Gamma-ray bursts and the production of cosmogenic radionuclides in the Earth’s atmosphere

Supernovae and Single-Year Anomalies in the Atmospheric Radiocarbon Record

“…commonly$between$10 46 $-$10 49 $erg$ (Povinec$&$Tokar$1970;$Miyake$et#al.#2012;$ Melott$ et# al.$ 2015;$ Güttler$ et# al.# 2015).$ A$ further$ complication$ is$ that$ SNe$ may$ emit$γPrays$isotropically$or$in$a$highly$collimated$fashion,$making$estimation$of$ their$impact$on$Earth$even$more$difficult.$$ $ Damon$et#al.$(1995)$claimed$that$a$rise$in$atmospheric$ 14 C$levels$around$1006$CE$ was$ attributable$ to$ the$ wellPattested$ Type$ 1a$ supernova$ at$ this$ time,$ denoted$ SN1006$ (supernova$ in$ the$ year$ 1006$ CE).$ Their$ study$ comprised$ 75$ conventional$ radiocarbon$ measurements$ on$ annual$ treePrings$ between$ 1000$ -$ 1010$ CE.$ The$ observed$ rise$ in$ 14 C$ (~$ 6$ ‰)$ actually$ peaked$ some$ 2$ -$ 3$ years$ after$ the$ star$ was$ first$ documented$ (see$ Table$ 1).$ Whilst$ this$ offset$ was$ perplexing$to$the$authors,$it$concurs$well$with$recent$modelling$of$ 14 C$transport$ through$the$stratosphere$and$troposphere $(Pavlov#et#al.$2013;$Levin$et#al.#2010;$ Güttler# et# al.# 2015).$ Only$ one$ attempt$ has$ since$ been$ made$ to$ replicate$ these$ findings,$ and$ it$ could$ not$ discern$ any$ significant$ uplift$ around$ 1006$ CE$ (see $ Menjo$ et# al.$ 2005).$ The$ study$ also$ failed$ to$ detect$ SN1054,$ the$ explosion$ that$ generated$the$Crab$Nebula.$Indeed,$the$authors$doubted$whether$any$historical$ SNe$ was$ energetic$ enough$ to$ be$ visible$ in$ the$ 14 C$ record,$ especially$ given$ the$ ebbs$and$flows$of$the$Schwabe$cycle$ (Menjo$et#al.$2005).$ $ Attention$ recently$ returned$ to$ this$ issue$ after$ Miyake$ et# al.$ (2012)$ reported$ a$ rapid$ increase$ in$ atmospheric$ 14 C$ levels$ in$ Japanese$ treePrings$ between$ 774$ -$ 775$ CE.$ The$ singlePyear$ anomaly$ was$ of$ unprecedented$ magnitude$ (~$ 12$ ‰).$$ Just$one$year$later,$the$same$team$reported$very$similar$data$for$the$years$993$-$ 994$ CE$ (Miyake$ et# al.$ 2013).$ Importantly,$ the$ uplifts$ were$ only$ apparent$ when$ annual$sequences$of$treePrings$were$measured,$as$opposed$to$the$more$common$ practice$ of$ analysing$ decadal$ blocks$ (see$ Figure$ 1). $ Furthermore,$ it$ has$ since$ been$ established$ that$ the$ anomalies$ were$ globally$ synchronous$ and$ approximately$ uniform$ in$ magnitude.$ The$ 775$ CE$ spike$ has$ already$ been$ uncovered$in$dendrochronological$archives$from$Germany$ (Usoskin$et#al.$2013),$ the$ USA$ and$ Russia$ (Jull$ et# al.$ 2014),$ and$ New$ Zealand$ (Güttler$ et# al.$ 2015).$ Henceforth,$ these$ singlePyear$ spikes$ in$ 14 C$ concentration$ will$ be$ referred$ to$ as$ Miyake#Events.$$ $ In$addition$to$their$unprecedented$abruptness$and$scale,$Miyake$Events$are$also$ unique$because$they$represent$significant$increases$in$ 14 C.$A$myriad$of$geological$ and$ oceanographic$ processes$ can$ drive$ depletions,$ but$ no$ terrestrial$ process$ -$ prior$ to$ the$ nuclear$ age$-$could$be$responsible$for$such$sharp$enrichments.$On$ this$ basis,$ as$ well$ as$ ...…”

“…$ Furthermore,$ it$ has$ since$ been$ established$ that$ the$ anomalies$ were$ globally$ synchronous$ and$ approximately$ uniform$ in$ magnitude.$ The$ 775$ CE$ spike$ has$ already$ been$ uncovered$in$dendrochronological$archives$from$Germany$ (Usoskin$et#al.$2013),$ the$ USA$ and$ Russia$ (Jull$ et# al.$ 2014),$ and$ New$ Zealand$ (Güttler$ et# al.$ 2015).$ Henceforth,$ these$ singlePyear$ spikes$ in$ 14 C$ concentration$ will$ be$ referred$ to$ as$ Miyake#Events.$$ $ In$addition$to$their$unprecedented$abruptness$and$scale,$Miyake$Events$are$also$ unique$because$they$represent$significant$increases$in$ 14 C.$A$myriad$of$geological$ and$ oceanographic$ processes$ can$ drive$ depletions,$ but$ no$ terrestrial$ process$ -$ prior$ to$ the$ nuclear$ age$-$could$be$responsible$for$such$sharp$enrichments.$On$ this$ basis,$ as$ well$ as$ their$ global$ impact,$ it$ was$ deduced$ that$ the$ spikes$ must$ have$ been$ the$ result$ of$ intense$ pulses$ of$ radiation$ from$ space.$ At$ first,$ the$ sun$ was$ not$ considered$ a$ likely$ cause,$ as$ it$ was$ not$ thought$ capable$ of$ emitting$ radiation$ of$ the$ required$ energy,$ so$ supernovae$ and$ other$ γPray$ sources$ were$ preferred$ (Miyake$ et# al.$ 2012;$ Pavlov$ et# al.$ 2013;$ Hambaryan$ $ &$ Neühauser$ 2013).$However,$the$consensus$now$is$that$intense$Solar$Energetic$Particle$(SEP)$ events$ were$ indeed$ responsible$ (Melott$ &$ Thomas$ 2012;$ Thomas$ et# al.$ 2013;$ Usoskin$et#al.$2013;$Güttler$et#al.$2015;$Mekhaldi$et#al.$2015).$SEPs$either$arise$ because$ of$ extreme$ solar$ flares$ or$ Interplanetary$ Coronal$ Mass$ Ejections$ (ICMEs).$ A$ supernova$ origin$ has$ now$ effectively$ been$ discounted,$ on$ two$ main$ grounds.$ Firstly,$ no$ historical$ observations$ exist$ for$ supernovae$ around$ 775$ or$ 994$ CE;$ although,$ the$ expected$ galactic$ SN$ rate$ of$~$ 1$ -$ 2$ per$ century$ does$ suggest$that$many$past$events$have$gone$undetected$ (Tammann$et#al.$1994).$As$ is$ shown$ in$ Table$ 1,$ only$ a$ handful$ of$ observations$ do$ exist,$ and$ none$ of$ them$ pertain$ to$ the$ night$ sky$ of$ the$ Southern$ Hemisphere.$ $ Secondly,$ no$ Galactic$ supernova$remnant$can$be$attributed$to$an$event$at$either$of$these$dates.$$ The$aim$of$this$study$is$to$establish$categorically$whether$any$historical$SNe$can$ be$detected$in$the$past$atmospheric$ 14 C$record.$$ * Methods* We$ combined$ new$ and$ existing$ 14 C$ measurements$ on$ annual$ treePrings$ that$ traversed$the$following$historical$astronomical$records.$ Figure$1.$If$anything,$a$levelling$or$gradual$decrease$in$atmospheric$ 14 C$levels$can$ be$discerned$in$the$data$for$the$ten$years$following$each$historical$observation.$It$ is$ important$ to$ emphasise$ that$ the$ observation$ dates$ of$ the$ supernovae$ in$ the$ second$ millennium$ CE$ are$ exactly$ known,$ although$ the$ evidence$ pertaining$ to$ the$ earlier$ events$ is$ more$ equivocal.$ Thus,$ any$ rise$ in$ 14 C,$ which$ predates# the$ historical$observation,$as$can$be$seen$in$the$profile$relating$to$SN1054,$cannot$be$ causally$ linked$ with$ the$ stellar$ explosi...…”

Cosmic ray event in 994 C.E. recorded in radiocarbon from Danish oak

“…Miyake et al [2012] originally proposed two explanations: a supernova explosion or a solar proton event (SPE). Other proposed explanations include a cometary impact on the Sun [Eichler and Mordecai, 2012] and a gamma ray burst (GRB) [Hambaryan and Neuhäuser, 2013;Pavlov et al, 2013], but such sources are now considered less likely, in part because the 775 C.E. Liu et al [2014] suggested a cometary impact on the Earth's atmosphere as the explanation of the first cosmic ray event, but this is considered unlikely due to the size of the comet required to produce the amount of excess radiocarbon and an erroneous interpretation of a historical text describing a comet in 773 C.E.…”

“…Subsequently, Allen [2012] argued in favor of a supernova explosion, but since no remnant of such an explosion has been observed, it is not considered a very likely source of the cosmic ray events [Miyake et al, 2012]. Also, GRBs would not produce the 10 Be anomalies observed in ice cores from Greenland and Antarctica, and they are consequently an unlikely source of the cosmic ray events [Hambaryan and Neuhäuser, 2013;Pavlov et al, 2013]. [Overholt and Melott, 2013;Usoskin and Kovaltsov, 2014;Chapman et al, 2014].…”

Radiocarbon Production by Thunderstorms

“…Geophysical Research Letters Thereby, with the above magnitudes of R flash , n str , _ N cosm 14 6 C À Á , δ, and σ abs /σ 14 for the initial and moderated neutron spectra, numbers of neutrons per lightning stroke N n1 required to account for 10% (k = 0.1), and a half (k = 0.5) of the observed RPR, at different areas of the globe varies as given in Table 1. Note that the fraction k = 0.1 corresponds to the observed fluctuations in the 14 6 C production (Dorman, 2004, section 17;Lingenfelter, 1963;Pavlov et al, 2013;Rakowski et al, 2015;Suess, 1965;Usoskin et al, 2013).…”