Rise and Fall of the X-ray flash : an off-axis jet? C.Guidorzi 1,2,3 on behalf of a large collaboration of the Swift, Liverpool and Faulkes Telescopes, GROND, NOT, REM, TAROT teams and in particular S. Kobayashi and J. Granot C.Guidorzi 1,2,3 on behalf of a large collaboration of the Swift, Liverpool and Faulkes Telescopes, GROND, NOT, REM, TAROT teams and in particular S. Kobayashi and J. Granot 1 INAF-Osservatorio Astronomico Brera, Italy 2 Astrophysics Research Institute, Liverpool John Moores University, UK 3 Physics Dept. University of Ferrara, Italy 1 INAF-Osservatorio Astronomico Brera, Italy 2 Astrophysics Research Institute, Liverpool John Moores University, UK 3 Physics Dept. University of Ferrara, Italy

Egypt Outline  X-Ray Flashes (XRFs) as a class of GRBs  XRF : broadband data set  Observed properties:  prompt  -ray emission  Broadband (X-ray,UV,B,V,r,i,z,J,H,Ks) afterglow (light curves, SED)  Interpretation of XRF properties  X-Ray Flashes (XRFs) as a class of GRBs  XRF : broadband data set  Observed properties:  prompt  -ray emission  Broadband (X-ray,UV,B,V,r,i,z,J,H,Ks) afterglow (light curves, SED)  Interpretation of XRF properties

Egypt X-ray Flashes (XRFs) A softer and less energetic version of classical GRBs (Heise et al. 2001; Kippen et al. 2001) e.g. Ep vs. Eiso relation (Amati et al. 2008)

Egypt XRFs vs. c-GRBs =  Overall, same prompt temporal properties  On average, same afterglow properties (although see Sakamoto et al and the Swift sample)  Associations (or lack of) with hypernovae ≠  XRFs are softer, due to a lower Ep (≤ 30 keV), while c-GRBs have Ep of a few 100 keV.  In some cases, less energetic and smoother  - ray light curves (e.g , Campana et al., 2006) =  Overall, same prompt temporal properties  On average, same afterglow properties (although see Sakamoto et al and the Swift sample)  Associations (or lack of) with hypernovae ≠  XRFs are softer, due to a lower Ep (≤ 30 keV), while c-GRBs have Ep of a few 100 keV.  In some cases, less energetic and smoother  - ray light curves (e.g , Campana et al., 2006)

Egypt F Peak Energy: E p Sakamoto et al XRF XRR GRB

Egypt XRF  Swift-BAT ( keV) detected and promptly localised it.  Swift-XRT and UVOT promptly followed it up and began at 77 sec post trigger time  X-ray and UV afterglow.  Several robotic facilities promptly reacted and discovered the rising optical counterpart: in particular, 2-m class telescopes (GROND, and LT).  Swift-BAT ( keV) detected and promptly localised it.  Swift-XRT and UVOT promptly followed it up and began at 77 sec post trigger time  X-ray and UV afterglow.  Several robotic facilities promptly reacted and discovered the rising optical counterpart: in particular, 2-m class telescopes (GROND, and LT).

Egypt  -ray prompt emission

Egypt  -ray prompt emission  Swift-BAT ( keV) detected and promptly localised it. 1.Ep < 35 keV 2.4 pulses 3.Marginal soft-to-hard evolution,    from 2 to S( keV)= 3.6 x erg cm -2 5.E iso < 2.2 x ergs XRT

Egypt Panchromatic Light curves (from 30 s out to a few days post burst)

Egypt X-ray  NIR Light Curve Shallow optical rise F o (t)  t +0.5

Egypt Spectral Energy Distributions: 1, 2  ox = 0.74 ± 0.03 Typical Band fit

Egypt X-ray  NIR Light Curve Plateau at every

Egypt SED 3: a single unextinguished PL!  ox = 0.79 ±0.01

Egypt Decay and late-time red Bump (at 1 day)

Egypt At 1 day it got redder! Red bump  o = 1.05 ± 0.06

Egypt Did you measure z? -Yes, we did.

Egypt z = 1.51 NOT: absorption spectrum Taken at t=46 min

Egypt Multi-band simultaneous Modeling F(t)  t -   1  -0.6  2  0.15  3  1.1  4  3.5 F(t)  t -   1  -0.4  2  2.0 t 1  600 s t 2  34 ks

Egypt Main Properties: Summary  Soft, long 4-pulsed event.  X-ray steep decay is high-latitude emission of the last pulse  end of the prompt emission  Long plateau (typical X-rays, not so much in optical), single PL spectrum with almost no dust: A v <0.02  Rise-plateau-decay is ACHROMATIC  Red bump at 1 day  Soft, long 4-pulsed event.  X-ray steep decay is high-latitude emission of the last pulse  end of the prompt emission  Long plateau (typical X-rays, not so much in optical), single PL spectrum with almost no dust: A v <0.02  Rise-plateau-decay is ACHROMATIC  Red bump at 1 day

Egypt Interpretation(s)Interpretation(s)

Egypt Interpretation(s)  Does the optical rise mark the afterglow onset? No, too slow!  Achromatic evolution  geometry  jet(s)  How many jets?  With just one jet, red bump is the reverse shock of a late energy injection episode.  2 is also OK (e.g. see B), but more contrived! Mind Okkham’s razor!  Does the optical rise mark the afterglow onset? No, too slow!  Achromatic evolution  geometry  jet(s)  How many jets?  With just one jet, red bump is the reverse shock of a late energy injection episode.  2 is also OK (e.g. see B), but more contrived! Mind Okkham’s razor!

Egypt Off-axis jet Granot et al  obs  2  0, (  0  few degrees)

Egypt Why does the Sphynx look so tiny? Maybe you’re an off-axis observer…