ROSAT observations of NGC 4258
We performed deep follow up observations of the active spiral galaxy NGC 4258 with the ROSAT HRI and PSPC to study the different emission components. The overall luminosity of NGC 4258 is L x∼2×1040 erg s−1 in the 0.1–2.4 keV ROSAT band. Besides a weak nuclear point source (L x≲1038 erg s−1) fourteen point sources are detected in the NGC 4258 disk (integral L x∼3×1039 erg s−1). The bulk of the X-ray emission is not resolved. The main contributions are explained by hot interstellar medium along the anomalous spiral arms of NGC 4258 (L x∼1×1040 erg s−1, T∼0.4 keV) and by interstellar medium escaping from NGC 4258 disk into the approaching halo hemisphere (L x∼4×1039 erg s−1, T∼0.2 keV)
Surface brightness, temperature and absorption profiles have been taken for the X-rays in the regions of the anomalous arms. The highest and lowest absorption was received for the NW and SE tips of the arms, respectively. Our X-ray findings are compared to a model of the anomalous arms which suggests that the bar of the galaxy causes shocks in the interstellar medium and might heat a small part of it to X-ray temperatures.
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