We describe the Energetic X-ray Imaging Survey Telescope EXIST, designed to carry out a sensitive all-sky survey in the 10 keV – 600 keV band. The primary goal of EXIST is to find black holes in the local and distant universe. EXIST also traces cosmic star formation via gamma-ray bursts and gamma-ray lines from radioactive elements ejected by supernovae and novae

Band, D.

Blandford, R.

Craig, W.

Fishman, J.

Gehrels, N.

Grindlay, J.

Harrison, F.

Hartmann, D. H.

Hong, J. S.

Kouveliotou, C.

Loeb, A.

Woosley, S. E.

English

Caltech Authors - Main

Observing GRBs with EXIST
D. H. Hartmann, J. Grindlay†, J. Hong†, A. Loeb†, R. Blandford, W.
Craig‡, J. Fishman§, C. Kouveliotou§, N. Gehrels¶, D. Band¶, F. Harrison
and S. E. Woosley††
Department of Physics & Astronomy, Clemson University, Clemson, SC
†Harvard-Smithsonian Center for Astrophysics, Cambridge, MA
Stanford Linear Accelerator, Stanford University, Stanford, CA
‡Lawrence Livermore National Laboratory, Livermore, CA
§NASA, Marshal Space Flight Center, and NSSTC, Huntsville, AL
¶NASA, Goddard Space Flight Center, Greenbelt, MD
California Institute of Technology, Pasadena, CA
††Dept. of Astronomy & Astrophysics, The University of California, Santa Cruz, CA
Abstract. We describe the Energetic X-ray Imaging Survey Telescope EXIST, designed to carry
out a sensitive all-sky survey in the 10 keV - 600 keV band. The primary goal of EXIST is to find
black holes in the local and distant universe. EXIST also traces cosmic star formation via gamma-
ray bursts and gamma-ray lines from radioactive elements ejected by supernovae and novae.
EXIST is proposed as a black hole finder probe in NASA’s Beyond Einstein Program,
and would operate in zenith pointing scanning mode (FoV of 180ox75o), to provide all-
sky coverage every orbit. Variable sources on the sky would be monitored daily. Each
source would be in the FoV for at least 20 min every 95 min orbit, and sampled with
ms resolution. EXIST will monitor known variable sources, detect outbursts of known
and new sources, and detect Gamma-Ray Bursts (GRBs) with a coverage probability
of P = FoV/4π0.5. Technical details are presented at http://exist.gsfc.nasa.gov/. The
"reference design" (Fig. 1) will be refined in a proposed mission concept study. EXIST
surveys the sky from a low-inclination (22o), low-altitude (500 km) orbit. With a
mission life of five to ten years, EXIST could explore the hard X-ray universe in 2010
to 2020, a century after Albert Einstein developed special and general relativity.
EXIST employs 2.7-m2 CZT for each of its three telescopes, and images the sky in
the 10 keV - 600 keV range with Tungsten coded masks with angular resolution of a few
arcmin, and 10-50 arcsec source localization. In the 10 - 200 keV band EXIST will have
a continuum sensitivity of 2 mCrab (each orbit), and 0.05 mCrab for a one year survey.
Above 200 keV the per-orbit sensitivity would be 20 mCrab, and 0.5 mCrab for a 1 year
survey. EXIST would complement observations with GLAST, which will study sources
in the 20 MeV - 300 GeV regime [1], and ground-based VHE/UHE instrumentation,
such as HESS, MAGIC, and VERITAS. The development of new detector technology is
launching gamma-ray astronomy into an exciting new era of breakthroughs in the MeV
to TeV regime [2].
GRBs are associated with host galaxies at large redshifts [3, 4]. The red shift record
is z = 4.5 for GRB000131 [5]. In at least two cases evidence exists for supernova
CP727, Gamma-Ray Bursts: 30 Years of Discovery, edited by E. E. Fenimore and M. Galassi
© 2004 American Institute of Physics 0-7354-0208-6/04/$22.00
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FIGURE 1. The current reference design of EXIST.
associations: GRB 980425 and SN1998bw at z = 0.008 and GRB030329-SN2003dh
[6] at z = 0.169. The spectra of these two supernovae are very similar and characteristic
of Type Ic hypernovae, such as SN1997ef [7, 8, 9]. The emerging paradigm is a link of
massive stars with (long) GRBs, consistent with the predictions of the collapsar model
[11]. In this scenario the collapse of a rotating, massive star to a black hole ultimately
drives relativistic outflows through a collapsing envelope (e.g., [12] producing a GRB-jet
after the breakout, and a subsequent supernova. Under some circumstances the formation
of a stellar mass black hole is thus heralded by a burst of gamma-rays, followed by a
decaying afterglow from X-rays to radio [3]. GRBs thus provide a unique opportunity to
trace the process of star formation to large, cosmological distances. Theoretical studies
[13, 14, 15] indicate that the first generation of stars may have formed at z > 10, re-
ionizing the universe, perhaps with a bias towards more massive stars due to the low
metallicity in the early universe. Observational support for the emergence of the first
stars in the red shift range z10-30 (100 to 400 Myrs after the bigbang) comes from
the polarization of the CMB [16]. Black holes from these population III stars may have
played a significant role in seeding AGN cores. Even at such large distances it is easy to
detect a red shifted GRB. A sensitivity of 1 mCrab in the hard X-ray band is sufficient
to detect GRBs like GRB 990123 at essentially all realistic distances. Based on the
assumption that the GRB rate traces the cosmic star formation rate, we estimate that 7%
of all GRBs detected by EXIST originate at z > 10 (Fig. 2) To enable ground-based and
space-based (e.g., NGST) studies of these bursts, EXIST provides 10”-50” locations
in near real time. The total burst rate will be a few per day. EXIST would serve as
the primary GRB observatory in the post-Swift era [17], during a time when sensitive
neutrino detectors (IceCube) and gravity wave detectors (LISA, LIGO-II) may be able
to detect the high-energy (> PeV) neutrino and gravity wave signature of GRBs.
Detection of the first generation of stars may require GRBs as a tracer, as galaxies
beginning to form stars are faint. Spectroscopy of host galaxies will require observations
with large aperture telescopes [15], and are likely to revolutionize our ability to trace
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FIGURE 2. The estimated fraction of GRBs with red shift greater than z. Here, “all GRBs” is based on
the assumption that GRBs trace the cosmic SFR. Estimates were made for EXIST, BATSE, and Swift.
and probe structure formation and galaxy evolution to the earliest times. GRBs provide
signposts along "the road to galaxy formation" [18], and shed light on the crucial
question of halo formation via a more or less smooth collapse or successive mergers
of independently evolving proto-galactic fragments. The star formation rate during halo
collapse is sensitive to stellar feedback (e.g., [19, 20]. Thus high-z GRBs could improve
our understanding of a key ingredient in galaxy formation and evolution.
The star formation rate and GRB rate are related, but not one-to-one. As metallicity
decreases, the IMF changes due to changes in the cooling function of the gas. After
formation, mass loss from stellar winds is a sensitive function of the metal content in
the stellar envelope, affecting subsequent evolution and probabilities for creating the
right conditions for GRBs [21]. GRBs provide a new tool for studies of early galaxy
evolution, and may lead to the elusive Population III stars and their feedback on proto-
galaxies [22].
EXIST will also detect many X-ray rich GRBs (the so called X-ray Flashes, [23, 24].
This new burst phenomenon is in many ways similar to classical long duration GRBs,
but, as the name indicates, characterized by a lower energy of the bulk of the emission.
While the peak in the νFν spectrum of GRBs is clustered around 200 keV, the currently
small sample of XRFs suggests a peak value of 50 keV. The nature of XRFs is not yet
clear. XRFs could be highly red shifted GRBs, but observations of the host galaxies of
XRF 011030 and XRF 020427 [25] argue against that interpretation.
REFERENCES
1. Gehrels, N. & Michelson, (1999).
2. Schonfelder (2001).
3. van Paradijs, J., Kouveliotou, C., & Wijers, R. A. M. J., ARAA 38, 379 (2002).
4. Meszaros, P., Ann. Rev. Astr. & Astrophys. 40, 137 (2002).
679
Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp
5. Andersen, M. I. et al., A&A 364, L54 (2000).
6. Hjorth, J., et al., Nature 423, 847 (2003).
7. Woosley, S. E., Eastman, R., & Schmidt, B. P., ApJ 516, 788 (1999).
8. Branch, D., in "Supernovae & Gamma-Ray Bursts" (Cambridge U. Press), p. 96 (2001).
9. Nomoto (2001).
10. Kawabato (2003).
11. Woosley, S. E., ApJ 405, 273 (1993).
12. MacFadyen, A., & Woosley, S. E., ApJ 524, 262 (1999).
13. Abel, T., Bryan, G. L., & Norman, M. L., Science 295, 93 (2002).
14. Bromm, V., and Loeb, A., ApJ 575, 111 (2002).
15. Loeb, A., astro-ph/0307231 (2003).
16. Kogut, A., New Astronomy Reviews astro-ph/0306048 (2003).
17. Grindlay, J. et al., astro-ph/0205323 (2002).
18. Keel, W. C., "The Road to Galaxy Formation""(Springer) (2002).
19. Hartmann, D. H., Myers, J., & The, L.-S., in "From Twilight to Highlight", eds. W. Hillebrandt & B.
Leibundgut (Springer), p. 384 (2003).
20. Marri, S., & White, S. D. M., astro-ph/0207448 (2002).
21. Heger, A., et al., ApJ 591, 288 (2003).
22. Barkana, R. & Loeb, A., Phys. Rep. 349, 125 (2001).
23. Heise, J., in Gamma-Ray Burst and Afterglow Astronomy eds. G. R. Ricker & R. K. Vanderspek,
AIP 662, 229 (2003).
24. Heise, J., Nature, submitted (2003).
25. Bloom, J. S., et al., astro-ph/0303514 (2003).
680
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Observing GRBs with EXIST

From Twilight to Highlight&quot;,

in &quot;Supernovae & Gamma-Ray Bursts&quot;

New Astronomy Reviews

New Astronomy Reviews astro-ph/0306048(2003).

The Road to Galaxy Formation&quot;&quot;(Springer)

The Road to Galaxy Formation&quot;&quot;(Springer)(2002).

to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp

to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp5.

http://authors.library.caltech.edu/12271/1/HARaipcp04.pdf

Observing GRBs with EXIST

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