Variations of 14-C around AD 775 and AD 1795 - due to solar activity

The motivation for our study is the disputed cause for the strong variation of 14-C around AD 775. Our method is to compare the 14-C variation around AD 775 with other periods of strong variability. Our results are: (a) We see three periods, where 14-C varied over 200 yr in a special way showing a certain pattern of strong secular variation: after a Grand Minimum with strongly increasing 14-C, there is a series of strong short-term drop(s), rise(s), and again drop(s) within 60 yr, ending up to 200 yr after the start of the Grand Minimum. These three periods include the strong rises around BC 671, AD 775, and AD 1795. (b) We show with several solar activity proxies (radioisotopes, sunspots, and aurorae) for the AD 770s and 1790s that such intense rapid 14-C increases can be explained by strong rapid decreases in solar activity and, hence, wind, so that the decrease in solar modulation potential leads to an increase in radioisotope production. (c) The strong rises around AD 775 and 1795 are due to three effects, (i) very strong activity in the previous cycles (i.e. very low 14-C level), (ii) the declining phase of a very strong Schwabe cycle, and (iii) a phase of very weak activity after the strong 14-C rise -- very short and/or weak cycle(s) like the suddenly starting Dalton minimum. (d) Furthermore, we can show that the strong change at AD 1795 happened after a pair of two packages of four Schwabe cycles with certain hemispheric leadership (each package consists of two Gnevyshev-Ohl pairs, respectively two Hale-Babcock pairs). We show with several additional arguments that the rise around AD 775 was not that special. ...Comment: 25 pages with 11 figures and 2 tables - Astronomical Notes, in pres

Presumable European aurorae in the mid AD 770s were halo displays

The interpretation of the strong 14-C variation around AD 775 as one (or several) solar super-flare(s) by, e.g., Usoskin et al. (2013) is based on alleged aurora sightings in the mid AD 770s in Europe: A "red cross/crucifix" in AD 773/4/6 from the Anglo-Saxon Chronicle, "inflamed shields" in AD 776 (both listed in the aurora catalogue of Link 1962), and "riders on white horses" in AD 773 (newly proposed as aurora in Usoskin et al. 2013), the two latter from the Royal Frankish Annals. We discuss the reports about these three sightings in detail here. We can show that all three were halo displays: The "red cross" or "crucifix" is formed by the horizontal arc and a vertical pillar of light (either with the Sun during sunset or with the moon after sunset); the "inflamed shields" and the "riders on white horses" were both two mock suns, especially the latter narrated in form of a Christian adaptation of the antique dioscuri motive. While the latter event took place early in AD 774 (dated AD 773 in Usoskin et al. 2013), the two other sightings have to be dated AD 776, i.e. anyway too late for being in connection with a 14-C rise that started before AD 775. We also sketch the ideological background of those sightings and there were many similar reports throughout that time. In addition, we present a small drawing of a lunar halo display with horizontal arc and vertical pillar forming a cross for shortly later, namely AD 806 June 4, the night of full moon, also from the Anglo-Saxon Chronicle; we also show historic drawings of solar and lunar halo crosses from G. Kirch and Helevius and a modern photograph.Comment: 17 pages with 6 figures Astronomical Notes in pres

Solar activity around AD 775 from aurorae and radiocarbon

A large variation in 14 C around AD 775 has been considered to be caused by one or more solar super-flares within one year. We critically review all known aurora reports from Europe as well as the Near, Middle, and Far East from AD 731 to 825 and find 39 likely true aurorae plus four more potential aurorae and 24 other reports about halos, meteors, thunderstorms etc., which were previously misinterpreted as aurorae or misdated; we assign probabilities for all events according to five aurora criteria. We find very likely true aurorae in AD 743, 745, 762, 765, 772, 773, 793, 796, 807, and 817. There were two aurorae in the early 770s observed near Amida (now Diyarbakir in Turkey near the Turkish-Syrian border), which were not only red, but also green-yellow - being at a relatively low geo-magnetic latidude, they indicate a relatively strong solar storm. However, it cannot be argued that those aurorae (geo-magnetical latitude 43 to 50 deg, considering five different reconstructions of the geo-magnetic pole) could be connected to one or more solar super-flares causing the 14 C increase around AD 775: There are several reports about low- to mid-latitude aurorae at 32 to 44 deg geo-magnetical latitude in China and Iraq; some of them were likely observed (quasi-)simultaneously in two of three areas (Europe, Byzantium/Arabia, East Asia), one lasted several nights, and some indicate a particulary strong geo-magnetic storm (red colour and dynamics), namely in AD 745, 762, 793, 807, and 817 - always without 14 C peaks. We use 39 likely true aurorae as well as historic reports about sunspots together with the radiocarbon content from tree rings to reconstruct solar activity: From about AD 733 to 823, we see at least nine Schwabe cycles ...Comment: 24 pages with 1 table and 2 figures, paper to appear in Astronomical Notes 24 Apr 201

Sunspot numbers based on historic records in the 1610s - early telescopic observations by Simon Marius and others

Hoyt & Schatten (1998) claim that Simon Marius would have observed the sun from 1617 Jun 7 to 1618 Dec 31 (Gregorian calendar) all days, except three short gaps in 1618, but would never have detected a sunspot -- based on a quotation from Marius in Wolf (1857), but misinterpreted by Hoyt & Schatten. Marius himself specified in early 1619 that "for one and a half year ... rather few or more often no spots could be detected ... which was never observed before" (Marius 1619). The generic statement by Marius can be interpreted such that the active day fraction was below 0.5 (but not zero) from fall 1617 to spring 1619 and that it was 1 before fall 1617 (since August 1611). Hoyt & Schatten cite Zinner (1952), who referred to Zinner (1942), where observing dates by Marius since 1611 are given, but which were not used by Hoyt & Schatten. We present all relevant texts from Marius where he clearly stated that he observed many spots in different form on and since 1611 Aug 3 (Julian) = Aug 13 (Greg.) (on the first day together with Ahasverus Schmidnerus), 14 spots on 1612 May 30 (Julian) = Jun 9 (Greg.), which is consistent with drawings by Galilei and Jungius for that day, the latter is shown here for the first time, at least one spot on 1611 Oct 3 and/or 11 (Julian), i.e. Oct 13 and/or 21 (Greg.), when he changed his sunspot observing technique, he also mentioned that he has drawn sunspots for 1611 Nov 17 (Julian) = Nov 27 (Greg.), in addition to those clearly datable detections, there is evidence in the texts for regular observations. ... Sunspots records by Malapert from 1618 to 1621 show that the last low-latitude spot was seen in Dec 1620, while the first high-latitude spots were noticed in June and Oct 1620, so that the Schwabe cycle turnover (minimum) took place around that time, ...Comment: 40 pages with 6 tables and 13 figures (paper in press), Astronomical Notes 201

New sunspots and aurorae in the historical Chinese text corpus? Comments on uncritical digital search applications

We review some applications of the method of electronic searching for historical observations of sunspots and aurorae in the Chinese text corpus by Hayakawa et al. etc. However, we show strong shortcomings in the digital search technique as applied by them: almost all likely true sunspot and aurora records were presented before (e.g. Xu et al. 2000), which is not mentioned in those papers; the remaining records are dubious and often refer to other phenomena, neither spots nor aurorae (this also applies to Hayakawa et al. 2017c). Most of the above publications include very few Chinese texts and translations, and their tables with abbreviated keywords do not allow the reader to consider alternative interpretations (the tables also do not specify which records mention night-time). We have compared some of their event tables with previously published catalogs and found various discrepancies. There are also intrinsic inconsistencies, misleading information (lunar phase for day-time events), and dating errors. We present Chinese texts and translations for some of their presumable new aurorae: only one can be considered a likely true aurora (AD 604 Jan); some others were selected on the sole basis of the use of the word "light" or "rainbow". Several alleged new aurorae present observations beside the Sun during day-time. There are well-known comets among their presumable aurorae. We also discuss, (i) whether "heiqi ri pang" can stand for black spot(s) "on one side of" or "beside" the sun, (ii) aurora color confusion in Hayakawa et al. (2015, 2016), and (iii) whether "white" and "unusual rainbows" can be aurorae.Comment: 20 pages with 2 figures, Astronomical Notes, in pres

GQ Lup and its common proper motion companion

Recently, Neuhaeuser et al. (2005) presented evidence for a sub-stellar, common proper motion companion to GQ Lup. With two theoretical mass estimates, both below the Deuterium burning minimum mass limit, the companion is probably a planet imaged directly. We present here a more detailed astrometric analysis of the GQ Lup system, using all the (different) proper motions published for the primary. The common proper motion is significant in all cases, also when taking into account the error in parallax or distance (140 +- 50 pc). When using the weighted mean, the significance for common proper motion of GQ Lup and its companion is 7 + 4 sigma for no change in separation plus 8 sigma for no change in position angle. We also discuss the question, whether GQ Lup and its common-proper motion companion are not bound, but share the same or similar proper motion as two independent members of the Lupus T association, which is a moving group, where most members should have the same motion anyway. Given our discussion, this hypothesis can be rejected by several sigma: The probability to find by chance an L-dwarf fainter than Ks = 14 mag within 0.7325 arcsec with (almost) the same proper motion of GQ Lup is only < 3 10^{-10}. The orbital motion of the system is not yet detected (1.4 +- 2.2 mas/yr), but is probably smaller than the escape velocity (5.3 +- 2.1 mas/yr), so that the system may well be gravitationally bound and stable. This is different for the 2MASSWJ1207334-393254 system, as we also show.Comment: 8 pages, 8 figure

Supernova SN 1006 in two historic Yemeni reports

We present two Arabic texts of historic observations of supernova SN 1006 from Yemen as reported by al-Yamani and Ibn al-Dayba (14th to 16th century AD). An English translation of the report by the latter was given before (Stephenson & Green 2002), but the original Arabic text was not yet published. In addition, we present for the first time the earlier report, also from Yemen, namely by al-Yamani in its original Arabic and with our English translation. It is quite obvious that the report by Ibn al-Dayba is based on the report by al-Yamani (or a common source), but the earlier report by al-Yamani is more detailed and in better (Arabic) language. We discuss in detail the dating of these observations. The most striking difference to other reports about SN 1006 is the apparent early discovery in Yemen in the evening of 15th of Rajab of the year 396h (i.e. AD 1006 Apr 17 \pm 2 on the Julian calendar), as reported by both al-Yamani and Ibn al-Dayba. i.e. about 1.5 weeks earlier than the otherwise earliest known reports. We also briefly discuss other information from the Yemeni reports on brightness, light curve, duration of visibility, location, stationarity, and color.Comment: 9 pages with 3 figure

Interpretation of the historic Yemeni reports of supernova SN 1006: early discovery in mid-April 1006 ?

The recently published Yemeni observing report about SN 1006 from al-Yamani clearly gives AD 1006 Apr $17 \pm 2$ (mid-Rajab 396h) as first observation date. Since this is about 1.5 weeks earlier than the otherwise earliest reports (Apr 28 or 30) as discussed so far, we were motivated to investigate an early sighting in more depth. We searched for additional evidences from other areas like East Asia and Europe. We found that the date given by al-Yamani is fully consistent with other evidence, including: (a) SN 1006 "rose several times half an hour after sunset" (al-Yamani), which is correct for the location of Sana in Yemen for the time around Apr 17, but it would not be correct for late Apr or early May; (b) the date (3rd year, 3rd lunar month, 28th day wuzi, Ichidai Yoki) for an observation of a guest star in Japan is inconsistent (there is no day wuzi in that lunar month), but may be dated to Apr 16 by reading wuwu date rather than a wuzi date; (c) there is observational evidence that SN 1006 was observed in East Asia early or mid April; for the second half of April, a bad weather (early monsoon) period is not unlikely -- there is a lack of night reports; (d) the observer in St. Gallen reported to have seen SN 1006 "for three months", which must have ended at the very latest on AD 1006 Jul 10, given his northern location, so that his observations probably started in April. We conclude that the correctly reported details give quite high confidence in the fully self-consistent report of al-Yamani, so that the early discovery date should be considered seriously.Comment: 11 pages, 2 figures, 1 table (in press) in Astronomical Notes 201

On the number of accreting and cooling isolated neutron stars detectable with the ROSAT All-Sky Survey

We present limits to the log N - log S curve for isolated neutron stars, both cooling and accreting neutron stars, which are not active as radio pulsars, as observed with the ROSAT All-Sky Survey and compare it with theoretical expectations. So far, only one isolated neutron star is identified optically among ROSAT sources, namely RXJ185635-3754 (Walter & Matthews 1997). Three more promising candidates have been suggested. In addition, several upper limit estimates are available on the space density of such neutron stars from different optical follow-up studies. We show that the log N - log S curve according to the current observations, including the identified neutron star, the three additional candidates, and the upper limits, lies between the theoretical expectations for middle-aged cooling neutron stars and old accreting neutron stars. At least one of the neutron star candidates found so far with ROSAT may be cooling instead of accreting. We suggest that the fact that more accreting isolated old neutron stars were expected (e.g., Madau & Blaes 1994) than observed is mostly due to the velocity distribution used in those calculations. More recent radio observations indicate that there are fewer slow neutron stars, ie., fewer accreting X-ray bright old neutron stars. At the X-ray bright end of the log N - log S curve, however, the ROSAT observations agree well with the theoretical expectations.Comment: text with one table and one figure, A&A in pres

A transient event in AD 775 reported by al-Tabari: A bolide - not a nova, supernova, or kilonova

Given that the cause for the strong increase in 14C in AD 774/5 in Japanese and German trees is still a matter of debate (e.g. short Gamma-Ray Burst or solar super-flare), we have searched in Arabic chronicles for reports about unusual transient celestial events. In the History of al-Tabari we found two (almost identical) reports about such an event. The group around caliph al-Mansur observed a transient event while on the way from Baghdad to Mecca on AD 775 Aug 29 - Sep 1 (Julian calendar). A celestial object (kawkab) was seen to fall or set (inqadda), and its trace (atharuhu) was seen for at least tens of minutes (up to 70-90 min) during morning twilight. The reports use the Arabic words kawkab and athar(uhu), which were also used in the known Arabic reports about supernovae SN 1006 and 1054, so that one might consider an interpretation as a nova-like event. The kawkab (celestial object) was observed only during the morning twilight at a brightness of probably between about -3 and 0 mag. Such a brightness and time-scale would be expected for optical kilonovae (at 3 to 9 kpc) in the context of short Gamma-Ray Bursts. There are no similar reports from eastern Asia for this time. However, the short reports are fully consistent with a bolide: The word kawkab can be used for meteor, the verb inqadda normally means "falling down", the word atharuhu can mean "its trace". We therefore prefer the interpretation as bolide. We discuss in detail how to convert the Muslim calendar date to a date in the Julian calendar using first the calculated Islamic calendar and then considering the time when the crescent new moon could be visible at the given location.Comment: 12 pages with three figures, paper in press (Astronomical Notes 2014) - small corrections applie