The role of GLAST in multiwavelength observations of bright TeV blazars

1. The role of GLAST in multiwavelength observations of bright TeV blazars Gamma-ray Large Area Space Telescope D. Paneque (dpaneque@slac.stanford.edu) J.Chiang, B. Giebels, V. Lonjou, B.Lott, G. Madejski on behalf of the GLAST/LAT collaboration Abstract:The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST) satellite, which will be launched in December 2007, aims to perform gamma-ray astronomy in the energy range 20 MeV to greater than 300 GeV. The sensitivity of LAT is about 25 times better than its predecessor, EGRET, which presumably allows one to detect the bright TeV sources Mrk 421, Mrk 501, PKS2155-309 and 1ES1959+650 in time scales of only few days, even in quiescent state. Together with the enhanced sensitivity of the current generationn of Imaging Air Cherenkov Telescopes (IACTs) in the energy range 100 GeV - 500 GeV, LAT observations offer unprecedented capabilities to study the high energy emission of these objects in both quiescent and flaring state. Simultaneous LAT-IACT observations will provide spectral coverage of the peak and rollover of the high energy SED components. Coupled with coordinated X-ray optical and radio observations, the data will provide constraints on the models that were not available before. We present the capabilities of the LAT instrument to study these objects. 1 - The LAT instrument on board of the GLAST satellite Science Performance Requirements Angular resolution and sensitivity vs Energy The main instrument onboard of the GLAST satellite is the Large Array Telescope (LAT) The LAT consists of 16 identical towers in a four-by-four grid, each one containing the following three elements: Tracker Precision Si-strip Tracker (TKR) 18 XY tracking planes with tungsten foil converters. It measures the photon direction; gamma ID Hodoscopic CsI Calorimeter (CAL) Array of 1536 CsI(Tl) crystals in 8 layers. Measures the photon energy; image the shower. The differential sensitivity points are defined as the flux level over an energy interval of 1/4 of a decade over which the statistical significnce is 2 standard deviations in the specified time (1 day, month, year) 1 day1 month1 year Segmented Anticoincidence Detector (ACD) 89 plastic scintillator tiles. Rejects background of charged cosmic rays; segmentation mitigates self-veto effects at high energy. The systems work together to identify and measure the flux and direction of cosmic -rays with energy ~20 MeV to ~300 GeV Detail performance of the GLAST/LAT instrument can be found at: www-glast.slac.stanford.edu/software/IS/glast_lat_performance.htm 2 - LAT capabilities on bright TeV blazars: Mrk 421, Mrk 501, PKS 2155-304, 1ES1959+650 Simple estimates for the expected photon flux in the LAT energy range according to the the SSC model fits of past data show that LAT should detect those objects in timescales of several days The physics related to TeV blazars (and AGNs in general) is not yet understood, despite some of these objects had been studied for >10 years Power law function to describe the differential photon fluxes in the 0.1-10 GeV energy range Culprits for the relatively poor knowledge of these objects 1 - Time evolving broad band spectra For the several cases, we report the required time for a 5 sigma detection, as well as the statistical undertainty in the photon spectral index a and photon flux above 0.1 GeV F>0.1GeV achievied in that obs. time with LAT. Because of the LAT sensitivity and the hard spectra of these sources at LAT energies, F improves at high energies (~1 GeV) Coordination of instruments covering different energies needed 2 - Poor sensitivity to study high energy part (E>0.1 GeV) Large observation times (with EGRET and “old” IACTs) were required for signal detection Data NOT truly simulteneous, and most of our HBL’s knowledge relates to the high state High K = 2.1 x10-9 GeV-1cm-2s-1 ; a = 1.60 F(>0.1GeV) = 1.3 x10-8 ph cm-2 s-1 Time for 5 sigma detection: 17 days F>0.1GeV ~ 66% ; a ~ 13% High K = 1.4x10-8 GeV-1cm-2s-1 ; a = 1.45 F(>0.1GeV) = 9.0 x10-8 ph cm-2 s-1 Time for 5 sigma detection: 0.7 days F>0.1GeV ~ 63% ; a ~ 13% Mrk 501 1es1959+650 Current experimental data allows for a big inter-model and intra-model degeneracy. More and “higher quality” data required to constrain models Low K = 1.5x10-9 GeV-1cm-2s-1 ; a = 1.65 F(>0.1GeV) = 1.0 x10-8 ph cm-2 s-1 Time for 5 sigma detection: 33 days F>0.1GeV ~ 62% ; a ~ 12% Low K = 2.3x10-9 GeV-1cm-2s-1 ; a = 1.45 F(>0.1GeV) = 1.42 x10-8 ph cm-2 s-1 Time for 5 sigma detection: 7 days F>0.1GeV ~ 62% ; a ~ 13% 3EG J1959+6342 • Leptonic vs hadronic emission models • Intrinsic spectra vs EBL-affected spectra • Production of flares with timescales down to 1 min • Acceleration/cooling in single or multi-zone • Role of external photon fields • Time-resolve emission models EGRET EGRET flux, Hartman 1999, ApJS 123 The EGRET source 3EG J1959+6342 is located∼1.5 degrees away from 1ES1959+650, and can be considered as an upper limit for the average emission of this blazar K = 6.8x10-9 GeV-1cm-2s-1 ; a = 2.45 F(>0.1GeV) = 13.3 x10-8 ph cm-2 s-1 Time for 5 sigma detection: 10 days F>0.1GeV ~ 28% ; a ~ 8% EGRET high, Kataoka 1996, ApJ 514 This is the ONLY measurement of Mrk501 at these energies; it is a ~5 sigma detection K = 2.7x10-8 GeV-1cm-2s-1 ; a = 1.3 F(>0.1GeV) = 1.8x10-7 ph cm-2 s-1 Time for 5 sigma detection: 0.2 days F>0.1GeV ~ 68% ; a ~ 13% Tavecchio 2001 ApJ 554 Present and near future: New Generation of IACTs came online (low Eth, high sensitivity) GLAST in operation next year (~25 more sensitive than EGRET) 0.1-10 GeV 0.1-10 GeV EGRET flux HIGH K = 3.4x10-8 GeV-1cm-2s-1 ; a = 1.70 F(>0.1GeV) = 2.4 x10-7 ph cm-2 s-1 Time for 5 sigma detection: 0.5 days F>0.1GeV ~ 52% ; a ~ 13% Mrk 421 PKS 2155-304 High K = 6.0 x10-8 GeV-1cm-2s-1 ; a = 1.60 F(>0.1GeV) = 3.9 x10-7 ph cm-2 s-1 Time for 5 sigma detection: 0.2 days F>0.1GeV ~ 56% ; a ~ 13% Great capability to cover entirely and simultaneosly the High Energy peak in relatively short observation times regardless of high/low activity of the source. Together with simultaneous observations at X-ray frequencies, these new data will permit to study: EGRET flux LOW Hartman 1999, ApJS 123 K = 8.0x10-9 GeV-1cm-2s-1 ; a = 2.35 F(>0.1GeV) = 13.2 x10-8 ph cm-2 s-1 Time for 5 sigma detection: 5 days F>0.1GeV ~ 34% ; a ~ 9% • Variability, correlation and time lags between different energies • Evolution of spectra with time, displacement of peaks … EGRET flux, Hartman 1999, ApJS 123 K = 2.13x10-8 GeV-1cm-2s-1; a = 1.60 F(>0.1GeV) = 13.9 x10-8 ph cm-2 s-1 Time for 5 sigma detection: 0.6 days F>0.1GeV ~ 60% ; a ~ 14% 3EG J1104+3809 Low K = 3.6x10-9 GeV-1cm-2s-1 ; a = 1.40 F(>0.1GeV) = 2.3 x10-8 ph cm-2 s-1 Time for 5 sigma detection: 4 days F>0.1GeV ~ 58% ; a ~ 12% LAT data (<10 GeV) will not be affected by the EBL, which will permit disentangling the intrinsic spectra of the sources. This will help to rule out/confirm emission models Krawczynski 2001 (Apj 559) 3 - Concluding remarks LAT instrument assembled and working since >1 year. Currently being characterized/validated. LAT operation (beginning 2008) will boost our current capabilities to study blazars. Information on the blazar and AGN related topics we aim to address with LAT data can be found at http://www.slac.stanford.edu/~lott/agn.html LAT will bring key data from a poorly sampled energy range (0.02-100 GeV). However, simultaneous MW observations are needed to understand the broad spectra of these objects. Campaigns on these four bright TeV blazars are being planned for 2008; agreements with instruments covering radio to TeV energies are currently being made. Do not hesitate in contacting us if you are interested in participating. Observations at X-ray frequencies with RXTE have already been granted. More information on multiwavelength campaigns with GLAST/LAT on these and other objects can be obtained at http://glast.gsfc.nasa.gov/science/multi/