arXiv subjects

K. Pottschmidt

Publications and source records attributed to K. Pottschmidt.

At least 109 records · Page 6Linked to original sources

arXiv2005

3A 0535+262 in outburst

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.

astro-ph↗

arXiv2005

Observation of V0332+53 over the 2004/2005 outburst with Integral

We present the spectral and temporal analysis of the 2004/2005 outburst of the transient X-ray pulsar V0332+53 as observed with Integral. After the discovery of the third cyclotron line in phase averaged spectra (Kreykenbohm et al 2005, Pottschmidt et al 2005), detailed pulse phase spectroscopy revealed remarkably little variability of the cyclotron lines through the 4.4s X-ray pulse (Pottschmidt et al 2005). During the decline of the outburst, the flux was observed to decay exponentially until 2005 Feb 10 and linearly thereafter. The spectrum was found to become harder with time, while the folding energy remained constant. The energy of the fundamental cyclotron line increased with time from 26.5kev in the RXTE observation up to 29.5kev in the last Integral one indicating that the emission region is moving closer to the surface of the neutron star. For a detailed analysis, see Mowlavi et al (2005).

astro-ph↗

arXiv2005

RXTE Discovery of Multiple Cyclotron Lines during the 2004 December Outburst of V0332+53

We present an analysis of the 2-150 keV spectrum of the transient X-ray pulsar V0332+53 taken with the Rossi X-Ray Timing Explorer (RXTE) in 2004 December. We report on the detection of three cyclotron resonance features at 27, 51, and 74 keV in the phase-averaged data, corresponding to a polar magnetic field of 2.7 x 10^12 G. After 4U0115+63, this makes V0332+53 the second accreting neutron star in which more than two cyclotron lines have been detected; this has now also been confirmed by INTEGRAL. Pulse-phase spectroscopy reveals remarkably little variability of the cyclotron line through the 4.4 s X-ray pulse.

astro-ph↗

arXiv2005

Long Term Variability of Cygnus X-1. IV. Spectral Evolution 1999-2004

(abbreviated abstract) We present the long term spectral evolution of the Galactic black hole candidate Cygnus X-1 in the X-rays and at 15GHz using ~200 pointed observations taken between early 1999 and late 2004 with RXTE and the Ryle radio telescope. The X-ray spectra are remarkably well described by a simple broken power law spectrum with an exponential cutoff. Physically motivated Comptonization models, e.g., compTT or eqpair, can reproduce this simplicity. Broken power law models reveal a significant linear correlation between the photon index of the lower energy power law and the hardening of the power law at approximately 10keV. Comptonization models show that the bolometric flux of a soft excess (e.g., disk component) is strongly correlated with the compactness ratio of the Comptonizing medium. We also find that the fraction of the time spent in low radio emission/soft X-ray spectral states has increased from ~10% in 1996-2000 to ~34% since early 2000. Radio flares typically occur during state transitions and failed state transitions. There is also a strong correlation between the 10-50keV X-ray flux and the radio luminosity of the source. We demonstrate that rather than there being distinctly separated states, in contrast to the timing properties the spectrum of Cyg X-1 shows variations between extremes of properties, with clear cut examples of spectra at every intermediate point in the observed spectral correlations.

astro-ph↗

arXiv2005

INTEGRAL & RXTE Power Spectra of Cygnus X-1

We evaluate 0.03-20 Hz power spectra of the bright black hole binary Cyg X-1 obtained from non-deconvolved INTEGRAL-ISGRI event data. The ISGRI power spectra are compared to contemporary RXTE-PCA ones in the same hard X-ray energy band of 15-70 keV. They agree well in shape. Since the ISGRI power spectrum of Cyg X-1 is not background corrected it lies about an order of magnitude below the PCA values. In 2003 a soft outburst of Cyg X-1 occurred. From the RXTE-ASM and Ryle radio long term lightcurves and the RXTE spectra we see a canonical ``hard state -- intermediate state -- soft state'' evolution. We discuss the evolution of the power spectra in the 15-70 keV range which so far is much less well studied than that at softer energies. We interpret our results regarding the origin of certain variability components.

astro-ph↗

arXiv2004

Multi-wavelength observations of the Galactic black hole transient 4U1543-47 during outburst decay: state transitions and jet contribution

Multiwavelength observations of Galactic black hole (GBH) transients during the state transitions and in the low/hard state may provide detailed information on the accretion structure of these systems. 4U1543-47 is a GBH transient that was covered exceptionally well in X-ray and infrared (daily observations) and reasonably well in optical and radio during its outburst decay in 2002. When all the available information is gathered in the intermediate and the low/hard state, 4U1543-47 makes an important contribution to our understanding of state transitions and the role of outflows on the high energy emission properties of black hole binaries. The evolution of the X-ray spectral and temporal properties and the IR light curve place strong constraints on different models for explaining the overall emission from accreting black holes. The overall spectral energy distribution is consistent with synchrotron origin for the optical and infrared emission, however, the X-ray flux is above the power-law continuation of the optical and infrared flux. The infrared light curve, the HEXTE light curve and the evolution of the X-ray photon index indicate that the major source of hard X-rays cannot be direct synchrotron radiation from an acceleration region in a jet for most of the outburst decay.

astro-ph↗

arXiv2004

Multifrequency Observations of the Gamma-Ray Blazar 3C 279 in Low-State during Integral AO-1

We report first results of a multifrequency campaign from radio to hard X-ray energies of the prominent gamma-ray blazar 3C 279 during the first year of the INTEGRAL mission. The variable blazar was found at a low activity level, but was detected by all participating instruments. Subsequently a multifrequency spectrum could be compiled. The individual measurements as well as the compiled multifrequency spectrum are presented. In addition, this 2003 broadband spectrum is compared to one measured in 1999 during a high activity period of 3C 279.

astro-ph↗

arXiv2004

Long term variability of Cygnus X-1, III. Radio-X-ray correlations

Long time scale radio-X-ray correlations in black holes during the hard state have been found in many sources and there seems to emerge a universal underlying relationship which quantitatively describes this behavior. Although it would appear only natural to detect short term emission patterns in the X-ray and - with a certain time lag - in the radio, there has been little evidence for this up to now. The most prominent source for radio-X-ray correlations on short time scales (minutes) so far remains GRS 1915+105 where a single mass ejection could be detected successively in the X-ray, IR, and radio wavebands. We analyze a database of more than 4 years of simultaneous radio-X-ray data for Cygnus X-1 from the Ryle Telescope and RXTE PCA/HEXTE. We confirm the existence of a radio-X-ray correlation on long time scales, especially at hard energies. We show that apparent correlations on short time scales in the lightcurves of Cygnus X-1 are most likely the coincidental outcome of white noise statistics. Interpreting this result as a breakdown of radio-X-ray correlations on shorter time scales, this sets a limit to the speed of the jet.

astro-ph↗

arXiv2004

GX 301-2 as seen by Integral

We present observations of the High Mass X-ray Binary GX 301-2 taken during the Galactic Plane Scan (GPS) with Integral following our RXTE observations (Kreykenbohm et al. 2004). The optical companion of GX 301-2 is the B1Ia+ hypergiant Wray 977 with a luminosity of 1.3 x 10^6 Lsun and a mass of ~48 Msun making the system one of the most massive X-ray binaries known. The system was observed 24 times during the GPS thus covering many orbital phases including the pre-periastron flare. The source is clearly detected in all Integral instruments in most pointings. The derived X-ray light curves show strong variability on all timescales. Depending on the orbital phase of the pointings, the luminosity changes by factor of more than 10 during the pre-periastron flare compared to other pointings. Furthermore, broad band spectra using all instruments available on Integral are compared with data taken by the RXTE instruments PCA and HEXTE (using the same data as in Kreykenbohm et al. 2004).

astro-ph↗

arXiv2004

INTEGRAL broadband spectroscopy of Vela X-1

The wind-accreting X-ray binary pulsar and cyclotron line source Vela X-1 has been observed extensively during INTEGRAL Core Program observations of the Vela region in June-July and November-December 2003. In the latter set of observations the source showed intense flaring -- see also Staubert et al. (2004), these proceedings. We present early results on time averaged and time resolved spectra, of both epochs of observations. A cyclotron line feature at ~53 keV is clearly detected in the INTEGRAL spectra and its broad shape is resolved in SPI spectra. The remaining issues in the calibration of the instruments do not allow to resolve the question of the disputed line feature at 20-25 keV. During the first main flare the average luminosity increases by a factor of \~10, but the spectral shape remains very similar, except for a moderate softening.

astro-ph↗

arXiv2004

Scientific Performance of the ISDC Quick Look Analysis

The INTEGRAL Science Data Centre (ISDC) routinely monitors the Near Real Time data (NRT) from the INTEGRAL satellite. A first scientific analysis is made in order to check for the detection of new, transient or highly variable sources in the data. Of primary importance for this work is the Interactive Quick Look Analysis (IQLA), which produces JEM-X and ISGRI images and monitors them for interesting astrophysical events

astro-ph↗

arXiv2004

Different kinds of long-term variability from Cygnus X-1

We present a study of the long-term variability of Cyg X-1 using data from the RXTE/ASM and the RXTE/PCA during the time between the two soft states of 1996 and 2001/2002. This period has been characterized by many short ASM flaring episodes which we have identified as "failed state transitions". The 150 d period which has been seen before and shortly after the 1996 soft state is not obviously present in the ASM rate during most of this time. Applying selection criteria from our pointed RXTE/PCA observations to exclude the flaring episodes we show that the 150 d period can indeed still be significantly detected in the hard state. Furthermore, while the ~420 d timescale associated with the flaring is reduced in the selected hard state count rate, it is still pronounced in the temporal evolution of the corresponding hardness ratios. The Ryle radio flux is also consistent with the 150 d period being present but distorted during this time.

astro-ph↗

arXiv2003

Short-Term Radio-X-ray Correlations of Cygnus X-1

We analyze simultaneous radio-X-ray data of Cygnus X-1 from the Ryle telescope (RT) and RXTE over more than 4 a. We show that apparent correlations on short time scales in the lightcurves of Cyg X-1 are probably the coincidental outcome of white noise statistics.

astro-ph↗

arXiv2003

Transitions of black hole transients to the low/hard state under the microscope

We characterized the evolution of spectral and temporal properties of several Galactic black hole transients observed between 1996-2001 using the data from well sampled PCA observations close to the transition to the low/hard state. We showed that the changes in temporal properties are much sharper than the changes in the spectral properties, and it is much easier to identify a state transition with the temporal properties. The ratio of the power-law flux to the total flux in the 3-25 keV band increases close to the transition, and the power-law flux shows a sharp increase along with the changes in temporal properties during the transitions. In this work we concentrate on the decay of two recent outbursts, from 4U 1543$-$47, and H1743$-$322 and discuss the state transitions by tracking their daily, and sometimes hourly evolution, and interpret results based on the expectations from our earlier observations.

astro-ph↗

arXiv2003

Long Term Variability of Cyg X-1, II. The rms-Flux Relation

We study the long term evolution of the relationship between the root mean square (rms) variability and flux (the ``rms-flux relation'') for the black hole Cygnus X-1 as monitored from 1996 to 2003 with the Rossi X-ray Timing Explorer (RXTE). We confirm earlier results by Uttley & McHardy (2001) of a linear relationship between rms and flux in the hard state on time scales > 5 s reflecting in its slope the fractional rms variability. We demonstrate the perpetuation of the linear rms-flux relation in the soft and the intermediate state. The existence of a non-zero intercept in the linear rms-flux relation argues for two lightcurve components, for example, one variable and one non-variable component, or a possible constant rms component. The relationship between these two hypothesized components can be described by a fundamental dependence of slope and intercept at time scales ~< 10 ksec with long term averages of the flux.

astro-ph↗

arXiv2003

A close look at the state transitions of Galactic black hole transients during outburst decay

We characterize the evolution of spectral and temporal properties of several Galactic black hole transients during outburst decay using the data from well sampled PCA/\rxte observations close to the transition to the low/hard state. We find several global patterns of evolution for spectral and temporal parameters before, during, and after the transition. We show that the changes in temporal properties (sudden increase or decrease in the rms amplitude of variability) are much sharper than the changes in the spectral properties, and it is much easier to identify a state transition with the temporal properties. The spectral index shows a drop 3-5 days before the transition for some of our sources. The ratio of the power-law flux to the total flux in the 3-25 keV band increases close to the transition, which may mean that the system must be dominated by the coronal emission for the transition to occur. We also show that the power-law flux shows a sharp change along with the temporal properties during the transitions which may indicate a threshold transition volume for the corona. The evolution of the spectral and temporal properties after the transition is consistent with the idea that the inner accretion disk moves away from the black hole. Based on the evolution of spectral and temporal parameters and changes during the transitions, we discuss possible scenarios of how the transition is happening.

astro-ph↗

arXiv2003

Long Term Variability of Cyg X-1 I. X-ray spectral-temporal correlations in the hard state

We present the long term evolution of the timing properties of the black hole candidate Cygnus X-1 in the 0.002-128 Hz frequency range as monitored from 1998 to 2001 with the RXTE. The hard state power spectral density (PSD) is well modeled as the sum of four Lorentzians, which describe distinct broad noise components. Before 1998 July, Cyg X-1 was in a "quiet" hard state characterized primarily by the first three of these broad Lorentzians. Around 1998 May, this behavior changed: the total fractional rms amplitude decreased, the peak frequencies of the Lorentzians increased, the average time lag slightly increased, and the X-ray spectrum softened. The change in the timing parameters is mainly due to a strong decrease in the amplitude of the third Lorentzian. Since then, an unusually large number of X-ray flares have been observed. During these "failed state transitions", the X-ray power spectrum changes to that of the intermediate state. Modeling this PSD with the four Lorentzians, we find that the first Lorentzian component is suppressed relative to the second and third Lorentzian. Also the frequency-dependent time lags increase significantly. We confirm the interpretation as failed state transitions with observations from the 2001 Jan. and 2001 Oct. soft states. Such behavior suggests that some or all of the Lorentzian components are associated with the accretion disk corona. We discuss the physical interpretation of our results.

astro-ph↗

arXiv2003

INTEGRAL-RXTE observations of Cygnus X-1

We present first results from contemporaneous observations of Cygnus X-1 with INTEGRAL and RXTE, made during INTEGRAL's performance verification phase in 2002 November and December. Consistent with earlier results, the 3-250 keV data are well described by Comptonization spectra from a Compton corona with a temperature of kT~50-90 keV and an optical depth of tau~1.0-1.3 plus reflection from a cold or mildly ionized slab with a covering factor of Omega/2pi~0.2-0.3. A soft excess below 10 keV, interpreted as emission from the accretion disk, is seen to decrease during the 1.5 months spanned by our observations. Our results indicate a remarkable consistency among the independently calibrated detectors, with the remaining issues being mainly related to the flux calibration of INTEGRAL.

astro-ph↗