TY - JOUR
T1 - GRB 180418A
T2 - a possibly short gamma-ray burst with a wide-angle outflow in a faint host galaxy
AU - Rouco Escorial, A.
AU - Fong, W.
AU - Veres, P.
AU - Laskar, T.
AU - Lien, A.
AU - Paterson, K.
AU - Lally, M.
AU - Blanchard, P. K.
AU - Nugent, A. E.
AU - Tanvir, N. R.
AU - Cornish, D.
AU - Berger, E.
AU - Burns, E.
AU - Cenko, S. B.
AU - Cobb, B. E.
AU - Cucchiara, A.
AU - Goldstein, A.
AU - Margutti, R.
AU - Metzger, B. D.
AU - Milne, P.
AU - Levan, A.
AU - Nicholl, M.
AU - Smith, Nathan
N1 - Publisher Copyright:
© 2021. The American Astronomical Society. All rights reserved..
PY - 2021/5/10
Y1 - 2021/5/10
N2 - We present X-ray and multiband optical observations of the afterglow and host galaxy of GRB 180418A, discovered by Swift/BAT and Fermi/GBM. We present a reanalysis of the GBM and BAT data deriving durations of the prompt emission of T90 ≍ 2.56 and 1.90 s, respectively. Modeling the Fermi/GBM catalog of 1405 bursts (2008-2014) in the hardness-T90 plane, we obtain a probability of ≍60% that GRB 180418A is a short-hard burst. From a combination of Swift/XRT and Chandra observations, the X-ray afterglow is detected to ≍38.5 days after the burst and exhibits a single power-law decline with FX ∝ t-0.98. Late-time Gemini observations reveal a faint r ≍ 25.69 mag host galaxy at an angular offset of ≍0"16. At the likely redshift range of z ≍ 1-2.25, we find that the X-ray afterglow luminosity of GRB 180418A is intermediate between short and long gamma-ray bursts (GRBs) at all epochs during which there are contemporaneous data and that GRB 180418A lies closer to the Eγ,peak-Eγ,iso correlation for short GRBs. Modeling the multiwavelength afterglow with the standard synchrotron model, we derive the burst explosion properties and find a jet opening angle of θj ≳ 9°-14°. If GRB 180418A is a short GRB that originated from a neutron star merger, it has one of the brightest and longest-lived afterglows along with an extremely faint host galaxy. If, instead, the event is a long GRB that originated from a massive star collapse, it has among the lowest-luminosity afterglows and lies in a peculiar space in terms of the hardness-T90 and Eγ,peak-Eγ,iso planes....
AB - We present X-ray and multiband optical observations of the afterglow and host galaxy of GRB 180418A, discovered by Swift/BAT and Fermi/GBM. We present a reanalysis of the GBM and BAT data deriving durations of the prompt emission of T90 ≍ 2.56 and 1.90 s, respectively. Modeling the Fermi/GBM catalog of 1405 bursts (2008-2014) in the hardness-T90 plane, we obtain a probability of ≍60% that GRB 180418A is a short-hard burst. From a combination of Swift/XRT and Chandra observations, the X-ray afterglow is detected to ≍38.5 days after the burst and exhibits a single power-law decline with FX ∝ t-0.98. Late-time Gemini observations reveal a faint r ≍ 25.69 mag host galaxy at an angular offset of ≍0"16. At the likely redshift range of z ≍ 1-2.25, we find that the X-ray afterglow luminosity of GRB 180418A is intermediate between short and long gamma-ray bursts (GRBs) at all epochs during which there are contemporaneous data and that GRB 180418A lies closer to the Eγ,peak-Eγ,iso correlation for short GRBs. Modeling the multiwavelength afterglow with the standard synchrotron model, we derive the burst explosion properties and find a jet opening angle of θj ≳ 9°-14°. If GRB 180418A is a short GRB that originated from a neutron star merger, it has one of the brightest and longest-lived afterglows along with an extremely faint host galaxy. If, instead, the event is a long GRB that originated from a massive star collapse, it has among the lowest-luminosity afterglows and lies in a peculiar space in terms of the hardness-T90 and Eγ,peak-Eγ,iso planes....
KW - Gamma-ray transient sources
KW - Gamma-ray bursts
UR - http://www.scopus.com/inward/record.url?scp=85106322315&partnerID=8YFLogxK
UR - https://arxiv.org/abs/2012.09961
U2 - 10.3847/1538-4357/abee85
DO - 10.3847/1538-4357/abee85
M3 - Article
SN - 0004-637X
VL - 912
JO - The Astrophysical Journal
JF - The Astrophysical Journal
IS - 2
M1 - 95
ER -