LNGS Summer Institute 2005
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LNGS Summer Institute 2005. GRB: Modern Status. Elena Pian - INAF, Trieste Astronomical Observatory, Italy. Outline. Connection between Supernovae and long GRBs / X-ray Flashes Swift: early GRB counterparts Short Gamma-Ray Bursts. long. Bimodal distribution of GRB durations. short.

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Elena Pian - INAF, Trieste Astronomical Observatory, Italy

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LNGS Summer Institute 2005

GRB: Modern Status

Elena Pian - INAF, Trieste Astronomical Observatory, Italy


Outline

Connection between Supernovae and long GRBs / X-ray Flashes

Swift: early GRB counterparts

Short Gamma-Ray Bursts


long

Bimodal

distribution

of GRB

durations

short

The progenitors of

short bursts are still

to be identified!!!

Binary neutron stars?

Kulkarni 2000


GRB980425

Supernova 1998bw (Type Ic)

z = 0.0085


GRB030329/SN 2003dh

z = 0.168

ESO VLT + FORS

Photospheric velocity

Si II 6355

Hjorth et al. 2003


GRB031202/SN2003lw

z = 0.105

ESO VLT FORS

Malesani et al. 2004


z = 0.695

SN1998bw

Galama et al. 2000


X-ray Flashes


XRF030723

Fynbo et al. 2004

Soderberg et al. 2004

Tominaga et al. 2004


Is there a unifying scheme for SNe and GRBs?

Four clear cases of SN-GRB association have been detected spectroscopically, all are Type Ic SNe. In all of these, the SN is very powerful (high luminosity, large kinetic energy), i.e. it is a “Hypernova” (Paczynski 1998; Iwamoto et al. 1998)

SNe with hypernova characteristics have been detected, although they are not accompanied by a GRB (SNe 1997dq, 1997ef, 2002ap, 2004aw…); see also IPN survey

The rate of GRBs (taking into account collimation) corresponds to the relative rate of hypernovae with respect to the total number of Ic SNe (i.e. ~5%, Podsiadlowski et al. 2004)

Do all hypernovae have jets and produce GRBs, so that only those aligned with the line of sight are detected?

Can we test this “unified scenario”?


In nebular spectra of SN1998bw, Fe lines are broader than O lines

A spherically symmetric explosion of a massive star would result in the opposite

Signatures of asphericity in SN1998bw

[OI] 6300A

O

[FeII] 5200A

Fe

SN 1998bw


0.7 s

1.5 s

2D explosion: KE=11foe, MBH(final)=5.9M, M(56Ni)=0.11M

Outflow

Inflow

Maeda et al. 2002


Spherical

56Fe

16O

Aspherical explosion: confined nucleosynthesis

[OI] 6300A

FeII] 5200A

SN 1998bw

Aspherical

Orientation 15 deg

Maeda et al. 2002


The bright Type Ic SN 2003jd

Discovered 25 Oct 2003; distance: 80 Mpc

Courtesy: K. Kawabata


The bright Type Ic SN 2003jd

  • SN 2003jd was as bright at peak as SN1998bw (Mv = -18.7)

  • Early-time spectra had broad lines, similar to hypernova SN2002ap

  • No GRB or XRF


SN 2003jd:

an aspherical SN viewed off-axis

Observations:

Subaru+FOCAS, at 330 days

Keck+LRIS, at 370 days

The [O I] 6300A line shows a double peak, suggesting an explosion similar to SN1998bw but viewed ~70° from the axis

Subaru

Mazzali et al. 2005, Science 308, 1284


SN2003jd: an aspherical supernova viewed off-axis

Keck+LRIS

Subaru+FOCAS

Mg I]

[Ca II]

[Fe II]

[O I]

Mazzali et al. 2005


[O I] nebular

emission

[O I] line:

strong

dependence

on viewing

angle

Mazzali et al. 2005


Was SN 2003jd also a GRB/HN?

radio

  • Radio and X-ray upper limits are not in contradiction with a GRB viewed off-axis

X-ray

Mazzali et al. 2005


Swift

Launched 20 Nov 2004


Swift localization of GRBs


Examples of Swift-XRT light curves

Steep decline common

Gets shallower around here

Nousek et al. 2005


GRB990123

WFC

MECS

2-10 keV

15-28 keV

PDS

Maiorano et al. 2004

Corsi et al. 2004


GRB990123 (z = 1.6)

Fruchter et al. 1999


GRB041219a: Optical flash from internal shocks

RAPTOR

Internal shock

ROTSE-I

Reverse shock

Akerlof et al. 1999; Vestrand et al. 2005


Optical Flashes

Guidorzi et al. 2005


GRB050502a

z = 3.793

Liverpool 2m telescope

+ Robonet consortium

Forward shock in ISM

In variable density

Environment

Guidorzi et al. 2005


GRB050509b (T90=0.04s)

1 keV X-ray light curve

BAT+XRT emission consistent with a single decay rate of 1.2±0.09

Gehrels et al. 2005


Comparison with other X-ray transients


GRB050509b

Host galaxy

Bloom et al. 2005


GRB050509b (z = 0.22)

Upper limits on optical

Flux are inconsistent

With supernova

Hjorth et al. 2005


GRB050724 looks long to BAT (T90=153s), but would be short to BATSE (<1s)

GRB050724 (z = 0.257)

t-4 ν-1


Optical afterglow of the short GRB050724 (T = 0.25 s)

Berger et al. 2005


Host Galaxy of the Short GRB050724 (z = 0.257)

SFR < 0.03 Msun/yr

Bloom et al. 2005


Isotropic irradiated –ray energy vs redshift

GRB/SN

Short GRB

GRB050904

z = 6.29


Conclusions

The nebular spectrum of the Type Ic energetic SN2003jd is different

from that of SN1998bw: it exhibits a double-peaked [O I] emission line,

which suggests an aspherical geometry and an equatorial view. This is

consistent with the lack of a detected GRB, and could support a unified

scenario for SNe and GRBs

Are hypernovae the only aspherical SNe Ic? No, normal Ic are polarized

Are hypernovae the most aspherical SNe? Possibly, and this would be

related to the presence of GRBs

In this picture, X-ray flashes may be off-axis GRBs or weaker explosions

Short GRBs have afterglows similar to those of long GRBs. They are

Preferentially detected at lower redshifts, and in galaxies with scarce

Star formation. The evidence that they are not associated with supernovae

is increasing. They are probably double neutron star mergers

Optical flashes probe the early emission mechanisms and circumburst

medium


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