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.
Aims.The aim of this paper is to study the evolution of the broadband spectrum of one of the brightest and nearest quasars 3C 273. Methods.We analyze the data obtained during quasi-simultaneous ...INTEGRAL and XMM-Newton monitoring of the blazar 3C 273 in 2003–2005 in the UV, X-ray and soft γ-ray bands and study the results in the context of the long-term evolution of the source. Results.The 0.2–100 keV spectrum of the source is well fitted by a combination of a soft cut-off power law and a hard power law. No improvement of the fit is achieved if one replaces the soft cut-off power law by either a blackbody, or a disk reflection model. During the observation period the source has reached the historically softest state in the hard X-ray domain with a photon index Γ = 1.82 ± 0.01. Comparing our data with available archived X-ray data from previous years, we find a secular evolution of the source toward softer X-ray emission (the photon index has increased by $\Delta\Gamma\simeq$ 0.3-0.4 over the last thirty years). We argue that existing theoretical models have to be significantly modified to account for the observed spectral evolution of the source.
The thermal stability of poly(
N-vinyl-2-pyrrolidone-co-methacrylic acid) copolymers was studied by thermogravimetry and infrared spectroscopy in inert atmosphere. The thermogravimetric curves ...suggested that the effective degradation of both systems occurred in the temperature range 350–500 °C with more than 60% mass loss. At this temperature, the activation energy was in the range 160–200 kJ mol
−1 (average values), suggesting that the degradation occurred by a random scission of the chain. The FTIR results indicated that the main volatile products of degradation are CO
2, CO and hydrocarbons (unsaturated structures) with low molecular weight. Pure PVP also showed the formation of NH
3 which was apparently suppressed in the copolymer by the formation of large amounts of CO
2 and CO. The results suggested that the thermal stability of the copolymers was essentially associated with the
N-vinyl-2-pyrrolidone monomer, losing stability when the percentage of methacrylic acid in the copolymer system was increased.
On the past activity of Sgr A Ponti, G.; Morris, M. R.; Clavel, M. ...
Proceedings of the International Astronomical Union,
10/2013, Letnik:
9, Številka:
S303
Journal Article
Recenzirano
Odprti dostop
Recent X-ray emission events in the Galactic center would be expected to generate an X-ray reflection response within the surrounding clouds of the central molecular zone, in the Galactic disk and ...even, if powerful enough, in clouds outside our Galaxy. We review here the current constraints on Sgr A*'s past activity obtained through this method, with particular emphasis on the strong evidence that has been gathered for multiple X-ray flashes during the past few hundred years.
The effects of maleated ethylene propylene diene (EPDM-g-MA) on the thermal stability of polyamide/EPDM and polyamide/poly(ethylene terephthalate) (PET) systems were studied by thermogravimetric ...analysis and infrared spectroscopy in nitrogen. Based on the activation energy (
E) and reaction products, it is suggested that the thermal degradation of pure polyamide 12.10 (PA-12.10) and polyamide 6.10 (PA-6.10) occurred firstly by chain scission of the weakest C–N and –C(O)–NH bonds. The average value of
E for pure PA-12.10 was ca. 280 kJ mol
−1. In the binary and ternary blends, the decrease of
E to ca. 180–200 kJ mol
−1 indicated a more favourable degradation. For the systems containing PA-6.10,
E decreased from ca. 210 kJ mol
−1 (pure PA-6.10) to ca. 160 kJ mol
−1 in the ternary blends. The results suggest that the presence of EPDM-g-MA in the blend decreased the thermal stability of the polyamides.
We report on the preparation and properties of soy protein isolate (SPI)‐sodium dodecyl sulfate (SDS)‐polycaprolactone‐triol (PCL‐T) films obtained by solvent casting from solutions containing ...variable amounts of SDS or SDS/PCL‐T. It is shown that the mechanical and thermal properties, and the morphology of SPI‐based biofilms can be easily controlled by changing SDS, PCL‐T, and moisture contents, enabling the fabrication of rigid and flexible materials as pure SPI films Young's modulus ∼ 1 400 MPa, elongation at break (E) ∼ 2%, and glass transition temperature (Tg) ∼ 150 °C and SPI/SDS/PCL‐T films with PCL‐T ≥ 18% (Young's modulus ∼ 50 MPa, E ∼ 90%, and Tg ∼ 135 °C), respectively. Micrographs taken at the cross‐section of biofilms whose PCL‐T ≥ 18% revealed the occurrence of a porous matrix, whereas a dense bulk phase was otherwise observed (pure SPI, SPI/SDS, and SPI/SDS/PCL‐T films with PCL‐T < 18%).
The High-Energy Spectrum of NGC 4151 Beckmann, V; Shrader, C. R; Gehrels, N ...
Astrophysical journal/The Astrophysical journal,
12/2005, Letnik:
634, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present the first INTEGRAL observations of the type 1.5 Seyfert galaxy NGC 4151. Combining several INTEGRAL observations performed during 2003, totaling 6400 ks of exposure time, allows us to ...study the spectrum in the 2-300 keV range. The measurements presented here reveal an overall spectrum from X-rays up to soft gamma-rays that can be described by an absorbed (N sub(H) = 6.9 x 10 super(22) cm super(-2)) model based on a Compton continuum from a hot electron population (kT sub(e) = 94 keV) from an optically thick (t = 1.3) corona, reflected on cold material (R = 0.7), consistent with earlier claims. The time-resolved analysis shows little variation of the spectral parameters over the duration of the INTEGRAL observations. The comparison with CGRO OSSE data shows that the same spectral model can be applied over a time span of 15 yr, with flux variations of the order of a factor of 2 and changes in the underlying continuum reflected by the temperature of the electron population (kT sub(e) = 50-100 keV). When modeled with an exponential cutoff power law plus Compton reflection, this results in photon indices ranging from = 1.5 to 1.9 and a cutoff energy in the range 100-500 keV.
The supermassive black hole at the Galactic center, Sagittarius A* has experienced periods of higher activity in the past. The reflection of these past outbursts is observed in the molecular material ...surrounding the black hole but reconstructing its precise lightcurve is difficult since the distribution of the clouds along the line of sight is poorly constrained. Using Chandra high-resolution data collected from 1999 to 2011 we studied both the 6.4 keV and the 4–8 keV emission of the region located between Sgr A* and the Radio arc, characterizing its variations down to 15″ angular scale and 1-year time scale. The emission from the molecular clouds in the region varies significantly, showing either a 2-year peaked emission or 10-year linear variations. This is the first time that such fast variations are measured. Based on the cloud parameters, we conclude that these two behaviors are likely due to two distinct past outbursts of Sgr A* during which its luminosity rose to at least 1039 erg s−1.
Studies on elemental analysis, Fourier transform infrared spectroscopy (FT-IR) and thermal decomposition (thermogravimetry, TG; and derivative thermogravimetry, DTG) of sedimentary fulvic (FA) and ...humic acids (HA) from marine, estuarine, lacustrine and terrestrial environments are presented. In general, H/C and N/C atomic ratios, as well as the infrared spectra, reflected the extent of the influence of algal and/or terrestrial organic matter sources on the samples, the aquatic (both, marine and freshwater) humic substances (HS) being richer in nitrogen and more saturated, than terrestrial materials. Comparison of properties of FA and HA from the same parent sediments showed that the latter are relatively richer in nitrogen and unsubstituted aliphatic chains and poorer in carboxylic groups. FT-IR spectra showed that the nitrogen present is mostly as forming part of amide groups. Concerning thermal degradation, two main steps were observed for all samples: the first, relative to the loss of moisture, being located between 40°C and 100°C and the second between 270°C and 440°C. FT-IR spectra of the samples which had been heated to 90°C, 400°C and 900°C showed that, upon heating, the carboxyl content decreases (especially for FA), the aliphaticity decreases and the aromaticity increases (especially for HA), indicating that the 270°C-470°C degradation step might be related to decarboxylation and unsaturation losses. In spite of this, both kinds of HS, were shown to be highly thermo-resistant materials retaining most of their typical original infrared spectral features, even after being heated to 400°C.
Aims.The nature of Cygnus X-3 is still not understood well. This binary system might host a black hole or a neutron star. Recent observations by INTEGRAL have shown that Cygnus X-3 was again in an ...extremely ultrasoft state. Here we present our analysis of the transition from the ultrasoft state, dominated by blackbody radiation at soft X-rays plus non-thermal emission in the hard X-rays, to the low hard state. Methods.INTEGRAL observed Cyg X-3 six times during three weeks in late May and early June 2007. Data from IBIS/ISGRI and JEM-X1 were analysed to show the spectral transition. Results.During the ultrasoft state, the soft X-ray spectrum is well-described by an absorbed ($N_{\rm H} = 1.5$ $\times$ $10^{22}~\rm cm^{-2}$) black body model, whereas the X-ray spectrum above 20 keV appears to be extremely low and hard ($\Gamma \simeq 1.7$). During the transition, the radio flux rises to a level of >$1~\rm Jy$, and the soft X-ray emission drops by a factor of ~3, while the hard X-ray emission rises by a factor of ~14 and becomes steeper (up to $\Gamma = 4$). Conclusions.The ultrasoft state apparently precedes the emission of a jet, which is apparent in the radio and hard X-ray domain.
PDF
