GRB 090426 An oddball event in the outskirts of two interacting - - PowerPoint PPT Presentation

Christina Thöne (INAF - Osservatorio Astronomico di Brera) Sergio Campana, Davide Lazzati, Johan Fynbo, Antonio de Ugarte Postigo, Lise Christensen, Andrew Levan, Miguel Aloy, Jens Hjorth, Pall Jakobsson, Emily Levesque, Daniele Malesani, Bo Milvang-Jensen, Pete Roming, Nial Tanvir & Klaas Wiersema Deciphering the ancient universe with GRBs Kyoto, April 19-23

see also papers by Levesque et al. 2010 and Antonelli et al. 2009

GRB 090426 An oddball event in the outskirts of two interacting galaxies

Prompt emission and afterglow

❖ Detected by Swift (BAT, XRT, UVOT) ❖ T90 (observed) = 1.2s ❖ relatively bright afterglow

• ptical afterglow powerlaw (α=-1.12)

with energy injection?

❖ z = 2.609 from Keck

(Levesque et al. 2010)

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

R-BAND LIGHTCURVE FROM LITERATURE

HOST GALAXY MAGNITUDE

Prompt emission and afterglow

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

!"# $ $"# % %"# ! !"# &'()*+',-./*01/(2)3*4!%$$*+.$5 6'718*,97*:;')'/*2/01<

=

❖ Detected by Swift (BAT, XRT, UVOT) ❖ T90 (observed) = 1.2s ❖ relatively bright afterglow

• ptical afterglow powerlaw (α=-1.12)

with energy injection?

❖ z = 2.609 from Keck

(Levesque et al. 2010)

❖ X-ray spectrum: log NH = 21.7

(average, see Campana et al. 2010) nothing special here...

!"" !""" !"# !"$ !"!# !"!% "&"! "&! ! '()*+,-.+/,0"&%!!",1/23,04 !3 567/,46*8/,9:5,+;6<</;,043 ;/=>,?' @A6B+CD-5,=.+.,(B,E-9,"F"#GH

A puzzling afterglow spectrum

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

❖ First spectrum of a short GRB? ❖ low Lyman α absorption

log NH = 18.7

❖ high NH optical/NH X-rays

indication for ionized medium?

❖ common low ionization lines

(Si II, CII, Fe II...) absent/weak

❖ instead very strong high

ionization lines (SiIV, CIV, NV)

17 18 19 20 21 22 23 logNHI (cm-2) 2 4 6 8 Number

090426 SWIFT GRB LOG NH DISTRIBUTION (FYNBO ET AL. 2009)

Short? Long? Or something else?

❖ T90 (rest) = 0.3 s ❖ no spectral lag (with large errors) ❖ relatively high energy release:

Eiso = 2.8 x 1051 erg

❖ consistent with Amati relation

(see Antonelli et al. 2009)

❖ Very soft spectrum

(compared to „real“ short GRBs, long GRBs and other GRBs with low optical Lyman α absorption)

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

Short? Long? Or something else?

❖ Afterglow average for a long GRB

but 4 mag brighter then short GRBs

❖ Too high z for supernova search ❖ Likely a collapsar, not a merger ❖ Question: How can we produce such

a short collapsar?

• ff-axis?

jet shut off before it reaches surface? different progenitor?

• r... ??

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

1E-4 1E-3 0,01 0,1 1 10 100 32 30 28 26 24 22 20 18 16 14 12 10 8 6

050911 080503

050509B 060121 (z=1.7)

Corrected Rc magnitude assuming z = 1 t (days after burst in the observer frame assuming z = 1)

060121 (z=4.6) 061201

GRB 090426

LONG BURSTS SHORT BURSTS

The host galaxy/-ies

❖ „Host galaxy“ are two galaxies at

z = 2.609 (GRB on top of the fainter one) Lyman α emission lines (FORS 2) [OIII], Hβ emission (X-shooter)

❖ Bright galaxies:

MAB(1500Å) = -21.05 & -20.43 (1.5 & 0.8 L*)

❖ Moderate SFR (host: 3.1 Msolar/yr) ❖ Distance only 1.1 arcsec or 9 kpc!! ❖ Complex kinematics of afterglow absorption

• vs. host/companion emission lines

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

Back to the afterglow spectrum...

❖ Comparison with Keck spectrum from

Levesque et al. (1.1h after the burst):

!!! Lyman α is varying !!! (3.8 σ)

1.1h: EW=3.09±0.20 Å, 12h: 1.94±0.23 Å (other lines constant within errors)

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

Back to the afterglow spectrum...

❖ Comparison with Keck spectrum from

Levesque et al. (1.1h after the burst):

!!! Lyman α is varying !!! (3.8 σ)

1.1h: EW=3.09±0.20 Å, 12h: 1.94±0.23 Å (other lines constant within errors)

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

Back to the afterglow spectrum...

❖ Comparison with Keck spectrum from

Levesque et al. (1.1h after the burst):

!!! Lyman α is varying !!! (3.8 σ)

1.1h: EW=3.09±0.20 Å, 12h: 1.94±0.23 Å (other lines constant within errors)

❖ Si IV shows two components separated

by 300 km/s

❖ Lyman α shifted compared to other

emission lines (outflow??)

❖ Detection of NV

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

Comparison to other GRB afterglow spectra

Sample of >70 spectra (Fynbo et al. 2009) & average GRB spectrum (Christensen et al. in prep.)

❖ exceptional in all ratios, also compared to other low NH (Ly α) bursts ❖ high ionization of BOTH Si IV and C IV

This burst is different!!

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

Photoionization modeling

Photoionization code by Perna & Lazzati: Shell at T=100 K Results: radius = 80 pc (!!) mass = 63,000 Msolar density = 1.2 cm-3 An isolated molecular cloud?!? Other GRBs: Finestructure lines & variability/Mg I nonvariability: distances few 100 - few kpc

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

GRB 090426 - the first time we

• bserve material close to the GRB
• GRB was likely a collapsar
• GRB occurred in a complex of two interacting galaxies
• Variability of Lyman α, material highly ionized:
• bserved material close to the GRB (predicted by e.g. Perna&Loeb 1998)
• Merging creates tidal tail with relatively isolated SF regions?

No contaminations by „normal“ host galaxy ISM in spectrum Other examples known? 021004, 080310...? We need more time resolved spectroscopy!!

Results submitted a while ago, waiting for referee report, hopefully online soon ....

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426

APRIL 2009

MT FUJI?!!?? :-( APRIL 2010

APRIL 2010

MT FUJI!! :-) APRIL 2010

ありがとうございます!