Maria Chernyakova

The multiwavelength variability of 3C 273

Aims. We present an update of the 3C 273’s database hosted by the ISDC, completed with data from radio to gamma-ray observations over the last 10 years. We use this large data set to study the multiwavelength properties of this quasar, especially focussing on its variability behaviour. Methods. We study the amplitude of the variations and the maximum variability time scales across the broad-band spectrum and correlate the light curves in different bands, specifically with the X-rays, to search for possible connections between the emission at different energies. Results. 3C 273 shows variability at all frequencies, with amplitudes and time scales strongly depending on the energy and being the signatures of the different emission mechanisms. The variability properties of the X-ray band imply the presence of either two separate components (possibly a Seyfert-like and a blazar-like) or at least two parameters with distinct timing properties to account for the X-ray emission below and above ∼20 keV. The dominant hard X-ray emission is most probably not due to electrons accelerated by the shock waves in the jet as their variability does not correlate with the flaring millimeter emission, but seems to be associated to long-timescale variations in the optical. This optical component is consistent with being optically thin synchrotron radiation from the base of the jet and the hard X-rays would be produced through inverse Compton processes (SSC and/or EC) by the same electron population. We show evidence that this synchrotron component extends from the optical to the near-infrared domain, where it is blended by emission of heated dust that we find to be located within about 1 light-year from the ultraviolet source.

A compact pulsar wind nebula model of the γ-ray-loud binary LS I +61°303

We study a model of LS I +61°303 in which its radio to TeV emission is due to interaction of a relativistic wind from a young pulsar with the wind from its companion Be star. The detailed structure of the stellar wind plays a critical role in explaining the properties of the system. We assume the fast polar wind is clumpy, which is typical for radiatively driven winds. The clumpiness and some plasma instabilities cause the two winds to mix. The relativistic electrons from the pulsar wind are retained in the moving clumps by inhomogeneities of the magnetic field, which explains the X-ray variability observed on time-scales much shorter than the orbital period. We calculate detailed inhomogeneous spectral models reproducing the average broad-band spectrum from radio to TeV Given the uncertainties on the magnetic field within the wind and the form of the distribution of relativistic electrons, the X-ray spectrum could be dominated by either Compton or synchrotron emission. The recent Fermi observations constrain the high-energy cut-off in the electron distribution to be at the Lorentz factor of 2 x 10 4 or ∼ 10 8 in the former and latter model, respectively. We provide formulae comparing the losses of the relativistic electrons due to Compton, synchrotron and Coulomb processes versus the distance from the Be star. We calculate the optical depth of the wind to free-free absorption, showing that it will suppress most of the radio emission within the orbit, including the pulsed signal of the rotating neutron star. We point out the importance of Compton and Coulomb heating of the stellar wind within and around the y -ray emitting region. Then, we find the most likely mechanism explaining the orbital modulation at TeV energies is anisotropy of emission, with relativistic electrons accelerated along the surface of equal ram pressure of the two winds. Pair absorption of the TeV emission suppresses one of the two maxima expected in an orbit.

INTEGRAL hard X-ray spectra of the cosmic X-ray background and Galactic ridge emission

Aims. We derive the spectra of the cosmic X-ray background (CXB) and of the Galactic ridge X-ray emission (GRXE) in the � 20‐200 keV range from the data of the IBIS instrument aboard the INTEGRALsatellite obtained during the four dedicated Earthoccultation observations in early 2006. Methods. We analyze the modulation of the IBIS/ISGRI detector counts induced by the passage of the Earth through the field of view of the instrument. Unlike previous studies, we do not fix the spectral shape of the various contributions, but model i nstead their spatial distribution and derive for each of them the expected modulation of the detector counts. The spectra of the diffuse emission components are obtained by fitting the normalizations of the model lightcurves to the observed modulation in different energy bins. Because of degeneracy, we guide the fits with a realistic choi ce of the input parameters and a constraint for spectral smoothness. Results. The obtained CXB spectrum is consistent with the historic HEAO-1results and falls slightly below the spectrum derived with Swift/BAT. A 10 % higher normalization of the CXB cannot be completely excluded, but it would imply an unrealistically high albedo of the Earth. The derived spectrum of the GRXE confirms the pre sence of a minimum around 80 keV with improved statistics and

Radio-to-TeV γ-ray emission from PSR B1259–63

We discuss the implications of the recent X-ray and TeV gamma-ray observations of the PSR B1259-63 system (a young rotation powered pulsar orbiting a Be star) for the theoretical models of interaction of pulsar and stellar winds. We show that previously considered models in which the pulsar wind is purely electron loaded have problems to account for the observed behaviour of the system in the TeV and X-ray bands. We develop a model in which the broad band (radio, X-ray and high energy gamma-ray) emission from the binary system is produced in result of collisions of GeV-TeV energy protons accelerated by the pulsar wind and interacting with the stellar disk. In this model the high energy gamma-rays are produced in the decays of secondary neutral pions, while radio and X-ray emission are synchrotron and inverse Compton emission produced by low-energy (<100 MeV) electrons from the decays of secondary charged pi mesons. This model can explain not only the observed energy spectra, but also the correlations between TeV, X-ray and radio emission components.

A Rotating Hollow Cone Anisotropy of TeV Emission from Binary Systems

We show that TeV gamma-ray emission produced via interactions of high-energy particles with anisotropic radiation field of a massive star in binary systems should have a characteristic rotating hollow cone anisotropy pattern. The hollow cone, whose axis is directed away from the massive star, rotates with the period equal to the orbital period of the system. We note that the two maxima pattern of the TeV energy band lightcurve of the gamma-ray loud binary LS 5039 can be interpreted in terms of this rotating hollow cone model. Adopting such an interpretation, we are able to constrain the geometry of the system - either the inclination angle of the binary orbit, or the elevation of the gamma-ray emission region above the orbital plane.

Glimpses of the past activity of Sgr A★ inferred from X-ray echoes in Sgr C

Author(s): Chuard, D; Terrier, R; Goldwurm, A; Clavel, M; Soldi, S; Morris, MR; Ponti, G; Walls, M; Chernyakova, M | Abstract: Context. For a decade now, evidence has accumulated that giant molecular clouds located within the central molecular zone of our Galaxy reflect X-rays coming from past outbursts of the Galactic supermassive black hole. However, the number of illuminating events as well as their ages and durations are still unresolved questions. Aims. We aim to reconstruct parts of the history of the supermassive black hole Sgr A★ by studying this reflection phenomenon in the molecular complex Sgr C and by determining the line-of-sight positions of its main bright substructures. Methods. Using observations made with the X-ray observatories XMM-Newton and Chandra and between 2000 and 2014, we investigated the variability of the reflected emission, which consists of a Fe Kα line at 6.4 keV and a Compton continuum. We carried out an imaging and a spectral analysis. We also used a Monte Carlo model of the reflected spectra to constrain the line-of-sight positions of the brightest clumps, and hence to assign an approximate date to the associated illuminating events. Results. We show that the Fe Kα emission from Sgr C exhibits significant variability in both space and time, which confirms its reflection origin. The most likely illuminating source is Sgr A★. On the one hand, we report two distinct variability timescales, as one clump undergoes a sudden rise and fall in about 2005, while two others vary smoothly throughout the whole 2000–2014 period. On the other hand, by fitting the Monte Carlo model to the data, we are able to place tight constraints on the 3D positions of the clumps. These two independent approaches provide a consistent picture of the past activity of Sgr A★, since the two slowly varying clumps are located on the same wavefront, while the third (rapidly varying) clump corresponds to a different wavefront, that is, to a different illuminating event. Conclusions. This work shows that Sgr A★ experienced at least two powerful outbursts in the past 300 yrs, and for the first time, we provide an estimation of their age. Extending this approach to other molecular complexes, such as Sgr A, will allow this two-event scenario to be tested further.

X‐ray Observations of PSR B1259‐63 2007 Periastron Passage

PSR B1259‐63 is a 48 ms radio pulsar in a highly eccentric 3.4 year orbit with a Be star SS 2883. Unpulsed γ‐ray, X‐ray and radio emission is observed from the binary system and the collision of the pulsar wind with the anisotropic wind of the Be star plays a crucial role in the generation of the observed emission. The 2007 periastron passage was observed in unprecedented details with Suzaku, Swift, XMM‐Newton and Chandra missions. We present here the results of this campaign, compare them with previous observations and discuss the physical implications.

Radio-to-TeV gamma-ray emission from PSR B1259-63

We discuss the implications of the recent X-ray and TeV gamma-ray observations of the PSR B1259-63 system (a young rotation powered pulsar orbiting a Be star) for the theoretical models of interaction of pulsar and stellar winds. We show that previously considered models in which the pulsar wind is purely electron loaded have problems to account for the observed behaviour of the system in the TeV and X-ray bands. We develop a model in which the broad band (radio, X-ray and high energy gamma-ray) emission from the binary system is produced in result of collisions of GeV-TeV energy protons accelerated by the pulsar wind and interacting with the stellar disk. In this model the high energy gamma-rays are produced in the decays of secondary neutral pions, while radio and X-ray emission are synchrotron and inverse Compton emission produced by low-energy (<100 MeV) electrons from the decays of secondary charged pi mesons. This model can explain not only the observed energy spectra, but also the correlations between TeV, X-ray and radio emission components.