Şölen Balman

The X-Ray Spectral Evolution of Classical Nova V1974 Cygni 1992: A Reanalysis of the ROSAT Data

We present a spectral analysis of the archival X-ray data of classical Nova V1974 Cygni 1992 (Nova Cygni 1992) obtained by the ROSAT Position Sensitive Proportional Counter (PSPC). The X-ray spectrum is fitted with a two-component model. The first component is a white dwarf atmosphere emission model developed for the remnants of classical novae near the Eddington luminosity. The model is used to fit the soft X-ray data in the ~0.1-1.0 keV range, where the bulk of emission is below 0.7 keV. The second component is a Raymond-Smith model of thermal plasma applied to the hard X-ray emission above ~1.0 keV. The postoutburst X-ray spectrum of the remnant white dwarf is examined in the context of evolution on the Hertzsprung-Russell diagram using an O-Ne- and a C-O-enhanced atmosphere emission model. A constant bolometric luminosity evolution is detected with increasing effective temperature and decreasing photospheric radius using the O-Ne-enhanced model. The unabsorbed soft X-ray flux for the constant bolometric luminosity phase is found to be in the range (1.7-2.2) × 10-7 ergs s-1 cm-2. A peak effective temperature of 51 eV (5.9 ×105 K) is detected 511 days after outburst. We also present the spectral development of the hard X-ray component. It is found to evolve independently of the soft one. The maximum of the hard X-ray emission is reached at ~150 days after outburst with an unabsorbed flux of ~2.0 × 10-11 ergs s-1 cm-2 corresponding to a luminosity of (0.8-2.0) × 1034 ergs s-1 at a 2-3 kpc source distance. The time evolution of the hard X-ray flux and the plasma temperatures decreasing from 10 keV to 1 keV suggest emission from shock-heated gas as the origin of the hard X-ray component.

Chandra Observation of the Shell of Nova Persei 1901 (GK Persei): Detection of Localized Nonthermal X-Ray Emission from a Miniature Supernova Remnant

I present data on the shell of classical Nova Persei (1901) obtained by the Advanced CCD Imaging Spectrometer S3 detector on board the Chandra X-Ray 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 the bulk of the emission coming from the southwestern quadrant. The brightest X-ray emission is detected as an arc that covers the region from the west to the south of the central source. Part of this feature, which is cospatial with the brightest nonthermal radio emission region, is found to be a source of nonthermal (synchrotron) X-ray emission with a power-law photon index of 2.3 and α = 0.68 at about a flux of 1.7 × 10-13 ergs cm-2 s-1. This confirms that the shell is a site 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 nonthermal X-ray flux of 1.0 × 10-14 ergs 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 kTs = 0.1-0.3 keV with an X-ray flux of 1.6 × 10-11 ergs cm-2 s-1. There is also a higher temperature, kTs = 0.5-2.6 keV, embedded, NH = (4.0-22.0) × 1022 cm-2 emission component prominent above 2 keV. The unabsorbed X-ray flux from this component is 1.5 × 10-10 ergs 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 the ranges 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 conelike structure with wings extending toward the northwest and southeast at expansion velocities ~2600 km s-1 in the X-ray wavelengths. The emission measures yield an average electron density in the 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 × 1032 ergs 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.

SWIFT X-RAY TELESCOPE OBSERVATIONS OF THE NOVA-LIKE CATACLYSMIC VARIABLES MV Lyr, BZ Cam, AND V592 Cas

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 multiple-temperature cooling flow type emission spectra with X-ray temperatures (kT max) of 21-50 keV. These hard X-ray-emitting 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) × 1032 erg s–1. The ratio of the X-ray and disk luminosities (calculated from the UV-optical wavelengths) yields an efficiency (Lx /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.

[ITAL]ROSAT[/ITAL] Observation of the Old Classical Nova CP Puppis

CP PUPPIS is an old classical nova, that had an outburst in 1942 as one of the fastest and brightest novae ever recorded (Δ m=17 mag, t3 = 6.5 days ; V ej ≥ 1000 km/sec, Payne-Gaposhkin 1957 ). We observed it in X-rays with the ROSAT Position Sensitive Proportional Counter in April 1993. The source was detected with a count rate of 0.067 ± 0.004 c/s. The total X-ray flux between 0.1 and 2.4 keV was ~ 2.88 x10-12 ergs s-1 cm-2. The spectrum is best fitted by a thermal bremsstrahlung emission model with temperature ≥ 1 keV. Temperatures as high as 30 keV are allowed within 2σ errors. The X-ray count rates are modulated with the ≃1.5 hrs. spectroscopic and photometric orbital periods (Bianchini et al. 1985; Warner 1985; O’Donoghue et al. 1989; Diaz & Steiner 1991, White et al. 1993). The significance of the modulations at the spectroscopic period detected by White et al., (1993) ( P ~ 5295 s ) was tested by a phase dispersion method and found to be at the 3σ confidence level. Considering the variation of X-ray flux with the orbital period and the possibility of high plasma temperatures in the emitting medium, we favor an intermediate polar interpretation for this system.

A STUDY OF THE LOW-MASS X-RAY BINARY DIP SOURCES XB 1916 – 053, XB 1323 – 619, X 1624 – 490 AND 4U 1746 – 371 OBSERVED WITH INTEGRAL

We detect dipping activity/modulations in the light curve of the four low-mass X-ray binaries in the 3-10 keV and 20-40 keV energy ranges. The spectral parameters derived from the fits to the International Gamma-Ray Astrophysics Laboratory data are consistent with hot coronal structures in these systems where we find a range of plasma temperatures 3.0-224.9 keV. The unabsorbed X-ray to soft gamma-ray fluxes between 4 keV and 200 keV are 5.9 × 10–10 erg s–1 cm–2 for XB 1916 – 053, 3.3 × 10–10 erg s–1 cm–2 for XB 1323 – 619, 21.6 × 10–10 erg s–1 cm–2 for X 1624 – 490, and 11.0 × 10–10 erg s–1 cm–2 for 4U 1746 – 371. The optical depth to Compton scattering, τ, varies in a range 4.4-0.002 consistent with electron densities n e < 1.4 × 1015 cm–3. In general, we find no significant difference in the dip and non-dip spectra in the ISGRI energy range (above 20 keV) for all the four sources. We only detect absorption differences between dipping and non-dipping intervals for XB 1916 – 053 and X 1624 – 490 in the JEM-X energy range. Fits in the 4-200 keV range including an additional photoionized absorber model for the two sources show that XB 1916 – 053 has the highest ionized absorber among the two.

THE DETECTION OF A 3.5 hr PERIOD IN THE CLASSICAL NOVA VELORUM 1999 (V382 VEL) AND THE LONG-TERM BEHAVIOR OF THE NOVA LIGHT CURVE

We present CCD photometry, light-curve, and time series analysis of the classical nova V382 Vel (Nova Vel 1999). The source was observed for 2 nights in 2000, 21 nights in 2001, and 7 nights in 2002 using clear filters. We report the detection of a distinct period in the light curve of the nova P = 0.146126(18) days (3.5 hr). The period is evident in all data sets, and we interpret it as the binary period of the system. We also measured an increase in the amplitude modulation of the optical light (in magnitudes) by more than 55% from 2000 to 2001 and about 64% from 2001 to 2002. The pulse profiles in 2001 show deviations from a pure sinusoidal shape that progressively become more sinusoidal by 2002. The main cause of the variations in 2001 and 2002 can be explained with the occultation of the accretion disk by the secondary star. We interpret the observed deviations from a pure sinusoidal shape as additional flux resulting from the aspect variations of the irradiated face of the secondary star.

Discovery of irradiation-induced variations in the light curve of the classical nova V2275 Cyg (N Cyg 2001 No. 2)

We present charge-coupled device (CCD) photometry, light curve and time-series analysis of the classical nova V2275 Cyg (N Cyg 2001 No. 2). The source was observed for 14 nights in total in 2002 and 2003 using an R filter with the 1.5-m Russian-Turkish joint telescope (RTT150) at the TUBITAK National Observatory in Antalya, Turkey, as part of a large programme on the CCD photometry of cataclysmic variables. We report the detection of two distinct periodicities in the light curve of the nova: (a) P 1 = 0.31449(15) d [7.6 h], and (b) P 2 = 0.017079(17) d [24.6 min]. The first period is evident in both 2002 and 2003 whereas the second period is only detected in the 2003 data set. We interpret the first period as the orbital period of the system and attribute the orbital variations to aspect changes of the secondary irradiated by the hot white dwarf (WD). We suggest that the nova was a supersoft X-ray source in 2002 and, perhaps, in 2003. The second period could be a quasi-periodic pscillation originating from the oscillation of the ionization front (due to a hot WD) below the inner Lagrange point or a beat frequency in the system as a result of the magnetic nature of the WD if steady accretion has already been re-established.

Modifying the Standard Disk Model for the Ultraviolet Spectral Analysis of Disk-dominated Cataclysmic Variables. I. The Novalikes MV Lyrae, BZ Camelopardalis, and V592 Cassiopeiae

The standard disk is often inadequate to model disk-dominated cataclysmic variables (CVs) and generates a spectrum that is bluer than the observed UV spectra. X-ray observations of these systems reveal an optically thin boundary layer (BL) expected to appear as an inner hole in the disk. Consequently, we truncate the inner disk. However, instead of removing the inner disk, we impose the no-shear boundary condition at the truncation radius, thereby lowering the disk temperature and generating a spectrum that better fits the UV data. With our modified disk, we analyze the archival UV spectra of three novalikes that cannot be fitted with standard disks. For the VY Scl systems MV Lyr and BZ Cam, we fit a hot inflated white dwarf (WD) with a cold modified disk ( [Formula: see text] ~ a few 10-9M⊙ yr-1). For V592 Cas, the slightly modified disk ( [Formula: see text] ~ 6 × 10-9M⊙ yr-1) completely dominates the UV. These results are consistent with Swift X-ray observations of these systems, revealing BLs merged with ADAF-like flows and/or hot coronae, where the advection of energy is likely launching an outflow and heating the WD, thereby explaining the high WD temperature in VY Scl systems. This is further supported by the fact that the X-ray hardness ratio increases with the shallowness of the UV slope in a small CV sample we examine. Furthermore, for 105 disk-dominated systems, the International Ultraviolet Explorer spectra UV slope decreases in the same order as the ratio of the X-ray flux to optical/UV flux: from SU UMas, to U Gems, Z Cams, UX UMas, and VY Scls.

Orbital-phase-resolved Spectroscopy of the Intermediate Polar FO Aqr Using XMM-Newton Observatory Data

We present the orbital-phase resolved analysis of an archival FO Aqr observation obtained using the X-ray Multi-Mirror Mission (XMM-Newton), European Photon Imaging Camera (pn instrument). We investigate the variation of the spin pulse amplitudes over the orbital period in order to account for the effects of orbital motion on spin modulation. The semi-amplitude variations are in phase with the orbital modulation, changing from (38.0 +/- 1.8)% at the orbital maximum to (13.3 +/- 3.7)% at the orbital minimum. The spectral parameters also show changes over the orbital period. One of the absorption components increase by a factor of 5 between the orbital minimum and maximum. We interpret that this absorption arises from the bulge where accretion stream from the secondary impacts the disk. The spectrum extracted from the orbital minima and maxima can be fitted with a warm absorber model yielding values N_H = 2.09 (+0.98 -1.09) \times 10^22 and 0.56 (+0.26 -0.15) \times 1022 cm^{-2} ; and log({\xi}) = 0.23 (+0.37 -0.26) and <0.30 erg cm s^{-1} respectively, indicating the existence of ionized absorption from the bulge at the impact zone which is spread out on the disk. The absorption due to accretion curtain and/or column which causes the spin modulation can be distinguished from the disk absorption via spectral modeling.

Photometric Observations of Cataclysmic Variables with the 1.5-m Telescope at the TÜBITAK National Observatory (TUG): V2275 Cyg, RW UMi, PX And and FO Per

We present the light curve and time series analysis of classical novae and dwarf novae systems monitored/observed with the 1.5 m Russian-Turkish Joint telescope (RTT150) at the TUBITAK (The Scientific and Technical Research Council of Turkey) National Observatory in Antalya, Turkey. As part of a large program on CCD photometry of Cataclysmic Variables, V2275 Cyg (N 2001 No.2), RW UMi, FO Per and PX And were observed for a total of about 25 nights. The results on V2275 Cyg show that the system has a period of 0.463±0.014 or the 1-d alias 0.316±0.007 with a wide eclipse-like pattern (IAUC 8074). The power spectral analysis of the data on RW UMi reveal possible periodicities at around several frequencies (eg., 14.4, 16.7, 19, 30, 39, 46, 68, 108 in cycles per day) that could be interpreted as the binary period, spin period of the white dwarf and/or orbital sidebands of the system. We find that the radial velocity profiles of H-alpha lines and the photometry of the Dwarf Nova FO Per indicates the possible presence of a period around 0.1828 d.