We report the discovery of a new X-ray pulsar, XTE J1810Ϫ197, that was serendipitously discovered on 2003 July 15 by the Rossi X-Ray Timing Explorer (RXTE) while observing the soft gamma repeater SGR 1806Ϫ20. The pulsar has a 5.54 s spin period, a soft X-ray spectrum (with a photon index of ≈4), and is detectable in earlier RXTE observations back to 2003 January but not before. These show that a transient outburst began between 2002 November 17 and 2003 January 23 and that the source's persistent X-ray flux has been declining since then. The pulsar exhibits a high spin-down rate s s Ϫ1 with no evidence of Doppler shifts due to Ϫ11 P ≈ 10 a binary companion. The rapid spin-down rate and slow spin period imply a supercritical characteristic magnetic field G and a young age yr. Follow-up Chandra observations provided an accurate 14 B Ӎ 3 # 10 t ≤ 7600 position of the source. Within its error radius, the 1.5 m Russian-Turkish Optical Telescope found a limiting magnitude . All such properties are strikingly similar to those of anomalous X-ray pulsars and soft R p 21.5 C gamma repeaters, providing strong evidence that the source is a new magnetar. However, archival ASCA and ROSAT observations found the source nearly 2 orders of magnitude fainter. This transient behavior and the observed long-term flux variability of the source in absence of an observed SGR-like burst activity make it the first confirmed transient magnetar and suggest that other neutron stars that share the properties of XTE J1810Ϫ197 during its inactive phase may be unidentified transient magnetars awaiting detection via a similar activity. This implies a larger population of magnetars than previously surmised and a possible evolutionary connection between magnetars and other neutron star families.

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V4743 Sgr (Nova Sgr 2002 No. 3) was discovered on 20 September 2002. We obtained a 5 ks ACIS-S spectrum in November 2002 and found that the nova was faint in X-rays. We then obtained a 25 ks CHANDRA LETGS observation on 19 March 2003. By this time, it had evolved into the Super Soft X-ray phase exhibiting a continuous spectrum with deep absorption features. The light curve from the observation showed large amplitude oscillations with a period of 1325 s (22 min) followed by a decline in total count rate after ∼ 13 ks of observations. The count rate dropped from ∼ 40 cts s −1 to practically zero within ∼ 6 ks and stayed low for the rest of the observation (∼ 6 ks. The spectral hardness ratio changed from maxima to minima in correlation with the oscillations, and then became significantly softer during the decay. Strong H-like and He-like lines of oxygen, nitrogen, and carbon were found in absorption during the bright phase, indicating temperatures between 1-2 MK, but they were shifted in wavelength corresponding to a Doppler velocity of -2400 km s −1 . The spectrum obtained after the decline in count rate showed emission lines of C vi, N vi, and N vii suggesting that we were seeing expanding gas ejected during the outburst, probably originating from CNO-cycled material. An XMM-Newton ToO observation, obtained on 4 April 2003 and a later LETGS observation from 18 July 2003 also showed oscillations, but with smaller amplitudes.

We have obtained optical and infrared photometry of the quiescent soft Xray transient XTE J1118+480. In addition to optical and J-band variations, we present the first observed H-and K s -band ellipsoidal variations for this system. We model the variations in all bands simultaneously with the WD98 light curve modeling code. The infrared colors of the secondary star in this system are consistent with a K7V, while there is evidence for light from the accretion disk in the optical. Combining the models with the observed spectral energy distribution of the system, the most likely value for the orbital inclination angle is 68 • ± 2 • . This inclination angle corresponds to a primary black hole mass of 8.53±0.60 M ⊙ . Based on the derived physical parameters and infrared colors of the system, we determine a distance of 1.72±0.10 kpc to XTE J1118+480.

Aims. We study the inner disk structure of dwarf novae (DNe; i.e., nonmagnetic cataclysmic variables). Methods. We performed power spectral analysis of the X-ray light curves obtained using the Rossi X-ray Timing Explorer (RXTE) and X-ray Multi-mirror Mission (XMM-Newton) data. We fit the power spectra with a simple model that describes variability as a result of matter fluctuations. In addition, we applied cross-correlation analysis of simultaneous UV and X-ray light curves using the XMM-Newton data to determine time lags between the different wavelength data. Results. For five DN systems, SS Cyg, VW Hyi, RU Peg, WW Cet, and T Leo we show that the UV and X-ray power spectra of their time variable light curves are similar in quiescence. All of them show a break in their power spectra, which in the framework of the model of propagating fluctuations indicates inner disk truncation. We derive the inner disk radii for these systems in a range of (10−3) × 10 9 cm. We analyze the RXTE data of SS Cyg in outburst and compare it with the power spectra, obtained during the period of quiescence. We show that during the outburst the disk moves towards the white dwarf and recedes as the outburst declines. We calculate the correlation between the simultaneous UV and X-ray light curves of the five DN studied in this work, using the XMMNewton data obtained in the quiescence and find X-ray time lags of 96−181 s. This can be explained by the travel time of matter from a truncated inner disk to the white dwarf surface. Conclusions. We suggest that, in general, DN may have truncated accretion disks in quiescence, which can also explain the UV and X-ray delays in the outburst stage and that the accretion may occur through coronal flows in the disk (e.g., rotating accretion disk coronae). Within the framework of the model of propagating fluctuations, the comparison of the X-ray/UV time lags observed by us in the case of DN systems with those detected for a magnetic intermediate polar allows us to make a rough estimate of the viscosity parameter α ∼ 0.25 in the innermost parts of the accretion flow of DN systems.

We present a total of ∼45 ks (3 × 15 ks) of Swift X-Ray Telescope (XRT) observations for three nonmagnetic nova-like (NL) cataclysmic variables (CVs; MV Lyr, BZ Cam, V592 Cas) in order to study characteristics of boundary layers (BLs) in CVs. The nonmagnetic NLs are found mostly in a state of high mass accretion rate ( 1 × 10 −9 M yr −1 ), and some show occasional low states. Using the XRT data, we find optically thin multipletemperature cooling flow type emission spectra with X-ray temperatures (kT max ) of 21-50 keV. These hard X-rayemitting BLs diverge from simple isobaric cooling flows, indicating X-ray temperatures that are of virial values in the disk. In addition, we detect power-law emission components from MV Lyr and BZ Cam and plausibly from V592 Cas, which may be a result of the Compton scattering of the optically thin emission from the fast wind outflows in these systems and/or Compton upscattering of the soft disk photons. The X-ray luminosities of the (multitemperature) thermal plasma emission in the 0.1-50.0 keV range are (0.9-5.0) × 10 32 erg s −1 . The ratio of the X-ray and disk luminosities (calculated from the UV-optical wavelengths) yields an efficiency (L x /L disk ) ∼ 0.01-0.001. Given this non-radiative ratio for the X-ray-emitting BLs with no significant optically thick blackbody emission in the soft X-rays (consistent with ROSAT observations), together with the high/virial X-ray temperatures, we suggest that high-state NL systems may have optically thin BLs merged with ADAF-like flows and/or X-ray coronae. In addition, we note that the axisymmetric bipolar and/or rotation-dominated fast-wind outflows detected in these three NLs (particularly BZ Cam and V592 Cas) or some other NL may also be explained in the context of ADAF-like BL regions.

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I present the data of the shell of classical Nova Persei (1901) obtained by the Advanced CCD Imaging Spectrometer S3 detector on-board Chandra Observatory. The X-ray nebula is affected mostly by the complex interstellar medium around the nova and has not developed a regular shell. The X-ray nebula is lumpy and asymmetric with bulk of emission coming from the southwestern quadrant. The brightest X-ray emission is detected as an arc that covers from the west to the south of the central source. Part of this feature, which is co-spatial with the brightest non-thermal radio emission region, is found to be a source of nonthermal (synchrotron) X-ray emission with a power law photon index of 2.3 +1.5 −0.9 and α=0.68 +0.03 −0.15 at about a flux of 1.7×10 −13 erg cm −2 s −1 . This confirms that the shell is a cite of particle acceleration, mainly in the reverse shock zone. There are strong indications for nonlinear diffusive shock acceleration occurring in the forward shock/transition zone with an upper limit on the non-thermal X-ray flux of 1.0×10 −14 erg cm −2 s −1 . The total X-ray spectrum of the nebula consists of two prominent components of emission (other than the resolved synchrotron X-ray emission). The component dominant below 2 keV is most likely a nonequilibrium ionization thermal plasma of kT s =0.1-0.3 keV with an X-ray flux of 1.6×10 −11 erg cm −2 s −1 . There is also a higher temperature, kT s =0.5-2.6 keV, embedded, N H =(4.0-22.0)×10 22 cm −2 , emission component prominent above 2 keV. The unabsorbed X-ray flux from this component is 1.5×10 −10 erg cm −2 s −1 . The X-ray emitting plasma is of solar composition except for enhancement in the elemental abundances (mean abundances over the remnant) of Ne/Ne ⊙ and N/N ⊙ in a range 13-21 and 1-5, respectively. A distinct emission line of neon, He-like Ne IX, is detected which reveals a distribution of several emission knots/blobs and shows a cone-like structure with wings extending toward NW and SE at expansion velocities about 2600 km s −1 in the X-ray wavelengths.The emission measures yield an average electron density in a range 0.6-11.2 cm −3 for both of the components (filling factor=1). The electron density increases to higher values ∼ 300 cm −3 if the filling factor is decreased substantially. The mass in the X-ray emitting nebula is (2.1-38.5)×10 −4 M ⊙ . The X-ray luminosity of the forward shock ∼ 4.3×10 32 erg s −1 indicates that it is adiabatic. The shocked mass, the X-ray luminosity and comparisons with other wavelengths suggest that the remnant has started cooling and most likely is in a Sedov phase.