A ROSAT observation of the dipping, flaring and eclipsing polar MN Hya (RX J0929.1-2404)

We present the results of a 22.5 ks 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 similar to 0.45, a morphology consistent with two-pole accretion. Strong aperiodic flaring activity, with flux enhancements of similar to 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 similar to 50 eV blackbody and a thermal bremsstrahlung component of kT greater than or similar to 1.6 keV, with a total absorption column of N-H = 2.9 x 10(20)cm(-2). The primary maximum (phi similar to 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 similar to 0.1 for the best-fitting average spectral models. This implies a magnetic field strength less than or similar to 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 (less than or similar to 55 MG).