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 T 90 ≈ 2.56 and 1.90 s, respectively. Modeling the Fermi/GBM catalog of 1405 bursts (2008-2014) in the hardness-T 90 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 F X ∝ 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 E γ,peak-E γ,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 θ j 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-T 90 and E γ,peak-E γ,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 T 90 ≈ 2.56 and 1.90 s, respectively. Modeling the Fermi/GBM catalog of 1405 bursts (2008-2014) in the hardness-T 90 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 F X ∝ 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 E γ,peak-E γ,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 θ j 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-T 90 and E γ,peak-E γ,iso planes.
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U2 - 10.3847/1538-4357/abee85
DO - 10.3847/1538-4357/abee85
M3 - Article
AN - SCOPUS:85106322315
SN - 0004-637X
VL - 912
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 95
ER -