Examinando por Autor "Motta, Sara E."

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Accretion in strong field gravity with eXTP
(Springer Link, 2018-12-07) De Rosa, A.; Uttley, P.; Gou, L.; Liu, Y.; Bambi, C.; Barret, Didier; Belloni, T.; Berti, E.; Bianchi, S.; Caiazzo, I.; Casella, P.; Cui, W. K.; D´Ammando, F.; Dauser, T.; Del Santo, M.; De Marco, B.; Di Salvo, T.; Done, C.; Dovciak, M.; Fabian, A. C.; Falanga, M.; Gambino, A. F.; Gendre, B.; Grinberg, V.; Heger, A.; Homan, J.; Iaria, R.; Jiang, J.; Jin, C. C.; Koerding, E.; Linares, M.; Liu, Z.; Maccarone, Thomas J.; Malzac, J.; Manousakis, A.; Marin, F.; Marinucci, A.; Mehdipour, M.; Méndez, M.; Migliari, S.; Miller, C.; Miniutti, G.; Nardini, E.; O´Brien, P. T.; Osborne, Julian P.; Petrucci, P. O.; Possenti, A.; Riggio, A.; Rodríguez, J.; Sanna, A.; Shao, L. J.; Sobolewska, M.; Sramkova, E.; Stevens, A. L.; Stiele, H.; Stratta, G.; Stuchlik, Z.; Svoboda, J.; Tamburini, F.; Tauris, T. M.; Tombesi, F.; Torok, G.; Urbanec, M.; Vicent, F.; Wu, Q. W.; Yuan, F.; Zand, J. J. M.; Zdziarski, A. A.; Zhou, X.; Feroci, M.; Ferrari, V.; Gualtieri, L.; Heyl, J.; Ingram, A.; Karas, V.; Lu, F. J.; Luo, B.; Matt, G.; Motta, S. E.; Neilsen, J.; Pani, P.; Santangelo, A.; Shu, X. W.; Wang, J. F.; Wang, J. M.; Xue, Y. Q.; Xu, Y. P.; Yuan, W. M.; Yuan, Y. F.; Zhang, S. N.; Zhang, S.; Agudo, I.; Amati, L.; Andersson, N. A.; Baglio, C.; Bakala, P.; Baykal, A.; Bhattacharyya, S.; Bombaci, I.; Bucciantini, N.; Capitanio, F.; Ciolfi, R.; Istituto Nazionale di Astrofisica (INAF); Chinese Academy of Sciences (CAS); National Science Centre, Poland (NCN)
In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive black-holes. eXTP has the unique capability of using advanced “spectral-timing-polarimetry” techniques to analyze the rapid variations with three orthogonal diagnostics of the flow and its geometry, yielding unprecedented insight into the inner accreting regions, the effects of strong field gravity on the material within them and the powerful outflows which are driven by the accretion process. X-spinmeasurements
Acceso Abierto
Observations of a radio-bright, X-ray obscured GRS 1915+105
(Oxford Academics: Oxford University Press, 2021-02-24) Motta, Sara E.; Kajava, J. J. E.; Giustini, M.; Williams, D. R. A.; Del Santo, M.; Fender, R.; Green, D. A.; Heywood, I.; Rhodes, L.; Segreto, A.; Sivakoff, G.; Woudt, P. A.; Science and Technology Facilities Council (STFC); Agencia Estatal de Investigación (AEI); Comunidad de Madrid; Istituto Nazionale di Astrofisica (INAF); European Commission (EC); Motta, S. E. [0000-0002-6154-5843]; Kajava, J. J. E. [0000-0002-3010-8333]; Williams, D. R. A. [0000-0001-7361-0246]; Del Santo, M. [0000-0002-1793-1050]; Green, D. A. [0000-0003-3189-9998]; Woudt, P. A. [0000-0002-6896-1655]
The Galactic black hole transient GRS 1915+105 is famous for its markedly variable X-ray and radio behaviour, and for being the archetypal galactic source of relativistic jets. It entered an X-ray outburst in 1992 and has been active ever since. Since 2018 GRS 1915+105 has declined into an extended low-flux X-ray plateau, occasionally interrupted by multiwavelength flares. Here, we report the radio and X-ray properties of GRS 1915+105 collected in this new phase, and compare the recent data to historic observations. We find that while the X-ray emission remained unprecedentedly low for most of the time following the decline in 2018, the radio emission shows a clear mode change half way through the extended X-ray plateau in 2019 June: from low flux (∼3 mJy) and limited variability, to marked flaring with fluxes two orders of magnitude larger. GRS 1915+105 appears to have entered a low-luminosity canonical hard state, and then transitioned to an unusual accretion phase, characterized by heavy X-ray absorption/obscuration. Hence, we argue that a local absorber hides from the observer the accretion processes feeding the variable jet responsible for the radio flaring. The radio–X-ray correlation suggests that the current low X-ray flux state may be a signature of a super-Eddington state akin to the X-ray binaries SS433 or V404 Cyg.
Acceso Abierto
Rapid spectral transition of the black hole binary V404 Cygni
(EDP Sciences, 2020-02-13) Kajava, J. J. E.; Sánchez Fernández, C.; Alfonso Garzón, J.; Motta, Sara E.; Veledina, A.; Science and Technology Facilities Council (STFC); Academy of Finland (AKA); Agencia Estatal de Investigación (AEI); Ministry of Education and Science of the Russian Federation (Minobrnauka); Kajava, J. J. E. [0000-0002-3010-8333]; Alfonso Garzón, J. [0000-0003-0852-3474]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
During the June 2015 outburst of the black hole binary V404 Cyg, rapid changes in the X-ray brightness and spectra were common. The INTEGRAL monitoring campaign detected spectacular Eddington-limited X-ray flares, but also rapid variations at much lower flux levels. On 2015 June 21 at 20 h 50 min, the 3–10 keV JEM-X data as well as simultaneous optical data started to display a gradual brightening from one of these low-flux states. This was followed 15 min later by an order-of-magnitude increase of flux in the 20–40 keV IBIS/ISGRI light curve in just 15 s. The best-fitting model for both the pre- and post-transition spectra required a Compton-thick partially covering absorber. The absorber parameters remained constant, but the spectral slope varied significantly during the event, with the photon index decreasing from Γ ≈ 3.7 to Γ ≈ 2.3. We propose that the rapid 20–40 keV flux increase was either caused by a spectral state transition that was hidden from our direct view, or that there was a sudden reduction in the amount of Compton down-scattering of the primary X-ray emission in the disk outflow.