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Register a new userFast Timing Analysis of Cygnus X-1 using SPI on board INTEGRAL
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For the very first time, we report the high frequency analysis of Cyg X-1 up to hard X-ray using SPI on-board INTEGRAL. After analyzing the possible contribution fromthe background, and using INTEGRAL archive from March 2005 to May 2008, Power Density Spectra (PDS) were obtained until 130 keV. First, we show that their overall shape is very similar to that observed at lower energies, as they are well described by sets of Lorentzians. The strength of this fast variability (up to 40 Hz) does not drop at high energy since we show that it remains at ~25% rms, even in the highest energy bands. Second, the hard X-ray variability patterns of Cyg X-1 are state dependent: the softer the spectrum (or the lower the hardness ratio), the lower the total fractional variability and the higher the typical frequencies observed. The strength of total variability as a function of energy and state is then investigated. By comparison with simultaneous and published RXTE/PCA data, we showed that in the hard state, it remains quite constant in the 2-130 keV energy range. In our softer state, it is also flat until 50 keV and may increase at higher energy. The implications of this behavior on the models are then discussed.
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We present simultaneous multi-band radio and X-ray observations of the black hole X-ray binary Cygnus X-1, taken with the Karl G. Jansky Very Large Array and the Nuclear Spectroscopic Telescope Array. With these data, we detect clear flux variability consistent with emission from a variable compact jet. To probe how the variability signal propagates down the jet flow, we perform detailed timing analyses of our data. We find that the radio jet emission shows no significant power at Fourier frequencies $fgtrsim0.03$ Hz (below $sim30$ sec timescales), and that the higher frequency radio bands (9/11 GHz) are strongly correlated over a range of timescales, displaying a roughly constant time lag with Fourier frequency of a few tens of seconds. However, in the lower frequency radio bands (2.5/3.5 GHz) we find a significant loss of coherence over the same range of timescales. Further, we detect a correlation between the X-ray/radio emission, measuring time lags between the X-ray/radio bands on the order of tens of minutes. We use these lags to solve for the compact jet speed, finding that the Cyg X-1 jet is more relativistic than usually assumed for compact jets, where $beta=0.92^{+0.03}_{-0.06}$, ($Gamma=2.59^{+0.79}_{-0.61}$). Lastly, we constrain how the jet size scale changes with frequency, finding a shallower relation ($propto u^{-0.4}$) than predicted by simple jet models ($propto u^{-1}$), and estimate a jet opening angle of $phisim0.4-1.8$ degrees. With this study, we have developed observational techniques designed to overcome the challenges of radio timing analyses and created the tools needed to connect rapid radio jet variability properties to internal jet physics.
We have verified the absolute timing capabilities of the high-energy instruments aboard INTEGRAL, i.e. the imager IBIS, the spectrometer SPI and the X-ray monitor JEM-X. Calibration observations of the Crab, contemporaneous with the Rossi X-ray Timing Explorer (RXTE), have been used to measure the absolute phase of the main pulse of the Crab pulse profile using the same Jodrell Bank radio ephemeris. The three INTEGRAL instruments and RXTE give within the statistical and systematic uncertainties consistent results: The X-ray main pulse is leading the radio pulse by 280 +/- 40 microsec. Also the shapes of the X-ray pulse profiles as measured by the different instruments are fully consistent with each other.
During the first observing run of LIGO, two gravitational wave events and one lower-significance trigger (LVT151012) were reported by the LIGO/Virgo collaboration. At the time of LVT151012, the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) was pointing at a region of the sky coincident with the high localization probability area of the event and thus permitted us to search for its electromagnetic counterpart (both prompt and afterglow emission). The imaging instruments on-board INTEGRAL (IBIS/ISGRI, IBIS/PICsIT, SPI, and the two JEM-X modules) have been exploited to attempt the detection of any electromagnetic emission associated with LVT151012 over 3 decades in energy (from 3 keV to 8 MeV). The omni-directional instruments on-board the satellite, i.e. the SPI-ACS and IBIS monitored the entire LVT151012 localization region at energies above 75 keV. We did not find any significant transient source that was spatially and/or temporally coincident with LVT151012, obtaining tight upper limits on the associated hard X-ray and $gamma$-ray radiation. For typical spectral models, the upper limits on the fluence of the emission from any 1 s long-lasting counterpart of LVT151012 ranges from $F_{gamma}=$3.5$times$10$^{-8}$ erg cm$^{-2}$ (20 - 200 keV) to $F_{gamma}$=7.1$times$10$^{-7}$ erg cm$^{-2}$ (75 - 2000 keV), constraining the ratio of the isotropic equivalent energy released in the electromagnetic emission to the total energy of the gravitational waves: $E_{75-2000~keV}/E_{GW}<$4.4$times$10$^{-5}$. Finally, we provide an exhaustive summary of the capabilities of all instruments on-board INTEGRAL to hunt for $gamma$-ray counterparts of gravitational wave events, exploiting both serendipitous and pointed follow-up observations. This will serve as a reference for all future searches.
We present the analysis of an extended textit{INTEGRAL} dataset of the high-mass microquasar Cygnus X-1. We first classify, in a model-independent way, all the textit{INTEGRAL} individual pointings taken between 2003 and 2016 in three basic spectral states. This, in particular, allows us to triple the exposure time of the soft state in comparison with previous publication. We then study the spectral properties of the 5--400 keV stacked spectra of the soft and hard states and provide the parameters obtained with our modelling. Using a refined alternative method of extracting the Compton double events of the IBIS telescope, we then extract high-energy ($>$400 keV) spectra in the two states. We do detect an hard tail in both states. Our refined analysis allows us to obtain a hard state (count) spectrum at a flux lower than previously published by our team. Although a full estimate of the calibration property of this improved software is still needed, this seems to be more inline with the hard state hard tail seen with other instruments.
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.
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