Abstract
V2487 Oph (Nova Oph 1998) is a nova that exploded in 1998. XMM-Newton observations performed between 2 and 9 years after the explosion showed emission related to restablished accretion, and indicative of a magnetic white dwarf. The spectrum looks like that of a cataclysmic variable of the polar type. Anyway, we don't have yet a definitive confirmation of the polar character, through determination of spin and orbital periods. Although it is not the first nova exploding in a magnetic white dwarf, it is always challenging to reach explosive conditions when a stan- dard accretion disk can't be formed, because of the magnetic field. In addition, V2487 Oph has been the first nova where a detection of X-rays - in the host binary system - has been reported prior to its eruption, in 1990 with the ROSAT satellite. V2487 Oph has been also detected in hard X-rays with INTEGRAL/IBIS and RXTE/PCA. Last but not least, V2487 Oph has been identified as a nova in 2008, since a prior eruption in 1900 has been reported through analysis of Harvard photographic plates. Therefore, it is expected to host a massive white dwarf and be a candidate for a type Ia supernova explo- sion. In a recent study of the progenitors of galactic novae, it has been emphasized that V2487 Oph is an important and interesting object, intermediate between the standard novae and other historical and well-known novae with shorter recur- rence periods. It could be that in the end there's a continuous distribution of recurrence periods, instead of the common understanding up to now that classical and recurrent novae were quite apart (with recurrence periods of more than 10 4 years and less than 100 years - approximately - respectively). We present the results of our campaign of sev- eral observations with XMM-Newton. The consequences for the understanding of such a puzzling object are discussed.
Highlights
V2487 Oph (Nova Oph 1998) is a classical nova that exploded in 1998
In the so-called intermediate polars (IPs, or DQ Her stars), the pressure associated to the magnetic field - less intense than in the polars - partially truncates the accretion disk, so that matter accretes into the poles of the White dwarfs (WDs), but through an "accretion curtain"
The WD rotates synchronously with the binary orbit, whereas in intermediate polars the WD rotates with a period shorter than the orbital period
Summary
White dwarfs (WDs) can explode as classical novae in two types of binary systems, a cataclysmic variable (the most common case) and a symbiotic binary. There are only a handful of novae which have been recorded more than once, being their recurrence times smaller than 100 years; they are called recurrent novae Some of these explosions are known to be hosted by symbiotic binaries, where larger (than in CVs) accretion rates are possible; it is worth noticing that the WD mass should be quite large to enable such short recurrence periods; in addition, the WD mass is expected to grow in each eruption, and recurrent novae are good candidates for type Ia supernovae explosions. The duration of this super soft X-ray emitting phase depends on the nuclear burning timescale of the remaining H-rich envelope, i.e., on the amount of H-rich mass left after the explosion, which is related to the efficiency of mass-ejection during the nova explosion [28, 29, 34]
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