Deep eROSITA observations of the "magnificent seven" isolated neutron stars

Abstract

We report the initial results of deep eROSITA monitoring of the magnificent seven isolated neutron stars (INSs). Thanks to a combination of high count statistics and good energy resolution, the eROSITA datasets unveil the increasingly complex energy distribution of these presumably simple thermal emitters. For three targets, we report the detection of multiple (in some cases, phase-dependent) spectral absorption features and deviations from the dominant thermal continuum. Unexpected long-term changes of spectral state and timing behaviour have additionally been observed for two INSs. The results pose challenging theoretical questions on the nature of the variations and absorption features and ultimately impact the modeling of the atmosphere and cooling of highly magnetised neutron stars.

XMM-Newton and SRG/eROSITA observations of the isolated neutron star candidate 4XMM J022141.5−735632

“…Previous detection at a similar flux level by ROSAT PSPC and the Swift X-ray Telescope suggest that the emission is fairly stable over decade-long time scales. Additional monitoring with higher quality data will be necessary to exclude the few-percent level of spectral variation as reported for the M7 INSs RX J0720.4-3125 and RX J1605.3+3249 (de Vries et al 2004;Pires et al 2022).…”