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 , 2007

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

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

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

Narrow Field X-ray telescopes ( keV)  a factor 100 better sensitivity than direct viewing detectors; GRBM (~all sky, 0.5 ms time resolution, 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). Why BeppoSAX?

An account 10 yrs after GRB  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 > erg/cm 2 s;  40% showed optical afterglow;  30% showed radio afterglow;  Most of them are famous, e.g., GRB

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

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

Some topical results from the BeppoSAX GRBs  Discovery of decreasing NH during the prompt emission (for various GRBs, outstanding );  Discovery of transient absorption features during the prompt emission (GRB , GRB011211). A new evidence (971227) under evaluation;  E p -E iso relationship (Amati et al. 2002);

Decreasing NH from GRB  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 x10 5 cm -3 ) shell-like at a distance from 5.6x10 16 to 1.8x10 17 cm. Frontera et al. 2004

Transient absorption features Amati et al Frontera et al Common property: feature visible only during the rise of the event. A B C D

Transient absorption features (cont.d)  Both features consistent with resonant scattering of GRB photons off H-like Fe + Co;  For , red-shifted line (z ~ 0.86, vs ) and thermal velocities of the material;  For (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) Amati et al Frontera et al. 2004

E’p-Eiso relation: an introduction  High dispersion of the gamma-ray energy released E iso assuming isotropy;  Much lower dispersion when E iso is collimation corrected (E γ ), assuming a jet emission (Frail 2001). = 53  = 0.9 Amati 2006

E’ p vs. E iso relation 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: , (?), short GRBs. E’ p,i = kE iso (0.52+/-0.06) Amati et al Amati et al. 2002

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

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

 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 E p -E γ correlation, while Ghirlanda et al. (2007) claim the contrary. Campana et al Ghirlanda et al. 2007

In order to definitely establish validity and/or applicability of the E p -E iso (or E p - E γ ) correlation: it is crucial to understand the underlying physics

Further investigation of the E p vs. E iso relation  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. Frontera et al. 2000

Test of the E’ p -L iso /E’ p -L γ relation at the GRB peak (GRBs with time breaks)  Evidence of a lower spread assuming a jetted emission and a WIND-like environment. Lγ (10 52 erg/s) ISM α ~ 0.32 WIND α ~ L iso (10 52 erg/s) E’ p keV E’ p keV Isotropic α ~ 0.26

Test of the E’p-Liso/E’p-Lγ relation during the GRB decay (GRBs with time breaks)  High spread, at low luminosities, mainly assuming a jetted emission. L γ (10 52 erg/s) ISM WIND α ~ 0.59 α ~ 0.72 Liso (10 52 erg/s) E’ p keV E’ p keV L γ (10 52 erg/s) E’ p keV α ~ 0.46

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).

Thanks