L. Piro - Moriond 2005 Gamma-Ray Bursts and X-ray afterglows Luigi Piro Istituto Astrofisica...

L. Piro - Moriond 2005

Gamma-Ray Gamma-Ray Bursts Bursts

and X-ray and X-ray afterglowsafterglows

Gamma-Ray Gamma-Ray Bursts Bursts

and X-ray and X-ray afterglowsafterglows

Luigi PiroLuigi Piro

Istituto Astrofisica Istituto Astrofisica SpazialeSpaziale Fisica Fisica

CosmicaCosmica, INAF, INAF, , RomaRoma


Outline• Prompt vs afterglow observational signatures. Fireball

model• Environment and progenitor:

– X-ray lines– X-ray absorption, – Wind vs ISM– Late-time rebursting – Precursors

• Deviations from standard fireball model• Dark GRB• X-Ray Flashes


The deepest mysteryThe deepest mystery

• Out of 40 GRB localized by BSAX, about 30 went off during Italian night time, week end, holydays

• One (GRB980703) during the penalties of the world championship soccer game ITALY vs FRANCE

• Terrestrial origin?


GRB970228: the 1st X-ray and GRB970228: the 1st X-ray and O afterglowO afterglow

• Triggered by GRBM and localized by WFC

•A second pointing 3 days after the GRB: fading X-ray counterpart (Costa et al 1997)

• Optical fading source (van Paradijs

et al 1997)

•Fast follow up with NFI in 8 hrs: a bright unknown X-ray source


PPower lawsower laws: the : the hallmarkhallmark of afterglows of afterglows • F≈ t x≈1.4; x≈1.0

Costa et al 97Piro et al 99GB000926:Piro et al, 01


Prompt vs afterglow emission: internal vs external shock

• In contrast with the afterglow, the prompt emission is characterized by strong hard-to-soft spectral evolution from X- to Gamma rays (e.g. GRB960720 Piro et al 1997)


Prompt vs afterglow emissionPrompt vs afterglow emissionPrompt vs afterglow emissionPrompt vs afterglow emission

Prompt: hard-to-soft

Afterglow: power-law =1; no spectral variation


Testing the fireball modelTesting the fireball modelTesting the fireball modelTesting the fireball model

106 cm

t-1

1016 cm

1013 cm

taft

X-ray afterglow

RB

tGRB


The progenitors of GRBThe progenitors of GRB The progenitors of GRBThe progenitors of GRB

• NS-NS (BH-NS & BH-WD) travel far from their formation sites before producing GRB’s (Fryer et al 2000) => “clean environment”: no lines

The nature of the progenitor can be inferred from the environment

• NS- NS merging Hypernova

• Hypernovae/collapsar evolve much faster, going off in their formation site => “mass-rich environment” => lines


Iron featuresIron features•GB970508 (Piro et al 1999)

•GB980828 (Yoshida et al 1999)

•GB990705 (Amati et al 2000)

•GB000214 (Antonelli et al 2000)

•GB991216 (Piro et al 2000)


Soft X-ray lines The GRB-SN connection furtherly confirmed by the detection of He/H-like Mg, Si, S, Ar metal lines blueshifted at v/c=0.1 in the afterglow spectra of GRB011211 (by XMM, Reeves et al 02), GRB020813 (by Chandra, Butler et al 03) and GRB030227 (by XMM, Watson et al 03)


Line models vs time behaviour

• In the distant reprocessor scenario (=preSN explosion= Supranova): line intensity=const => line EW (vs continuum) increases with t: lines detectable after t>few hours (not easily detectable by SWIFT)

• In the “local” reprocessor scenario (Meszaros& Rees2000,2003): line EW should be roughly constant = visible after few minutes (SWIFT:OK)


X-ray absorption

X-ray absorption column densities in the afterglow: NH=1021-22 cm-2 (Stratta et al, ApJ03)

Powerful probe of the environment of GRB and of the medium in the line of sight to the GRB


GRB, star forming region & standard fireball model

• Association of GRB with star-forming regions:– X-ray lines– Distribution of OT location in their host galaxies (Bloom et al)– SN-GRB connection– X-ray absorption column densities consistent with NH=1021-22 cm-2 in GMC

• Since the typical density in a GMC is n=102-104 cm-3 why the density derived from the standard fireball (e.g. Panaitescu, Kumar et al..) model is 3-4 orders of magnitude lower ? Wind ejection by progenitor.

• Wind environment is expected from progenitor (collapsar, in particular) but most afterglows are consistent with constant density profile ..


GRB (high )

XRF (low )

X-ray lines (local reprocessor scenario (Mesaros & Rees 00)); Thermal precursor (Ramirez-Ruiz et al 02)

Woosley et al

Collapsar model


Wind vs ISM• Telltale of wind: X-ray

decay SLOWER than optical (oc x ) by 0.25

• Distribution of x-O From BSAX + Optical

• ISM preferred • Wind cases: 040106 (Gendre

et al A&A, 2004), GRB011121, XRR011211 (Piro et al ApJ05), XRF011030 (Galli tak)

ISMWind


GRB011121• X-ray precursor• Hard prompt emission• X-ray rebursting• Late afterglow

Piro et al. 05,

ApJ, in press.


GRB011121

• Wind suggested e.g. by Price et al (O+R)

• BSAX data (Piro et al, ApJ 05)

Prompt: hard-to-soft

Afterglow: =1


GRB011121: late afterglow onset in a WIND

• Setting t0 at the beginnig of the rebursting:

• Power law X=1.29 ± 0.04 vs O=1.66 ± 0.06 (Price et al 02), consistent only with WIND

• Interpretation + other examples: talk by A. Galli


Deviations from standard model

• GRB010222 (in’t Zand 2002) and GRB990123 (Maiorano et al 2005, Corsi et al 2005) do not fulfill closure relationship AND the X-ray data are above the extrapolation of the optical spectrum

• IC component? (Corsi et al 2005)


Dark GRBDark GRB• With BeppoSAX:

30 X-ray afterglow candidates out of 36 GRB follow up observations in X-rays (Piro et al 2004, De Pasquale et al 2004)

X-ray afterglowsX-ray afterglows > 90% > 90%Optical afterglowsOptical afterglows ~ 40% - 50% ~ 40% - 50%Radio afterglowsRadio afterglows ~ 35% - 40% ~ 35% - 40%


Ly- forest by intergalactic H clouds

Spectrum of high-z quasar (z=5.73, Djorgovski et al 2001)

GRB00013C: z=4.5 (Andersen et al 01)


Are there really dark GRB? Yes• From the BSAX sample we find (De Pasquale, LP etal 03, ApJ) that • Dark GRB are on average 6 times fainter in X-rays than

OTGRB (explaining why HETE2 SXC localization lead to OTGRB)

• about 20% of dark GRB are “truly dark”, being their ratio of optical-to-X-ray fluxes smaller by a factor of about 6 compared to OTGRB

• Not consistent with the fireball model unless:• OT heavily absorbed by star forming region ? • Or located at z>5 (such that intragalactic gas will absorb

photons below Lyman limit)


OT GRB

Dark


Dark GRB000210: BeppoSAX & Dark GRB000210: BeppoSAX & Chandra, ESO-VLTChandra, ESO-VLT

• GRB localized by BeppoSAX. • Simultaneous obs of the X-ray afterglow with Chandra.• No OT >23.5• Deep VLT imaging and spectroscopy: z=0.86 (Piro et al ApJ 2002)


X-ray flashesX-ray flashesX-ray flashesX-ray flashes• X-ray rich GRB/ X-Ray Flash: a

new class discovered by BSAX and confirmed by HETE2: about 30% GRB’s with no or very faint or gamma-ray emission (Sx/S>1).

• Several are dark• A different type of GRB’s or

events at z>5-10? (Few events at z<3) or GRB seen off axis (unification scenario as in AGN…)

Heise et al 2001


XRF 031220• Trigger by HETE 2, we carried out

Chandra observation to pintpoint the location of the afterglow at 1”

• No OT, Extremely red host galaxy: R-K’=5.3 Note: GRB000131@z=4.5 R-K=3.7 (z>5 ?)

• Fitting with galaxy SED (vs stellar population, internal absorption, Lya absorption):

• z=1.9: => dark due to dust extinction (Melandri et al05)

mailto:GRB000131@z%3D4.5


Origin of X-ray flashes• We compiled a homogeneous BSAX+HETE2 sample

of XRF • By comparing the properties of afterglows of GRB vs

XRF => strong implications on off-axis (and high z) models… talk by Valeria D’Alessio


The quest for high-z GRB

• Why so much excitement? They can pinpoint obscured star-forming galaxies (X-rays and gamma-rays pierce through) and probe the region z=10-20 where the first stars & galaxies formed (current record holder is a qso at z=6.7)

• If GRB=SFR, about 20% of them at z>5 (Bromm & Loeb 03) • Events at z>5 will not be visible in the optical range, (Lyalpha

forest absorption): they have to be “dark” • Most of the redshift are now derived from optical obs =>

strong bias against high-z GRB • X-ray redshift or IR photometric/spectroscopy z


Conclusions • Massive star progenitor from the environment: X-ray lines, X-ray

absorption, SN association • Prompt vs afterglow emission: different spectral (and temporal) behaviour• Wind vs ISM: comparison with optical decay slopes shows ISM is slightly

preferred. Way out: wind termination shock produces a constant density region (Chevalier &Li 99). Nonetheless we have found so far 3 cases where the wind is preferred (GRB011121, 040106, XRF011030

• New features: X-ray precursors and rebursting (about 10% on BSAX bursts)• Precursor is NOT thermal black body (power law)


Conclusions (II)

• Late-time (200-1000 sec) rebursting (in 3 cases) is identified with the onset of the afterglow. Same spectral index and falls on the same power law decay when t0 is set at the onset of the reburst (talk by Galli)

• About 20% truly dark/optically faint GRB• Origin of XRF (talk by D’Alessio)• GRB and cosmology


Gamma-Ray Bursts: from Astrophysics to Cosmology

• International Space Science School:• At L’Aquila (Italy) from Sept.12-16, 2005• Advanced school for PhD, Post Doc and young

researchers: tutorials, lessons, and seminars in the different branches of Physics and Astrophysics relevant to the comprehension of the GRB phenomenon. GRB in Cosmology. Experiments and methods used in the field. A session devoted to data analysis of all instruments of SWIFT.

L. Piro - Moriond 2005 Gamma-Ray Bursts and X-ray afterglows Luigi Piro Istituto Astrofisica...

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