(CAB) Artículos

URI permanente para esta colecciónhttps://inta.metricsalad.com/handle/123456789/7

Buscar

Mostrando 1 - 8 de 8

Restringido
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
Restringido
Detection of a possible multiphase ultra-fast outflow in IRAS 13349+2438 with NuSTAR and XMM-Newton.
(Oxford Academics: Blackwell Publishing, 2020-08-25) Parker, M. L.; Matzeu, G. A.; Alston, W. N.; Fabian, A. C.; Lobban, A.; Miniutti, G.; Pinto, C.; Santos Lleó, M.; Schartel, N.; European Space Agency (ESA); 0000-0002-5635-5340; 0000-0003-1994-5322; 0000-0003-2658-6559; 0000-0001-5948-8360; 0000-0003-2532-7379; 0000-0002-9378-4072; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
We present joint NuSTAR and XMM–Newton observations of the bright, variable quasar IRAS 13349+2438. This combined data set shows two clear iron absorption lines at 8 and 9 keV, which are most likely associated with two layers of mildly relativistic blueshifted absorption, with velocities of ∼0.14c and ∼0.27c. We also find strong evidence for a series of Ly α absorption lines at intermediate energies in a stacked XMM–Newton EPIC-pn spectrum, at the same blueshift as the lower velocity iron feature. This is consistent with a scenario where an outflowing wind is radially stratified, so faster, higher ionization material is observed closer to the black hole, and cooler, slower material is seen from streamlines at larger radii.
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 late-time X-ray brightening of the tidal disruption event OGLE16aaa
(EDP Sciences, 2020-07-16) Kajava, J. J. E.; Giustini, M.; Saxton, R. D.; Miniutti, G.; Agencia Estatal de Investigación (AEI); Comunidad de Madrid; Kajava, J. J. E. [0000-0002-3010-8333]; Giustini, M. [0000-0002-1329-658X]; Unidad de Excelencia Científica María de Maeztu del Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Stars that pass too close to a super-massive black hole may be disrupted by strong tidal forces. OGLE16aaa is one such tidal disruption event (TDE) which rapidly brightened and peaked in the optical/UV bands in early 2016 and subsequently decayed over the rest of the year. OGLE16aaa was detected in an XMM-Newton X-ray observation on June 9, 2016 with a flux slightly below the Swift/XRT upper limits obtained during the optical light curve peak. Between June 16–21, 2016, Swift/XRT also detected OGLE16aaa and based on the stacked spectrum, we could infer that the X-ray luminosity had jumped up by more than a factor of ten in just one week. No brightening signal was seen in the simultaneous optical/UV data to cause the X-ray luminosity to exceed the optical/UV one. A further XMM-Newton observation on November 30, 2016 showed that almost a year after the optical/UV peak, the X-ray emission was still at an elevated level, while the optical/UV flux decay had already leveled off to values comparable to those of the host galaxy. In all X-ray observations, the spectra were nicely modeled with a 50–70 eV thermal component with no intrinsic absorption, with a weak X-ray tail seen only in the November 30 XMM-Newton observation. The late-time X-ray behavior of OGLE16aaa strongly resembles the tidal disruption events ASASSN-15oi and AT2019azh. We were able to pinpoint the time delay between the initial optical TDE onset and the X-ray brightening to 182 ± 5 days, which may possibly represent the timescale between the initial circularization of the disrupted star around the super-massive black hole and the subsequent delayed accretion. Alternatively, the delayed X-ray brightening could be related to a rapid clearing of a thick envelope that covers the central X-ray engine during the first six months.
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.
Acceso Abierto
The accretion rates and mechanisms of Herbig Ae/Be stars
(Oxford Academics: Oxford University Press, 2020-01-20) Wichittanakom, C.; Oudmaijer, R. D.; Fairlamb, J. R.; Mendigutía, I.; Vioque, M.; Ababakr, K. M.; Comunidad de Madrid; European Research Council (ERC); National Science Foundation (NSF); Mendigutía, I. [0000-0002-0233-5328]; Farlamb, J. [0000-0002-2833-2344]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
This work presents a spectroscopic study of 163 Herbig Ac/Be stars. Amongst these, we present new data for 30 objects. Stellar parameters such as temperature, reddening, mass, luminosity, and age are homogeneously determined. Mass accretion rates are determined from Ha emission line measurements. Our data is complemented with the X-Shooter sample from previous studies and we update results using Gain DR2 parallaxes giving a total of 78 objects with homogeneously determined stellar parameters and mass accretion rates. In addition, mass accretion rates of an additional 85 HAeBes are determined. We confirm previous findings that the mass accretion rate increases as a function of stellar mass, and the existence of a different slope for lower and higher mass stars, respectively. The mass where the slope changes is determined to be 3.98(-0.94)(+1.37) M-circle dot. We discuss this break in the context of different modes of disc accretion for low- and high-mass stars. Because of their similarities with T Tauri stars, we identify the accretion mechanism for the late-type Herbig stars with the Magnetospheric Accretion. The possibilities for the earlier-type stars are still open, we suggest the Boundary Layer accretion model may be a viable alternative. Finally, we investigated the mass accretion age relationship. Even using the superior Gaia based data, it proved hard to select a large enough sub-sample to remove the mass dependence in this relationship, Yet, it would appear that the mass accretion does decline with age as expected from basic theoretical considerations.
Acceso Abierto
The Gaia-ESO Survey: Age spread in the star forming region NGC 6530 from the HR diagram and gravity indicators
(EDP Sciences, 2019-03-26) Prisinzano, L.; Damiani, F.; Kalari, V.; Jeffries, R. D.; Bonito, R.; Micela, G.; Wright, N. James; Jackson, R. J.; Tognelli, E.; Guarcello, M. G.; Vink, Jorick S.; Klutsch, A.; Jiménez Esteban, F. M.; Roccatagliata, V.; Tautvaisilenè, G.; Gilmore, G.; Randich, S.; Alfaro, Emilio J.; Flaccomio, E.; Koposov, S.; Lanzafame, A. C.; Pancino, E.; Bergemann, M.; Carraro, G.; Franciosini, E.; Frasca, A.; Gonneau, A.; Hourihane, A.; Jofre, P.; Lewis, J.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, Charlotte C.; Zaggia, S.; European Commission (EC); Leverhulme Trust; Istituto Nazionale di Astrofisica (INAF); Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR); Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. In very young clusters, stellar age distribution is empirical proof of the duration of star cluster formation and thus it gives indications of the physical mechanisms involved in the star formation process. Determining the amount of interstellar extinction and the correct reddening law are crucial steps to derive fundamental stellar parameters and in particular accurate ages from the Hertzsprung-Russell diagram. Aims. In this context, we seek to derive accurate stellar ages for NGC 6530, the young cluster associated with the Lagoon Nebula to infer the star formation history of this region. Methods. We used the Gaia-ESO survey observations of the Lagoon Nebula, together with photometric literature data and Gaia DR2 kinematics, to derive cluster membership and fundamental stellar parameters. Using spectroscopic effective temperatures, we analysed the reddening properties of all objects and derived accurate stellar ages for cluster members. Results. We identified 652 confirmed and 9 probable members. The reddening inferred for members and non-members allows us to distinguish foreground objects, mainly main-sequence stars, and background objects, mainly giants, and to trace the three-dimensional structure of the nebula. This classification is in agreement with the distances inferred from Gaia DR2 parallaxes for these objects. Finally, we derive stellar ages for 382 confirmed cluster members for which we obtained the individual reddening values. In addition, we find that the gravity-sensitive γ index distribution for the M-type stars is correlated with stellar age. Conclusions. For all members with Teff < 5500 K, the mean logarithmic age is 5.84 (units of years) with a dispersion of 0.36 dex. The age distribution of stars with accretion or discs, i.e. classical T Tauri stars with excess (CTTSe), is similar to that of stars without accretion and without discs, i.e. weak T Tauri stars with photospheric emission (WTTSp). We interpret this dispersion as evidence of a real age spread since the total uncertainties on age determinations, derived from Monte Carlo simulations, are significantly smaller than the observed spread. This conclusion is supported by evidence of the decrease of the gravity-sensitive γ index as a function of stellar ages. The presence of a small age spread is also supported by the spatial distribution and kinematics of old and young members. In particular, members with accretion or discs, formed in the last 1 Myr, show evidence of subclustering around the cluster centre, in the Hourglass Nebula and in the M8-E region, suggesting a possible triggering of star formation events by the O-type star ionization fronts.
Acceso Abierto
The widest Hα survey of accreting protoplanets around nearby transition disks
(EDP Sciences, 2020-01-21) Zurlo, A.; Cugno, G.; Montesinos, M.; Canovas, H.; Casassus, S.; Christiaens, V.; Cieza, L.; Huélamo, N.; Pérez Barrio, Sandra; Comisión Nacional de Investigación Científica y Tecnológica (CONICYT); Swiss National Science Foundation (SNSF); Agencia Estatal de Investigación (AEI); The Chinese Academy of Science South America Center for Astronomy (CASSACA); Huelamo, N. [0000-0002-2711-8143]; Pérez, S. [0000-0003-2953-755X]; Zurlo, A. [0000-0002-5903-8316]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. The mechanisms of planet formation are still under debate. We know little about how planets form, even if more than 4000 exoplanets have been detected to date. Recent investigations target the cot of newly born planets: the protoplanetary disk. At the first stages of their life, exoplanets still accrete material from the gas-rich disk in which they are embedded. Transitional disks are indeed disks that show peculiarities, such as gaps, spiral arms, and rings, which can be connected to the presence of substellar companions. Aims. To investigate what is responsible for these features, we selected all the known transitional disks in the solar neighborhood (<200 pc) that are visible from the southern hemisphere. We conducted a survey of 11 transitional disks with the SPHERE instrument at the Very Large Telescope. This is the largest Hα survey that has been conducted so far to look for protoplanets. The observations were performed with the Hα filter of ZIMPOL in order to target protoplanets that are still in the accretion stage. All the selected targets are very young stars, less than 20 Myr, and show low extinction in the visible. Methods. We reduced the ZIMPOL pupil stabilized data by applying the method of the angular spectral differential imaging (ASDI), which combines both techniques. The datacubes are composed of the Cnt_Hα and the narrow band filter Hα, which are taken simultaneously to permit the suppression of the speckle pattern. The principal component analysis method was employed for the reduction of the data. For each dataset, we derived the 5σ contrast limit and converted it in upper limits on the accretion luminosity. Results. We do not detect any new accreting substellar companions around the targeted transition disks down to an average contrast of 12 magnitudes at 0.′′2 from the central star. We have recovered the signal of the accreting M star companion around the star HD 142527. We have detected and resolved, for the first time in visible light, the quadruple system HD 98800. For every other system, we can exclude the presence of massive actively accreting companions, assuming that the accretion is not episodic and that the extinction is negligible. The mean accretion luminosity limit is 10−6 L⊙ at a separation of 0.′′2 from the host.

Buscar

Examinando (CAB) Artículos por Materia "Accretion"