J/A+A/708/A60ivo://CDS.VizieR/J/A+A/708/A60CDSRossi A.Izzo L.Maeda K.Schady P.Malesani D.B.Kann D.A.,Klose S.Amati L.D'Avanzo P.de Ugarte Postigo A.Heintz K.E.,Kumar A.Lipunov V.Martin-Carrillo A.Melandri A.,Nicuesa Guelbenzu A.M.Oates S.R.Schulze S.Selsing J.,Starling R.L.C.Stratta G.Vlasenko D.Balanutsa P.Brivio R.,D'Elia V.Milvang-Jensen B.Palazzi E.Perley D.A.Rau A.,Sollerman J.Tanvir N.R.Zafar T.2026-03-26T08:19:48Z2026-03-26T08:50:38ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frsupernovaephotometryspectroscopyvisible-astronomyinfrared-astronomyThe long GRB 180728A, at a redshift of z=0.1171, stands out due to its high isotropic energy of E_gamma,iso_~2.5x10^51^erg, in contrast with most events at redshift z<0.2. We analyze the properties of GRB 180728A's prompt emission, afterglow, and associated supernova SN 2018fip, comparing them with other GRB-SN events. This study employs a dense photometric and spectroscopic follow-up of the afterglow and the SN up to 80 days after the burst, supported by image subtraction to remove the presence of a nearby bright star, and modelling of both the afterglow and the supernova. GRB 180728A lies on the E_p,i_-E_gamma,iso_ plane occupied by classical collapsar events, and the prompt emission is one of the most energetic at z<0.2 after GRB 030329 and GRB 221009A. The afterglow of GRB 180728A is less luminous than that of most long GRBs, showing a shallow early phase that steepens around 5 hours (0.2 days). The GRB exploded in an irregular, low-mass, blue, star-forming galaxy, typical of low-z collapsar events. Because of the relatively faint afterglow, the light curve bump of SN 2018fip dominates the optical emission already after ~3 days and is one of the best sampled to date. The strong suppression below ~4000 angstrom and a largely featureless continuum in the early 6--9 days spectra favor aspherical two-component ejecta with a high-velocity collimated component (>20000km/s), dominant early-on, and a more massive, low-velocity component, which dominates at much later epochs. Our findings indicate that asymmetries need to be considered in order to better understand GRB-SNe. In any case, SN 2018fip shares many characteristics with typical GRB-SNe. Its kinetic energy is below the common range of 10^52^-10^53^erg and does not correlate with the high energy of the GRB, highlighting the diversity of the GRB-SN energy budget partition.2026A&A...708A..60Rhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/708/A60CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/708/A60https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/708/A60http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/708/A60https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/708/A60https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/708/A60http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/708/A60GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticalInfrareddefaultJ/A+A/708/A60/tablec3Photometry of the afterglow of GRB 180728ArecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTimeTime since GRB trigger (days) (1)dtime.epochdoublel_magUpper limit flag on magmeta.code.errorcharmagAB magnitude in Filter (2)magphot.magfloate_mag? magnitude in Filter error (3)magstat.error;phot.magfloatnullableFilterFilter used (4)instr.setup;instr.filtercharTel/InstTelescope/Instrument usedinstr.setupchar