1. The Next Generation of X-ray – Sensitive Observatories and their Potential for Blazar Variability Studies
Greg Madejski (SLAC/KIPAC)
including results from collaboration with:
Jeff Scargle, Rie Sato, Jun Kataoka, Tad Takahashi, Marek Sikora, others
Outline:
Motivation: impending launch of GLAST as the “next big tool” for blazar studies
Why the X-ray band?
Two aspects of X-ray variability: characterization of the time series, cross-band variability studies – and successes in both
New technique applied to Asca data for search of the most rapid variability
Future X-ray satellites: mission parameters relevant to blazar studies

2. EGRET All Sky g-ray Map (>100 MeV)
3C279
Cygnus
Region
Vela
Geminga
Crab
PKS
LMC
Cosmic Ray
Interactions
With ISM
PSR B
PKS

3. Schematic principle of operation of the GLAST Large Area Telescope
* g-rays interact with the hi-z material in the foils, pair-produce: e+/e- are tracked with silicon strip detectors: GLAST is a transistor, vs. EGRET – a vacuum tube
* The instrument “looks” simultaneously into ~ 2 steradians of the sky with the peak effective area of ~ 10,000 cm2
* Energy range is ~ 30 MeV – 300 GeV - allows an overlap with TeV observatories

4. GLAST LAT’s expected performance
GLAST sensitivity - time required to measure
the flux to 20% (solid), PL index to +/ (dashed)
as a function of source flux (E>100 MeV)
Expected flux and spectral index
measurements by GLAST for 3C279

5. Why is the X-ray band important?
Broad-band spectra of two classes of blazars:
3C279 (data from Wehrle et al. 1998) Mkn 421 (data from Macomb et al. 1995)
Compton component: X-rays probe the total jet content (particles radiating at the low end of the distribution are most numerous)
Synchrotron component: X-rays probe the most energetic end of particle distribution

6. Two facets of time variability
Two “directions” for variability studies:
(1) Sensitive measurements of the properties of the time series (PDS, structure f’n, …) – Kataoka’s, McHardy’s talks
(2) Cross-correlations with multiple energy bands
Recent successes:
* Location of the “blazar dissipation zone” –
probably >pc from the central source:
* D. Harris’s/T. Cheung’s M87 results
* A. Marscher’s BL Lacertae
* Implications of the 3C454.3 monitoring
(Sikora, Moderski, GM 2008)
* Acceleration / cooling time scales -
Suzaku observations (Sato et
al. 2008)
Edelson et al. voiced concerns about reliability of measurement of lags that are smaller than the orbital periods of low Earth orbit satellites.
Hence the situation is very complex and still under debate.

7. Time series analysis – in search for the shortest variability time scales: Results for Mkn 421(work in progress)
A scalegram technique (variation of a wavelet method) can be fruitfully used to search for variability power at the shortest time scales (work with Jeff Scargle)
This particular implementation requires for photons to be time-tagged to a precision much better than the photon interarrival time, and data must be free of background (hence Asca GIS data)
Results of an application of the wavelet scalegram to the Asca GIS data for Mkn 421:
- there is some residual significant power at about 500 sec time scale, the extrapolation to the longer time scales consistent with the PDS / structure f’n calculated by Kataoka et al. 2001
Asca light curve from
“long look” of Mkn 421
(Takahashi et al. 2001)

8. Recent results from Suzaku X-ray variability of TeV-emitting blazars (see Rie Sato’s poster for details)
Asca data for Mkn 421
Photon Index
Flux
2.3
2.4
2.5
Suzaku observed another TeV blazar, , reveals that hard X-rays lag soft X-rays:
20 ks delay of 6 keV vs. 0.6 keV X-rays -
clear energy-dependent acceleration time scale?
(Sato et al. 2008)
-> Implications on the structure of B-field
From Asca data: Mkn 421 showed that during flares
the spectrum gets “hard” very quickly, then if softens as
the source gets fainter: signature of energy-dependent electron cooling time scale (Takahashi, GM, +, 1996)

9. X-ray facilities for blazar monitoring
Current
Suzaku: v. sensitive, keV bandpass (for blazars), but constrained pointing (90+/-15 deg to the Sun)-> ~ 1 month max at a time, low-Earth orbit
XMM-Newton: also sensitive but limited bandpass ( keV), deep orbit
RXTE: keV bandpass, good all-sky coverage, but limited sensitivity (~ erg/cm2/s), nearing the end of its lifetime
Swift: reasonable sensitivity, quick slew, all-sky pointing, but low Earth orbit, GRBs a priority
Chandra: v. good for structure studies (extended jets), but suffers from photon pile-up for bright sources. Great for difficult IDs!

10. Near future for GLAST/X-ray monitoring: Suzaku
Hard X-ray detector
(HXD: keV)
X-ray spectrometer
(XRS: keV)
X-ray imaging spectrometer
(XIS: keV)
Suzaku carries a three instrument. But one od them X-ray micro-calorimeter XRS, but the XRT lost all its cryogen before routine scientific observations could begin.
Suzaku covers the energy range keV with the two instruments,
X-ray CCDs (XIS) and the hard X-ray detector (HXD).

11. X-ray facilities for blazar monitoring
Future:
MAXI: to be launched soon, all-sky monitor
NuSTAR: launch, hard X-ray bandpass ( keV): blazars a priority
NeXT: 2013 launch, but the calorimeter is the primary instrument -> high resolution X-ray spectroscopy a priority (clusters, SNR rather than blazars)
Constellation-X: In principle might be excellent, but probably far in the future (2018?); high-resolution spectroscopy a priority
EXIST: great all-sky capability, hard X-ray band (~ 20 – 600 keV), but probably will be approved / launched beyond GLAST (2018?)
Simbol-X: Hard X-ray bandpass, but still in the study phase, launch 2015?
Astrosat? Spectrum X-Gamma? Xeus?

12. MAXI Payload To be attached to the Space Station in March 2009
Radiator for X-ray CCD camera
Mass: 530 kg
80cm
107cm
185cm
ISS JEM/EF
Optical Star Sensor
(for attitude
determination ）
X-ray Gas Camera
Gas Slit Cameras (GSC)
Xe-filled proportional counter
2—30 keV; cm2
Ｘ-ray CCD Camera
Solid-state Slit
Cameras (SSC)
32 CCD chips
0.5—15 keV; 200 cm2

13. MAXI sensitivity and targets
1 orbit
1 day
1 week
1 Month
2 Years

14. Hard X-ray imaging satellite NuSTAR
Star tracker
NASA’s Small Explorer mission, slated to fly in
Two identical coaligned grazing incidence hard X-ray telescopes:
Multilayer coated segmented glass optics
Actively shielded solid state CdZnTe pixel detectors
Extendable mast provides 10-m focal length
Pegasus rocket / satellite in low-Earth orbit, inclination TBD
Energy bandpass 6 – 80 keV
Blazar observations joint w/GLAST important part of the science drivers:
plan is for 3 months of observing time
for blazars alone
Mast Adjustment Mechanism
X-ray optics
Mast
Shielded focal plane detectors

15. NuSTAR performance and blazar observing strategy
Parameter
Performance
Mission launch
August 2011
Mission duration
2 years (prime mission)
Energy band
keV
Angular resolution
40” HPD
Spectral resolution
1 keV keV
Field of View
13 arcmin
Sensitivity ( keV, 106 s)
1 microCrab
* The duration and cadence of monitoring will
become more clear once GLAST is in orbit
* Sensitivity: for the brightest GLAST blazars,
average keV flux is ~ erg cm-2 s-1
-> we should get about 0.1 NuSTAR count/s
-> Dflux ~ 7% , Da~0.1 in a NuSTAR orbit
* Probably will do “continuous looks”

16. Advertisement: a tool to announce MW campaigns (Adler Planetarium: from Lucy Fortson)