Browsing by Author "Rothschild, R.E."
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Item The cyclotron line energy in Her X-1: stable after the decay(2020-08-17) Staubert, R.; Ducci, L.; Ji, L.; Fürst, F.; Wilms, J.; Rothschild, R.E.; Pottschmid, K.; Brumback, M.; Harrison, F.We summarize the results of a dedicated effort between 2012 and 2019 to follow the evolution of the cyclotron line in Her~X-1 through repeated NuSTAR observations. The previously observed nearly 20-year long decay of the cyclotron line energy has ended around 2012: from there onward the pulse phase averaged flux corrected cyclotron line energy has remained stable and constant at an average value of Ecyc= (37.44+/-0.07) keV (normalized to a flux level of 6.8 RXTE/ASM-cts/s). The flux dependence of Ecyc discovered in 2007 is now measured with high precision, giving a slope of (0.675+/-0.075) keV/(ASM-cts/s), corresponding to an increase of 6.5% of Ecyc for an increase in flux by a factor of two. We also find that all line parameters as well as the continuum parameters show a correlation with X-ray flux. While a correlation between Ecyc and X-ray flux (both positive and negative) is now known for several accreting binaries with various suggestions for the underlying physics, the phenomenon of a long-term decay has so far only been seen in Her~X-1 and Vela~X-1, with far less convincing explanations.Item Cyclotron line energy in Hercules X-1: stable after the decay(EDP sciences, 2020-10-20) Staubert, R.; Ducci, L.; Ji, L.; Fürst, F.; Wilms, J.; Rothschild, R.E.; Pottschmidt, K.; Brumback, M.; Harrison, F.We summarize the results of a dedicated effort made between 2012 and 2019 to follow the evolution of the cyclotron line in Her X-1 through repeated NuSTAR observations. The previously observed nearly 20-year-long decay of the cyclotron line energy has ended in 2012: from then on, the pulse-phase-averaged flux-corrected cyclotron line energy has remained stable and constant at an average value of Ecyc = (37.44 ± 0.07) keV (normalized to a flux level of 6.8 RXTE/ASM-cts/s). The flux dependence on Ecyc discovered in 2007 is now measured with high precision, giving a slope of (0.675 ± 0.075) keV/(ASM-cts/s), corresponding to an increase of 6.5% of Ecyc for an increase in flux by a factor of two. We also find that all line parameters as well as the continuum parameters show a correlation with X-ray flux. While a correlation between Ecyc and X-ray flux (both positive and negative) is now known for several accreting binaries with various suggestions for the underlying physics, the phenomenon of a long-term decay has so far only been seen in Her X-1 and Vela X-1, with far less convincing explanations.Item Cygnus X-1: shedding light on the spectral variability of a black hole(Proceedings of Science, 2013-07-18) Grinberg, V.; Hell, N.; Wilms, J.; Rodriguez, J.; Pottschmidt, Katja; Nowak, M.A.; Böck, M.; Bodaghee, A.; Bel, M. Cadolle; Fürst, F.; Hanke, M.; Kühnel, M.; Laurent, P.; Markoff, S.B.; Markowitz, A.; Marcu, D.M.; Pooley, G.G.; Popp, A.; Rothschild, R.E.; Tomsick, J.A.The knowledge of the spectral state of a black hole is essential for the interpretation of data from black holes in terms of their emission models. Based on pointed observations of Cyg X-1 with the Rossi X-ray timing Explorer (RXTE) that are used to classify simultaneous RXTE-ASM observations, we develop a scheme based on RXTE-ASM colors and count rates that can be used to classify all observations of this canonical black hole that were performed between 1996 and 2011. We show that a simple count rate criterion, as used previously, leads to a significantly higher fraction of misclassified observations. This scheme enables us to classify single INTEGRALIBIS science windows and to obtain summed spectra for the soft, intermediate and hard state with low contamination by other states.Item Discovery of a 65 Hz QPO and possible inner radius retreat in XTE J1550–564 during outburst decay(2002-02-25) Kalemci, E.; Tomsick, J.A.; Rothschild, R.E.; Pottschmidt, Katja; Kaaret, P.Item The magnetic field of neutron stars: What cyclotron lines can tell us(2009-09) Schönherr, Gabriele; Wilms, J.; Kreykenbohm, I.; Kretschmar, P.; Rothschild, R.E.; Suchy, S.; Pottschmidt, Katja; McBride, V.; Caballero, I.; Ferrigno, C.; Klochkov, D.; Santangelo, A.; Staubert, R.Item Measuring strong magnetic fields of neutron stars with the next-generation of X-ray instruments(Proceedings of Science, 2011-12-30) Schönherr, G.; Kretschmar, P.; Wilms, J.; Kreykenbohm, I.; Schwarm, F.; Pottschmidt, Katja; Rothschild, R.E.To date, the only direct method to assess the strong magnetic fields of High-Mass X-ray Binaries containing accreting neutron stars is the observation and analysis of electron cyclotron resonance features (short: "cyclotron lines" or CRSFs) in their high-energy X-ray spectra. We dicuss how the upcoming era of new observatories and instrumentation like IXO will change our "magnetic" view of those objects. The science case for IXO in this respect does not focus on the measurement of the cyclotron lines themselves (which are typically at 10–100 keV) but on obtaining new constraints on the accreting sources’ geometries and physical parameters as key ingredients to disentangle their influences and understand the overall timing and spectral properties of neutron star highmass X-ray binaries.Item Orbital Parameters and phase resolved Spectroscopy of 4U 0115+634(Proceedings of Science, 2011-11-16) Mueller, S.; Obst, M.; Kreykenbohm, I.; Fuerst, F.; Kühnel, M.; Wilms, J.; Klochkov, D.; Staubert, R.; Santangelo, A.; Pottschmidt, Katja; Suchy, S.; Rothschild, R.E.; Caballero, I.; Kretschmar, P.; Schoenherr, G.We report on an outburst of the high mass X-ray binary 4U 0115+63 with a pulse period of 3.6 s in spring 2008 as observed with INTEGRAL and RXTE. By analyzing the lightcurves we derive an updated orbital- and pulse period ephemeris of the neutron star. We also study the pulse profile variations as a function of time and energy as well as the variability of the spectral parameters. We find clear evidence for at least three cyclotron line features. In agreement with previous observations of 4U 0115+63, we detect an anti-correlation between the luminosity and the fundamental cyclotron line energy.Item RXTE Studies of Cyclotron Lines in Accreting Pulsars(AIP, 2000-04-12) Heindl, W.A.; Coburn, W.; Gruber, D.E.; Pelling, M.; Rothschild, R.E.; Kretschmar, P.; Kreykenbohm, I.; Wilms, J.; Pottschmidt, Katja; Staubert, R.In this paper, we summarize the RXTE measurements of cyclotron resonance scattering features in 8 accreting pulsars. The wide bandpass and modest resolution of the RXTE instruments make them ideal for measuring these generally broad features. In particular, the high energy response of HEXTE provides a window for discovery of new lines not detectable with proportional counters such as Ginga or the PCA alone.