BeppoSAX Observations of GRBs: 10 yrs after

1. BeppoSAX Observations of GRBs: 10 yrs after Filippo Frontera Physics Department, University of Ferrara, Ferrara, Italy and INAF/IASF, Bologna, Italy Aspen Meeting on “Supernova 1987A: 20 Years After”, February 19 - 23, 2007

2. 28 February 1997 The first discovery of an X-ray afterglow with BeppoSAX GRB970228 Costa, Frontera, Heise et al., Nature, 1997, Frontera, Costa, Piro et al., ApJL, 1998

3. By following-up the 1’ NFI error box: first discovery of a GRB optical counterpart GRB970228, Van Paradijs et al., Nature, 1997 Frontera et al. , A&A, 2008

4. First GRB redshift measurement: GRB 970508 Metzger et al., Nature, 1997

5. Why BeppoSAX? • Narrow Field X-ray telescopes (0.1-10 keV)  a factor 100 better sensitivity than direct viewing detectors; • GRBM (~all sky, 0.5 ms time resolution, 40-700 keV)  GRB automatic trigger. • WFCs (20x20 deg FOV, 2-28 keV)  X-ray accurate localization (~5 arcmin). • Well designed ground segment and motivated GRB team: • Prompt determination of GRB coordinates; • Prompt follow-up (few hrs).

6. An account 10 yrs after GRB980227 • 1082 GRBs detected with the GRBM (a catalog is being published); • 51 detected with WFCs +GRBM (our golden sample) • Of them 37 followed-up with BSAX/NFIs; • 86% showed X-ray afterglow >10-13 erg/cm2 s; • 40% showed optical afterglow; • 30% showed radio afterglow; • Most of them are famous, e.g., GRB 980425.

7. BSAX/GRBM catalog of GRBs 1 Format Log N – log P

8. Some of the catalog derived properties Hardness Fluence distribution Quiescent times Peak flux distribution

9. Some topical results from the BeppoSAX GRBs • Discovery of decreasing NH during the prompt emission (for various GRBs, outstanding 000528); • Discovery of transient absorption features during the prompt emission (GRB 990705, GRB011211). A new evidence (971227) under evaluation; • Ep-Eiso relationship (Amati et al. 2002);

10. Decreasing NH from GRB000528 • Model: photo-ionization of the local CBM by GRB photons (Lazzati & Perna 2002); • Consistency with the presence of an overdense molecular cloud (n~4.5 x105 cm-3) shell-like at a distance from 5.6x1016 to 1.8x1017 cm. Frontera et al. 2004

11. Transient absorption features 011211 990705 • Common property: • feature visible only during the rise of the event. A B C D Amati et al. 2000 Frontera et al. 2004

12. Transient absorption features (cont.d) Amati et al. 2000 • Both features consistent with resonant scattering of GRB photons off H-like Fe + Co; • For 990705, red-shifted line (z ~ 0.86, vs. 0.835) and thermal velocities of the material; • For 011211 (z=2.14), blue-shifted line, (v ≈ 0.7c)  high outflowing velocities of the absorbing medium. • In both cases, CMB environment typical of a SN explosion site (Fe-rich). 990705 Frontera et al. 2004 011211

13. E’p-Eiso relation: an introduction Amati 2006 <log(Eiso)> = 53 s = 0.9 • High dispersion of the gamma-ray energy released Eiso assuming isotropy; • Much lower dispersion when Eiso is collimation corrected (Eγ) , assuming a jet emission (Frail 2001).

14. E’p vs. Eiso relation Amati et al. 2002 E’p,i= kEiso (0.52+/-0.06) • Found with time averaged spectra of 12 GRBs with known z. • Now confirmed by many long (HETE2, SWIFT) GRBs and XRFs of known z. • Outliers: 980425, 031203 (?), short GRBs. Amati et al. 2006

15. Applications of the E’p-Eiso relation: • Study of the fireball properties (e.g., baryon load), • Radiation production mechanisms (internal, external shocks) • Test of the prompt emission mechanisms (e.g., synchrotron vs. thermal emission); • Emission geometry (jet vs. spherical) and its structure (uniform vs. structured jets; e.g., Lamb et al. 2005); • XRF-GRB unification models; • Viewing angle effects. Zhang & Meszaros 2002

16. Other application of the Ep-Eiso correlation: Nava et al. 2006 • Estimate of pseudo-redshifts; • Derivation of a similar relation between E’p and Eγ (Ghirlanda et al. 2004). • Ep-Eγ proposed for the estimate of cosmological parameters.

17. Debate: • Some authors (e.g., Band & Preece 2005) claim that a high fraction of BATSE events (unknown z) is inconsistent with the correlation. However Ghirlanda et al. (2005) find the opposite result. • Campana et al. (2007) find that the Swift GRBs weaken the Ep-Eγcorrelation, while Ghirlanda et al. (2007) claim the contrary. Ghirlanda et al. 2007 Campana et al. 2007

18. In order to definitely establish validity and/or applicability of the Ep-Eiso (or Ep-Eγ) correlation: it is crucial to understand the underlying physics

19. Further investigation of the Ep vs. Eiso relation Frontera et al. 2000 • Given the evolution of the GRB spectra: • Is this relation still valid within single GRBs? • Do all GRB show the same correlation slope? • In which of the GRB phases (Rise, Peak, Decay) does it show lower spread? • Effect of collimation correction • ……………. • Analysis in progress.

20. Test of the E’p-Liso/E’p-Lγ relation at the GRB peak (GRBs with time breaks) ISM α~ 0.32 Isotropic α~ 0.26 E’p keV E’p keV Lγ(1052 erg/s) Liso (1052 erg/s) WIND α~ 0..60 • Evidence of a lower spread assuming a jetted emission and a WIND-like environment.

21. Test of the E’p-Liso/E’p-Lγ relation during the GRB decay (GRBs with time breaks) ISM α~ 0.59 α~ 0.46 E’p keV E’p keV Lγ(1052 erg/s) Liso (1052 erg/s) α~ 0.72 WIND E’p keV • High spread, at low luminosities, mainly assuming a jetted emission. Lγ(1052 erg/s)

22. Conclusions • BeppoSAX, after having opened a new era in the GRB astronomy, has continued to provide key results for the understanding of the GRB physics and for possible application of GRBs as cosmic rulers. • Swift is providing key results for the understanding of the GRB afterglow, but, given the BAT narrow bandwidth, is limited for Ep / Eiso measurement. • New missions are required to extend the results obtained by BeppoSAX during the prompt emission (e.g., LOBSTER-ISS, ECLAIRS, EDGE).

23. Thanks