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GRB 171205A/SN2017iuk: A local low-luminosity gamma-ray burst

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journal contribution
posted on 2019-09-17, 15:24 authored by V D'Elia, S Campana, A D'Ai, M De Pasquale, SWK Emery, DD Frederiks, A Lien, A Melandri, KL Page, RLC Starling, DN Burrows, AA Breeveld, SR Oates, PT O'Brien, JP Osborne, MH Siegel, G Tagliaferri, PJ Brown, SB Cenko, DS Svinkin, A Tohuvavohu, AE Tsvetkova
Context. Gamma-ray bursts (GRBs) occurring in the local Universe constitute an interesting sub-class of the GRB family, since their luminosity is on average lower than that of their cosmological analogs. Attempts to understand in a global way this peculiar behaviour is still not possible, since the sample of low redshift GRBs is small, and the properties of individual objects are too different from each other. In addition, their closeness (and consequently high fluxes) make these sources ideal targets for extensive follow-up even with small telescopes, considering also that these GRBs are conclusively associated with supernova (SN) explosions. Aims. We aim to contribute to the study of local bursts by reporting the case of GRB 171205A. This source was discovered by Swift Burst Alert Telescope (BAT) on 2017, December 5 and soon associated with a low redshift host galaxy (z = 0.037), and an emerging SN (SN 2017iuk). Methods. We analyzed the full Swift dataset, comprising the UV-Optical Telescope (UVOT), X-ray Telescope (XRT) and BAT data. In addition, we employed the Konus-Wind high energy data as a valuable extension at γ-ray energies. Results. The photometric SN signature is clearly visible in the UVOT u, b and ν filters. The maximum emission is reached at ∼13 (rest frame) days, and the whole bump resembles that of SN 2006aj, but lower in magnitude and with a shift in time of +2 d. A prebump in the ν-band is also clearly visible, and this is the first time that such a feature is not observed achromatically in GRB–SNe. Its physical origin cannot be easily explained. The X-ray spectrum shows an intrinsic Hydrogen column density NH,int = 7.4 +4.1 −3.6 ×1020 cm−2 , which is at the low end of the NH,int, even considering just low redshift GRBs. The spectrum also features a thermal component, which is quite common in GRBs associated with SNe, but whose origin is still a matter of debate. Finally, the isotropic energy in the γ-ray band, Eiso = 2.18+0.63 −0.50 × 1049 erg, is lower than those of cosmological GRBs. Combining this value with the peak energy in the same band, Ep = 125+141 −37 keV, implies that GRB 171205A is an outlier of the Amati relation, as are some other low redshift GRBs, and its emission mechanism should be different from that of canonical, farther away GRBs.


The Swift team would like to devote this paper to the memory of Neil Gehrels. RLCS acknowledges funding from STFC. KLP and JPO acknowledge support from the UK Space Agency. DDF, DSS, and AET acknowledge support from RSF grant 17-12-01378. DNB and AT acknowledge support from NASA contract NAS5-00136. SRO gratefully acknowledges the support of the Leverhulme Trust Early Career Fellowship.



Astronomy and Astrophysics, 2018, 619, A66

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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