posted on 2019-09-17, 15:24authored byV 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.
Funding
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.
History
Citation
Astronomy and Astrophysics, 2018, 619, A66
Author affiliation
/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy
Version
VoR (Version of Record)
Published in
Astronomy and Astrophysics
Publisher
EDP Sciences for European Southern Observatory (ESO)