A remarkable recurrent nova in M 31: The 2010 eruption recovered and evidence of a six-month period

Abstract

The Andromeda Galaxy recurrent nova M31N 2008-12a has been caught in eruption nine times. Six observed eruptions in the seven years from 2008 to 2014 suggested a duty cycle of ∼1 yr, which makes this the most rapidly recurring system known and the leading single-degenerate Type Ia Supernova progenitor candidate; but no 2010 eruption has been found so far. Here we present evidence supporting the recovery of the 2010 eruption, based on archival images taken at and around the time of eruption. We detect the 2010 eruption in a pair of images at 2010 Nov. 20.52 UT, with a magnitude of m R = 17.84 ± 0.19. The sequence of seven eruptions shows significant indications of a duty cycle slightly shorter than one year, which makes successive eruptions occur progressively earlier in the year. We compared three archival X-ray detections with the well-observed multi-wavelength light curve of the 2014 eruption to accurately constrain the time of their optical peaks. The results imply that M31N 2008-12a might actually have a recurrence period of ∼6 months (175 ± 11 days), making it even more exceptional. If this is the case, then we predict that two eruptions per year will be observable soon. Furthermore, we predict that the next eruption will occur in late Sep. 2015. We encourage additional observations.

X-RAY FLASHES IN RECURRENT NOVAE: M31N 2008-12a AND THE IMPLICATIONS OF THE SWIFT NONDETECTION

“…We calculated recurrent nova models on 1.38 and 1.385 M ⊙ WDs accreting hydrogen-rich matter (X = 0.70, Y = 0.28, and Z = 0.02 for hydrogen, helium, and heavy elements, respectively) with mass-accretion rates of 1.4 -2.5 ×10 −7 M ⊙ yr −1 , corresponding to recurrence periods from one year to half a year (Darnley et al 2015;Henze et al 2015b). We also calculated models for a 1.35 M ⊙ WD of 1.0 and 12 year recurrence periods for comparison.…”

“…Thus, we conclude that the Xray flash should last at least a half day as in Table 1 (Darnley et al 2014(Darnley et al , 2015Henze et al 2014aHenze et al , 2015a resulted in significantly improved predictions of future eruptions. Moreover, Henze et al (2015b) combined new findings with archival data to arrive at a 1σ prediction accuracy of ±1 month (and suggest a recurrence period of 175 ± 11 days). Based on the updated forecast we designed an observational campaign to monitor the emerging 2015 eruption and catch the elusive X-ray flash.…”

“…This is the ideal object to detect X-ray flashes because its recurrence period is as short as a year, possibly even half a year (Henze et al 2015b). Such a very short recurrence period allows us to predict the eruption date with unprecedented accuracy (±1 month) and thereby makes any observational campaigns significantly more feasible than for any other novae.…”

The Galactic Nova Rate Revisited

“…Indeed, perhaps the most promising SN Ia progenitor extant is the recurrent nova, M31N 2008-12a (Henze et al 2015a;Tang et al 2014;Darnley et al 2015). M31N 2008-12a has an extremely short recurrence time of just under a year, possibly as short as 6 months (Henze et al 2015b), which constrains the accretion rate to be 2 − 3 × 10 −7 M yr −1 and the mass of the white dwarf to be near the Chandrasekhar limit (Kato et al 2014;Wolf et al 2013). These models also suggest that the white dwarf is gaining mass, and that it will reach the Chandrasekhar limit in less than 10 6 years.…”

A Millennium-long Evolution of the 1 yr Recurrence Period Nova—Search for Any Indication of the Forthcoming He Flash

“…1 Kato et al (2015Kato et al ( , 2017) presented the outburst model of a 1.38 M ⊙ WD with a mass-accretion mariko.kato@hc.st.keio.ac.jp 1 Henze et al (2015b) proposed a 0.5 yr recurrence period to explain the discrepancy between the early (around 2000) and recent trends of the outburst cycles. Even if an outburst occurred in the middle of the 1 yr cycle, we could not observe it due to Sun constraint.…”