# Presentation: 111073

## EXIST Concept for BHFP:Hard X-ray Black Hole Surveys in Space and Time

- Josh Grindlay
- Harvard
- (on behalf of EXIST Concept Study Team)
**NRC Beyond Einstein Program Assessment Committee**
- Washington, DC
- November 7, 2006

## Black Holes as Fundamental Objects(Background for Black Hole Finder Probe Science)

- Black holes, long conjectured and now confirmed with masses ranging from ~4 – 4 billion solar masses, are essential for understanding the physics of the Universe as well as the extremes of space-time near their horizons
- BHs power the most energetic phenomena (quasars, gamma-ray bursts...) yet may be essential for formation of galaxies and ultimately life
- Accretion onto BHs is a significant (but still uncertain) fraction of the Luminosity of the Universe, but BH growth from stellar to intermediate (?) to supermassive still highly uncertain
- Black Hole Finder Probe (*EXIST*) will survey BHs on all size and luminosity scales to give first Global View of BH numbers, total energy output, and detailed phenomena

## Context for BHFP to EXIST

*Black holes are best revealed by their accretion of matter, which often obscures them except at “hard” X-rays (>10 keV)*
- Hard X-ray (HX) band is still poorly explored, but the promise of rich source counts and physics has been revealed by pathfinder coded aperture imaging missions ***INTEGRAL**** *and ***Swift***
- BHs are inherently time-variable; and some classes (luminous obscured quasars) are rare: need _*All-Sky, All-time Surveys with >10-20X previous sensitivity (for sample) and <10” positions*_* *
*EXIST (**Energetic X-ray Imaging Survey Telescope**)*, *recommended by AANM Decadal Survey*,* *provides science and mission best matched to BHFP and highly complementary to future missions:
- BH survey for detailed spectroscopy with ***Con-X***
- Tidal disruption of stars onto massive BHs: trigger for ***LISA ***
- Essential HX spectra to measure IR background with ***GLAST ***
- Trigger deep mid-IR spectroscopy of z >7-10 GRBs with ***JWST***

## EXIST Science objectives(from the earliest stellar BHs to supermassive BHs in Galaxies)

- Obscured SMBHs and origin of the Cosmic X-ray Bkgd
- Dormant SMBHs (tidal disruption of stars & ***LISA*** triggers)
- SMBH masses & spins from timing & spectra
- Blazar spectra from ***EXIST*** vs. ***GLAST***: Cosmic IR Bkgd
- GRBs from z ≥ 7-10: birth of 1st BHs & probes of universe
- Nature/number of BHs (vs. NSs, WDs) in Galaxy

## Overview of BHFP-EXIST Science and Design

**Overview of *****BHFP-EXIST***** Science and Design**

**Hard X-ray (~3-600 keV) all-sky imaging *****each orbit *****to measure:**** **
- GRBs out to z ~20 and *first stellar Black Holes* ***( ~5-20X Swift  sensitivity)***
- Obscured AGN and accretion (BHs) vs. nuclear (stars) luminosity of universe
- Stellar Black Holes in Galaxy & IMBHs in Local Group & BHs

***Mission Design***** *****parameters:***
- Extend ROSAT sens. (~5 x 10-13cgs) to 3-150 keV with 0.9-5’ resolution & ~10” positions
- Two wide-field coded aperture telescopes: 10-600 keV (*6m**2** CZT*) & 3-30 keV (*1.3m**2 **Si*)

***http://EXIST.gsfc.nasa.gov***

**EXIST  measures Cen-A **_**every orbit**_**: *****characteristic time variability (QPOs) constrain BH mass and spin***

***High Energy Telescopes***
***HET***** (10-600keV)**
**(Array of 19 coded **
**aperture telescopes;**
**154****o ****x 65****o ****FoV)**

***Low Energy Telescopes***
***LET***** (3-30 keV)**
**(Array of  32 coded **
**aperture telescopes;**
**160****o ****x 64****o ****FoV)**

## EXIST Survey Sensitivities vs. previous missions

***EXIST***** Survey Sensitivities vs. previous missions**
- (5σ survey threshold, 1year survey, full-sky)

**5****σ**** in 1 yr (calendar) sensitivities over band E****low****      2E****low***** *****with 20% duty cycle:**
**0.05mCrab = 5 x 10****-13**** cgs, (~20X *****Swift/BAT*****) for LET 3-30 keV & HET 10-100 keV**
**~0.5mCrab = 5 x 10****-12**** cgs ( ****~20-100X *****INTEGRAL******) *****for HET 100-600 keV**
***unique***** ~20-40% duty cycle coverage on any source, *****full-sky ea. 95min***

## Hard X-ray Sky

**Previous Hard X-ray Sky**
- HEAO-1, BeppoSAX

***2015(?) Hard X-ray Sky***
- EXIST

**≤****2010 Hard X-ray Sky**
- Swift & INTEGRAL

** ****Hard X-ray (10-600 keV) sky not yet surveyed to ROSAT sensitivity.  *****EXIST*****   would be ~20X more sensitive than *****Swift *****or *****INTEGRAL *****and cover full sky**
** *****EXIST *****will detect ≥3 x 10****4 ****sources,  ≤10******** positions,  3-600 keV spectra**
*** ******EXIST *****would provide unique temporal survey: *****full sky imaging each orbit***

## Obscured AGN and origin of the Cosmic X-ray Background(the cumulative glow of BHs in active galactic nuclei measured by EXIST) 

- NGC1068
- NGC6240
- (Vignati et al 99)

**Chandra **& **XMM ** surveys find >40% unresolved CXB from obscured AGN
-      but at peak of CXB, E ~20-30 keV, only ~10% of CXB is resolved!

## Obscured Seyferts, Radio Galaxies & QSOs vs. z?

*EXIST**** ***can detect and discover obscured AGN over a broad range of Lx and absorption column NH to further constrain NH vs. z growth of BHs

- e.g., Narrow-line radio galaxy (NLRG) and Type 2
- QSO, 3C234  barely detected with Einstein Obs.,
- with XMM spectrum shown from Piconcelli
- et al. 2006, would be found with the *EXIST *survey.* *

*EXIST *survey will explore the recent evidence (La Franca et al 2005 and Treister & Urry, astroph/0610525) that obscured AGN are *increasing as *(1+z)0.4

## EXIST measures Cosmic X-ray Background from all BHs(EXIST detector backgrounds dominated by CXB from faint AGN)

***EXIST ***optimally matched in Energy band to measure still uncertain CXB spectrum, isotropy, and spatial fluctuations with HET (5arcmin) vs. LET (1arcmin). High CXB count rate and HET vs. LET collimator FoVs and continuous scanning allow low-systematics measurements.

## Dormant SMBHs revealed by Tidal disruption of stars(and predicting gravitational waves from “invisible” supermassive BHs)

- Artists conception of tidal disruption of star
- in RXJ1242-1119 detected with ROSAT (1991) and
- confirmed with Chandra (Komossa et al 2004).

***Tidal disruption of stars spiraling  into ***
***Dormant SMBHs***** ****with mass ~10****7**** Mo****:**
*if 1% of L**acc** in HX band, ~10**-5 **events/year/Mpc**3 **allow ****EXIST**** to see ~*10-30* flares/yr out to ~200Mpc** *(Grindlay 2004).
- _HX spectral comp. “confirmed”_
- _with_ _PL spectral decay of RX1242_
- _measured with Chandra/XMM!_
**	**
***Sub-giants with WD cores are***
***gravitational wave LISA triggers.***

*Possible soft (~5keV) prompt (~1d) burst detectable out to ~100 Mpc *
*directly with EXIST (LET); ****LISA trigger***
***Measure 10******6-8******M********** ****** SMBH content/evolution of nearby galaxies***
***(to understand BH-Galaxy Bulge mass relation & BH-galaxy evolution)***

## AGN variability constrains SMBH masses(Variability frequencies correlate with BH mass – Uttley & McHardy 2005)

- Power spectral density (PSD) for NGC 3227
- derived from RXTE (PCA) data.

- PSD break vs. BH mass measured from
- optical reverberation mapping (filled circles).

- Pointed X-ray telescopes get very limited samples; <10 thus far!
*EXIST *will go factor of 10-30X deeper than RXTE and measure
- variability spectrum for ≥103 AGN to give BH masses vs. z and NH

## EBL: Hard x-ray (synchrotron) spectral breaks (~5-200keV) for Blazars at known redshift allow SSC gamma-ray (~10 GeV - 10 TeV) spectral breaks measured by GLAST & HESS/VERITAS to constrain poorly known diffuse IR background from total stellar light of universe absorbing gammas to e+-e-

Time-variability: spectral breaks required from simultaneous HX measurements. Wide-field HX imaging needed for simultaneous X,Gamma-ray observations of Blazars

- EXIST

- VERITAS

- GLAST

- SSC model for Mkn 501 (Coppi & Aharonian 1999)

***EXIST ***will provide the _*continuous HX spectral-monitoring*_ to study Blazars and non-thermal AGN to constrain  diffuse IR (~10-100μ) background from obscured AGN and thus*** ***_***nuclear vs. accretion luminosity of the universe***_
_***Complements GRB science: star formation vs. redshift from L***__***GRBs***__*** vs. z***_

**Blazar Spectral variability **
*Extragalactic Background Light (EBL): Stellar vs. Accretion Luminosity of Universe*

***EBL*****:** Hard x-ray (synchrotron) spectral breaks (~5-200keV) for *Blazars* at known redshift allow SSC gamma-ray (~10 GeV - 10 TeV)** **spectral** **breaks measured by *GLAST** **&* *HESS/VERITAS* to constrain poorly known diffuse IR background from total stellar light of universe *absorbing gammas to e**+**-e**-*
***Time-variability:*** spectral breaks *required *from _*simultaneous*__ HX measurements_. Wide-field HX imaging needed for simultaneous X,Gamma-ray observations of Blazars

## EXIST measures Gamma-ray Bursts at z~0.1-15 (Birth of stellar-mass Black Holes, including the very First?)

***“******Long”-GRBs*** are  from SNIb,c & likely due to stellar BH formation
-  Likely that first stars were ~100Mo and collapse to BHs       GRBs
-  ***“******Short”-GRBs*** from merging NSs in globulars (Grindlay et al 2006):      are Short GRBs enhanced at z of globular cluster formation?

***EXIST***** could detect GRBs to z~10-15**
**from PopIII BHs at re-ioniz.**
**epoch suggested by WMAP.**
**Photometric z from Lum-E****peak**
**       ****need **_**response to E>300keV**_**,**
***And *****from Lum-Variability (Firmani**
**Relation)         need **_**large area det**_**.**
**X-ray flashes and high z GRBs**
**        ****need **_**response to E~3 keV**_
**~5sr instantaneous GRB coverage**
**& increased sensivity: ****~700GRBs/y**
**        ****capture *****rare***** (high z?) events**

_**Horizontal curves**_**: flux at detection threshold vs. E****peak **_**Vertical curves**_**: observed flux and E****peak ****for same GRB at z=1 (top +) to 10 (bottom +)  (Band 2004).**

## Most distant stars & galaxies probed by GRBs

**Most distant stars & galaxies probed by GRBs**

*Swift* GRB at z = 6.3 & Spitzer galaxies at z ~8 show *GRBs* *must be detectable out to at least z ~8-10*
- Broader energy band, higher
-        sensitivity & FoV needed for large sample at z ≥ 8-10
- IR from space (***JWST***) needed for z ≥10!

- Record redshift vs. time: GRBs nearly max!

-  *EXIST *measures Epk and T0.45 and  Firmani reln. gives “photo-z”  with uncertainties typically ∆(log(1+z)) ~0.1.
-  *EXIST *measures Epk up to 3 MeV using active shields
-  GRBs provide “back-light”  for IR spectroscopy of      IGM, gas, & galactic structure  back to re-ionization

- Firmani et al 2006, MNRAS, 370, 185

- GRB luminosity and thus z from
- Measured Epk and variability index T0.45

- GRB Luminosity correlates with spectrum: gives z !

## Predicted EXIST GRB rate opens universe to z ≥ 10

- Predicted GRB rates vs. z based on Bromm and Loeb (2005). *EXIST** *will detect many GRBs at z >7 and may detect Pop III GRBs for which models are uncertain.
- GRBs allow cosmology at highest redshifts (non-CMB), and *EXIST *will open this window.

***EXIST will ***** probe:**

*EXIST *GRBs vs. z will probe the star
- formation rate (SFR) vs. z at highest
- redshifts, and constrain/measure Pop III.

## EXIST measures stellar BHs & IMBHs in Local Group

***EXIST***** detects all bright stellar BHs in transients** (Lx(>10 keV) ~1037-38 erg/s) throughout Galaxy, LMC/SMC and M31. ***Reveal population of obscured HX sources found with INTEGRAL/Swift: discrete sources at >10 keV***
***Isolated***** stellar BHs in Galaxy and IMBHs** in Local Group accreting
- 	via Bondi-Hoyle (with ~10-4 efficiency) from GMCs nearly Compton thick
**Faint BH transients in *****Central***** *****Galactic Bulge****?*: BHs in
- 	nuclear cusp (cf. Alexander & Livio 04) detected if Lx(>10 keV) ~1035 erg/s
- 	CI Cam type outbursts (~1-2d?) of Bulge BH vs. WD binaries around *SgrA* *

**Chandra view**
**of central Bulge**
**(~ 2****o****  x 1****o****)**

## Expected EXIST Sensitivity for Variability

**Short**
**GRB**

**Long**
**GRB**

**XRB**
**QPO**
**Var.**

**AGN**
**QPO**
**Var.**

**Type II**
**AGN**

**Type I**
**AGN**

**ULX**

**POP III**
**GRB?**

**Expected *****EXIST***** Sensitivity for Variability**

*EXIST *sensitivity on each timescale allows key measurements across BH types

## EXIST: current Baseline Mission Design Concept

***EXIST: *****current Baseline Mission Design Concept**

- Survey the hard X-ray sky 10-50x deeper than previous HX missions,
- 	        with <10 source positions (for >5 survey threshold)
- Cover the 3 - 600 keV band with two telescope systems:
- 	        HET: 10 - 600 keV (6 m2 CZT pix* *) and LET: 3 - 30 keV (1.3 m2 Si pix)

- (General Dynamics mission concept)

**In Delta IV or Atlas V (5m Fairing)**

## EXIST Mission  Design Parameters

***EXIST***** Mission  Design Parameters**

**Orbit  **
**Normal**

***Nod direction, ******┴ ******scan***
***(+/-15******o ******ea. ~16min)***

***Orbital scan ***
***direction***
**(orbital **
**velocity vector)**

- Zenith pointer - scanning  & nodding for full-sky coverage each orbit (95min)
- 19 coded aperture HE telescopes (6m2 total area CZT pixel  det.)
- 32 coded aperture LE telescopes (1.3m2  total area Si pixel det.)
- Mass, power, telemetry:  	9500kg, 3kW, 3Mbps
- Delta IVH launch to 500 km orbit (i ~5o) _*or*_* *Atlas V-551 launch         (i ~20o) – *study** **bkgd. trades*
- Mission lifetime: 5 years
- Cost: $650M (incl. 20% conting. IMDC costing FY05 $)

## EXIST scan/nod sweeps out full sky each orbit

**Scan the *****full***** sky every 95min orbit**
**20 deg orbit Incl., +/-15 deg Nodding at 5 times/orbit**
**Movie: orbits 0 .. 3; jumps to 15th orbit**

- HET telescopes field of view (LET very
- similar) defines sky view in **movie**

## EXIST mission operations

*Very simple operations*: nominal continuous scan
- Can do pre-planned pointings for longer continuous observations (but gain factor ≤2 vs. scan ea. orbit)
- GRB positions (~2/d) processed on board and QL link (TDRSS?) to ground within 10sec; all data (photon times, positions, energies) dumped each 1-2 orbits
- 5y mission life desired to accumulate large samples of survey objects and rare events

## Detector packaging: Cd-Zn-Te crystals to Telescope

**Detector packaging: Cd-Zn-Te crystals to Telescope**
- (building a very large area CZT detector/telescope)

**Detector Crystal **
**Array (DCA)**
-     2x4 DCUs (4x8 cm2)
-     + FPGA Board

**Sub-Tel Module**
- 1x7 DMs (56x56 cm2)
**Active ****& ****Passive shields**

**Detector Crystal Unit (DCU)**
- Cd-Zn-Te (CZT) Crystal (2x2 cm2)
-     (*with Interposer Board?*)
-     + 2 x 128 channel ASIC
*    *(*with micro-via tech?*)

**HET**
- 19 Sub-Tels (6 m2)

**Detector Module (DM)**
- 1x7 DCAs (8x56 cm2)
- + FPGA Board

## CZT Imager for EXIST: detectors for ProtoEXIST1

**CZT (8x8 pix)**
**2 x 2 x 0.5 cm****3**

**Interposer **
**Board**

**RadNet **
**ASIC (64 ch.)**

**2x4 DCUs **
**(4x8 cm****2****)**

**Socket **
**Board**

**FPGA **
**Board**

**Detector Crystal Array **
**(DCA: 32 cm****2****)**

**Detector Crystal Unit **
**(DCU: 4 cm****2****)**

## ProtoEXIST imaging detectors exist for EXIST!

** **(multipixel imaging with CZT & *depth-sensing*-corrected spectra)

- Multipixel correction reduces FWHM by 40% and improves photopeak efficiency by 60%. We achieve 2% FWHM at 356 keV (~1% at 662 keV). Resolution improves by additional ~30% with improved flight boards. Depth-sensing req. for large FoV imaging. *EXIST *will have spectacular energy resolution (~1-3% across full band).
- See Hong et al 2006, astro-ph/0608711

## Two options for LET imager(R&A needed for further development by 2009)

**DEPFET detectors**
- Developed by MPE for XEUS  and possible for EXIST with commerical development. Allows Intl. Collab.
- Excellent energy resolution (200 eV) and modest cooling (-30deg C)
- Low power (300W) for full array

**Vs. Hybrid pixel detectors**
- Similar to candidate LSST camera, but charge/pixel gives ~200eV resolution
- Low power and allows thicker (1mm) Si for better response to 30 keV
- Packaging and tiling for large arrays require further development

## Ensuring EXIST imaging sensitivity 

-  The main factor for limiting the performance in coded-aperture telescopes is noise caused by unknown systematics in the system (pixel efficiency & background variations, etc.)
-  ***EXIST’s***** ****scanning/nodding**** motion designed for surveying the sky is also ****a key to reduce the unknown systematics**
-  We demonstrate imaging performance of *EXIST* by a series of progressively realistic simulations. *Swift/BAT* slew imaging tests are in progress; and demonstration of *EXIST* detectors and imaging planned with ***ProtoEXIST**** *balloon experiments

**Ensuring *****EXIST***** imaging**** ****sensitivity **
- (to enable imaging for Signal/Background from ~10-4 to 1)

## Swift/BAT slew imaging provides on-orbit test

- (and new *BAT *slew* *survey (***BATSS)*** science...)

- Stacked slews (60sec ea.) vs. pointing on Crab vs. Gal. Ctr. region
**Noise reduced vs. equiv. time pointing due to averaging effects of scan**

## Prototyping EXIST: ProtoEXIST 

** **Balloon borne Hard X-ray Survey Telescope
- (Harvard, GSFC, Caltech, Stanford collaboration)

** ****Pathfinder & technology development for**** *****EXIST *****HET (CZT imager)**
** ****Building a large area CZT detector with  fine resolution, covering 10 – 600 keV**
*** ******ProtoEXIST1***** ~ 1000 cm****2 ****(2.5 mm pixels)**
*** ******ProtoEXIST2***** ~ > 256-1000 cm****2 ****(1.25 mm pixels)**** **
** *****EXIST (HET)***** ~ 6  m****2 **** ****(1.25 mm pixels)**
-  **Prototype for LET needed: package Si **
**pixel *****DepFET***** (MPE collab. ) or CMOS pixel **
**Sensor (LSST imager option)**

## Summary and Prospects

*INTEGRAL *and *Swift *imaging* *have glimpsed the *rich HX sky* (obscured binaries, AGN, high z GRBs...!)
- Broad band (3 – 600 keV), large area &  FoV are unique for *EXIST*: image all-sky each orbit. ALL sources observed with ≥20% continuous coverage; *EXIST** **opens temporal universe in the extreme; complements **LSST*
- Highest z universe uniquely measured via GRBs: >7X *Swift* rate; trigger *JWST*
- Both obscured and dormant SMBHs best studied with HX imager: complete BH census/evolution & accretion luminosity of* *universe
- HX Blazar surveys combined with GeV-TeV (*GLAST-VERITAS*): measure EBL and thermal (stellar) luminosity of universe ; complements *WISE*
*ProtoEXIST1* balloon flight in 2008, *ProtoEXIST2* in 2009 to establish readiness
*EXIST* Technology & costs relatively well-understood; TRL-7 for HET but TRL-5 for LET (need R&A by 2009). Candidate for 2009 BHFP start!
***EXIST***** **under study for BHFP** – *****can ***launch in ~2013-2015 window if 2009 start
- See *EXIST *website (***http://EXIST.gsfc.nasa.gov******)*** for Study & **Team**