TY - JOUR
T1 - Chandra observations of the recurrent nova IM Normae
AU - Orio, Marina
AU - Tepedelenlioglu, Emre
AU - Starrfield, Sumner
AU - Woodward, Charles E.
AU - Della Valle, Massimo
PY - 2005/2/20
Y1 - 2005/2/20
N2 - The recurrent nova IM Nor was observed twice in X-rays with the Chandra ACIS-S, 1 and 6 months after the optical outburst. It was not detected in the first observation, with an upper limit on the X-ray luminosity in the 0.2-10 keV range LX < 4.8 × 1030(d kpc-1) 2 ergs s-1 (where d is the distance to the nova). Five months later, a hard X-ray source with LX = (1.4-2.5) × 10 32(d kpc)2 ergss-1was detected. The X-ray spectrum appears to be thermal, but we cannot rule out additional components due to unresolved emission lines. A blackbody component is likely to contribute to the observed spectrum, but it has bolometric luminosity Lbol = 2.5 × 1033 (d kpc-1)2 ergs s-1; therefore, it is not sufficiently luminous to be caused by a central white dwarf that is still burning hydrogen on the surface. An optical spectrum, taken 5 months postoutburst, indicates no intrinsic reddening of the ejecta. Therefore, we conclude that the shell had already become optically thin to supersoft X-rays, but nuclear burning had turned off or was in the process of turning off at this time. We discuss why this implies that recurrent novae, even the rare ones with long optical decays like IM Nor, indicating a large envelope mass, are not statistically significant as Type la supernova candidates.
AB - The recurrent nova IM Nor was observed twice in X-rays with the Chandra ACIS-S, 1 and 6 months after the optical outburst. It was not detected in the first observation, with an upper limit on the X-ray luminosity in the 0.2-10 keV range LX < 4.8 × 1030(d kpc-1) 2 ergs s-1 (where d is the distance to the nova). Five months later, a hard X-ray source with LX = (1.4-2.5) × 10 32(d kpc)2 ergss-1was detected. The X-ray spectrum appears to be thermal, but we cannot rule out additional components due to unresolved emission lines. A blackbody component is likely to contribute to the observed spectrum, but it has bolometric luminosity Lbol = 2.5 × 1033 (d kpc-1)2 ergs s-1; therefore, it is not sufficiently luminous to be caused by a central white dwarf that is still burning hydrogen on the surface. An optical spectrum, taken 5 months postoutburst, indicates no intrinsic reddening of the ejecta. Therefore, we conclude that the shell had already become optically thin to supersoft X-rays, but nuclear burning had turned off or was in the process of turning off at this time. We discuss why this implies that recurrent novae, even the rare ones with long optical decays like IM Nor, indicating a large envelope mass, are not statistically significant as Type la supernova candidates.
KW - Binaries: close
KW - Novae, cataclysmic variables
KW - Stars: individual (IM Normae)
KW - X-rays: stars
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U2 - 10.1086/427207
DO - 10.1086/427207
M3 - Article
AN - SCOPUS:17044437059
SN - 0004-637X
VL - 620
SP - 938
EP - 942
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2 I
ER -