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Modern soft X-ray observatories can yield unique insights into time domain astrophysics, and a huge amount of information is stored - and largely unexploited - in data archives. Like a treasure-hunt, the EXTraS project harvested the hitherto unexplored temporal domain information buried in the serendipitous data collected by the European Photon Imaging Camera instrument onboard the ESA XMM-Newton, in 16 years of observations. All results have been released to the scientific community, together with new software analysis tools. This paper presents the architecture of the EXTraS science gateway, that has the goal to provide the software to the scientific community through a Web based portal using the EGI Federated Cloud infrastructure. The main focus is on the light software architecture of the portal and on the technological insights for an effective use of the EGI ecosystem.

Modern soft X-ray observatories can yield unique insights into time domain astrophysics, and a huge amount of information is stored - and largely unexploited - in data archives. Like a treasure-hunt, the EXTraS project harvested the hitherto unexplored temporal domain information buried in the serendipitous data collected by the European Photon Imaging Camera instrument onboard the XMM- Newton satellite in 20 years of observations. The result is a vast catalogue, describing the temporal behaviour of hundreds of thousands of X-ray sources. But the catalogue is just a starting point because it has to be, in its turn, further analysed. During the project an education activity has been defined and run in several workshops for high school students in Italy, Germany and UK. The final goal is to engage the students, and in perspective citizen scientists, to go through the whole validation process: they look into the data and try to discover new sources, or to characterize already known sources. This paper describes how the EXTraS science gateway is used to accomplish these tasks and highlights the first discovery, a flaring X-ray source in the globular cluster NGC 6540., Comment: Accepted for publication in Future Generation Computing Systems, Special issue on Science gateways 2018

Ultraluminous X-ray sources (ULXs) are extragalactic X-ray emitters located off-center of their host galaxy and with a luminosity in excess of a few ${10^{39}\text{ erg s}^{-1}}$, if emitted isotropically. The discovery of periodic modulation revealed that in some ULXs the accreting compact object is a neutron star, indicating luminosities substantially above their Eddington limit. The most extreme object in this respect is ${NGC 5907~ULX-1}$ (ULX1), with a peak luminosity that is 500 times its Eddington limit. During a Chandra observation to probe a low state of ULX1, we detected diffuse X-ray emission at the position of ULX1. Its diameter is $2.7 \pm 1.0$ arcsec and contains 25 photons, none below 0.8 keV. We interpret this extended structure as an expanding nebula powered by the wind of ULX1. Its diameter of about ${200\text{ pc}}$, characteristic energy of ${\sim 1.9\text{ keV}}$, and luminosity of ${\sim 2\times10^{38}\text{ erg s}^{-1}}$ imply a mechanical power of ${1.3\times10^{41}\text{ erg s}^{-1}}$ and an age ${\sim 7 \times 10^{4}\text{ yr}}$. This interpretation suggests that a genuinely super-Eddington regime can be sustained for time scales much longer than the spin-up time of the neutron star powering the system. As the mechanical power from a single ULX nebula can rival the injection rate of cosmic rays of an entire galaxy, ULX nebulae could be important cosmic ray accelerators., Comment: 28 pages, 6 figures, 1 table - accepted for publication

X-ray emission from Young Stellar Objects (YSOs) is crucial to understand star formation. A very limited amount of X-ray results is available for the protostellar (ClassI) phase. A systematic search of transient X-ray phenomena combined with a careful evaluation of the evolutionary stage offer a widely unexplored window to our understanding of YSOs X-ray properties. Within the EXTraS project, a search for transients and variability in the whole XMM-Newton archive, we discover transient X-ray emission consistent with ISO-Oph 85, a strongly embedded YSO in the rho Ophiuchi region, not detected in previous time-averaged X-ray studies. We extract an X-ray light curve for the flare and determine its spectral parameters from XMM-Newton/EPIC (European Photon Imaging Camera) data using quantile analysis. The X-ray flare ($2500\,s$), the only one detected in the XMM-Newton archive for ISO-Oph 85, has a luminosity of $LogL_X[erg/s]=31.1$ and a spectrum consistent with a highly-absorbed one-component thermal model ($N_H=1.0^{+1.2}_{-0.5}10^{23}\,cm^{-2}$, $kT=1.15^{+2.35}_{-0.65}\,keV)$. We set an upper limit of $LogL_X[erg/s]<29.5$ to the quiescent X-ray luminosity. We build a SED with IR to mm photometry drawn from literature and mid-IR Spitzer and sub-mm Herschel photometry analysed by us, and compare it with pre-computed models. The sub-mm emission peak in the Herschel data suggests that the object is a ClassI protostar. However, the Herschel/IR position offset is larger than for other YSOs in the region, leaving some doubt on the association. This is the first X-ray flare from a YSO recognised as a candidate ClassI YSO via the analysis of its complete SED. This work shows how the analysis of the whole SED is fundamental for the classification of YSOs, and how the X-ray source detection techniques we developed can open a new era in time-resolved analysis of the X-ray emission from stars., Comment: 10 pages, 7 figures, 2 tables Accepted for publication by Astronomy&Astrophysics