BeppoSAX Observations of GRBs: 10 yrs after

Filippo FronteraPhysics Department, University of Ferrara, Ferrara, Italy

andINAF/IASF, Bologna, Italy

Aspen Meeting on “Supernova 1987A: 20 Years After”, February 19 - 23, 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 970508

• 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).

Why BeppoSAX?

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.

BSAX/GRBM catalog of GRBs 1 Format

Log N – log P

Some of the catalog derived properties Fluence distribution

Peak flux distributionQuiescent times

Hardness

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);

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

Transient absorption features 990705 011211

Amati et al. 2000Frontera et al. 2004

• 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 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

011211

Amatiet al.2000

Fronteraet al.2004

E’p-Eiso relation: an introduction

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).

<log(Eiso)> = 53 = 0.9

Amati 2006

E’p vs. Eiso 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: 980425, 031203 (?), short GRBs.

E’p,i = kEiso(0.52+/-0.06)

Amati et al. 2006

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 Eγ (Ghirlanda et al. 2004). Ep-Eγ 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 Ep-Eγ correlation, while Ghirlanda et al. (2007) claim the contrary.

Campana et al. 2007 Ghirlanda et al. 2007

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

Further investigation of the Ep vs. Eiso 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-Liso/E’p-Lγ relation at the GRB peak (GRBs with time breaks)

Evidence of a lower spread assuming a jetted emission and a WIND-like environment.

Lγ (1052 erg/s)

ISM α ~ 0.32

WIND α ~ 0..60Liso (1052 erg/s)

E’p

keVE’p

keVIsotropic 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.

Lγ (1052 erg/s)

ISM

WIND

α ~ 0.59

α ~ 0.72

Liso (1052 erg/s)

E’p

keV

E’p

keV

Lγ (1052 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