Análisis e interpretación de la encuesta aplicada al Personal Operativo

By the end of 2015 eROSITA, the successor of the ROSAT mission, will start to image the entire X-ray sky with a surpassing sensitivity and a higher spatial and spectral resolution than ROSAT. It will be composed of seven identical telescopes which all have a CCD in its focus. The eROSITA telescopes on board of the Russian Spektrum-Roentgen-Gamma mission will be approximately 20 times more sensitive in the soft X-ray band than the RASS. Furthermore, in the hard X-ray regime (2-10 keV) it will survey the sky for the first time with an imaging telescope (Merloni et al., 2012). It will have a resolution of 25 arcsec to 30 arcsec in survey mode, the average exposure in the galactic plane will be about 3 ksec (Predehl et al., 2010).

Therefore, it will be possible to study the SNR candidates presented in Chapter 4 in much more detail: The higher resolution will allow a spatial investigation of the sources. This will reveal whether the RASS emission of the candidates is coming from one extended source or from two or more point sources. In addition, the deeper exposure times and the higher spectral resolution will provide data for a spectral analysis of the candidates to rule out an extragalactic origin. Additionally, if the candidates show emission from a thermal plasma it will be possible to calculate fundamental parameters for the remnant, e.g., age and distance. In particular, the remnant candidates with a large extent can be studied in detail with eROSITA, because the cur- rent X-ray observatories have a field of view of only_∼30′ and need several pointings to cover the larger remnants. The prospects of X-ray all-sky surveys for large SNRs was impressively shown with the HEAO-1 survey and RASS, where a large, close-by and old SNR with a di- ameter of approximately 25 degrees was detected, the Monogem Ring (Plucinsky et al., 1996). With current telescopes, e.g., XMM-Newton, more than 1000 pointings would be necessary to cover the remnant and in a single observation the remnant would only be recorded as high X-ray background.

It should be mentioned that some of the candidates may be missed. The ROSAT PSPC detector used for the RASS had the major advantage of very low detector noise and a spectral response down to 0.1 keV provided perfect conditions to search for SNRs (Voges et al., 1999). This is because extended sources can be strongly affected by the background and SNRs emit mostly in the soft X-ray band. On the other hand, the eROSITA detectors are CCDs, which are only sensitive to incoming photons in the energy range 0.3-10 keV, and have a higher background, comparable with the EPIC cameras on-board of XMM-Newton (Merloni et al., 2012). Thus, faint extended sources will be harder to detect, as in the RASS. This was already shown for the SNR candidate G309.8–2.5 in Chapter 4, where a bright source is detected in RASS, but a deep observation with XMM-Newton of this region did not show any extended source emission.

For all 274 known SNRs which emit X-rays, a detailed analysis will be possible and for the remaining sources X-ray counterparts can be searched for. In particular, the remnants G38.7–1.4, G296.7–0.9 and G308.4–1.4, which were explored in this work can be studied in more detail. In the case of G308.4–1.4 a deep spectro-imaging analysis was already done, but the origin of the

central compact objects is still not solved. It could be the compact remnant belonging to the SNR.

The identification of previously unknown SNR with eROSITA will allow a search for neu- tron stars residing within the diffuse remnants. This could be a central neutron star without a counterpart in other wavelength regimes. Only seven members of this class of neutron stars are known to date and finding more of these sources may help to understand how this manifestation of neutron stars is related to other classes and which parameters decided that a neutron star can be observed as central compact object.

Further, the eROSITA survey will add data to the analysis done in Chapter 7 with a larger and even less biased sample. In the eROSITA survey a detailed search for X-ray counterparts of all known pulsars without detected X-ray counterpart can be conducted. The pulsars in the eROSITA sample will have equal exposures and will cover the whole galactic plane. However, the exposure will be only 3 ksec. The average exposure in the sample studied with XMM-Newton in Chapter 7 was ten times higher. In the case of a non-detection a upper limit on the thermal and non-thermal flux can be calculated, which will be in general lower than the already derived limits. Nevertheless, it will further constrain the cooling of neutron stars and the dependence of the non-thermal X-ray luminosity and the spin-down energy loss, because of the ten times larger sample of observed neutron stars.

Because microcalorimeters are now operating in space (e.g., NuSTAR; Harrison et al., 2013) it will be possible to study the emission of X-ray sources in much more detail. These detectors will have a typical spectral resolution of 2.5 eV at 5 keV, 60 times better than current observato- ries (Nandra et al., 2013). However, the energy range of the microcalorimeter operating on the NuSTAR satellite, which was launched in June 2012, is not suitable for studying SNRs. There- fore, one has to wait for future missions, like Athena+ (Nandra et al., 2013), the next large X-ray mission that is proposed to be launched after 2028. It will probably have an effective area of 2 m2 at 1 keV and an angular resolution on-axis of 5 arcsec (Nandra et al., 2013). Two detectors are planned, a CCD camera and an X-ray microcalorimeter. The latter will have a spectral resolution of 2.5 eV at 6 keV and hence, will allow investigations of SNRs by different spectral line diag- nostics, which are hardly possible to date. In addition, the large collection power will make it possible to study neutron stars in much more detail. For example, it might enable a investigation of the cooling of a very young NS in the SN 1987A, which has to be found yet (Manchester, 2007).

Not only in the X-ray band new larger telescopes are planned. For example in the radio band the square kilometer array will start to observe the radio sky with 10 to 100 times higher sensitivity using single telescopes build all around the world. These telescopes will have a total collecting power of nearly one million square meters (Smits et al., 2009) and will lead to the detection of many new pulsars and supernova remnants. Additionally, the sample of neutron stars with accurate mass and radius measurement will increase even further. Finally, it could help to identify the 123 SNR candidates presented in Chapter 4.