Upload
stewart-wilkinson
View
224
Download
0
Embed Size (px)
DESCRIPTION
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
Citation preview
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