Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998mnras.299..998b&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 299, Issue 4, pp. 998-1006.
Astronomy and Astrophysics
Astronomy
4
Accretion, Accretion Discs, Stars: Individual: Mn Hya (Rx J0929.1-2404 ), Stars: Magnetic Fields, Novae, Cataclysmic Variables, White Dwarfs, X-Rays: Stars
Scientific paper
We present the results of a 22.5ks pointed ROSAT PSPC observation of the 3.4-h period eclipsing polar MN Hya (RX J0929.1-2404). The X-ray light curve exhibits a `double-humped' shape, with a secondary minimum occuring at phi ~0.45, a morphology consistent with two-pole accretion. Strong aperiodic flaring activity, with flux enhancements of ~6x the quiescent level, is also observed. A pre-eclipse `dip' occurs in the phase interval phi = 0.87-0.95 with the X-rays becoming harder, indicative of photoelectric absorption by the pre-shock flow. There is also evidence of a secondary spectrally hard `dip' near phi=0.45-0.55, which might be associated with a second accretion stream flowing to the other magnetic pole. The X-ray spectrum is best represented by a combination of a ~50 eV blackbody and a thermal bremsstrahlung component of kT 1.6 keV, with a total absorption column of N_H=2.9x10^20cm^-2. The primary maximum (phi ~ 0.65) has a slightly larger column and normalization compared to the secondary maximum. Although there are few photons, the dip spectrum is very flat in comparison to other phases, and is best represented by a single bremsstrahlung component. This is indicative of the spectral hardening seen in the light curves attributed to photoabsorption. The ratio of unabsorbed bremsstrahlung and blackbody luminosities is ~0.1 for the best-fitting average spectral models. This implies a magnetic field strength 30 MG on the basis of the empirical L_hard/L_soft-B relationships, although consideration of the cyclotron flux and aspect effects could allow for an even higher field (55 MG).
Barrett Paul Everett
Buckley David A. H.
Haberl Frank
Sekiguchi Kazuhiro
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