The nature of the late achromatic bump in GRB 120326A

A. Melandri; F. J. Virgili; C. Guidorzi; M. G. Bernardini; S. Kobayashi; C. G. Mundell; A. Gomboc; B. Dintinjana; V. -P. Hentunen; J. Japelj; D. Kopač; D. Kuroda; A. N. Morgan; I. A. Steele; U. Quadri; G. Arici; D. Arnold; R. Girelli; H. Hanayama; N. Kawai; H. Mikuž; M. Nissinen; T. Salmi; R. J. Smith; L. Strabla; M. Tonincelli; A. Quadri

doi:10.1051/0004-6361/201424338

The nature of the late achromatic bump in GRB 120326A

A. Melandri, F. J. Virgili, C. Guidorzi, M. G. Bernardini, S. Kobayashi, C. G. Mundell, A. Gomboc, B. Dintinjana, V. -P. Hentunen, J. Japelj, D. Kopač, D. Kuroda, A. N. Morgan, I. A. Steele, U. Quadri, G. Arici, D. Arnold, R. Girelli, H. Hanayama, N. KawaiH. Mikuž, M. Nissinen, T. Salmi, R. J. Smith, L. Strabla, M. Tonincelli, A. Quadri

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Abstract

The long ${\it Swift}$ gamma-ray burst GRB 120326A at redshift $z=1.798$ exhibited a multi-band light curve with a striking feature: a late-time, long-lasting achromatic rebrightening, rarely seen in such events. Peaking in optical and X-ray bands $\sim 35$ ks ($\sim 12.5$ ks in the GRB rest frame) after the 70-s GRB prompt burst, the feature brightens nearly two orders of magnitude above the underlying optical power-law decay. Modelling the multiwavelength light curves, we investigate possible causes of the rebrightening in the context of the standard fireball model. We exclude a range of scenarios for the origin of this feature: reverse-shock flash, late-time forward shock peak due to the passage of the maximal synchrotron frequency through the optical band, late central engine optical/X-ray flares, interaction between the expanding blast wave and a density enhancement in the circumburst medium and gravitational microlensing. Instead we conclude that the achromatic rebrightening may be caused by a refreshed forward shock or a geometrical effect. In addition, we identify an additional component after the end of the prompt emission, that shapes the observed X-ray and optical light curves differently, ruling out a single overall emission component to explain the observed early time emission.

Original language	English
Article number	A55
Number of pages	7
Journal	Astronomy & Astrophysics
Volume	572
DOIs	https://doi.org/10.1051/0004-6361/201424338
Publication status	Published - 23 Sept 2014

Keywords

astro-ph.HE

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10.1051/0004-6361/201424338

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Melandri, A., Virgili, F. J., Guidorzi, C., Bernardini, M. G., Kobayashi, S., Mundell, C. G., Gomboc, A., Dintinjana, B., Hentunen, V. .-P., Japelj, J., Kopač, D., Kuroda, D., Morgan, A. N., Steele, I. A., Quadri, U., Arici, G., Arnold, D., Girelli, R., Hanayama, H., ... Quadri, A. (2014). The nature of the late achromatic bump in GRB 120326A. Astronomy & Astrophysics, 572, Article A55. https://doi.org/10.1051/0004-6361/201424338

Melandri, A, Virgili, FJ, Guidorzi, C, Bernardini, MG, Kobayashi, S, Mundell, CG, Gomboc, A, Dintinjana, B, Hentunen, V-P, Japelj, J, Kopač, D, Kuroda, D, Morgan, AN, Steele, IA, Quadri, U, Arici, G, Arnold, D, Girelli, R, Hanayama, H, Kawai, N, Mikuž, H, Nissinen, M, Salmi, T, Smith, RJ, Strabla, L, Tonincelli, M & Quadri, A 2014, 'The nature of the late achromatic bump in GRB 120326A', Astronomy & Astrophysics, vol. 572, A55. https://doi.org/10.1051/0004-6361/201424338

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title = "The nature of the late achromatic bump in GRB 120326A",

abstract = "The long ${\it Swift}$ gamma-ray burst GRB 120326A at redshift $z=1.798$ exhibited a multi-band light curve with a striking feature: a late-time, long-lasting achromatic rebrightening, rarely seen in such events. Peaking in optical and X-ray bands $\sim 35$ ks ($\sim 12.5$ ks in the GRB rest frame) after the 70-s GRB prompt burst, the feature brightens nearly two orders of magnitude above the underlying optical power-law decay. Modelling the multiwavelength light curves, we investigate possible causes of the rebrightening in the context of the standard fireball model. We exclude a range of scenarios for the origin of this feature: reverse-shock flash, late-time forward shock peak due to the passage of the maximal synchrotron frequency through the optical band, late central engine optical/X-ray flares, interaction between the expanding blast wave and a density enhancement in the circumburst medium and gravitational microlensing. Instead we conclude that the achromatic rebrightening may be caused by a refreshed forward shock or a geometrical effect. In addition, we identify an additional component after the end of the prompt emission, that shapes the observed X-ray and optical light curves differently, ruling out a single overall emission component to explain the observed early time emission.",

keywords = "astro-ph.HE",

author = "A. Melandri and Virgili, {F. J.} and C. Guidorzi and Bernardini, {M. G.} and S. Kobayashi and Mundell, {C. G.} and A. Gomboc and B. Dintinjana and Hentunen, {V. -P.} and J. Japelj and D. Kopa{\v c} and D. Kuroda and Morgan, {A. N.} and Steele, {I. A.} and U. Quadri and G. Arici and D. Arnold and R. Girelli and H. Hanayama and N. Kawai and H. Miku{\v z} and M. Nissinen and T. Salmi and Smith, {R. J.} and L. Strabla and M. Tonincelli and A. Quadri",

year = "2014",

month = sep,

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doi = "10.1051/0004-6361/201424338",

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TY - JOUR

T1 - The nature of the late achromatic bump in GRB 120326A

AU - Melandri, A.

AU - Virgili, F. J.

AU - Guidorzi, C.

AU - Bernardini, M. G.

AU - Kobayashi, S.

AU - Mundell, C. G.

AU - Gomboc, A.

AU - Dintinjana, B.

AU - Hentunen, V. -P.

AU - Japelj, J.

AU - Kopač, D.

AU - Kuroda, D.

AU - Morgan, A. N.

AU - Steele, I. A.

AU - Quadri, U.

AU - Arici, G.

AU - Arnold, D.

AU - Girelli, R.

AU - Hanayama, H.

AU - Kawai, N.

AU - Mikuž, H.

AU - Nissinen, M.

AU - Salmi, T.

AU - Smith, R. J.

AU - Strabla, L.

AU - Tonincelli, M.

AU - Quadri, A.

PY - 2014/9/23

Y1 - 2014/9/23

N2 - The long ${\it Swift}$ gamma-ray burst GRB 120326A at redshift $z=1.798$ exhibited a multi-band light curve with a striking feature: a late-time, long-lasting achromatic rebrightening, rarely seen in such events. Peaking in optical and X-ray bands $\sim 35$ ks ($\sim 12.5$ ks in the GRB rest frame) after the 70-s GRB prompt burst, the feature brightens nearly two orders of magnitude above the underlying optical power-law decay. Modelling the multiwavelength light curves, we investigate possible causes of the rebrightening in the context of the standard fireball model. We exclude a range of scenarios for the origin of this feature: reverse-shock flash, late-time forward shock peak due to the passage of the maximal synchrotron frequency through the optical band, late central engine optical/X-ray flares, interaction between the expanding blast wave and a density enhancement in the circumburst medium and gravitational microlensing. Instead we conclude that the achromatic rebrightening may be caused by a refreshed forward shock or a geometrical effect. In addition, we identify an additional component after the end of the prompt emission, that shapes the observed X-ray and optical light curves differently, ruling out a single overall emission component to explain the observed early time emission.

AB - The long ${\it Swift}$ gamma-ray burst GRB 120326A at redshift $z=1.798$ exhibited a multi-band light curve with a striking feature: a late-time, long-lasting achromatic rebrightening, rarely seen in such events. Peaking in optical and X-ray bands $\sim 35$ ks ($\sim 12.5$ ks in the GRB rest frame) after the 70-s GRB prompt burst, the feature brightens nearly two orders of magnitude above the underlying optical power-law decay. Modelling the multiwavelength light curves, we investigate possible causes of the rebrightening in the context of the standard fireball model. We exclude a range of scenarios for the origin of this feature: reverse-shock flash, late-time forward shock peak due to the passage of the maximal synchrotron frequency through the optical band, late central engine optical/X-ray flares, interaction between the expanding blast wave and a density enhancement in the circumburst medium and gravitational microlensing. Instead we conclude that the achromatic rebrightening may be caused by a refreshed forward shock or a geometrical effect. In addition, we identify an additional component after the end of the prompt emission, that shapes the observed X-ray and optical light curves differently, ruling out a single overall emission component to explain the observed early time emission.

KW - astro-ph.HE

UR - http://arxiv.org/abs/1409.6467

UR - http://dx.doi.org/10.1051/0004-6361/201424338

U2 - 10.1051/0004-6361/201424338

DO - 10.1051/0004-6361/201424338

M3 - Article

SN - 0004-6361

VL - 572

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

M1 - A55

ER -

The nature of the late achromatic bump in GRB 120326A

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