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

Deciphering the ancient universe with GRBs Kyoto, April 19-23 GRB 090426 An oddball event in the outskirts of two interacting galaxies 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 see also papers by Levesque et al. 2010 and Antonelli et al. 2009

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426 Prompt emission and afterglow ❖ Detected by Swift (BAT, XRT, UVOT) ❖ T 90 (observed) = 1.2s R-BAND LIGHTCURVE FROM LITERATURE ❖ relatively bright afterglow optical afterglow powerlaw ( α =-1.12) with energy injection? ❖ z = 2.609 from Keck (Levesque et al. 2010) HOST GALAXY MAGNITUDE

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426 Prompt emission and afterglow @A6B+CD-5,=.+.,(B,E-9,"F"#GH ;/=>,?' ! ❖ Detected by Swift (BAT, XRT, UVOT) '()*+,-.+/,0"&% ! !",1/23,04 ! 3 "&! ❖ T 90 (observed) = 1.2s "&"! ❖ relatively bright afterglow !" ! % optical afterglow powerlaw ( α =-1.12) with energy injection? !" ! # !"" !""" !" # !" $ 567/,46*8/,9:5,+;6<</;,043 !"# ❖ z = 2.609 from Keck (Levesque et al. 2010) &'()*+',-./*01/(2)3*4!% $$ *+. � $ 5 ! ❖ X-ray spectrum: log N H = 21.7 (average, see Campana et al. 2010) %"# = nothing special here... % !"# $ $"# 6'718*,97*:;')'/*2/01<

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426 A puzzling afterglow spectrum 8 ❖ First spectrum of a short GRB? 090426 6 Number 4 ❖ low Lyman α absorption 2 log N H = 18.7 0 SWIFT GRB LOG N H DISTRIBUTION ❖ high N H optical/N H X-rays 17 18 19 20 21 22 23 logN HI (cm -2 ) (FYNBO ET AL. 2009) indication for ionized medium? ❖ common low ionization lines (Si II, CII, Fe II...) absent/weak ❖ instead very strong high ionization lines (SiIV, CIV, NV)

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426 Short? Long? Or something else? ❖ T 90 (rest) = 0.3 s ❖ no spectral lag (with large errors) ❖ relatively high energy release: E iso = 2.8 x 10 51 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 6 ❖ Too high z for supernova search 8 10 Corrected R c magnitude assuming z = 1 LONG BURSTS GRB 090426 12 ❖ Likely a collapsar, not a merger 14 060121 (z=4.6) 16 ❖ Question: How can we produce such 060121 (z=1.7) 18 a short collapsar? 20 050509B off-axis? 22 24 jet shut off before it reaches surface? 061201 26 different progenitor? 28 080503 or... ?? 050911 30 SHORT BURSTS 32 1E-4 1E-3 0,01 0,1 1 10 100 t (days after burst in the observer frame assuming z = 1)

CHRISTINA THÖNE KYOTO, APRIL 23, 2010 GRB 090426 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], H β emission (X-shooter) ❖ Bright galaxies: M AB (1500Å) = -21.05 & -20.43 (1.5 & 0.8 L*) ❖ Moderate SFR (host: 3.1 M solar /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 N H (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 M solar 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 observe 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: observed 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 ....

APRIL 2009

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

APRIL 2010

APRIL 2010 MT FUJI!! :-)

ありがとうございます !