Browsing by Author "Wilms, J."
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Item A 0535+26 in the August/September 2005 outburst observed by RXTE and INTEGRAL(EDP Sciences, 2007-02-20) Caballero, I.; Kretschmar, P.; Santangelo, A.; Staubert, R.; Klochkov, D.; Camero, A.; Ferrigno, C.; Finger, M. H.; Kreykenbohm, I.; McBride, V. A.; Pottschmidt, Katja; Rothschild, R. E.; Schönherr, G.; Segreto, A.; Suchy, S.; Wilms, J.; Wilson, C. A.Aims. In this Letter we present results from INTEGRAL and RXTE observations of the spectral and timing behavior of the High Mass X-ray Binary A 0535+26 during its August/September 2005 normal (type I) outburst with an average flux F₍₅₋₁₀₀₎ ₖₑᵥ ~ 400 mCrab. The search for cyclotron resonance scattering features (fundamental and harmonic) is one major focus of the paper. Methods. Our analysis is based on data from INTEGRAL and RXTE Target of Opportunity Observations performed during the outburst. The pulse period is determined. X-ray pulse profiles in different energy ranges are analyzed. The broad band INTEGRAL and RXTE pulse phase averaged X-ray spectra are studied. The evolution of the fundamental cyclotron line at different luminosities is analyzed. Results.The pulse period P is measured to be 103.39315(5) s at MJD 53614.5137. Two absorption features are detected in the phase averaged spectra at E₁ ~ 45 keV and E₂ ~ 100 keV. These can be interpreted as the fundamental cyclotron resonance scattering feature and its first harmonic and therefore the magnetic field can be estimated to be B ~4 × 10¹² G.Item 3A 0535+262 in outburst(2005-11-21) Kretschmar, P.; Pottschmidt, Katja; Ferrigno, C.; Kreykenbohm, I.; Domingo, A.; Wilms, J.; Rothschild, R.; Coburn, W.; Kendziorra, E.; Staubert, R.; Schönherr, G.; Santangelo, A.; Segreto, A.The Be/X-ray binary 3A 0535+262 has the highest magnetic field determined by cyclotron line studies of all accreting X-ray pulsars, despite an open debate if the fundamental line was rather at ~50 or above 100 keV as observed by different instruments in past outbursts. The source went into quiescence for more than ten years since its last outbursts in 1994. Observing during a 'normal' outburst August/September 2005 with Integral and RXTE we find a strong cyclotron line feature at ~45 keV and have for the first time since 1975 determined the low energy pulse profile.Item 4U 0115+63: A Bonanza of Cyclotron Resonance Scattering Features(2011) Muller, S.; Kuhnel, M.; Ferrigno, C.; Kreykenbohm, I.; Furst, F.; Klochkov, D.; Obst, M.; Pottschmidt, Katja; Suchy, S.; Rothschild, R.; Caballero, I.; Kretschmar, P.; Schonherr, G.; Wilms, J.; Santangelo, A.; Staubert, R.We report on an outburst of the high mass X-ray binary 4U 0115+634 with a pulse period of 3.6 s in 2008 as observed with INTEGRAL and RXTE. By analysing the lightcurves we derived an updated orbital period of the binary system. We also studied the pulse profile variations as a function of time and energy. We find evidence for phase lags at ∼11 and ∼22 keV. In our spectral analysis we found clear evidence for at least two cyclotron features. The continuum can be described by two different models, which lead to a fundamental difference in the behavior of the cyclotron features. We discuss possible reasons for this disagreement.Item 4U 1630-47 still in outburst: Potential hard X-ray flaring recently detected by INTEGRAL and Swift/BAT(The Astronomer's Telegram, 2023-03-02) Bouchet, T.; Rodriguez, J.; Wilms, J.; Pottschmidt, Katja; Cangemi, F.; Grinberg, V.; Laurent, P.; Thalhammer, P.Item 4U 1909+07: A HIDDEN PEARL(EDP Science, 2011-01-01) Fürst, F.; Kreykenbohm, I.; Suchy, S.; Barragán, L.; Wilms, J.; Rothschild, R. E.; Pottschmidt, KatjaWe present a detailed spectral and timing analysis of the High Mass X-ray Binary (HMXB) 4U1909+07 with INTEGRAL and RXTE. 4U1909+07 is a persistent accreting X-ray pulsar with a period of approximately 605s. The period changes erratically consistent with a random walk expected for a wind accreting system. INTEGRAL detects the source with an average of 2.4cps (corresponding to 15mCrab), but sometimes exhibits flaring activity up to 50cps (i.e. 300mCrab).The strongly energy dependent pulse profile shows a double peaked structure at low energies and only a single narrow peak at energies above 20keV. The phase averaged spectrum is well described by a power law modified at higher energies by an exponential cutoff and photoelectric absorption at low energies. In addition at 6.4keV a strong iron fluorescence line and at lower energies a blackbody component are present. We performed phase resolved spectroscopy to study the pulse phase dependence of the spectral parameters: while most spectral parameters are constant within uncertainties, the blackbody normalization and the cutoff folding energy vary strongly with phase.Item 4U 1909+07: a well-hidden pearl (Conf. Proc.)(2010-10-28) Fürst, F.; Kreykenbohm, I.; Barragán, L.; Wilms, J.; Rothschild, R. E.; Suchy, S.; Pottschmidt, KatjaWe present the first detailed spectral and timing analysis of the High Mass X-ray Binary (HMXB) 4U 1909+07 with INTEGRAL and RXTE. 4U 1909+07 is detected with an average of 2.4 cps in ISGRI, but shows flares up to ∼50 cps. The system shows a pulse period of 605 s, but we found that the period changes erratically around this value. The pulse profile is extremely energy dependent: while it shows a double peaked structure at low energies, the secondary pulse decreases rapidly with increasing energy and above 20 keV only the primary pulse is visible. This evolution is consistent between PCA, HEXTE and ISGRI. We find that the phase averaged spectrum can be well fitted with a photoabsorbed power law with a cutoff at high energies and a blackbody component. To investigate the peculiar pulse profile, we performed phase resolved spectral analysis. We find that a change in the cutoff energy is required to fit the changing spectrum of the different pulse phases.Item 4U 1909+07: a well-hidden pearl(EDP Sciences, 2010-12-02) Fürst, F.; Kreykenbohm, I.; Suchy, S.; Barragán, L.; Wilms, J.; Rothschild, R. E.; Pottschmidt, KatjaWe present the first detailed spectral and timing analysis of the high mass X-ray binary (HMXB) 4U 1909+07 with INTEGRAL and RXTE. 4U 1909+07 is detected in the ISGRI 20–40 keV energy band with an average countrate of 2.6 cts s⁻¹. The pulse period of ~604 s is not stable, but changing erratically on timescales of years. The pulse profile is strongly energy dependent: it shows a double peaked structure at low energies, the secondary pulse decreases rapidly with increasing energy and above 20 keV only the primary pulse is visible. This evolution is consistent between PCA, HEXTE, and ISGRI. The phase averaged spectrum can be well described by the sum of a photoabsorbed power law with a cutoff at high energies and a blackbody component. To investigate the pulse profile, we performed phase resolved spectral analysis. We find that the changing spectrum can be best described with a variation of the folding energy. We rule out a correlation between the black body component and the continuum variation and discuss possible accretion geometries.Item Accreting on the edge: a luminosity-dependent cyclotron line in the Be/X-ray Binary 2S 1553-542 accompanied by accretion regimes transition(AAS, 2022-03-15) Malacaria, C.; Bhargava, Y.; Coley, Joel B.; Ducci, L.; Pradhan, P.; Ballhausen, R.; Fuerst, F.; Islam, N.; Jaisawal, G. K.; Jenke, P.; Kretschmar, P.; Kreykenbohm, I.; Pottschmidt, Katja; Sokolova-Lapa, E.; Staubert, R.; Wilms, J.; Wilson-Hodge, C.A.; Wolff, Michael T.Accreting X-ray pulsars (XRPs) undergo luminous X-ray outbursts during which the luminosity-dependent spectral and timing features of the neutron star's emission can be analyzed in detail, thus shedding light on the accretion regime at work. We took advantage of a monitoring campaign performed with NuSTAR, Swift/XRT, AstroSat and NICER, to follow the Be/X-ray Binary 2S 1553-542 along one of its rare outbursts and trace its spectral and timing evolution. We report the discovery of a luminosity-dependent cyclotron line energy for the first time in this source. The pulse profiles and pulsed fraction also show variability along the outburst, consistently with the interpretation that the source transitions from the sub-critical to the super-critical accretion regime, separated by a critical luminosity of Lᴄᵣᵢₜ≈ 4×10³⁷ erg/s.Item The Accreting Pulsar XTE J1946+274: Further Indication for a Cyclotron Line from Suzaku?(2013-04-11) Marcu, D.M.; Pottschmidt, Katja; Müller, S.; Kühnel, M.; Caballero, I.; Fürst, F.; Mahmoud, A.; Kreykenbohm, I.; Klochkov, D.; Rothschild, R. E.; Terada, Y.; Enoto, T.; Iwakiri, W.; Nakajima, M.; Wilms, J.We present a timing and spectral analysis of the X-ray pulsar XTE J1946+274 observed with Suzaku towards the end of a weak outburst in 2010 October and compare it with previous results. XTE J1946+274 is an X-ray transient with a Be-type companion and a neutron star with a ∼15.8 s pulse period. For this analysis we used both XIS(0,1,3) and PIN data. From the latter we confirm the previously determined pulse period and create pulse profiles for several energy bands. Despite a difference in the 20-60 keV flux of more than about one order of magnitude, we observe a comparatively good match between the pulse profiles for Suzaku and RXTE/PCA, the latter obtained during a different, brighter outburst in 2010, for the 20-40 keV energy range (while small differences are present in the 10-20 keV range). The X-ray spectrum can be well described by a Fermi-Dirac cutoff power law model along with a narrow Fe Kα fluorescence line at 6.4 keV. The strength of the Fe line is consistent with the continuum vs. line flux correlation observed in different outbursts of the source. We also investigate the possible presence of a Cyclotron Resonance Scattering Feature (CRSF) at 35 keV, which was detected in data from a previous outburst in 1998, and find marginal evidence for it in the Suzaku data. From an earlier analysis of the brighter 2010 outburst, a possible CRSF residual at 25 keV was reported, which is not visible in the Suzaku data.Item Addition to ATel #2306, "Light curve oscillations and flux decline in the Be/X-ray binary Swift J1626.6-5156"(The Astronomer's Telegram, 2009-04-29) DeCesar, M. E.; Pottschmidt, Katja; Belloni, T.; Reig, P.; Wilms, J.Item The Be X-ray Binary Outburst Zoo II(Proceedings of Science, 2015-03-16) Kühnel, M.; Kretschmar, P.; Nespoli, E.; Okazaki, A.; Schoenherr, G.; Wilson-Hodge, C.; Falkner, S.; Brand, T.; Anders, F.; Schwarm, F.; Kreykenbohm, I.; Mueller, S.; Pottschmidt, Katja; Fuerst, F.; Grinberg, V.; Wilms, J.We have continued our recently started systematic study of Be X-ray binary (BeXRB) outbursts. Specifically, we are developing a catalogue of outbursts including their basic properties based on nearly all available X-ray all-sky-monitors. These properties are derived by fitting asymmetric Gaussians to the outburst lightcurves. This model describes most of the outbursts covered by our preliminary catalogue well; only 13% of all datasets show more complex outburst shapes. Analyzing the basic properties, we reveal a strong correlation between the outburst length and the reached peak flux. As an example, we discuss possible models describing the observed correlation in EXO 2030+375Item Be-Phenomenon in Neutron Star X-ray Binaries(Astronomical Society of the Pacific, 2017) Kühnel, M.; Kretschmar, P.; Fürst, F.; Pottschmidt, Katja; Hemphill, P.; Rothschild, R. E.; Okazaki, A. T.; Sagredo, M.; Wilms, J.In this work we provide a brief insight into two aspects of Be/X-ray binaries, which are probably involved in production of X-ray outbursts: the evolution of the Be star disk, in particular of its size, and the binary geometry which drives gravitational interaction. Simultaneous X-ray and optical data will aid our investigation of the evolution of Be stars in binaries and the X-ray outburst mechanism.Item Brightening of MAXI J0903-531 Seen with Fermi GBM and Swift BAT, and a Candidate Orbital Period(The Astronomer's Telegram, 2021-06-21) Corbet, Robin; Jenke, P.; Ballhausen, R.; Becker, P. A.; Coley, J. B.; Fuerst, F.; Islam, Nazma; Jaisawal, G. K.; Kretschmar, P.; Malacaria, C.; Pottschmidt, Katja; Rothschild, R. E.; Thalhammer, P.; Wilms, J.; Wilson-Hodge, C. A.; Wolff, M. T.Item Broad band energy spectrum and a low frequency QPO from H1743-322 in the hard state revealed by INTEGRAL and Swift observations(The Astronomer's Telegram, 2011-04-13) Rodriguez, J.; Bel, M. Cadolle; Tomsick, J. A.; Hannikainen, D.; Pottschmidt, Katja; Kuulkers, E.; Corbel, S.; Coriat, M.; Goldwurm, A.; Russell, D. M.; Wilms, J.Item The Broad Band Spectrum of CYG X-1(2006) Fritz, S.; Wilms, J.; Pottschmidt, Katja; Nowak, M. A.; Kreykenbohm, I.; Santangelo, A.Item The broad iron Kα line of Cygnus X-1 as seen by XMM-Newton in the EPIC-pn modified timing mode(EDP Sciences, 2011-08-19) Duro, R.; Dauser, T.; Wilms, J.; Pottschmidt, Katja; Nowak, M. A.; Fritz, S.; Kendziorra, E.; Kirsch, M. G. F.; Reynolds, C. S.; Staubert, R.We present the analysis of the broadened, flourescent iron Kα line in simultaneous XMM-Newton and RXTE data from the black hole Cygnus X-1. The XMM-Newton data were taken in a modified version of the timing mode of the EPIC-pn camera. In this mode the lower energy threshold of the instrument is increased to 2.8 keV to avoid telemetry drop outs due to the brightness of the source, while at the same time preserving the signal-to-noise ratio in the Fe Kα band. We find that the best-fit spectrum consists of the sum of an exponentially cutoff power-law and relativistically smeared, ionized reflection. The shape of the broadened Fe Kα feature is due to strong Compton broadening combined with relativistic broadening. Assuming a standard, thin accretion disk, the black hole is close to rotating maximally.Item The broadband spectrum of Cygnus X-1(2007-06-14) Fritz, S.; Wilms, J.; Pottschmidt, Katja; Nowak, M. A.; Kendziorra, E.; Kirsch, M. G.; Kreykenbohm, I.; Santangelo, A.The Black Hole (BH) binary Cygnus X-1 has been observed simultaneously by INTEGRAL, RXTE, and XMM-Newton for four times in November and December 2004, when Cyg X-1 became first observable with XMM-Newton. During these observations the source was found in one of its transitional states between the hard state and the soft state. We obtained a high signal to noise spectrum of Cyg X-1 from 3 keV to 1 MeV which allows us to put constraints on the nature of the Comptonizing plasma by modeling the continuum with Comptonization models as eqpair (Coppi 1992). Using XMM-Newton we were also able to confirm the presence of a relativistically broadened Fe K-alpha line.Item The causal connection between disc and power-law variability in hard state black hole X-ray binaries(Oxford University Press, 2011-06-11) Uttley, P.; Wilkinson, T.; Cassatella, P.; Wilms, J.; Pottschmidt, Katja; Hanke, M.; Böck, M.We use the XMM-Newton EPIC-pn instrument in timing mode to extend spectral time-lag studies of hard state black hole X-ray binaries into the soft X-ray band. We show that variations of the disc blackbody emission substantially lead variations in the power-law emission, by tenths of a second on variability time-scales of seconds or longer. The large lags cannot be explained by Compton scattering but are consistent with time delays due to viscous propagation of mass accretion fluctuations in the disc. However, on time-scales less than a second the disc lags the power-law variations by a few milliseconds, consistent with the disc variations being dominated by X-ray heating by the power law, with the short lag corresponding to the light traveltime between the power-law emitting region and the disc. Our results indicate that instabilities in the accretion disc are responsible for continuum variability on time-scales of seconds or longer and probably also on shorter time-scales.Item The clumpy absorber in the high-mass X-ray binary Vela X-1(EDP Sciences, 2017-12-15) Grinberg, V.; Hell, N.; Mellah, I. El; Neilsen, J.; Sander, A. A. C.; Leutenegger, Maurice; Fürst, F.; Huenemoerder, D. P.; Kretschmar, P.; Kühnel, M.; Martínez-Núñez, S.; Niu, S.; Pottschmidt, Katja; Schulz, N. S.; Wilms, J.; Nowak, M. A.Bright and eclipsing, the high-mass X-ray binary Vela X-1 offers a unique opportunity to study accretion onto a neutron star from clumpy winds of O/B stars and to disentangle the complex accretion geometry of these systems. In Chandra-HETGS spectroscopy at orbital phase ~0.25, when our line of sight towards the source does not pass through the large-scale accretion structure such as the accretion wake, we observe changes in overall spectral shape on timescales of a few kiloseconds. This spectral variability is, at least in part, caused by changes in overall absorption and we show that such strongly variable absorption cannot be caused by unperturbed clumpy winds of O/B stars. We detect line features from high and low ionization species of silicon, magnesium, and neon whose strengths and presence depend on the overall level of absorption. These features imply a co-existence of cool and hot gas phases in the system, which we interpret as a highly variable, structured accretion flow close to the compact object such as has been recently seen in simulations of wind accretion in high-mass X-ray binaries.Item Confirming the thermal Comptonization model for black hole X-ray emission in the low-hard state(EDP Sciences, 2014-09-29) Castro, M.; D’Amico, F.; Braga, J.; Maiolino, T.; Pottschmidt, Katja; Wilms, J.Hard X-ray spectra of black hole binaries in the low/hard state are well modeled by thermal Comptonization of soft seed photons by a corona-type region with kT ~ 50 keV and optical depth around 1. Previous spectral studies of 1E 1740.7−2942, including both the soft and the hard X-ray bands, were always limited by gaps in the spectra or by a combination of observations with imaging and non-imaging instruments. In this study, we have used three rare nearly-simultaneous observations of 1E 1740.7−1942 by both XMM-Newton and INTEGRAL satellites to combine spectra from four different imaging instruments with no data gaps, and we successfully applied the Comptonization scenario to explain the broadband X-ray spectra of this source in the low/hard state. For two of the three observations, our analysis also shows that, models including Compton reflection can adequately fit the data, in agreement with previous reports. We show that the observations can also be modeled by a more detailed Comptonization scheme. Furthermore, we find the presence of an iron K-edge absorption feature in one occasion, which confirms what had been previously observed by Suzaku. Our broadband analysis of this limited sample shows a rich spectral variability in 1E 1740.7−2942 at the low/hard state, and we address the possible causes of these variations. More simultaneous soft/hard X-ray observations of this system and other black-hole binaries would be very helpful in constraining the Comptonization scenario and shedding more light on the physics of these systems.