Mariano Mendez - Groningen

Mariano Mendez
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Mariano Mendez

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High Energy Astrophysical Phenomena (33)
Astrophysics (17)
Cosmology and Nongalactic Astrophysics (3)
Instrumentation and Methods for Astrophysics (2)
Solar and Stellar Astrophysics (2)
Astrophysics of Galaxies (1)
Earth and Planetary Astrophysics (1)

Publications Authored By Mariano Mendez

We present 3-79 keV NuSTAR observations of the neutron star low-mass X-ray binary 4U 1636-53 in the soft, transitional and hard state. The spectra display a broad emission line at 5-10 keV. We applied several models to fit this line: A GAUSSIAN line, a relativistically broadened emission line model, KYRLINE, and two models including relativistically smeared and ionized reflection off the accretion disc with different coronal heights, RELXILL and RELXILLLP. Read More

We fitted the $3-180$-keV spectrum of all the observations of the neutron-star low-mass X-ray binary 4U 1636$-$53 taken with the {\it Rossi X-ray Timing Explorer} using a model that includes a thermal Comptonisation component. We found that in the low-hard state the power-law index of this component, $\Gamma$, gradually increases as the source moves in the colour-colour diagram. When the source undergoes a transition from the hard to the soft state $\Gamma$ drops abruptly; once the source is in the soft state $\Gamma$ increases again and then decreases gradually as the source spectrum softens further. Read More

We present a timing analysis of two Rossi X-ray Timing Explorer observations of the microquasar GRS 1915+105 during the heartbeat state. The phase-frequency-power maps show that the intermediate-frequency aperiodic X-ray variability weakens as the source softens in the slow rise phase, and when the quasi-periodic oscillation disappears in the rise phase of the pulse of the double-peaked class its sub-harmonic is still present with a hard phase lag. In the slow rise phase, the energy-frequency-power maps show that most of the aperiodic variability is produced in the corona, and may also induce the aperiodic variability observed at low energies from an accretion disk, which is further supported by the soft phase lag especially in the intermediate-frequency range (with a time delay up to 20 ms). Read More

Authors: Didier Barret, Thien Lam Trong, Jan-Willem den Herder, Luigi Piro, Xavier Barcons, Juhani Huovelin, Richard Kelley, J. Miguel Mas-Hesse, Kazuhisa Mitsuda, Stéphane Paltani, Gregor Rauw, Agata Rożanska, Joern Wilms, Marco Barbera, Enrico Bozzo, Maria Teresa Ceballos, Ivan Charles, Anne Decourchelle, Roland den Hartog, Jean-Marc Duval, Fabrizio Fiore, Flavio Gatti, Andrea Goldwurm, Brian Jackson, Peter Jonker, Caroline Kilbourne, Claudio Macculi, Mariano Mendez, Silvano Molendi, Piotr Orleanski, François Pajot, Etienne Pointecouteau, Frederick Porter, Gabriel W. Pratt, Damien Prêle, Laurent Ravera, Etienne Renotte, Joop Schaye, Keisuke Shinozaki, Luca Valenziano, Jacco Vink, Natalie Webb, Noriko Yamasaki, Françoise Delcelier-Douchin, Michel Le Du, Jean-Michel Mesnager, Alice Pradines, Graziella Branduardi-Raymont, Mauro Dadina, Alexis Finoguenov, Yasushi Fukazawa, Agnieszka Janiuk, Jon Miller, Yaël Nazé, Fabrizio Nicastro, Salvatore Sciortino, Jose Miguel Torrejon, Hervé Geoffray, Isabelle Hernandez, Laure Luno, Philippe Peille, Jérôme André, Christophe Daniel, Christophe Etcheverry, Emilie Gloaguen, Jérémie Hassin, Gilles Hervet, Irwin Maussang, Jérôme Moueza, Alexis Paillet, Bruno Vella, Gonzalo Campos Garrido, Jean-Charles Damery, Chantal Panem, Johan Panh, Simon Bandler, Jean-Marc Biffi, Kevin Boyce, Antoine Clénet, Michael DiPirro, Pierre Jamotton, Simone Lotti, Denis Schwander, Stephen Smith, Bert-Joost van Leeuwen, Henk van Weers, Thorsten Brand, Beatriz Cobo, Thomas Dauser, Jelle de Plaa, Edoardo Cucchetti

The X-ray Integral Field Unit (X-IFU) on board the Advanced Telescope for High-ENergy Astrophysics (Athena) will provide spatially resolved high-resolution X-ray spectroscopy from 0.2 to 12 keV, with 5 arc second pixels over a field of view of 5 arc minute equivalent diameter and a spectral resolution of 2.5 eV up to 7 keV. Read More

We investigated the convexity of all type I X-ray bursts with millihertz quasi-periodic oscillations (mHz QPOs) in 4U 1636-53 using archival observations with the Rossi X-ray Timing Explorer. We found that, at a 3.5 $\sigma$ confidence level, in all 39 cases in which the mHz QPOs disappeared at the time of an X-ray burst, the convexity of the burst is positive. Read More

While there are many dynamical mechanisms and models that try to explain the origin and phenomenology of the quasi-periodic oscillations (QPOs) seen in the X-ray light curves of low-mass X-ray binaries, few of them address how the radiative processes occurring in these extreme environments give rise to the rich set of variability features actually observed in these light curves. A step towards this end comes from the study of the energy and frequency dependence of the phase lags of these QPOs. Here we used a methodology that allowed us to study, for the first time, the dependence of the phase lags of all QPOs in the range of 1 Hz to 1300 Hz detected in the low-mass X-ray binary 4U 1636-53 upon energy and frequency as the source changes its states as it moves through the colour-colour diagram. Read More

Recent XMM-Newton observations of the black-hole candidate 4U 1630-47 during the 2012 outburst revealed three relativistically Doppler-shifted emission lines that were interpreted as arising from baryonic matter in the jet of this source. Here we reanalyse those data and find an alternative model that, with less free parameters than the model with Doppler-shifted emission lines, fits the data well. In our model we allow the abundance of S and Fe in the interstellar material along the line of sight to the source to be non solar. Read More

Coherent oscillations and the evolution of the X-ray spectrum during thermonuclear X-ray bursts in accreting neutron-star X-ray binaries have been studied intensively but separately. We analysed all the X-ray bursts of the source 4U 1728-34 with the Rossi X-ray Timing Explorer. We found that the presence of burst oscillations can be used to predict the behaviour of the blackbody radius during the cooling phase of the bursts. Read More

We investigate the spectral and timing properties of the millihertz quasi-periodic oscillations (mHz QPOs) in neutron-star low-mass X-ray binary 4U 1636-53 using XMM-Newton and Rossi X-ray Timing Explorer (RXTE) observations. The mHz QPOs in the XMM-Newton/RXTE observations show significant frequency variation and disappear right before type I X-ray bursts. We find no significant correlation between the mHz QPO frequency and the temperature of the neutron-star surface, which is different from theoretical predictions. Read More

We present an analysis of the energy and frequency dependence of the Fourier time lags of the hectoHertz quasi-periodic oscillations (QPOs) and of the QPOs at the frequency at which the power density spectrum shows a break in the neutron-star low-mass X-ray binary 4U 1636-53, using a large data set obtained with the Rossi X-ray Timing Explorer. We found that: (i) For the break frequency QPO: for low frequencies, in general the time lag is positive, but it is decreasing with increasing frequency, reaching zero lag at 20 Hz. Between 20 and 35 Hz there is a small fluctuation around zero, from where the time lags become positive again and increase slightly above zero up to 65 Hz. Read More

Owing to the frequency and reproducibility of its outbursts, the black-hole candidate GX 339-4 has become the standard against which the outbursts of other black-hole candidate are matched up. Here we present the first systematic study of the evolution of the X-ray lags of the broad-band variability component (0.008-5 Hz) in GX 339-4 as a function of the position of the source in the hardness-intensity diagram. Read More

We detected millihertz quasi-periodic oscillations (QPOs) in an XMM-Newton observation of the neutron-star low-mass X-ray binary 4U 1636-53. These QPOs have been interpreted as marginally-stable burning on the neutron-star surface. At the beginning of the observation the QPO was at around 8 mHz, together with a possible second harmonic. Read More

Both the broad iron (Fe) line and the frequency of the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (LMXBs) can potentially provide independent measures of the inner radius of the accretion disc. We use XMM-Newton and simultaneous Rossi X-ray Timing Explorer observations of the LMXB 4U 1636-53 to test this hypothesis. We study the properties of the Fe-K emission line as a function of the spectral state of the source and the frequency of the kHz QPOs. Read More

We used six simultaneous XMM-Newton and Rossi X-ray Timing Explorer plus five Suzaku observations to study the continuum spectrum and the iron emission line in the neutron-star low-mass X-ray binary 4U 1636-53. We modelled the spectra with two thermal components (representing the accretion disc and boundary layer), a Comptonised component (representing a hot corona), and either a Gaussian or a relativistic line component to model an iron emission line at about 6.5 keV. Read More

We report the serendipitous discovery with XMM-Newton that 3XMM J185246.6+003317 is an 11.56 s X-ray pulsar located 1' away from the southern boundary of supernova remnant Kes 79. Read More

Affiliations: 1Kapteyn Astronomical Institute, University of Groningen, The Netherlands, 2University of Amsterdam, The Netherlands, 3INAF-Osservatorio Astronomico di Brera, Italy, 4Dipartimento di Fisica, Universita degli Studi di Cagliari, Italy

We measured the phase-lag spectrum of the high-frequency quasi-periodic oscillations (QPO) in the black hole systems (at QPO frequencies) GRS 1915+105 (35 Hz and 67 Hz), GRO J1655-40 (300 Hz and 450 Hz), XTE J1550-564 (180 Hz and 280 Hz), and IGR J17091-3624 (67 Hz). The lag spectra of the 67-Hz QPO in, respectively, GRS 1915+105 and IGR J17091-3624, and the 450-Hz QPO in GRO J1655-40 are hard (hard photons lag the soft ones) and consistent with each other, with the hard lags increasing with energy. On the contrary, the lags of the 35-Hz QPO in GRS 1915+105 are soft, with the lags becoming softer as the energy increases; the lag spectrum of the 35-Hz QPO is inconsistent with that of the 67-Hz QPO. Read More

Authors: Kirpal Nandra1, Didier Barret2, Xavier Barcons3, Andy Fabian4, Jan-Willem den Herder5, Luigi Piro6, Mike Watson7, Christophe Adami8, James Aird9, Jose Manuel Afonso10, Dave Alexander11, Costanza Argiroffi12, Lorenzo Amati13, Monique Arnaud14, Jean-Luc Atteia15, Marc Audard16, Carles Badenes17, Jean Ballet18, Lucia Ballo19, Aya Bamba20, Anil Bhardwaj21, Elia Stefano Battistelli22, Werner Becker23, Michaël De Becker24, Ehud Behar25, Stefano Bianchi26, Veronica Biffi27, Laura Bîrzan28, Fabrizio Bocchino29, Slavko Bogdanov30, Laurence Boirin31, Thomas Boller32, Stefano Borgani33, Katharina Borm34, Nicolas Bouché35, Hervé Bourdin36, Richard Bower37, Valentina Braito38, Enzo Branchini39, Graziella Branduardi-Raymont40, Joel Bregman41, Laura Brenneman42, Murray Brightman43, Marcus Brüggen44, Johannes Buchner45, Esra Bulbul46, Marcella Brusa47, Michal Bursa48, Alessandro Caccianiga49, Ed Cackett50, Sergio Campana51, Nico Cappelluti52, Massimo Cappi53, Francisco Carrera54, Maite Ceballos55, Finn Christensen56, You-Hua Chu57, Eugene Churazov58, Nicolas Clerc59, Stephane Corbel60, Amalia Corral61, Andrea Comastri62, Elisa Costantini63, Judith Croston64, Mauro Dadina65, Antonino D'Ai66, Anne Decourchelle67, Roberto Della Ceca68, Konrad Dennerl69, Klaus Dolag70, Chris Done71, Michal Dovciak72, Jeremy Drake73, Dominique Eckert74, Alastair Edge75, Stefano Ettori76, Yuichiro Ezoe77, Eric Feigelson78, Rob Fender79, Chiara Feruglio80, Alexis Finoguenov81, Fabrizio Fiore82, Massimiliano Galeazzi83, Sarah Gallagher84, Poshak Gandhi85, Massimo Gaspari86, Fabio Gastaldello87, Antonis Georgakakis88, Ioannis Georgantopoulos89, Marat Gilfanov90, Myriam Gitti91, Randy Gladstone92, Rene Goosmann93, Eric Gosset94, Nicolas Grosso95, Manuel Guedel96, Martin Guerrero97, Frank Haberl98, Martin Hardcastle99, Sebastian Heinz100, Almudena Alonso Herrero101, Anthony Hervé102, Mats Holmstrom103, Kazushi Iwasawa104, Peter Jonker105, Jelle Kaastra106, Erin Kara107, Vladimir Karas108, Joel Kastner109, Andrew King110, Daria Kosenko111, Dimita Koutroumpa112, Ralph Kraft113, Ingo Kreykenbohm114, Rosine Lallement115, Giorgio Lanzuisi116, J. Lee117, Marianne Lemoine-Goumard118, Andrew Lobban119, Giuseppe Lodato120, Lorenzo Lovisari121, Simone Lotti122, Ian McCharthy123, Brian McNamara124, Antonio Maggio125, Roberto Maiolino126, Barbara De Marco127, Domitilla de Martino128, Silvia Mateos129, Giorgio Matt130, Ben Maughan131, Pasquale Mazzotta132, Mariano Mendez133, Andrea Merloni134, Giuseppina Micela135, Marco Miceli136, Robert Mignani137, Jon Miller138, Giovanni Miniutti139, Silvano Molendi140, Rodolfo Montez141, Alberto Moretti142, Christian Motch143, Yaël Nazé144, Jukka Nevalainen145, Fabrizio Nicastro146, Paul Nulsen147, Takaya Ohashi148, Paul O'Brien149, Julian Osborne150, Lida Oskinova151, Florian Pacaud152, Frederik Paerels153, Mat Page154, Iossif Papadakis155, Giovanni Pareschi156, Robert Petre157, Pierre-Olivier Petrucci158, Enrico Piconcelli159, Ignazio Pillitteri160, C. Pinto161, Jelle de Plaa162, Etienne Pointecouteau163, Trevor Ponman164, Gabriele Ponti165, Delphine Porquet166, Ken Pounds167, Gabriel Pratt168, Peter Predehl169, Daniel Proga170, Dimitrios Psaltis171, David Rafferty172, Miriam Ramos-Ceja173, Piero Ranalli174, Elena Rasia175, Arne Rau176, Gregor Rauw177, Nanda Rea178, Andy Read179, James Reeves180, Thomas Reiprich181, Matthieu Renaud182, Chris Reynolds183, Guido Risaliti184, Jerome Rodriguez185, Paola Rodriguez Hidalgo186, Mauro Roncarelli187, David Rosario188, Mariachiara Rossetti189, Agata Rozanska190, Emmanouil Rovilos191, Ruben Salvaterra192, Mara Salvato193, Tiziana Di Salvo194, Jeremy Sanders195, Jorge Sanz-Forcada196, Kevin Schawinski197, Joop Schaye198, Axel Schwope199, Salvatore Sciortino200, Paola Severgnini201, Francesco Shankar202, Debora Sijacki203, Stuart Sim204, Christian Schmid205, Randall Smith206, Andrew Steiner207, Beate Stelzer208, Gordon Stewart209, Tod Strohmayer210, Lothar Strüder211, Ming Sun212, Yoh Takei213, V. Tatischeff214, Andreas Tiengo215, Francesco Tombesi216, Ginevra Trinchieri217, T. G. Tsuru218, Asif Ud-Doula219, Eugenio Ursino220, Lynne Valencic221, Eros Vanzella222, Simon Vaughan223, Cristian Vignali224, Jacco Vink225, Fabio Vito226, Marta Volonteri227, Daniel Wang228, Natalie Webb229, Richard Willingale230, Joern Wilms231, Michael Wise232, Diana Worrall233, Andrew Young234, Luca Zampieri235, Jean In't Zand236, Silvia Zane237, Andreas Zezas238, Yuying Zhang239, Irina Zhuravleva240
Affiliations: 1DE, 2FR, 3ES, 4UK, 5NL, 6IT, 7UK, 8FR, 9UK, 10PT, 11UK, 12IT, 13IT, 14FR, 15FR, 16CH, 17US, 18FR, 19IT, 20JP, 21IN, 22IT, 23DE, 24BE, 25IL, 26IT, 27IT, 28NL, 29IT, 30US, 31FR, 32DE, 33IT, 34DE, 35FR, 36IT, 37UK, 38IT, 39IT, 40UK, 41US, 42US, 43DE, 44DE, 45DE, 46US, 47IT, 48CZ, 49IT, 50US, 51IT, 52IT, 53IT, 54ES, 55ES, 56DK, 57US, 58DE, 59DE, 60FR, 61GR, 62IT, 63NL, 64UK, 65IT, 66IT, 67FR, 68IT, 69DE, 70DE, 71UK, 72CZ, 73US, 74CH, 75UK, 76IT, 77JP, 78US, 79UK, 80FR, 81FI, 82IT, 83IT, 84CA, 85UK, 86IT, 87IT, 88DE, 89GR, 90DE, 91IT, 92US, 93FR, 94BE, 95FR, 96AT, 97ES, 98DE, 99UK, 100US, 101ES, 102FR, 103SE, 104ES, 105NL, 106NL, 107UK, 108CZ, 109US, 110UK, 111FR, 112FR, 113US, 114D, 115FR, 116GR, 117US, 118FR, 119UK, 120IT, 121DE, 122IT, 123UK, 124CA, 125IT, 126UK, 127DE, 128IT, 129ES, 130IT, 131UK, 132IT, 133NL, 134DE, 135IT, 136IT, 137IT, 138US, 139ES, 140IT, 141ES, 142IT, 143FR, 144BE, 145FI, 146IT, 147US, 148JP, 149UK, 150UK, 151DE, 152DE, 153US, 154UK, 155GR, 156IT, 157US, 158FR, 159IT, 160IT, 161UK, 162NL, 163FR, 164UK, 165DE, 166FR, 167UK, 168FR, 169DE, 170US, 171US, 172NL, 173DE, 174IT, 175US, 176DE, 177BE, 178IT, 179UK, 180UK, 181DE, 182FR, 183US, 184IT, 185FR, 186CA, 187IT, 188DE, 189IT, 190PL, 191UK, 192IT, 193DE, 194IT, 195DE, 196ES, 197CH, 198NL, 199D, 200IT, 201IT, 202FR, 203UK, 204IE, 205DE, 206US, 207US, 208IT, 209UK, 210US, 211DE, 212US, 213JP, 214FR, 215IT, 216US, 217IT, 218JP, 219US, 220NL, 221US, 222IT, 223UK, 224IT, 225NL, 226IT, 227FR, 228US, 229FR, 230UK, 231DE, 232NL, 233UK, 234UK, 235IT, 236NL, 237UK, 238GR, 239DE, 240US

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Read More

White dwarfs, neutron stars and stellar mass black holes are key laboratories to study matter in most extreme conditions of gravity and magnetic field. The unprecedented effective area of Athena+ will allow us to advance our understanding of emission mechanisms and accretion physics over a wide range of mass accretion rates, starting from lower and sub-luminous quiescent X-ray binaries up to super-Eddington ultra-luminous sources. Athena+ will measure stellar black hole spins in a much higher number of binaries than achievable now, opening the possibility to study how spin varies with black hole history. Read More

Affiliations: 1Groningen, 2Groningen, 3Groningen, 4Amsterdam, 5INAF-OAB, 6Canary Islands

We analysed the X-ray spectra of six observations, simultaneously taken with XMM-Newton and Rossi X-ray Timing Explorer (RXTE), of the neutron star low-mass X-ray binary 4U 1636-53. The observations cover several states of the source, and therefore a large range of inferred mass accretion rate. These six observations show a broad emission line in the spectrum at around 6. Read More

We present a spectral analysis of the black hole candidate and X-ray transient source Swift J1753.5 0127 making use of simultaneous observations of XMM-Newton and Rossi X-ray Timing Explorer (RXTE) in 2006, when the source was in outburst. The aim of this paper is to test whether a thermal component due to the accretion disc is present in the X-ray spectrum. Read More

Affiliations: 1IAR-CONICET, Argentina, 2Kapteyn Astronomical Institute, Groningen, The Netherlands, 3Kapteyn Astronomical Institute, Groningen, The Netherlands

We analysed the complete set of bursts from the neutron-star low-mass X-ray binary 4U 1820-30 detected with the Rossi X-ray Timing Explorer (RXTE). We found that all are photospheric radius expansion bursts, and have similar duration, peak flux and fluence. From the analysis of time-resolved spectra during the cooling phase of the bursts, we found that the relation between the bolometric flux and the temperature is very different from the canonical F - T^4 relation that is expected if the apparent emitting area on the surface of the neutron star remains constant. Read More

Affiliations: 1INAF-Brera Observatory, Italy, 2Univ. Groningen, the Netherlands, 3Univ. Groningen, the Netherlands

We present the results of the analysis of a large database of X-ray observations of 22 galactic black-hole transients with the Rossi X-Ray timing explorer throughout its operative life for a total exposure time of ~12 Ms. We excluded persistent systems and the peculiar source GRS 1915+105, as well as the most recently discovered sources. The semi-automatic homogeneous analysis was aimed at the detection of high-frequency (100-1000 Hz) quasi-periodic oscillations (QPO), of which several cases were previously reported in the literature. Read More

We analysed all archival RXTE observations of the neutron-star low-mass X-ray binary 4U 1636-53 up to May 2010. In 528 out of 1280 observations we detected kilohertz quasi-periodic oscillations (kHz QPOs), with ~ 65% of these detections corresponding to the so-called lower kHz QPO. Using this QPO we measured, for the first time, the rate at which the QPO frequency changes as a function of QPO frequency. Read More

We analysed all archival data of the low-mass X-ray binary 4U 1636--53 with the Rossi X-ray Timing Explorer (1490 observations). We found a total of 336 type-I X-ray bursts from this source. In the time-resolved spectra of 69 of these bursts, close to the peak of the burst, the best-fitting blackbody radius shows the sharp increase and decrease that is typical of photospheric radius-expansion (PRE) bursts. Read More

RX J0720.4-3125 is the most peculiar object among a group of seven isolated X-ray pulsars (the so-called "Magnificent Seven"), since it shows long-term variations of its spectral and temporal properties on time scales of years. This behaviour was explained by different authors either by free precession (with a seven or fourteen years period) or possibly a glitch that occurred around $\mathrm{MJD=52866\pm73 days}$. Read More

We present the results of continued monitoring of the quiescent neutron star low-mass X-ray binary XTE J1701-462 with Chandra and Swift. A new Chandra observation from 2010 October extends our tracking of the neutron star surface temperature from ~800 days to ~1160 days since the end of an exceptionally luminous 19 month outburst. This observation indicates that the neutron star crust may still be slowly cooling toward thermal equilibrium with the core; another observation further into quiescence is needed to verify this. Read More

Time-resolved spectra during the cooling phase of thermonuclear X-ray bursts in low-mass X-ray binaries (LMXBs) can be used to measure the radii and masses of neutron stars. We analyzed ~ 300 bursts of the LMXB 4U 1636-53 using data from the Rossi X-ray Timing Explorer. We divided the bursts in three groups, photospheric radius expansion (PRE), hard non-PRE and soft non-PRE bursts, based on the properties of the bursts and the state of the source at the time of the burst. Read More

Recently, the neutron star X-ray binary EXO 0748-676 underwent a transition to quiescence. We analyzed an XMM-Newton observation of this source in quiescence, where we fitted the spectrum with two different neutron-star atmosphere models. From the fits we constrained the allowed parameter space in the mass-radius diagram for this source for an assumed range of distances to the system. Read More

We report on an analysis of RXTE data of the transient neutron star low-mass X-ray binary (NS-LMXB) XTE J1701-462, obtained during its 2006-2007 outburst. The X-ray properties of the source changed between those of various types of NS-LMXB subclasses. At high luminosities the source switched between two types of Z source behavior and at low luminosities we observed a transition from Z source to atoll source behavior. Read More

We observed the new X-ray transient and black-hole candidate XTE J1652-453 simultaneously with XMM-Newton and the Rossi X-ray Timing Explorer (RXTE). The observation was done during the decay of the 2009 outburst, when XTE J1652-453 was in the hard-intermediate state. The spectrum shows a strong and broad iron emission line with an equivalent width of ~ 450 eV. Read More

We present Rossi X-Ray Timing Explorer and Swift observations made during the final three weeks of the 2006-2007 outburst of the super-Eddington neutron star (NS) transient XTE J1701-462, as well as Chandra and XMM-Newton observations covering the first ~800 days of the subsequent quiescent phase. The source transitioned quickly from active accretion to quiescence, with the luminosity dropping by over 3 orders of magnitude in ~13 days. The spectra obtained during quiescence exhibit both a thermal component, presumed to originate in emission from the NS surface, and a non-thermal component of uncertain origin, which has shown large and irregular variability. Read More

We have discovered a triple-peaked X-ray burst from the low-mass X-ray binary (LMXB) 4U 1636-53 with the Rossi X-ray Timing Explorer (RXTE). This is the first triple-peaked burst reported from any LMXB using RXTE, and it is only the second burst of this kind observed from any source. (The previous one was also from 4U 1636-53, and was observed with EXOSAT. Read More

We analyzed simultaneous archival XMM-Newton and RXTE observations of the X-ray binary and black hole candidate Swift J1753.5-0127. In a previous analysis of the same data a soft thermal component was found in the X-ray spectrum, and the presence of an accretion disk extending close to the innermost stable circular orbit was proposed. Read More

During a 200 ks observation with the XMM-Newton Reflection Grating Spectrometer, we detected 16 type-I X-ray bursts from GS 1826-24. We combined the burst spectra in an attempt to measure the gravitational redshifts from the surface of the neutron star. We divided the composite GS 1826-24 burst spectrum into three groups based on the blackbody temperature during the bursts. Read More

Affiliations: 1SRON - Netherlands Institute for Space Research, 2INAF - Osservatorio Astronomico di Brera
Category: Astrophysics

There is a general consensus that the frequencies of the kilohertz Quasi-Periodic Oscillations (kHz QPOs) in neutron-star low-mass X-ray binaries are directly linked to the spin of the neutron star. The root of this idea is the apparent clustering of the ratio of the frequency difference of the kHz QPOs and the neutron-star spin frequency, $\Delta\nu/\nu_s$, at around 0.5 and 1 in ten systems for which these two quantities have been measured. Read More

Affiliations: 1INAF-OAB, 2MIT, 3INAF-OAB, Univ. Milano Bicocca, 4INAF-OAB, Univ. Milano Bicocca, 5SRON Utrecht, Univ. Amsterdam, Univ. Utrecht
Category: Astrophysics

We have monitored the atoll-type neutron star low-mass X-ray binary 4U 1636-53 with the Rossi X-Ray Timing Explorer (RXTE) for more than 1.5 years. Our campaign consisted of short (~2 ks) pointings separated by two days, regularly monitoring the spectral and timing properties of the source. Read More

I study the behaviour of the maximum rms fractional amplitude, $r_{\rm max}$ and the maximum coherence, $Q_{\rm max}$, of the kilohertz quasi-periodic oscillations (kHz QPOs) in a dozen low-mass X-ray binaries. I find that: (i) The maximum rms amplitudes of the lower and the upper kHz QPO, $r^{\ell}_{\rm max}$ and $r^{\rm u}_{\rm max}$, respectively, decrease more or less exponentially with increasing luminosity of the source; (ii) the maximum coherence of the lower kHz QPO, $Q^{\ell}_{\rm max}$, first increases and then decreases exponentially with luminosity; (iii) the maximum coherence of the upper kHz QPO, $Q^{\rm u}_{\rm max}$, is more or less independent of luminosity; and (iv) $r_{\rm max}$ and $Q_{\rm max}$ show the opposite behaviour with hardness of the source, consistent with the fact that there is a general anticorrelation between luminosity and spectral hardness in these sources. Both $r_{\rm max}$ and $Q_{\rm max}$ in the sample of sources, and the rms amplitude and coherence of the kHz QPOs in individual sources show a similar behaviour with hardness. Read More

(Abridged) We report on ten weeks of RXTE observations of the X-ray transient XTE J1701-462. Comparisons with other sources suggest it had all the characteristics of the neutron star Z sources (the brightest persistent neutron star LMXBs). These include Z tracks in X-ray color diagrams and typical variability components detected in the power spectra. Read More

I study the behaviour of the maximum rms fractional amplitude, $r_{\rm max}$ and the maximum coherence, $Q_{\rm max}$, of the kilohertz quasi-periodic oscillations (kHz QPOs) in a dozen low-mass X-ray binaries. I find that: (i) The maximum rms amplitudes of the lower and the upper kHz QPO, $r^{\ell}_{\rm max}$ and $r^{\rm u}_{\rm max}$, respectively, decrease more or less exponentially with increasing luminosity of the source; (ii) the maximum coherence of the lower kHz QPO, $Q^{\ell}_{\rm max}$, first increases and then decreases exponentially with luminosity, at a faster rate than both $r^{\ell}_{\rm max}$ and $r^{\rm u}_{\rm max}$; (iii) the maximum coherence of the upper kHz QPO, $Q^{\rm u}_{\rm max}$, is more or less independent of luminosity; and (iv) $r_{\rm max}$ and $Q_{\rm max}$ show the opposite behaviour with hardness of the source, consistent with the fact that there is a general anticorrelation between luminosity and spectral hardness in these sources. Both $r_{\rm max}$ and $Q_{\rm max}$ in the sample of sources, and the rms amplitude and coherence of the kHz QPOs in individual sources show a similar behaviour with hardness. Read More

Affiliations: 1INAF-OAB, Merate, Italy, 2SRON Utrecht, the Netherlands, 3MIT, Cambridge, USA
Category: Astrophysics

We analyzed all published frequencies, nu_1 and nu_2, of the twin kilohertz quasi-periodic oscillations (kHz QPOs) in bright neutron star low-mass X-ray binaries. The two frequencies are well correlated but, contrary to recent suggestions, the frequency-frequency correlation is significantly different from a nu_2 = (3/2) nu_1 relation. To check whether, although not following the the 3/2 relation, the QPO frequencies cluster around a region where nu_2/nu_1 ~ 3/2, we re-analyzed the Sco X-1 data that were used to report that ratio and show that, because the distribution of ratios of linearly correlated measurements is intrinsically biased, although the significance of the clustering around nu_2/nu_1 ~ 3/2 previously reported in the case of Sco X-1 is formally correct, it does not provide any useful information about a possible underlying resonance mechanism in this source. Read More

Affiliations: 1INAF - Oss. Astr. Brera, Italy, 2SRON, Utrecht, the Netherlands, 3MIT, USA
Category: Astrophysics

The frequencies of kHz Quasi-Periodic Oscillations in the bright Low-Mass X-ray Binary Sco X-1 have been reported to appear preferentially in a 3:2 ratio. We show that a proper statistical analysis of those RXTE data upon which the claim is based indicated a 2.4 sigma deviation from a constant distribution in ratios. Read More

Affiliations: 1SRON, Utrecht, The Netherlands, 2SRON, Utrecht, The Netherlands, 3SRON, Utrecht, The Netherlands, 4Astronomical Institute, University Utrecht
Category: Astrophysics

We observed the isolated neutron star RX J720.4-3125 with Chandra's Low Energy Transmission Grating Spectrometer, following the XMM-Newton discovery of long term spectral evolution of this source. The new observation shows that the spectrum of RX J720. Read More

We detect a gradual, long-term change in the shape of the X-ray spectrum of the isolated neutron star RX J0720.4-3125, such that the spectrum of the source can no longer be described as a blackbody spectrum. The change is accompanied by an energy-dependent change in the pulse profile. Read More

Affiliations: 1INAF - Osservatorio Astronomico di Brera, Merate, Italy, 2INAF - Osservatorio Astronomico di Brera, Merate, Italy, 3INAF - Osservatorio Astronomico di Brera, Merate, Italy, 4CfA, Cambridge, USA, 5MIT, Cambridge, USA, 6SRON, Utrecht, the Netherlands, 7Univ. of Amsterdam, Amsterdam, the Netherlands
Category: Astrophysics

We report the results of an observation with the Rossi X-ray Timing Explorer of the black hole candidate GX 339-4 during its 2002/2003 outburst. This observation took place during a spectral transition from the hard to the soft state. A strong (6% rms) transient quasi-periodic oscillation (QPO) appears suddenly in the power density spectrum during this observation. Read More

Affiliations: 1Univ. Amsterdam, 2Univ. Amsterdam, 3SRON
Category: Astrophysics

We have studied the atoll source 4U 1608-52 using a large data set obtained with the Rossi X-ray Timing Explorer. We find that the timing properties of 4U 1608-52 are almost exactly identical to those of the atoll sources 4U 0614+09 and 4U 1728-34 despite the fact that contrary to these sources 4U 1608-52 is a transient covering two orders of magnitude in luminosity. The frequencies of the variability components of these three sources follow a universal scheme when plotted versus the frequency of the upper kilohertz QPO, suggesting a very similar accretion flow configuration. Read More

There exists a group of persistently faint galactic X-ray sources that, based on their location in the galaxy, high L_x/L_opt, association with X-ray bursts, and absence of low frequency X-ray pulsations, are thought to be low-mass X-ray binaries (LMXBs). We present results from Chandra observations for eight of these systems: 4U 1708-408, 2S 1711-339, KS 1739-304, SLX 1735-269, GRS 1736-297, SLX 1746-331, 1E 1746.7-3224, and 4U 1812-12. Read More

Powerful relativistic jets are among the most ubiquitous and energetic observational consequences of accretion around supermassive black holes in active galactic nuclei and neutron stars and stellar-mass black holes in x-ray binary (XRB) systems. But despite more than three decades of study, the structure and composition of these jets remain unknown. Here we present spatially resolved x-ray spectroscopy of arc second-scale x-ray jets from the XRB SS 433 analized with the Chandra advanced charge-coupled device imaging spectrometer. Read More

Contrary to theoretical expectations, observations with the Rossi X-ray Timing Explorer (RXTE) show that in X-ray binaries timing properties are not uniquely correlated with X-ray luminosity. For instance, although the frequencies of the kilohertz quasi-periodic oscillations (kHz QPOs) correlate with X-ray flux on short (~few hours) time scales, on time scales longer than a day the QPO appears at more or less the same frequency, whereas the luminosity may be a factor of a few different. The result is a set of almost parallel tracks in a QPO frequency vs. Read More

In the past five years observations with the Rossi X-ray Timing Explorer have revealed fast quasi-periodic oscillations in the X-ray flux of about 20 X-ray binaries. Thought to originate close to the surface of a neutron star, these oscillations provide unique information about the strong gravitational field in which they are produced. Read More

Affiliations: 1SRON, 2SRON
Category: Astrophysics

XEUS, the X-ray Evolving Universe Spectroscopy mission, is at present an ESA-ISAS initiative for the study of the evolution of the hot Universe in the post-Chandra/XMM-Newton era. The key science objectives of XEUS are: Search for the origin, and subsequent study of growth, of the first massive black holes in the early Universe; assessment of the formation of the first gravitationally bound dark matter dominated systems and their evolution; study of the evolution of metal synthesis up till the present epoch; characterization of the true intergalactic medium. To reach these ambitious science goals the two salient characteristics of the XEUS observatory entail: (1) Its effective spectroscopic grasp, combining a sensitive area > 20 m^2 below 2 keV with a spectral resolution better than 2 eV. Read More