The decline of the high mass X-ray transient V 0332+53 during the Dec. 2004 to Feb. 2005 outburst is analysed from the data recorded by INTEGRAL. The flux is shown to decrease exponentially until ...2005 Feb. 10, with a decay time scale of ~30 days above 20 keV and ~20 days at lower energies, and to decrease linearly thereafter. The energy spectrum is well modelled throughout the decay by a power law with a folding energy of ~7.5 keV, and with two cyclotron absorption features. The folding energy does not vary significantly over the decay, but the spectrum becomes harder with time. Most importantly, we show that the parameters describing the fundamental cyclotron line around 27 keV do vary with time: its energy and depth increase (by about 17% for the energy in ~6 weeks), while its width decreases. These changes of the cyclotron line parameters are interpreted as resulting from a change in the extent of the cyclotron scattering region. Two quasi-periodic oscillations are also observed at various times during the observations, one at 0.05 Hz and another one near the pulsation frequency around 0.23 Hz.
The nebula powered by the Vela pulsar is one of the best examples of an evolved pulsar wind nebula, allowing access to the particle injection history and the interaction with the supernova ejecta. We ...report on the INTEGRAL discovery of extended emission above 18 keV from the Vela nebula. The northern side has no known counterparts and it appears larger and more significant than the southern one, which is in turn partially coincident with the cocoon, the soft X-ray, and TeV filament toward the center of the remnant. We also present the spectrum of the Vela nebula in the 18-400 keV energy range as measured by IBIS/ISGRI and SPI on board the INTEGRAL satellite. The apparent discrepancy between IBIS/ISGRI, SPI, and previous measurements is understood in terms of the point-spread function, supporting the hypothesis of a nebula more diffuse than previously thought. A break at ~25 keV is found in the spectrum within 6' from the pulsar after including the Suzaku XIS data. Interpreted as a cooling break, this points out that the inner nebula is composed of electrons injected in the last ~2000 years. Broadband modeling also implies a magnetic field higher than 10 Delta *mG in this region. Finally, we discuss the nature of the northern emission, which might be due to fresh particles injected after the passage of the reverse shock.
Hard X-ray variability of active galactic nuclei Beckmann, V.; Barthelmy, S. D.; Courvoisier, T. J.-L. ...
Astronomy and astrophysics (Berlin),
12/2007, Letnik:
475, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Aims.Active Galactic Nuclei are known to be variable throughout the electromagnetic spectrum. An energy domain poorly studied in this respect is the hard X-ray range above 20 keV. Methods.The first 9 ...months of the Swift/BAT all-sky survey are used to study the 14-195 keV variability of the 44 brightest AGN. The sources have been selected due to their detection significance of >$10 \sigma$. We tested the variability using a maximum likelihood estimator and by analysing the structure function. Results.Probing different time scales, it appears that the absorbed AGN are more variable than the unabsorbed ones. The same applies for the comparison of Seyfert 2 and Seyfert 1 objects. As expected the blazars show stronger variability. 15% of the non-blazar AGN show variability of >$20\%$ compared to the average flux on time scales of 20 days, and 30% show at least $10\%$ flux variation. All the non-blazar AGN which show strong variability are low-luminosity objects with $L_{(14{-}195\,\rm~keV)} < 10^{44} \rm \, erg \, s^{-1}$ Conclusions.Concerning the variability pattern, there is a tendency of unabsorbed or type 1 galaxies being less variable than the absorbed or type 2 objects at hardest X-rays. A more solid anti-correlation is found between variability and luminosity, which has been previously observed in soft X-rays, in the UV, and in the optical domain.
The efficient low-mass Seyfert MCG–05–23–016 Beckmann, V.; Courvoisier, T. J. -L.; Gehrels, N. ...
Astronomy and astrophysics (Berlin),
12/2008, Letnik:
492, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Aims. The Seyfert 1.9 galaxy MCG–05–23–016 has been shown to exhibit a complex X-ray spectrum. This source has moderate X-ray luminosity, hosts a comparably low-mass black hole, but accretes at a ...high Eddington rate, and allows us to study a super massive black hole in an early stage. Methods. Three observations of the INTEGRAL satellite simultaneous with pointed Swift/XRT observations performed from December 2006 to June 2007 are used in combination with public data from the INTEGRAL archive to study the variability of the hard X-ray components and to generate a high-quality spectrum from 1 to 150 keV. Results. The AGN shows little variability in the hard X-ray spectrum, with some indication of a variation in the high-energy cut-off energy ranging from 50 keV to ≫100 keV, with an electron plasma temperature in the 10–90 keV range. The reflection component is not evident and, if present, the reflected fraction can be constrained to $R < 0.3$ for the combined data set. Comparison to previous observations shows that the reflection component has to be variable. No variability in the UV and optical range is observed on a time scale of 1.5 years. Conclusions. The hard X-ray spectrum of MCG–05–23–016 appears to be stable with the luminosity and underlying power law varying moderately and the optical/UV flux staying constant. The reflection component and the iron Kα line seem to have decreased between December 2005 and the observations presented here. The spectral energy distribution appears to be similar to that of Galactic black hole systems, e.g. XTE 1118+480 in the low state. The AGN exhibits a remarkably high Eddington ratio of $L_{\rm bol}/L_{\rm Edd} \mathrel{>\kern-1.0em\lower0.9ex\hbox{~}}0.8$ (or $L_{\rm bol}/L_{\rm Edd} \mathrel{>\kern-1.0em\lower0.9ex\hbox{~}}0.1$, if we consider a higher mass of the central engine) and, at the same time, a low cut-off energy around 70 keV. Objects like MCG–05–23–016 might indicate the early stages of super massive black holes, in which a strong accretion flow feeds the central engine.
We present the analysis of a 100 ks INTEGRAL (3-100 ${\rm keV}$) observation of the transient X-ray pulsar V 0332${+}53$in outburst. The source is pulsating at $P_{\rm Pulse}=4.3751\pm0.0002$ s with ...a clear double pulse from 6 ${\rm keV}$to 60 ${\rm keV}$. The average flux was ~550 mCrab between 20 ${\rm keV}$and 60 ${\rm keV}$. We modeled the broad band continuum from 5 ${\rm keV}$to 100 ${\rm keV}$with a power-law modified by an exponential cut off. We observe three cyclotron lines: the fundamental line at 24.9${^{+0.1}_{-0.1}}$ ${\rm keV}$, the first harmonic at 50.5${^{+0.1}_{-0.1}}$ ${\rm keV}$as well as the second harmonic at 71.7${^{+0.7}_{-0.8}}$ ${\rm keV}$, thus confirming the discovery of the harmonic lines by Coburn et al. (2005) in RXTEdata.
We present results on approximately one year of INTEGRAL observations of six AGN detected during the regular scans of the Galactic Plane. The sample is composed by five Seyfert 2 objects (MCG ...–05–23–16, NGC 4945, the Circinus galaxy, NGC 6300, ESO 103–G35) and the radio galaxy Centaurus A. The continuum emission of each of these sources is well represented by a highly absorbed ($N_{\rm H}>10^{22} \, \rm cm^{-2}$) power law, with average spectral index $\Gamma = 1.9 \pm 0.3$. A high energy exponential cut-off at $E_{\rm c} \sim 50 \rm \,~keV$ is required to fit the spectrum of the Circinus galaxy, whereas a lower limit of 130 keV has been found for NGC 4945 and no cut-off has been detected for NGC 6300 in the energy range covered by these INTEGRAL data. The flux of Centaurus A was found to vary by a factor of ~2 in 10 months, showing a spectral change between the high and low state, which can be modelled equally well by a change in the absorption (NH from 17 to $33 \times 10^{22} \rm \, cm^{-2}$) or by the presence of a cut-off at $\ga$120 keV in the low state spectrum. A comparison with recently reprocessed BeppoSAX/PDS data shows a general agreement with INTEGRAL results. The high energy cut-off in the hard X-ray spectra appears to be a common but not universal characteristic of Seyfert 2 and to span a wide range of energies.
The thermal stability of blends obtained from the mixture of 4-dodecylbenzenesulfonic acid doped polyaniline (PANI(DBSA)) and a terpolymer of ethylene-propylene-5-ethylidene-2-norbornene (EPDM) by ...casting from organic solvents, was studied by thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR) under nitrogen atmosphere. For the PANI(DBSA) complex and PANI(DBSA)/EPDM blends the TGA results showed more than one stage of degradation, of which the second (temperature range 380–520 °C) was observed to be the most significant. Apparently, in this stage, the simultaneous degradation of the bound dopant, the PANI and the elastomer occurred. The activation energy (
E) for the crosslinked blends was in the range 180–250 kJ mol
−1, higher values than those determined for pure components and non crosslinked blends which were in the range 150–210 kJ mol
−1. The
E values also indicated that the effects due to the PANI(DBSA) content and maleated EPDM were not significant and that the mechanism of degradation of both systems studied was associated with a random scission of the chain. The FTIR spectra for the PANI(DBSA)/EPDM crosslinked blend showed typical absorption bands associated with saturated and unsaturated hydrocarbons, water, carbon dioxide and nitrogen containing compounds.
Context. Extragalactic nuclear activity is most effectively explored with observations at high energies, where the most extreme flux and spectral variations are expected to occur, because of changes ...in either the accretion flow or the kinematics of the plasma. In active galactic nuclei of blazar type, these variations are the most dramatic. Aims. By following blazar outbursts from their onset and correlating the observed variations at many different wavelengths, we can reconstruct the behavior of the plasma and map out the development of the flare within the jet. Methods. The advent of the Fermi satellite has allowed the start of a systematic and intensive monitoring program of blazars. Blazar outbursts are very effectively detected by the LAT instrument in the MeV–GeV domain, and these can be promptly followed up with other facilities. Based on a Fermi LAT detection of a high MeV-GeV state, we observed the blazar PKS 1502+106 with the INTEGRAL satellite between 9 and 11 August 2008. Simultaneous Swift observations were also accomplished, as well as optical follow-up at the Nordic Optical Telescope. Results. The IBIS instrument onboard INTEGRAL detected a source at a position inconsistent with the optical coordinates of PKS 1502+106, but consistent with those of the Seyfert 1 galaxy Mkn 841, located at 6.8 arcmin south-west of the blazar, which is therefore responsible for all the hard X-ray flux detected by IBIS. At the location of the blazar, IBIS sets an upper limit of ~10-11 erg s-1 cm-2 on the 15–60 keV flux, which is consistent with a model of inverse Compton scattering accounting for the soft X-ray and gamma-ray spectra measured by Swift XRT and Fermi LAT, respectively. The gamma-ray spectrum during the outburst indicates substantial variability in the characteristic energy of the inverse Compton component in this blazar. The hard X-ray state of the Seyfert appears to be nearly unchanged with respect to the past. On the other hand, its soft X-ray flux (0.3–10 keV) varies with a ~50% amplitude on timescales from days to years. On long timescales, this is well correlated with the optical flux, with no measurable delay. Conclusions. In PKS 1502+106, the critical parameters that control variability are the accelerating power transferred to the relativistic electrons, and the magnetic field in the emitting region. The spectrum of Mkn 841 in the 0.3–100 keV range is well described by a power-law with a cutoff at ~150 keV and a Compton reflected continuum.
An X-ray view of Sagittarius C Chuard, D.; Terrier, R.; Goldwurm, A. ...
Proceedings of the International Astronomical Union,
07/2016, Letnik:
11, Številka:
S322
Journal Article
Recenzirano
Odprti dostop
Over the past 15 years, the molecular complex Sgr C has been repeatedly observed with both XMM-Newton and Chandra. These observations reveal new features indicating that the region might be more ...complex than previously thought. We find that its strong iron line emission at 6.4 keV varies significantly over time, which supports the X-ray reflection scenario.
On the duty-cycle of γ-ray blazars Vercellone, S.; Soldi, S.; Chen, A. W. ...
Monthly notices of the Royal Astronomical Society,
September 2004, Letnik:
353, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Abstract
We study several properties of blazars detected in the γ-ray energy range by comparing the Energetic Gamma Ray Experiment Telescope (EGRET) sources with a sample of radio blazars which can ...be considered possible γ-ray candidates. We define three classes: non-γ-ray blazars, blazars with quasi-steady γ-ray emission and γ-ray blazars with substantial activity level. We find that, on average, BL Lacertae objects show a relatively steady γ-ray emission, when detected. On the other hand, most flat-spectrum radio quasars (FSRQs) show substantial γ-ray variability. We attribute a γ-ray activity index ψ=ψ−7× 10−7 cm−2 s−1 to all EGRET blazars, and show that FSRQs dominate the sample with non-zero ψ in the range 0 < ψ−7 < 0.035. By combining the information of detected and candidate active galactic nuclei, we characterize the blazar activity, including the discovery of a region of consistency between the γ-ray flaring duty-cycle and the recurrence time between flares. We also find a possible relation between the activity index of FSRQs and their black hole mass. More optical and γ-ray data are crucially important to test this relation.
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