMT Cameras 3.5 o FOV

TECHNICAL PROGRESS Telescope: mount, mirrors Camera: PMTs, amps Electronics: FADCs, trigger DAQ: High speed Readout & analysis

TELESCOPE Overall Optical Support Structure Accomodates 12m mirror Pedestal

CAMERA PMT Installation Camera Box Construction Cabling inside

FRONT-END Amplifiers PMT Assembly Current Monitoring

Point Source Sensitivity Cangaroo III HESS MAGIC Stacee VERITAS

GLAST/VERITAS cross-calibration: Crab Nebula Hillas et al., ApJ, 503, 744 (1998) GLAST VERITAS Overlap: 50 GeV – 100 GeV - 1 TeV GLAST:   E/E ~ 10 GeV –100 GeV VERITAS:  E/E ~ 50 GeV-1000 GeV 20-25% uncertainty in the absolute energy of IACTs!  fix with GLAST/VERITAS cross- calibration using overlap! GLAST (40 days exposure)  150 (10) photons above 10 (100) GeV  10% accuracy in absolute E

Connections: Unified AGN picture  ~ several 10 3 GeV blazars  blazar classification studies (GeV blazars) Jet models  broad studies daily-yearly flux variations EBL cutoff  probe 0.1  m – 0.01  m Blazar spectra  20 MeV – 100 GeV Unified AGN picture  ~ 10 2 sub-TeV blazars  classification studies (extreme blazars) Jet models  detailed studies min. - yearly spectral variations EBL cutoff  probe 0.1  m – 50  m Blazar spectra  50 GeV – 50 TeV GLAST