arXiv:1112.0593v2 [astro-ph.HE] 14 Dec 2011 andi uttobifadnal dnia records identical (the nearly dynasty and brief Jin two the just from visibility. 393 in of in period seen tained long one month the eight is AD. nearly event 393 its SN and to likely 386, due most 369, the of these stars than second new Of less the by the namely, separated years; remarkably during (see 25 century 4th reported are event the or these stars of half Among SN ‘guest’ descriptions details). Chinese have Galactic for three 2002 AD likely Green 1000 & a Stephenson and indicating 1 durations years the rele- tween and with along material. sightings 1977) background SN and historic cultural (1976, likely vant (1962, analyses most Yoke detailed by Stephenson the Peng presenting & of (2002) Ho made Clark Green were and & Stephenson with searches SNe (1955), 20th Galactic Hsi extensive 1966), the of (1935), in 1934), sightings Kanda With early historic Zwicky (SNe) & Biot for (1921). (Baade supernovae of Lundmark of century and works discovery Humboldt (1890), (1871), the the and Clerke Williams Arabic, through (1867), (1871), Asian, ‘tem- Chambers chiefly ancient or (1846), texts in new recorded bright European pre-Tychonic stars about porary’ known have 02138 03755 NH Hanover, lege, 03755 NH Hanover, College, Dartmouth rpittpstuigL using Journal typeset Astronomical Preprint the by Accepted h hns ecito fte33sa scon- is star 393 the of description Chinese The be- reported objects celestial of handful a Only astronomers century, 19th the of middle the Since 3 2 1 mtsna srpyia bevtr,Cmrde MA Cambridge, Observatory, Col- Astrophysical Dartmouth Astronomy, History, Smithsonian of & Department Physics Hall, of Carson 6107 Department Lab, Wilder 6127 aebe iulybih beta aiu ih ( light maximum at object bright visually a been have oee,a h enn’ urn siae 1 t only text estimated stating current Chinese brightness remnant’s brief apparent the The its at about association. However, comment an th no such within make with position star consisten difficulties projected is star’s are 1997 guest in there the al. and et Wang properties by young made (G347.3-0.5) J1713.7-3946 RX nepce XJ73734 uenv rgtesadduration and des brightness headings: Roman supernova the Subject J1713.7-3946 nor 39 brigh RX Chinese the visual the expected probable reported neither an that calculate first conclude and Chinese su midday and accounts the Chinese in subtypes Roman when the even and March to seen Chinese in reference readily the midday a descr be near be Claudian visible could may poet that be account Roman a AD h this We the 393 suggested which to 2005cs. have around in supernova SN heavens record like J1713.7-3946 the European CCSNe in RX a than with the brightness fainter 393 or peak require SN to The would similar year. others event supernova a and over al. for et visible remained have would lhuhtecneto fteCiee‘us’sa f33A iht with AD 393 of star ‘guest’ Chinese the of connection the Although oetA Fesen A. Robert 1. A INTRODUCTION T E tl mltajv 5/2/11 v. emulateapj style X H N33–SRR 11.-96(37305 CONNECTION (G347.3-0.5) J1713.7-3946 RX SNR – 393 SN THE S:idvda G4.-.)-sproarmat-sas supern stars: - remnant supernova - (G347.3-0.5) individual ISM: S 393) (SN Songshu 1 ihr Kremer Richard , n the and cetdb h srnmclJournal Astronomical the by Accepted Jinshu ABSTRACT 2 ailPatnaude Daniel , ; − 1 . p itneand distance kpc 3 ae ote33getsa u otersalangular small their to due candi- star SNR 15 guest possible The of 393 as sizes G348.7+0.3 the seen 2009). exception, and to initially dates (Green 37A) no were Scorpius lo- (CTB 37B) is of remnants (CTB G348.5+0.1 393 supernova tail of of Galactic the remnants dozen within star a cated guest nearly the with Galactic and a difficult being has it sunset, for around evidence setting strong supernova. as began viewed it visibility, of been when period only region. long lack that month ending the eight in to star’s remnant due supernova the However, (1978) bright optically Bergh an den a van of reported by also suggested also records Chinese with or since star nova nova a plane. recurrent Galactic with a the consistent to 1997), close or al. in et Wang occurring supernova in 2 Fig. Chi- well-defined asterism ap- the tail. star nese bisects Scorpius’ virtually 393 of plane the boundaries Galactic The bowl-like that the implied within dy- strongly peared Jin hence the and during nasty recorded descriptions celestial among extinguished ‘ was term it when Nov) within 19 appeared – disappeared]. star [or Oct guest (22 a month AD) (27 nar year 393 18th of the Mar Wei al. of texts 28 et month translated Xu – second The Feb the 1997; during 2002). that al. Green state et & Wang Stephenson 1977; 2000; Stephenson & Clark dniyn h enn fahsoi Ni often is SN historic a of remnant the Identifying likely was star 393 the that argued (1972) Pskovskii the of use the that note (2002) Green & Stephenson − 3 teti fSopu)adlse ni h it lu- ninth the until lasted and Scorpius) of tail (the . to 5 zhong Wei − ′ sdi h etmaig‘ihn sunique is ‘within’ meaning text the in used ’ . ti’o h oselto Scorpius, constellation the of ‘tail’ e 5 n 17 and env f33 criswudnot would Scorpius 393, of pernova 3 . rpin r aiyrcnie with reconciled easily are criptions a Milisavljevic Dan & , a tdsperdatr8months. 8 after disappeared it hat ≃ a)if mag) 0 Wei n10 D oaitrrtto was interpretation nova A AD. 1600 in nse o ag fsupernova of range a for tnesses antd dpe yWang by adopted magnitude 0 ocrigte33A guest AD 393 the concerning s eGlci uenv remnant supernova Galactic he ihtermatsrelatively remnant’s the with t v enavr subluminous very a been ave A us tr erve both review We star. guest 3 s oepolm connecting problems note lso aigu h alo cris(see Scorpius of tail the up making ′ V epciey(lr Stephenson & (Clark respectively , bsavsal rlin star brilliant visually a ibes lhuhsvrlauthors several Although . ≃ M ,issproashould supernova its 3, V = − ve individual ovae: 7to 17 1 − 8and 18 2

1977; Stephenson & Green 2002). However, these rem- which is based on the much larger distance estimate of 6 nants lie ≃ 10 kpc away (Reynoso & Mangum 2000; kpc (Slane et al. 1999). Aharonian et al. 2008; Nakamura et al. 2009) and such The presence of a compact X-ray source 1WGA large distances near the Galactic center likely imply con- J1713.4-3949 at a projected location near the remnant’s siderable interstellar extinction decreasing the chance of center with a similar X-ray derived NH column density an associated visually bright guest star. The same is true to the remnant’s central regions (Cassam-Chena¨ıet al. for the apparently very young SNR G350.1-3.0 whose dis- 2004) implies it is associated with the remnant thereby tance is only ∼3.4 kpc but lies behind an estimated ≃ 20 indicating the remnant is from a core-collapse SN mag of visual extinction (Gaensler et al. 2008). (CCSN). The remnant’s 65′ × 55′ angular size and re- In 1996 Pfeffermann & Aschenbach (1996) announced cent distance estimates ∼ 1 − 1.3 kpc (Fukui et al. the ROSAT discovery of the Galactic remnant RX 2003; Moriguchi et al. 2005) when combined with a high- J1713.7-3946 (G347.3-0.5) in Scorpius. The remnant’s velocity shock suggests a relatively low ambient ISM den- location near the SN 393 reported position along with sity (∼ 0.01 cm−3) like that expected in a stellar wind Pfeffermann and Aschenbach’s estimated remnant dis- driven cavity generated by a high-mass progenitor which tance of 1.1 kpc and 2100 yr age led Wang et al. (1997) exploded as a Type II/Ib,c SN (Cassam-Chena¨ıet al. to suggest it as the likely remnant of SN 393. Although 2004). Stephenson & Green (2002) and Nickiforov (2010) have argued for the remnant’s distance of 6 ± 1 kpc based 3. PROBLEMS WITH A SN 393 - RX J1713.7-3946 on possible associations with nearby molecular clouds CONNECTION (Slane et al. 1999) which would rule out its associa- tion with SN 393, more recent distance estimates of Of the currently known SNRs located near the Chi- RX J1713.7-3946 firmly place it between 0.9 − 1.7 kpc, nese reported position of SN 393, RX J1713.7-3946would and most recent papers on RX J1713.7-3946 cite the seem a good candidate remnant for the presumed super- Wang et al. (1997) proposed SN 393 connection. nova of 393. It is a relatively young SNR and lies within We note here, however, that a distance less than 2 kpc the tail of Scorpius consistent with the Chinese report for RX J1713.7-3946 raises problems with the expected about the location of the 393 guest star. However, there supernova maximum apparent brightness and durations are difficulties with this SN–SNR connection. Below we which appear in conflict with the Chinese records. Be- discuss these difficulties along with a European report low we discuss how neither the Chinese record of the of a bright daytime star around 393 AD but which is guest star nor a long known but rarely cited European unlikely to be a sighting of the Chinese 393 SN. account of a bright star reported about that same year 3.1. Expected Brightness of a RX J1713.7-3946 SN are consistent with RX J1713.7-3946 as the remnant of the probable Chinese supernova of 393 AD. As shown in Table 1, recent distance estimates for RX − 2. J1713.7-3946 range between 0.9 1.7 kpc (Fukui et al. THE RX J1713.7-3946 REMNANT 2003; Koo 2003; Koo et al. 2004; Aharonian et al. 2004; The remnant RX J1713.7-3946 exhibits several proper- Cassam-Chena¨ıet al. 2004; Moriguchi et al. 2005) with ties suggesting a relatively young age, probably less than a concentration of recent values around 1−1.3 kpc. This a few thousand years and thus potentially consistent with would place an RX J1713.7-3946 supernova closer than a SN event around 393 AD. Its X-ray emission is that any historic Galactic SN recorded during the past two of a featureless nonthermal continuum consistent with millennia. A distance of just 1 − 1.3 kpc also means a shock velocity of several 1000 km s−1 (Koyama et al. that its SN should have been visually bright if: a) the 1997; Slane et al. 1999; Uchiyama et al. 2003, 2007; optical extinction to it is fairly low, and b) it was not an Fukui et al. 2003; Cassam-Chena¨ıet al. 2004). While unusually faint event. the shock’s velocity is probably high, it is likely less than X-ray derived NH column densities for the remnant’s 4500 km s−1 based on a limit of the angular displacement central X-ray emitting regions range from 4 − 8 × of the remnant’s outer X-ray emission over a 6 year pe- 1021 cm−2 depending on the blackbody or power law riod (Uchiyama et al. 2007). Ellison et al. (2010) found model adopted (Cassam-Chena¨ıet al. 2004). Adopt- −1 21 −2 velocities ∼ 3000 km s were required in order to model ing AV = NH /1.8 × 10 cm for a typical gas-to- the shock kinematics in an evacuated cavity at an as- dust ratio (Bohlin et al. 1978; Predehl & Schmitt 1995; sumed age of 1600 years. Kim & Martin 1996), yields AV values around 2.2 – 4.4 RX J1713.7-3946 is also one of only a few Galactic mag. In the following discussions, we will adopt an − SNRs which exhibit gamma-rays with energies up to 100 NH =5×1021 cm 2 consistent for the remnant’s central TeV. In this respect it resembles several other young compact X-ray source 1WGA J1713.4-3949 modeled by a Galactic SNRs including RCW 86 (SN 185) and the SN two-component blackbody (Cassam-Chena¨ıet al. 2004), 1006 remnant. Observations show a close correlation which translates to AV ≃ 2.8 or roughly 3 magnitudes of between the remnant’s X-ray and gamma-ray emissions extinction. suggesting a causal connection between the processes As shown in Tables 1 and 2, if the RX J1713.7-3946 generating both types of emissions (Aharonian et al. SN had an MV of −17 to −18 in line with the typi- 2007). Since high shock velocities are required to gener- cal absolute visual magnitudes for core-collapse SNe II ate a significant nonthermal X-ray and gamma-ray flux or SNe Ib,c (Richardson et al. 2002, 2006; Drout et al. (see e.g. Zirakashvili & Aharonian 2007), the presence of 2011), then the RX J1713.7-3946 supernova should have an X-ray synchrotron emission and coincident gamma- been a visually brilliant object. For example, at a dis- ray emission in RX J1713.7-3946 favor a distance of ∼ tance between 1.0 and 1.3 kpc and an AV = 3.0, a SN 1 kpc, which would rule out the age of 20,000–40,000 yr would have been mv = −3.5 to −5.0 for MV = −17 to 3

−18. In fact, it would have been a bright guest star al- brightnesses of either of the other two possible guest stars most regardless of the specific SN subtype, i.e., Type Ia, of 369 and 386. II, Ib,c, or IIn unless it was a very subluminous event. In the absence of any indication in the Chinese Pushing the numbers toward fainter apparent magni- records regarding the brightness for the 393 guest star, tudes limits by adopting the largest distance recently es- Clark & Stephenson (1977) estimated a peak visual mag- timated for RX J1713.7-3946, namely 1.7 kpc, and an nitude ≃ 0. They arrived at this value from the lack of 21 −2 AV = 4 (NH = 7 × 10 cm ; Cassam-Chena¨ıet al. any remark about any extraordinary brightness and a 2004), and a MV of −16.0 equal to the faintest Type consideration of atmospheric extinction since observers Ib,c SNe (Drout et al. 2011), the supernova would still at Nanjing could view the guest star no more than 20 have been quite bright with mv ≈ −1 and should have degrees above the horizon. remained visible well into 394 AD. Smaller distances of In like fashion, Wang et al. (1997) estimated it could around 1 kpc as suggested by Fukui et al. (2003) and have been no brighter than −2 magnitude, reasoning that Moriguchi et al. (2005) but keeping AV = 4.0 leads to had the guest star been brighter than this the Chinese apparent magnitudes around −2, or about as bright as astronomers would have compared it to the planets Sat- Jupiter. urn, Mars and Jupiter. All three planets were, in fact, To place these brightness estimates in context, we list visible in the morning sky in the early Spring of 393 AD in Table 1 the reported peak visual magnitudes (to the with apparent visual magnitudes of +0.27, +0.25, and nearest half magnitude where possible) of all Galactic −2.4 respectively, and located within 45 degrees of the SN over the last two millennia based on ancient records reported guest star in Scorpius. (Stephenson & Green 2002). The listed peak magni- Wang et al. (1997) further argued that if its peak mag- tudes, especially for the older SNe, are often uncertain nitude had been fainter than 0 mag then it would have due to the sometimes fragmentary nature of the exist- not been visible to the naked eye for as long as 8 months. ing records and possible observer error or exaggeration. Adopting a distance of 1.1 kpc, an AV = 2.0, and a For example, whereas the estimated distance and visual peak visual magnitude of −2 to 0, they estimated a extinction to the SN 1006 remnant implies a maximum RX J1713.7-3946 supernova to have been MV = −12 to apparent visual brightness around −7.5 (Winkler et al. −14. However, this would mean SN 393 was an unusu- 2003), analyses of reported descriptions suggest values 2 ally low-luminosity supernova event similar to SN 1987A, mag higher or lower (Stephenson 2010). This plus uncer- 1999br, and 2005cs with MV > −15 (Richardson et al. tainty in remnant distances has led to somewhat different 2002; Pastorello et al. 2004, 2006). On the other hand, values listed in Table 1 from other authors (e.g., Schaefer if the RX J1713.7-3946 supernova had a more common 1996). MV for core-collapse SNe of −17 to −18, it then should Despite these caveats, one finds that the peak mag- have been easily visible into early 394 AD. Yet there is nitude estimates from ancient descriptions is, in most no mention of this in the existing Chinese records. So, cases, in rough agreement with visual magnitude esti- if the 393 event only reached −2 to 0 mag and was con- mates based upon the likely SN event. We have identified nected to RX J1713.7-3946, then at the distance and core-collapse supernova events in cases where a compact visual extinction assumed by Wang et al. (1997) it must central object is present in the likely associated SNR. have been a very subluminous event (MV > −15) similar Listed in Table 1 are the current estimates for remnant to SN II/Ib,c events occupying the faint end of CCSNe distances and line of sight visual extinctions. Besides the (Richardson et al. 2002). 393 SN, the worst agreement between the predicted and 3.3. reported brightness is perhaps that of SN 1181 with the Reported Duration of SN 393 remnant 3C58 about which there has been considerable In March 393 when the Chinese reported the first sight- debate as to that remnant’s age and distance estimates ing of the 393 guest star, astronomers in Nanjing (lati- (see Fesen et al. 2008 and Kothes 2010 and references tude +32◦) would have been able to see the stars com- therein). prising Scorpius’ tail rise above the horizon around 1 am 3.2. local time and reach culmination 22 degrees above the Estimates on the Apparent Brightness of SN 393 southern horizon in the morning by 5 am, roughly a half As noted above, the Chinese records include no com- hour before the beginning of astronomical twilight. If the ment about the star’s brightness. This leaves one to guest star was as brilliant as we estimate if it were the wonder why they didn’t include a comment about bright- RX J1713.7-3946 supernova (−4.5 mag), it would have ness especially if SN 393 is related to RX J1713.7-3946 been easy to follow from night into twilight and then into it might have rivaled Jupiter or even Venus at its bright- daytime. est. One possible solution might simply lie in the extreme Such a guest star in Scorpius would remain visible at brevity of the existing Chinese records. The description night for the next several months right up until the time is about as short as one could write a record concerning it would set in evening twilight around mid-September. the appearance of a guest star. A star about as bright or brighter than the nine stars In considering this peak brightness issue, it is impor- comprising the Scorpius’s tail asterism, all but one of tant to note that the records that have survived from this which are fainter than 2nd magnitude, might stay visible period in China are condensed summaries of the Jin dy- a little longer. Thus it might have still been visible dur- nasty history written by imperial scholars many decades ing early twilight a week or two longer and hence possibly and even centuries after the actual events. Moreover, try- into early October. This would still fall short of the Chi- ing to interpret the meaning of the lack of a note about nese records which states it lasted until the ninth lunar the star’s brightness is made more difficult given the fact month, namely 22 October through 19 November. Of that no mention is made in the existing records on the course the description of ‘until’ the ninth month could 4 mean that its visibility was only up to the 9th month ibility limit of 6th mag some months after maximum. and not during it. This would make the star even more difficult to view in Stephenson & Green (2002) interpret the duration of early October 393 since it would be less than 5 degrees the guest star ‘until’ the Chinese 9th lunar month (22 above the western horizon at the end of twilight and thus October – 19 November) as meaning the star remained subject to significant atmospheric attenuation. visible into the the ninth month. However, on October 22 4. it would have set just some 15 minutes after sunset and to A POSSIBLE EUROPEAN SIGHTING OF SN 393 be visible under these circumstances the star would have Relevant to the apparent brightness of the SN 393 required a relatively bright object, thereby implying a guest star, there is an European text written around 398 brilliant object months earlier at maximum light. AD by the Roman poet Claudian describing a bright star In an attempt to resolve this dilemma, Stephenson and about which he said was plainly visible even in midday a Green propose a recording error of one month regarding few years earlier. Claudian viewed this star as an omen of the object’s disappearance (the 8th instead of the 9th Honorius being made emperor in 3934 thereby implying month), allowing the object to set well after sunset in a that it occurred around 393 AD. dark sky. Considering the visibility of Scorpius’ asterism The possibility of a connection between the bright Wei in late September and early October 393 and al- star described in the Claudian poem and the Chinese lowing for atmospheric extinction, Clark & Stephenson guest star of 393 AD has been made by several au- (1977) estimate a maximum apparent magnitude around thors including Dreyer (1913), Stothers (1977), Barrett 0 mag or perhaps a bit brighter, noting that had the star (1978), Clark & Stephenson (1982), Clark (1984), and been much brighter than this the Chinese likely would Ramsey (2006). However, no mention of this reference is have included a comment on its brightness. found in the most recent astronomical reviews of ancient In Table 2, we list the expected brightnesses eight guest star observations including discussions directly re- months (day 240) after maximum light for several differ- garding the suspected SN of 393 (Clark & Stephenson ent CCSN subtypes assuming a distance and AV equal 1975, 1977; Wang et al. 1997; Stephenson & Green 2002; to that of RX J1713.7-3946. The table shows that in all Green & Stephenson 2003; Wang 2006). cases the supernova1G would have been brighter than θ Interestingly, this Roman record has long been known, Sco (mv = 1.87), the brightest star in the tail of Scorpius. going back some 440 years to the time of Tycho Brahe. A Thus, if RX J1713.7-3946 is a CCSN and was the guest year after he sighted his supernova of 1572, Tycho learned star seen in 393, then its expected brightness between 0 about the Claudian text through a letter from Paul and +1.5 mag would make it possible for it to stay vis- Hainzel, a longtime friend and then mayor of Augsburg, ible a little longer but perhaps not past the middle of to the humanist Hieronymous Wolf in which Hainzel October as the Chinese reported. mentions the Claudian text about a bright new star in A more serious problem with this scenario is that there the sky, much like the 1572 star (Brahe 1602). Tycho is no mention of the star being recovered early in 394 AD never reached a definitive conclusion about the meaning when it would have again become visible from behind the of the Claudian poem, i.e., whether it was a description Sun. Given average luminosity decline times commonly of a comet, a daytime sighting of Venus, or something seen for core-collapse supernovae, a RX J1713.7-3946 su- else, but it was obvious, he concluded, that new stars like pernova should have been easily visible to observers with the one he saw in 1572 sometimes appear in the heavens an apparent brightness between 1st and 3rd mag, com- (Dreyer 1913). parable to the stars in Scorpius’s tail (see Table 2). Al- The relevant passages about the new star appear in though the very brief Chinese record should not be in- Claudian’s ‘The Fourth Consulship of Honorius’. Since terpreted as complete, it is unusual that there were no to our knowledge this text has never been presented further reports of its continued presence, especially since in the astronomical literature, we reproduce it here. reports of other guest stars returning from behind the According to the English translation of the Latin by Sun exist, such as SN 185. Platnauer (1922), the pertinent passages read: However, in light of the considerable spread in the de- cline rates of SN Type Ib,c events, the possibility exists Never was the encouragement of the gods that the supernova faded below widespread notice when more sure, never did heaven attend with it came from around the Sun three months later. Some more favouring omens. Black tempest had subluminous events exhibit a steepening of their light shrouded the light in darkness and the south curve at times beyond 120 days, diminishing in visual wind gathered thick rain-clouds, when of a brightness fairly rapidly. For instance, had a RX J1713.7- sudden, so soon as the soldiers had borne thee 3946 supernova followed the light curves of the SN 2005cs aloft with customary shout, Phoebus scat- or SN 2009md (Pastorello et al. 2009; Fraser et al. 2011), tered the clouds and at the same moment was it would have faded > 5 mag one year past maximum, given to thee the sceptre, to the world light. and hence possibly would have been missed. Bosporus, freed from clouds, permits a sight In closing, we note that if SN 393 had instead been of Chalcedon on the farther shore; nor is it a Type Ia event and unrelated to the CCSN remnant only the vicinity of Byzantium that is bathed RX J1713.7-3946, similar brightness issues at late times in brightness; the clouds are driven back and would apply. That is, at day 240 a Type Ia guest star all Thrace is cleared; Pangaeus shows afar ≃ would appear 6 magnitudes fainter than at maximum 4 Honorius was declared emperor Augustus at the age of nine in light (Leibundgut et al. 1991). A peak brightness of 393 by his father Theodosius I. With the death of their father in 0 mag estimated by Stephenson & Green (2002) would January 395, he and his brother Arcadius divided up the empire, mean the guest star would approach the naked eye vis- with Honorius becoming the Western Roman emperor. 5

and lake Maeotis makes quiver the rays he was near its maximum brilliance of −4.6 mag and near rarely sees. ’Tis not Boreas nor yet Phoe- the meridian at 9 am on 23 January 393 when Honorius bus’ warmer breath that has put the mists to was declared emperor (Augustus) by his father Theodo- flight. sius. At noon on that day, Venus would still have been That light was an emperor’s star. A visible some 25 degrees above the southwestern skies. prophetic radiance was over all things, and The waning crescent Moon would have already set by with thy brightness Nature laughed. Even at midday and might explain Claudian’s reference to a star’s midday did a wondering people gaze upon a visibility “though the moon lay hid”. So maybe a day- bold star (’twas clear to behold) no dulled nor time sighting of Venus is what Claudian was referring to in his poem of adoration to emperor Honorius. stunted beams but bright as Bo¨otes’ nightly 5. lamp. At a strange hour its brilliance lit up CONCLUSIONS the sky and its fires could be clearly seen Identifying the remnants of historic SNe is often dif- though the moon lay hid. May be it was ficult and this is especially true in the case of the 393 the Queen mother’s star or the return of thy guest star. Given the brief description of the guest star grandsire’s now become a god, or may be in the Chinese records and the nearly dozen Galactic the generous sun agreed to share the heav- supernova remnants currently known within the tail of ens with all the stars that hasted to behold Scorpius (Green 2009), doubts about any SN 393 – SNR thee. association will likely persist. The meaning of those signs is now unmistak- A connection between the ancient guest star and sus- able. Clear was the prophecy of Ascanius’ pected supernova of 393 and the X-ray bright super- coming power when an aureole crowned his nova remnant RX J1713.7-3946 has been proposed by locks, yet harmed them not, and when the Wang et al. (1997). While this connection has been of- fires of fate encircled his head and played ten cited in the literature on the RX J1713.7-3946 rem- about his temples. Thy future the very fires nant and is in line with some of its relatively youthful of heaven foretell. properties, the Wang et al. (1997) estimated MV values between −12 and −14 imply a very subluminous core- Although a similar translation is found in Barr (1981), collapse SN event. both these authors have taken some poetic license with In this paper, we reviewed both the Chinese and Ro- the text. A more literal translation of the key sentence man accounts and calculated probable visual bright- and a slight modification of that given by Ramsey (2006) nesses for a range of supernova subtype. We conclude is: “Even at midday, the marveling populace beheld a that neither the Chinese nor the Roman descriptions are bold and unmistakable star, which was not faint with easily reconciled with an expected RX J1713.7-3946 su- dimmed ray, but as bright as Bo¨otes is at night. It shone pernova brightness and duration. We further note that if forth, a guest in fiery regions at a strange hour, and it RX J1713.7-3946 were the SN 393 remnant, it would then could be recognized although the moon lay hidden.” rank as having been the nearest of all the known historic Although Claudian’s description concerning a star be- Galactic supernovae during the last 2000 years. It’s rel- ing “bold” (audax) and visible even at midday suggesting atively small distance of around 1 kpc plus a moderate a very bright object would seem consistent with our es- amount of optical extinction also means its supernova timated peak magnitude around −4.5 for a RX J1713.7- would have likely have been a visually brilliant object, 3946 supernova, it appears unlikely that it is a reference certainly as bright as Jupiter and maybe as bright as to the Chinese guest star of 393. The constellation Scor- Venus. pius would set by 9 am in the morning of early March Although a connection between SN 393 and RX 393 and hence no star located in its tail would be visible J1713.7-3946, or for that matter any other young SNR near midday. lying within Scorpius’ tail, will likely remain uncertain One possibility is that Claudian’s star is a sighting of due to limitations of the ancient records, such an associ- a brilliant −4.5 or brighter SN in late 392 when Scorpius ation does not appear consistent with the available his- would be near conjuction with the Sun. However, in torical records. It is hoped that future studies of the RX that case the Chinese then should have reported it in J1713.7-3946 remnant which provide better estimates as the early morning by mid-January when Scorpius rises to its age may help resolve the question of the remnant an hour before morning twilight. Additionally, there is of the suspected SN of 393 AD. no Chinese record concerning a daytime star in 392. Interestingly Venus, which can be seen during daylight when brighter than ≈ −3.5 magnitude (Weaver 1947),

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TABLE 1 Observed Galactic Supernovae Over the Last Two Millennia in Order of Increasing Distance

a b c SN Reported Duration Confirmed or Proposed SN SNR Distance AV Expected max max mv (months) SN Remnant Type (kpc) (mag) mv 393 ∼ 0 8 RX J1713.7-3946 CCSN 0.9–1.7 3.0 −3.8 to −5.2 1054 −5.0 21 Crab Nebula CCSN 1.8–2.0 1.6 −4.9 to −5.1 1181 ∼ 0 6 3C58 CCSN 2.0–3.2 2.1 −3.4 to −5.4 1006 −7.5 36 SNR 1006 SN Ia 2.1–2.3 0.3 −7.3 to −7.5 185 −6.0 8+ RCW 86 SN Ia 2.5–3.2 2.5 −4.4 to −4.9 1572 −4.5 18 Tycho’s SNR SN Ia 3.0–5.0 2.0 −4.0 to −5.0 1604 −3.0 13 Kepler’s SNR SN Ia 3.0–5.3 2.8 −3.2 to −4.4

References. — SN 185: Westerlund (1969); Rosado et al. (1996); Vink et al. (2006); Yamaguchi et al. (2008); SN 393: Koyama et al. (1997); Fukui et al. (2003); Uchiyama et al. (2003); Koo (2003); Koo et al. (2004); Aharonian et al. (2004); Cassam-Chena¨ıet al. (2004); Moriguchi et al. (2005); Tanaka et al. (2008); Acero et al. (2009); SN 1006: Schweizer & Middleditch (1980); Winkler et al. (2003); SN 1054: Trimble (1968); Davidson & Fesen (1985); SN 1181: Green & Gull (1982); Roberts et al. (1993); Fesen et al. (2008); Kothes (2010); SN 1572: van den Bergh (1978); Ruiz-Lapuente (2004); Warren et al. (2005); Krause et al. (2008); Cassam-Chena¨ıet al. (2007); Hayato et al. (2010); SN 1604: Reynoso & Goss (1999); Reynolds et al. (2007). a Estimated peak magnitudes and durations are from Clark & Stephenson (1977), Brecher et al. (1983), Schaefer (1996), Stephenson & Green (2002), Ruiz-Lapuente (2004), and Stephenson (2010). The value for SN 393 reflects the brightness adopted by Clark & Stephenson (1977) b Estimates of SN subtype are based on the presence (CCSN) or absence (SN Ia) of a compact stellar remnant in the confirmed or proposed associated SN remnant. c max max Estimated peak apparent visual brightnesses were calculated using the MV (SN Ia) = −19.4, (Leibundgut 2001; Riess et al. 2005); MV (CCSN) = −18.0, (Richardson et al. 2002, 2006).

TABLE 2 Apparent SN 393 Magnitudes by SN Typea

c SN MV mv b Type t0 t240 t360 SN II-P −17.0 −3.5 +1.0 +2.0 SN II-L −18.0 −4.5 +1.5 +2.5 SN IIb −17.5 −4.0 +1.5 +2.5 SN Ib,c −18.5 −5.0 +1.0 +3.0 SN IIn −19.0 −5.5 0.0 +1.0

a Rounded to the nearest half magnitude assuming d = 1.3 kpc and AV = 3.0 b Assuming SN light curves from Turatto et al. (1990) and templates provided by P. Nugent (http://supernova.lbl.gov/~nugent/nugent_templates.html). Reported values can deviate ±1.0 mag or more. For SN IIn, the t360 value is an extrapolation from the slope of late-time light curves. Peak absolute magnitudes are from Richardson et al. (2006). c Estimated visual magnitudes for March 393, September 393, and March 394, i.e., days 0, 240 and 360 post-maximum.