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Register a new userBroad-band BeppoSAX observation of the low-mass X-ray binary X1822-371
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A.N. Parmar
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Results of a 1997 September 9-10 BeppoSAX observation of the 5.57 hr low-mass X-ray binary (LMXRB) X1822-371 are presented. The 0.3-40 keV spectrum is unusually complex and cannot be fit by any of the standard models applied to other LMXRB. At least two components are required. One component has a shape consistent with that expected from the Comptonization of an input soft (Wein) spectrum while the other, contributing ~40% of the 1-10 keV flux, is consistent with being a blackbody. In addition, there is a ``dip in the spectrum which can be modeled by a 1.33 +0.05 -0.11 keV absorption edge with an optical depth, tau, of 0.28 +/- 0.06. If the same model is fit to ASCA Solid-State Imaging Spectrometer spectra obtained in 1993 and 1996, then reasonable fits are also obtained, with a similar absorption feature required. The nature of this feature is highly uncertain; its energy corresponds to the K-edges of highly ionized Ne x and neutral Mg, or to an L-edge of moderately ionized Fe. Surprisingly, no strong (tau > 0.05) Fe-K or (tau > 0.18) O-K edges are visible. The folded lightcurve of X1822-371 is similar to previous observations, except that no strong softening is seen near the eclipse. An updated orbital ephemeris is provided.
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We report on the analysis of high-speed multicolor photometry of the eclipsing X-ray binary X1822-371. We used new eclipse timings to derive a revised optical ephemeris. A quadratic fit to the eclipse timings is not statistically significant but suggests that the orbital period is increasing on a timescale of P/|Pdot|= (4.2 +/- 1.4) 10^6 yr. We find no systematic delay or advance of the optical timings with respect to the X-ray timings. Average UBVRI light curves show the deep eclipse of the disc by the secondary star superimposed on the broader and shallower occultation of the inner disc regions by the outer disc (dip), and an orbital hump centred at phase +0.25 which is mostly seen in the U and B bands. The starting phase of the dip occurs earlier for shorter wavelengths, while the egress occurs at the same phase in all bands. This suggests that the thickening of the outer, occulting disc rim is gradual with azimuth at ingress but decreases sharply at egress. We fit synthetic photometry to the extracted colors of the inner and outer disc regions to estimate their effective temperatures. We find Teff= (9+/-5) 10^7 K and Teff= (6+/-2) 10^4 K, respectively, for the inner and outer disc regions. The orbital dependency of the flickering activity is derived from the mean scatter of the individual light curves with respect to the average UBVRI light curves. The flickering curves show a broad eclipse at the dipping phases, the depth of which decreases with increasing wavelength. The blue, eclipsed flickering component is associated with the inner disc regions and can be fitted by a blackbody spectrum of Teff= (2.1+/-0.8) 10^8 K, whereas the uneclipsed flickering component probably arises from the outermost disc regions and is well described by a blackbody of Teff= (9.6+/-0.7) 10^3 K.
We report on the spectral (pulse averaged) and timing analysis of the ~ 20 ksec observation of the X-ray binary pulsar Vela X-1 performed during the BeppoSAX Science Verification Phase. The source was observed in two different intensity states: the low state is probably due to an erratic intensity dip and shows a decrease of a factor ~ 2 in intensity, and a factor 10 in Nh. We have not been able to fit the 2-100 keV continuum spectrum with the standard (for an X--ray pulsar) power law modified by a high energy cutoff because of the flattening of the spectrum in ~ 10-30 keV. The timing analysis confirms previous results: the pulse profile changes from a five-peak structure for energies less than 15 keV, to a simpler two-peak shape at higher energies. The Fourier analysis shows a very complex harmonic component: up to 23 harmonics are clearly visible in the power spectrum, with a dominant first harmonic for low energy data, and a second one as the more prominent for energies greater than 15 keV. The aperiodic component in the Vela X-1 power spectrum presents a knee at about 1 Hz. The pulse period, corrected for binary motion, is 283.206 +/- 0.001 sec.
We report our measurements for orbital and spin parameters of X 1822-371 using its X-ray partial eclipsing profile and pulsar timing from data collected by the Rossi X-ray Timing Explorer (RXTE). Four more X-ray eclipse times obtained by the RXTE 2011 observations were combined with historical records to trace evolution of orbital period. We found that a cubic ephemeris likely better describes evolution of the X-ray eclipse times during a time span of about 34 years with a marginal second order derivative of $ddot{P}_{orb}=(-1.05 pm 0.59) times 10^{-19}$ s$^{-1}$. Using the pulse arrival time delay technique, the orbital and spin parameters were obtained from RXTE observations from 1998 to 2011. The detected pulse periods show that the neutron star in X 1822-371 is continuously spun-up with a rate of $dot{P}_{s}=(-2.6288 pm 0.0095) times 10^{-12}$ s s$^{-1}$. Evolution of the epoch of the mean longitude $l=pi /2$ (i.e. $T_{pi / 2}$) gives an orbital period derivative value consistent with that obtained from the quadratic ephemeris evaluated by the X-ray eclipse but the detected $T_{pi / 2}$ values are significantly and systematically earlier than the corresponding expected X-ray eclipse times by $90 pm 11$ s. This deviation is probably caused by asymmetric X-ray emissions. We also attempted to constrain the mass and radius of the neutron star using the spin period change rate and concluded that the intrinsic luminosity of X 1822-371 is likely more than $10^{38}$ ergs s$^{-1}$.
We present a study of the central engine in the broad-line radio galaxy 3C 109. To investigate the immediate surrounding of this accreting, supermassive black hole, we perform a multi-epoch broad-band spectral analysis of a joint NuSTAR/XMM observation (2017), an archival xmm observation (2005) and the 105-month averaged Swift-BAT data. We are able to clearly separate the spectrum into a primary continuum, neutral and ionized absorption, and a reflection component. The photon index of the primary continuum has changed since 2005 ($Gamma = 1.61 substack{+0.02 -0.01} rightarrow 1.54 pm{0.02}$), while other components remain unchanged, indicative of minimal geometric changes to the central engine. We constrain the high-energy cutoff of 3C 109 (E$_{text{cut}}= 49 substack{+7 -5}$,keV ) for the first time. The reflector is found to be ionized (log $xi$ = $2.3 substack{+0.1 -0.2}$) but no relativistic blurring is required by the data. SED analysis confirms the super-Eddington nature of 3C 109 initially ($lambda_{Edd} >$ 2.09). However, we do not find any evidence for strong reflection (R = $0.18 substack{+0.04 -0.03}$) or a steep power law index, as expected from a super-Eddington source. This puts the existing virial mass estimate of 2 $times 10^{8}$M$_{odot}$ into question. We explore additional ways of estimating the Eddington ratio, some of which we find to be inconsistent with our initial SED estimate. We obtain a new black hole mass estimate of 9.3 $times 10^{8}$M$_{odot}$, which brings all Eddington ratio estimates into agreement and does not require 3C 109 to be super-Eddington.
(Abridged) We present results of several X-ray observations of the X-ray binary 4U 1954+31 performed with the satellites BeppoSAX, EXOSAT, ROSAT, RXTE, and Swift. We also studied the RXTE ASM data over a period of more than 10 years. Light curves of all observations show an erratic behaviour with sudden increases in the source emission on timescales variable from hundreds to thousands of seconds. There are no indications of changes in the source spectral hardness, with the possible exception of the RXTE pointed observation. Timing analysis does not reveal the presence of coherent pulsations or periodicities either in the pointed observations in the range from 2 ms to 2000 s or in the long-term RXTE ASM light curve on timescales from days to years. The 0.2-150 keV spectrum, obtained with BeppoSAX, is the widest for this source available to date in terms of spectral coverage and is well described by a model consisting of a lower-energy thermal component (hot diffuse gas) plus a higher-energy (Comptonization) emission, with the latter modified by a partially-covering cold absorber plus a warm (ionized) absorber. A blackbody modelization of our BeppoSAX low-energy data is ruled out. The presence of a complex absorber local to the source is also supported by the 0.1-2 keV ROSAT spectrum. RXTE, EXOSAT and Swift X-ray spectroscopy is consistent with the above results, but indicates variations in the density and the ionization of the local absorber. A 6.5 keV emission line is possibly detected in the BeppoSAX and RXTE spectra. All this information suggests that the scenario that better describes 4U 1954+31 consists of a binary system in which a neutron star orbits in a highly inhomogeneus medium from a stellar wind coming from its optical companion, an M-type giant star.
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