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C. Sanchez-Fernandez

Bio: C. Sanchez-Fernandez is an academic researcher from European Space Agency. The author has contributed to research in topics: Neutron star & Black hole. The author has an hindex of 14, co-authored 37 publications receiving 1195 citations. Previous affiliations of C. Sanchez-Fernandez include International Trademark Association.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors reported on the INTEGRAL observations of the soft gamma-ray repeater SGR 1935+2154 performed between 2020 April 28 and May 3.
Abstract: We report on INTEGRAL observations of the soft $\gamma$-ray repeater SGR 1935+2154 performed between 2020 April 28 and May 3. Several short bursts with fluence of $\sim10^{-7}-10^{-6}$ erg cm$^{-2}$ were detected by the IBIS instrument in the 20-200 keV range. The burst with the hardest spectrum, discovered and localized in real time by the INTEGRAL Burst Alert System, was spatially and temporally coincident with a short and very bright radio burst detected by the CHIME and STARE2 radio telescopes at 400-800 MHz and 1.4 GHz, respectively. Its lightcurve shows three narrow peaks separated by $\sim$29 ms time intervals, superimposed on a broad pulse lasting $\sim$0.6 s. The brightest peak had a delay of 6.5$\pm$1.0 ms with respect to the 1.4 GHz radio pulse (that coincides with the second and brightest component seen at lower frequencies). The burst spectrum, an exponentially cut-off power law with photon index $\Gamma=0.7_{-0.2}^{+0.4}$ and peak energy $E_p=65\pm5$ keV, is harder than those of the bursts usually observed from this and other magnetars. By the analysis of an expanding dust scattering ring seen in X-rays with the {\it Neil Gehrels Swift Observatory} XRT instrument, we derived a distance of 4.4$_{-1.3}^{+2.8}$ kpc for SGR 1935+2154, independent of its possible association with the supernova remnant G57.2+0.8. At this distance, the burst 20-200 keV fluence of $(6.1\pm 0.3)\times10^{-7}$ erg cm$^{-2}$ corresponds to an isotropic emitted energy of $\sim1.4\times10^{39}$ erg. This is the first burst with a radio counterpart observed from a soft $\gamma$-ray repeater and it strongly supports models based on magnetars that have been proposed for extragalactic fast radio bursts.

239 citations

Journal ArticleDOI
TL;DR: In this article, the authors observed the Galactic black hole candidate XTE J1650-500 early in its fall 2001 outburst with the XMM-Newton European Photon Imaging pn Camera (EPIC-pn).
Abstract: We observed the Galactic black hole candidate XTE J1650-500 early in its fall of 2001 outburst with the XMM-Newton European Photon Imaging pn Camera (EPIC-pn). The observed spectrum is consistent with the source having been in the "very high" state. We find a broad, skewed Fe Kα emission line that suggests the primary in this system may be a Kerr black hole and that indicates a steep disk emissivity profile that is hard to explain in terms of a standard accretion disk model. These results are quantitatively and qualitatively similar to those from an XMM-Newton observation of the Seyfert galaxy MCG -6-30-15. The steep emissivity in MCG -6-30-15 may be explained by the extraction and dissipation of rotational energy from a black hole with nearly maximal angular momentum or from material in the plunging region via magnetic connections to the inner accretion disk. If this process is at work in both sources, an exotic but fundamental general relativistic prediction may be confirmed across a factor of 106 in black hole mass. We discuss these results in terms of the accretion flow geometry in stellar-mass black holes and the variety of enigmatic phenomena often observed in the very high state.

220 citations

Journal ArticleDOI
TL;DR: In this article, the authors observed the Galactic black hole candidate XTE J1650-500 early in its Fall 2001 outburst with the XMM-Newton European Photon Imaging pn Camera (EPIC-pn).
Abstract: We observed the Galactic black hole candidate XTE J1650-500 early in its Fall, 2001 outburst with the XMM-Newton European Photon Imaging pn Camera (EPIC-pn). The observed spectrum is consistent with the source having been in the "very high" state. We find a broad, skewed Fe K-alpha emission line which suggests that the primary in this system may be a Kerr black hole, and which indicates a steep emissivity profile that is hard to explain in terms of a standard accretion disk model. These results are quantitatively and qualitatively similar to those from an XMM-Newton observation of the Seyfert galaxy MCG--6-30-15. The steep emissivity in MCG--6-30-15 may be explained by the extraction and dissipation of rotational energy from a black hole with nearly- maximal angular momentum or material in the plunging region via magnetic connections to the inner accretion disk. If this process is at work in both sources, an exotic but fundamental general relativistic prediction may be confirmed across a factor of 10^6 in black hole mass. We discuss these results in terms of the accretion flow geometry in stellar-mass black holes, and the variety of enigmatic phenomena often observed in the very high state.

203 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a detailed homogeneous (hard) X-ray view of a sample of 76 sources in the Galactic bulge region, and show the first results from the start of the monitoring up to 2006, April 21, during three visibility seasons.
Abstract: Aims.The Galactic bulge region is a rich host of variable high-energy point sources. Since 2005, February 17 we are monitoring the source activity in the Galactic bulge region regularly and frequently, i.e., about every three days, with the instruments onboard INTEGRAL. Thanks to the large field of view, the imaging capabilities and the sensitivity at hard X-rays, we are able to present for the first time a detailed homogeneous (hard) X-ray view of a sample of 76 sources in the Galactic bulge region. Methods: We describe the successful monitoring program and show the first results from the start of the monitoring up to 2006, April 21, i.e., for a period of about one and a half year, during three visibility seasons. We focus on the short (hour), medium (month) and long-term (year) variability in the hard X-ray bands, i.e., 20-60 keV and 60-150 keV. When available, we discuss the simultaneous observations in the soft X-ray, 3-10 keV and 10-25 keV, bands. Results: Almost all the sources in the Galactic bulge region we detect in the 20-60 keV and 60-150 keV bands are variable. During the last two and a half weeks of the third visibility season most of the known persistent (hard) X-ray sources in the Galactic Center region were not detected. Of our sample of sources, per visibility season we detect 32/33 sources in the 20-60 keV band and 8/9 sources in the 60-150 keV band above a signal to noise of 7. On average, we find per visibility season one active bright (âa†100 mCrab, 20-60 keV) black-hole candidate X-ray transient and three active weaker (âa‰25 mCrab, 20-60 keV) neutron star X-ray transients. Most of the time a clear anti-correlation can be seen between the soft and hard X-ray emission in some of the X-ray bursters. Hard X-ray flares or outbursts in X-ray bursters, which have a duration of the order of weeks are accompanied by soft X-ray drops. On the other hand, hard X-ray drops can be accompanied by soft X-ray flares/outbursts. During the course of our program we found a number of new sources, IGR J17354-3255, IGR 17453-2853, IGR J17454-2703, IGR J17456-2901b, IGR J17536-2339, and IGR J17541-2252. We report here on some of the high-energy properties of these sources. Conclusions: The high-energy light curves of all the sources in the field of view, and the high-energy images of the region, are made available through the WWW, as soon as possible after the observations have been performed, at http://isdc.unige.ch/Science/BULGE/. Appendices are only available in electronic form at http://www.aanda.org

94 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe the burst properties in relation to the persistent emission of the low-mass X-ray binary 4U 0614+091 and find bursts with a wide variety of characteristics in serendipitous wide-field X-r ay observations by the WATCH on EURECA, the ASM on RXTE, the WFCs on BeppoSAX, the FREGATE on HETE-2, the IBIS/ISGRI on INTEGRAL, and the BAT on Swift, as well as pointed observations with the
Abstract: The low-mass X-ray binary 4U 0614+091 is a source of sporadic thermonuclear (type I) X-ray burs ts. We find bursts with a wide variety of characteristics in serendipitous wide-field X-r ay observations by the WATCH on EURECA, the ASM on RXTE, the WFCs on BeppoSAX, the FREGATE on HETE-2, the IBIS/ISGRI on INTEGRAL, and the BAT on Swift, as well as pointed observations with the PCA and HEXTE on RXTE. Most of the bursts are bright, i.e., they reach a peak flux of a bout 15 Crab, but a few are weak and only reach a peak flux below a Crab. One of the bursts shows a ver y strong photospheric radius-expansion phase. This allows us to evaluate the distance to the source, which we estimate to be 3.2 kpc. The burst durations vary generally from about 10 sec t o 5 min. However, after one of the intermediate-duration bursts, a f aint tail is seen to at least about 2.4 hours after the start of the burst. One very long burst was observed, which lasted for several hours . This superburst candidate was followed by a normal type-I burst only 19 days later. This is, to our knowledge, the shortest burst- quench time among the superbursters. The observation of a superburst in this system is diffi cult to reconcile if the system is accreting at about 1% of the Eddington limit. We describe the burst properties in relation to the persistent emission. No strong correlation s are apparent, except that the intermediate-duration burs ts occurred when 4U 0614+091’s persistent emission was lowest and calm, and when burs ts were infrequent (on average roughly one every month to 3 months). The average burst rate increased significantly af ter this period. The maximum average burst recurrence rate i s about once every week to 2 weeks. The burst behaviour may be partly understood if there is at least an appreciable amount of helium pre sent in the accreted material from the donor star. If the system is an ultra-compact X-ray binary with a CO white-dwarf donor, as has been suggested, this is unexpected. If the bursts are powered by h elium, we find that the energy production per accumulated mas s is about 2.5 times less than expected for pure helium matter.

86 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, the authors review the properties and behavior of 20 X-ray binaries that contain a dynamically confirmed black hole, 17 of which are transient systems, during the past decade, many of these transien...
Abstract: We review the properties and behavior of 20 X-ray binaries that contain a dynamically-confirmed black hole, 17 of which are transient systems. During the past decade, many of these transien...

2,174 citations

Journal ArticleDOI
TL;DR: In this paper, the authors describe new optically thin solutions for rotating accretion flows around black holes and neutron stars, which are advection dominated, so that most of the viscously dissipated energy is advected radially with the flow.
Abstract: We describe new optically thin solutions for rotating accretion flows around black holes and neutron stars. These solutions are advection dominated, so that most of the viscously dissipated energy is advected radially with the flow. We model the accreting gas as a two temperature plasma and include cooling by bremsstrahlung, synchrotron, and Comptonization. We obtain electron temperatures $T_e\sim 10^{8.5}-10^{10}$K. The new solutions are present only for mass accretion rates $\dot M$ less than a critical rate $\dot M_{crit}$ which we calculate as a function of radius $R$ and viscosity parameter $\alpha$. For $\dot M<\dot M_{crit}$ we show that there are three equilibrium branches of solutions. One of the branches corresponds to a cool optically thick flow which is the well-known thin disk solution of Shakura \& Sunyaev (1973). Another branch corresponds to a hot optically thin flow, discovered originally by Shapiro, Lightman \& Eardley (1976, SLE). This solution is thermally unstable. The third branch corresponds to our new advection-dominated solution. This solution is hotter and more optically thin than the SLE solution, but is viscously and thermally stable. It is related to the ion torus model of Rees et al. (1982) and may potentially explain the hard X-ray and $\gamma$-ray emission from X-ray binaries and active galactic nuclei.

1,088 citations

01 Dec 1998
TL;DR: The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) as mentioned in this paper is dedicated to the fine spectroscopy (2.5 − 1.5 ) and fine imaging (angular resolution: 12 arcmin FWHM) of celestial gamma-ray sources in the energy range 15 − 10 − MeV with concurrent source monitoring in the X-ray ($3 − 35 ) and optical (V -band, 550 −nm) energy ranges.
Abstract: The ESA observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory) is dedicated to the fine spectroscopy (2.5 keV FWHM @ 1 MeV) and fine imaging (angular resolution: 12 arcmin FWHM) of celestial gamma-ray sources in the energy range 15 keV to 10 MeV with concurrent source monitoring in the X-ray ($3{-}35$ keV) and optical ( V -band, 550 nm) energy ranges. INTEGRAL carries two main gamma-ray instruments, the spectrometer SPI (Vedrenne et al. [CITE]) – optimized for the high-resolution gamma-ray line spectroscopy (20 keV–8 MeV), and the imager IBIS (Ubertini et al. [CITE]) – optimized for high-angular resolution imaging (15 keV–10 MeV). Two monitors, JEM-X (Lund et al. [CITE]) in the ($3{-}35$) keV X-ray band, and OMC (Mas-Hesse et al. [CITE]) in optical Johnson V -band complement the payload. The ground segment includes the Mission Operations Centre at ESOC, ESA and NASA ground stations, the Science Operations Centre at ESTEC and the Science Data Centre near Geneva. INTEGRAL was launched on 17 October 2002. The observing programme is well underway and sky exposure (until June 2003) reaches ~1800 ks in the Galactic plane. The prospects are excellent for the scientific community to observe the high energy sky using state-of-the-art gamma-ray imaging and spectroscopy. This paper presents a high-level overview of INTEGRAL.

726 citations

01 Jan 2016
TL;DR: The radiative processes in astrophysics is universally compatible with any devices to read, and is available in the digital library an online access to it is set as public so you can get it instantly.
Abstract: Thank you very much for reading radiative processes in astrophysics. Maybe you have knowledge that, people have look hundreds times for their favorite readings like this radiative processes in astrophysics, but end up in malicious downloads. Rather than reading a good book with a cup of tea in the afternoon, instead they juggled with some harmful virus inside their desktop computer. radiative processes in astrophysics is available in our digital library an online access to it is set as public so you can get it instantly. Our book servers saves in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Merely said, the radiative processes in astrophysics is universally compatible with any devices to read.

645 citations