1. Pharos: distant beacons as cosmological probes Fabrizio Fiore
The “Pharos” of Alexandria, one
of the Seven Wonders of the
ancient world, was the tallest
building on Earth (120m). Its
mysterious mirror, which reflection
could be seen more than 55 km
off-shore fascinated scientists for
centuries.
Fabrizio Fiore
and V. D’Elia, S. Piranomonte, R. Perna, D. Lazzati, D. Guetta,L. Stella,
A. Antonelli, P. Ward and many others

2. Gamma ray bursts: one of the great wonders of the Universe
GRBs combine 4 themes of
early 21st Century astrophysics:
Among the most energetic events in the Universe
1997 1st GRB redshift (thank to BeppoSAX)
Galaxies in the age of star formation
metal abundances, dynamics, gas ionization, dust
The recombination epoch
? Gunn-Peterson trough at z~6-?
The fate of the baryons & large scale structure
(See Nicastro et al. poster)
1999 Warm IGM simulations
2001 1st Warm IGM detection (thank to Chandra)

3. Can we use GRB to track star-formation at high-z? through:
Minutes after the GRB event their afterglows are the brightest
sources in the sky at cosmological redshift.
Afterglows can be used to probe the high redshift Universe :
Can we use GRB to track star-formation at high-z? through:
High resolution spectroscopy of UV lines
Statistical studies
GRB010222
10 Crab!
Crab
1mCrab i.e. a bright AGN

4. Galaxies in the Age of Star Formation
GRBs also probe normal high z galaxies
peak of star formation
Star formation in the Universe peaked at z~2
star formation rate
GRB Hosts
Studies of z=>1-2 galaxies are biased against dusty environments.
redshift, (1+z)
GRB hosts are normal galaxies
Mann et al MNRAS, 332, 549
GRB afterglows will reveal host
Galaxy dynamics, abundances, & dust content at z>1

5. The history of the metal enrichment in the Universe
Savaglio 2003
Prochaska et al. 2003

6. Spectroscopy of UV lines
Star-formation regions (and the interstellar matter in general) are complex.
Can we truly learn anything about star-forming regions from afterglow’s spectroscopy? Or, are we just doing meteorology?
Just like to try to understand the physics of the atmosphere from the observation of one (a few) lightning …

7. Statistical studies Selection effects complex and
Porciani & Madau 2001, Schmidt 2001,
Guetta et al. 2004, Jakobsson et al. 2005
and many others.
But…. Too few z, 30-50% only of well selected GRB samples.
Selection effects complex and
difficult to account for.

8. Redshift distributions
30 Swift GRB with spectroscopic redshift
27 BeppoSAX and HETE2 GRB with spectroscopic redshift

9. Peak flux distributions

10. NH distributions
118 Swift and 44 BeppoSAX+HETE2 GRBs localized in regions with NH(Gal)<41021
Due to the different Eband of localization? (BAT keV, WFC and WXC 2-20 keV)

11. Selection effect for different localization bands
X-ray localization: biased against large z=0 obscuration
==> BSAX and HETE2 samples miss highly obscured, low-z GRB.
==> Swift localizes highly obscured, low-z GRB, but dust extinction makes their optical afterglow faint, and so more difficult z determinations
Z=9
5.3 3
1 .5
0 NH=1024cm-2

12. Selection effects Redshift
1) Sensitivity: BSAX and HETE2 samples biased against X-ray faint GRB
2) Localization Eband: BSAX and HETE2 samples biased against highly obscured GRB (preferably at low z)
3) Spectroscopic identification: dust in the host galaxy plays a major role

13. Spectroscopy of UV lines
1- The GRB surrounding medium: its physical and dynamical state can be easily modified by the GRB and its afterglow. Geometry, density and physical state of the gas can be constrained by line variability and comparison of line ratios to expectation of time dependent photoionization codes.
2- The ISM of the host galaxy. Metal column densities, gas ionization and kinematics.These studies have so far relied upon either Lyman Break Galaxies or Damped Lyman Alpha systems, which may not truly be representative of the whole high-z galaxy population.
GRB afterglows can provide new, independent tools to study high z galaxies.

14. DATA GRB050730: z=3.968 - 4hr after the GRB; R18
UVES spectra A, slit 1”, resolution=42,000
FORS spectra A, slit 1”, resolution=1000
GRB020813: z= hours after the GRB; R=20.4
GRB021004: z= hours after the GRB; R=18.6
GRB050730: z= hr after the GRB; R18
GRB050922C: z=2.199 – 3.5hr after the GRB; R18

15. The ISM probed by GRB afterglow
Complex, with many components spanning a velocity ranges from a few hundred to a few thousands km/s

16. Comparison with CLOUDY models:
Ionization parameter assuming solar abundances
Ionization parameter constrained in a relatively small range with no clear trend with the system velocity. This can be interpreted as density fluctuations on top of a regular R-2 wind density profile.

17. GRB C UVES spectrum
Separating different components Piranomonte et al. 2006

18. GRB UVES spectrum
Strong fine structure transition: CII*, SiII*, OI*, OI**, FeII*, FeII**, FeII***. Prochaska et al. 2006: Observed abundances of excited ions are well explained by UV pumping with the gas at r~a few hundred pc from the GRB

19. GRB050730: a slightly different approach:
Separating different components
D’Elia et al. 2006

20. GRB050730
Strong CII* for both components 2 and 3

21. GRB050730
Strong SiII*,OI* and OI** only for
component 2

22. GRB050730
Strong FeII and FeII* transitions only for component 2

23. Fine structure lines Two main processes:
Radiative excitation; ) Collisional exitation

24. GRB050730 Fine structure lines
component 2
T= K
Ne>a few 100
Assuming collisional excitation
NCII/NCII*~0.5

25. GRB050730 fine structure lines
Component 3
NCII/NCII*~1.8, higher than that of Component 2!
Ne = a few 10
Assuming collisional excitation

26. and distance of the clouds from the GRB
GRB gas ionization
and distance of the clouds from the GRB
Huge (and variable) ionizing flux! CI<12.3
[CIV/CII] and [SiIV/SiII] of components 2 and 3 similar. If density is different by a factor 10 (100), the distance from the GRB of component 3 is 3 (10) times higher than that of component 2.
Similar conclusion reached assuming UV pumping as dominant mechanism for excited transitions
Need detailed time-dependent photoionization codes!

27. Time dependent photoionization Nicastro et al.1999
Perna, Lazzati et al.
Strong variation with time of ion abundances
A tool to constrain gas geometry and density through ion ratio variations
Lazzati et al. 2006

28. Metallicities
In case of multiple components it is truly difficult to estimate H columns for each, even with high quality spectroscopy.
The spatial distribution of heavy elements can be very different from that of H.
The star-forming regions hosting the GRB are likely to be much more enriched than the outer galaxy regions

29. GRB host galaxy metallicities
000926
050820
060206
050401
030323
050904
050730

30. GRB host galaxy metallicities
However… metallicity depends on:
Impact factor
Galaxy mass
Star-formation rate
Etc….

31. 1) Metallicity depend on impact factor
GRB021004
galaxy
DLA

32. 2) Metallicity depends on galaxy mass:
Savaglio et al. 2005, Berger et al. 2006
Host em. lines
050904, abs.

33. Statistical population studies
… should consider
Complex selection effects, different localization bands and NH distributions should be taken into account
SFR / metallicities / masses appropriate for the typical GRB hosts