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This study delves into the characteristics and implications of X-ray Flash (XRF) 080330, a softer and less energetic precursor to classical Gamma-Ray Bursts (GRBs). Employing a broad spectrum of data from various telescopes, we analyze the prompt gamma-ray emissions and the complex light curves across X-ray, UV, and optical wavelengths. Our findings indicate potential off-axis jet dynamics, as evidenced by the long duration of emission and achromatic evolution patterns. This research contributes to our understanding of XRFs and their association with cosmic events such as supernovae.
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Rise and Fall of the X-ray flash 080330: 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 1INAF-Osservatorio Astronomico Brera, Italy 2Astrophysics Research Institute, Liverpool John Moores University, UK 3Physics Dept. University of Ferrara, Italy
Outline • X-Ray Flashes (XRFs) as a class of GRBs • XRF 080330: 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 080330 properties Egypt 2009
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 2009
XRFs vs. c-GRBs = • Overall, same prompt temporal properties • On average, same afterglow properties(although see Sakamoto et al. 2008 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. 060218, Campana et al., 2006) Egypt 2009
F Peak Energy: Ep XRF XRR GRB Sakamoto et al. 2008 Egypt 2009
XRF 080330 • Swift-BAT (15-150 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 2009
-ray prompt emission Egypt 2009
-ray prompt emission • Swift-BAT (15-150 keV) detected and promptly localised it. • Ep < 35 keV • 4 pulses • Marginal soft-to-hard evolution, from 2 to 1.5 • S(15-150 keV)= 3.6 x 10-7 erg cm-2 • Eiso < 2.2 x 1052 ergs XRT Egypt 2009
Panchromatic Light curves (from 30 s out to a few days post burst) Egypt 2009
X-ray NIR Light Curve Shallow optical rise Fo(t) t+0.5 Egypt 2009
Spectral Energy Distributions: 1 , 2 Typical Band fit ox = 0.74 ± 0.03 Egypt 2009
X-ray NIR Light Curve Plateau at every Egypt 2009
SED 3: a single unextinguished PL! ox = 0.79 ±0.01 Egypt 2009
Decay and late-time red Bump (at 1 day) Egypt 2009
At 1 day it got redder! Red bump o = 1.05 ± 0.06 Egypt 2009
-Did you measure z?-Yes, we did. Egypt 2009
NOT: absorption spectrum z = 1.51 Taken at t=46 min Egypt 2009
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 t1 600 s t2 34 ks Egypt 2009
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: Av<0.02 • Rise-plateau-decay is ACHROMATIC • Red bump at 1 day Egypt 2009
Interpretation(s) Egypt 2009
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 080319B), but more contrived! Mind Okkham’s razor! Egypt 2009
Off-axis jet obs 2 0 , (0 few degrees) Granot et al. 2005 Egypt 2009
Why does the Sphynx look so tiny? Maybe you’re an off-axis observer… Egypt 2009
