arXiv subjects

Solen Balman

Publications and source records attributed to Solen Balman.

At least 19 recordsLinked to original sources

arXiv2026

High Resolution X-ray Spectroscopy of the Nova-Like Cataclysmic Variable BZ Cam using Chandra HETG: Diagnosis of the ADAF-like (Advective) Hot Flow

Nova-likes such as BZ Cam are high state Cataclysmic Variables showing hard X-ray emission that can be characterized with advective hot flows in the inner accretion disk. We explore Chandra High Energy Transmission Grating (HETG) observations of BZ~Cam for detailed line diagnosis and ionization conditions in the X-ray regime. We mostly find H- and He-like emission lines of Mg, Si, S, and Fe. All He-like line components of forbidden, intercombination and resonance lines are present. The R ratios of selected lines indicate plasma densities of a few $\times$10$^{12-14}$ cm$^{-3}$ and G ratios reveal temperatures (3-6)$\times$ 10$^6$ K where the Fe lines yield (1-3)$\times$ 10$^7$ K. The H to He line ratios and the R and G ratios show that the plasma is in a nonequilibrium ionization condition, which is consistent with our previous X-ray results and the accretion flow in the X-ray region being an ADAF-like (advective) hot flow. Simultaneous fits of the HEG and MEG spectra or the broadband joint spectra of ROSAT, Chandra zero order and NuSTAR yield temperatures 3.4-6.3 keV using a VNEI model of plasma emission (in XSPEC) or Bremsstrahlung emission. An additional power law is detected above 98\% Confidence Level in the broadband analysis. The orbital variations and the broadband spectra show dipping/veiling of the X-rays and an additional warm absorber model with an ionization parameter log($\xi$) = 2.7 is required at the 3$\sigma$ level, along with the VNEI model where the HEG and MEG simultaneous fits yield the log($\xi$) = 3.6 .

astro-ph.HE↗

arXiv2026

Plasma Dynamics of Radiative Cooling Accretion Flow in AM Herculis with XRISM

We present XRISM/Resolve high-resolution X-ray spectroscopy of the prototypical magnetic cataclysmic variable AM Herculis. All satellite lines of highly ionized Fe are fully resolved. Lighter element lines (Si, S, Ca) show 2 - 3 eV widths consistent with purely thermal broadening, while the broader 6 - 7 eV Fe lines require additional bulk Doppler broadening. Spin-phase-resolved modulations are clearly detected in the Fe XXV and Fe XXVI lines, with semi-amplitudes of $81.8\pm6$ km s$^{-1}$ and $132.5\pm9$ km s$^{-1}$, and mean velocities of $143.6\pm6$ km s$^{-1}$ and $225.6\pm8$ km s$^{-1}$, respectively. After removing these bulk Doppler shifts, we obtain intrinsic Doppler widths of $5.23_{-0.15}^{+0.16}$ eV for Fe XXV and $6.23_{-0.18}^{+0.19}$ eV for Fe XXVI, directly revealing gradients of bulk velocity and temperature in the cooling-flow plasma. We additionally examined the resonance anisotropy predicted by Terada et al. (1999, 2001): the equivalent widths of the Fe XXV and Fe XXVI resonance lines increase at the pole-on phase by factors of 1.30 - 1.35, in positive correlation with their oscillator strengths. Combining XRISM with simultaneous NuSTAR data and PSAC/MCVSPEC plasma models, we derive a self-consistent shock temperature of $24.0\pm0.1$ keV and shock velocity of $1,116\pm2$ km s$^{-1}$. Radiative transfer simulations of the resonance lines further constrain the shock density to about $(5 - 6)\times10^{15}$ cm$^{-3}$, providing a new density diagnostic for accretion columns. The resulting accretion column geometry has a height of 200 - 300 km and a radius of 200 - 400 km.

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arXiv2025

The Advanced X-ray Imaging Satellite (AXIS) Community Science Book

The AXIS Community Science Book represents the collective effort of 592 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24' field of view and an order of magnitude greater collecting area than Chandra in the 0.3-12 keV band. Combining sharp imaging, high throughput, and rapid response capabilities, AXIS will open new windows on virtually every aspect of modern astrophysics, exploring the birth and growth of supermassive black holes, the feedback processes that shape galaxies, the life cycles of stars and exoplanet environments, and the nature of compact stellar remnants, supernova remnants, and explosive transients. This book compiles 138 community-contributed science cases developed by five Science Working Groups focused on AGN and supermassive black holes, galaxy evolution and feedback, compact objects and supernova remnants, stellar physics and exoplanets, and time-domain and multi-messenger astrophysics. Together, these studies establish the scientific foundation for next-generation X-ray exploration in the 2030s and highlight strong synergies with facilities of the 2030s, such as JWST, Roman, Rubin/LSST, SKA, ALMA, ngVLA, and next-generation gravitational-wave and neutrino networks.

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arXiv2025

Broad Observational Perspectives Achieved by the Accreting White Dwarf Sciences in the XMM-Newton and Chandra Eras

Accreting white dwarf binaries (AWDs) comprise cataclysmic variables (CVs), symbiotics, AM CVns, and other related systems that host a primary white dwarf (WD) accreting from a main sequence or evolved companion star. AWDs are a product of close binary evolution; thus, they are important for understanding the evolution and population of X-ray binaries in the Milky Way and other galaxies. AWDs are essential for studying astrophysical plasmas under different conditions along with accretion physics and processes, transient events, matter ejection and outflows, compact binary evolution, mergers, angular momentum loss mechanisms, and nuclear processes leading to explosions. AWDs are also closely related to other objects in the late stages of stellar evolution, with other accreting objects in compact binaries, and even share common phenomena with young stellar objects, active galactic nuclei, quasars, and supernova remnants. As X-ray astronomy came to a climax with the start of the Chandra and XMM-Newton missions owing to their unprecedented instrumentation, new excellent imaging capabilities, good time resolution, and X-ray grating technologies allowed immense advancement in many aspects of astronomy and astrophysics. In this review, we lay out a panorama of developments on the study of AWDs that have been accomplished and have been made possible by these two observatories; we summarize the key observational achievements and the challenges ahead.

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arXiv2024

X-ray Spectroscopy of the Dwarf Nova Z Chamaeleontis in Quiescence and Outburst Using the XMM-Newton Observatory

We present X-ray spectroscopy of the SU UMa-type dwarf nova (DN) Z Cha using the EPIC and RGS instruments onboard the XMM-Newton Observatory. The quiescent system can be modeled by collisional equilibrium or nonequilibrium plasma models, yielding a kT of 8.2-13.0 keV at a luminosity of (5.0-6.0)$\times$10$^{30}$ erg/s. The spectra yield better reduced $\chi^{2}$ using partial covering absorbers of cold and photoionized nature. The ionized absorber has an equivalent N$_H$=(3.4-5.9)$\times$10$^{22}$ cm$^{-2}$ and a log($\xi$)=3.5-3.7 with (50-60)% covering fraction when VNEI model (XSPEC) is used. The line diagnosis in quiescence shows no resonance lines with only detected forbidden lines of Ne, Mg, Si. The H-like C, O, Ne, and Mg are detected. The strongest line is O VIII with (2.7-4.6)$\times$10$^{-14}$ erg/s/cm$^2$. The quiescent X-ray emitting plasma is not collisional and not in ionization equilibrium which is consistent with hot ADAF-like accretion flows. The line diagnosis in outburst shows He-like O, and Ne with intercombination lines being the strongest along with weaker resonance lines. This indicates the plasma is more collisional and denser, but yet not in a collisional equilibrium, revealing ionization timescales of (0.97-1.4)$\times$10$^{11}$ s cm$^{-3}$. The R-ratios in outburst yield electron densities of (7-90)$\times$10$^{11}$ cm$^{-3}$ and the G-ratios yield electron temperatures of (2-3)$\times$10$^{6}$ K. The outburst luminosity is (1.4-2.5)$\times$10$^{30}$ erg/s. The flow is inhomogeneous in density. All detected lines are narrow with widths limited by the resolution of RGS yielding Keplerian rotational velocities $<$1000 km/s. This is too low for boundary layers, consistent with the nature of ADAF-like hot flows.

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arXiv2021

The Remarkable Spin-down and Ultra-fast Outflows of the Highly-Pulsed Supersoft Source of Nova Hercules 2021

Nova Her 2021 (V1674 Her), which erupted on 2021 June 12, reached naked-eye brightness and has been detected from radio to $γ$-rays. An extremely fast optical decline of 2 magnitudes in 1.2 days and strong Ne lines imply a high-mass white dwarf. The optical pre-outburst detection of a 501.42s oscillation suggests a magnetic white dwarf. This is the first time that an oscillation of this magnitude has been detected in a classical nova prior to outburst. We report X-ray outburst observations from {\it Swift} and {\it Chandra} which uniquely show: (1) a very strong modulation of super-soft X-rays at a different period from reported optical periods; (2) strong pulse profile variations and the possible presence of period variations of the order of 0.1-0.3s; and (3) rich grating spectra that vary with modulation phase and show P Cygni-type emission lines with two dominant blue-shifted absorption components at $\sim 3000$ and 9000 km s$^{-1}$ indicating expansion velocities up to 11000 km s$^{-1}$. X-ray oscillations most likely arise from inhomogeneous photospheric emission related to the magnetic field. Period differences between reported pre- and post-outburst optical observations, if not due to other period drift mechanisms, suggest a large ejected mass for such a fast nova, in the range $2\times 10^{-5}$-$2\times 10^{-4} M_\odot$. A difference between the period found in the {\it Chandra} data and a reported contemporaneous post-outburst optical period, as well as the presence of period drifts, could be due to weakly non-rigid photospheric rotation.

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arXiv2020

Accretion Flows in Nonmagnetic White Dwarf Binaries as Observed in X-rays

Cataclysmic Variables (CVs) are compact binaries with white dwarf (WD) primaries. CVs and other accreting WD binaries (AWBs) are useful laboratories for studying accretion flows, gas dynamics, outflows, transient outbursts, and explosive nuclear burning under different astrophysical plasma conditions. They have been studied over decades and are important for population studies of galactic X-ray sources. Recent space- and ground-based high resolution spectral and timing studies, along with recent surveys indicate that we still have observational and theoretical complexities yet to answer. I review accretion in nonmagnetic AWBs in the light of X-ray observations. I present X-ray diagnostics of accretion in dwarf novae and the disk outbursts, the nova-like systems, and the state of the research on the disk winds and outflows in the nonmagnetic CVs together with comparisons and relations to classical and recurrent nova systems, AM CVns and Symbiotic systems. I discuss how the advective hot accretion flows (ADAF-like) in the inner regions of accretion disks (merged with boundary layer zones) in nonmagnetic CVs explain most of the discrepancies and complexities that have been encountered in the X-ray observations. I stress how flickering variability studies from optical to X-rays can be probes to determine accretion history and disk structure together with how the temporal and spectral variability of CVs are related to that of LMXBs and AGNs. Finally, I discuss the nature of accretion in nonmagnetic WDs in terms of ADAF-like accretion flows, and elaborate on the solutions it brings and its complications, constructing an observational framework to motivate new theoretical calculations that introduce this flow-type in disks, outflow and wind models together with disk-instability models of outbursts and nova outbursts in AWBs and WD physics, in general.

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arXiv2020

X-ray properties of dwarf nova EY Cyg and the companion star using an XMM-Newton observation

We present the X-ray analysis of dwarf nova EY Cyg using the 45 ks \textit{XMM-Newton} observatory archival data obtained in quiescence. We find orbital modulations in X-rays. We simultaneously fitted EPIC pn, MOS1 and MOS2 data using a model for interstellar medium absorption (\textit{tbabs}) and a multi-temperature plasma emission model with a power-law distribution of temperatures (CEVMKL) as expected from low accretion rate quiescent dwarf novae. The \textit{XMM-Newton} EPIC spectra of the source yields a maximum temperature $kT_{\rm max}$ $\sim$ 14.9$^{+3.3}_{-2.2}$ keV with an unabsorbed X-ray flux and luminosity of (1.8--2.0) $\times$ 10$^{-12}$ ergs$^{-1}$ cm$^{-1}$ and (8.7--9.7) $\times$ 10$^{31}$ ergs$^{-1}$, respectively, in the energy range 0.1 to 50 keV. There is 3--4 sigma excess at energies below 0.5 keV, we model the excess using \textit{MEKAL}, POWERLAW and BBODY models and favor the model \textit{MEKAL} which is physical. According to previous studies, the secondary in this system is thought to be a K-type star which may radiate in the soft X-ray region. The fit with an additive \textit{MEKAL} model gives a temperature of $kT$ $\sim$ 0.1 keV with an unabsorbed X-ray flux and luminosity of (2.7--8.8) $\times$ 10$^{-14}$ ergs$^{-1}$ cm$^{-1}$ and (1.3--4.2) $\times$ 10$^{30}$ ergs$^{-1}$, respectively, for the companion star. Based on the results from the timing and spectral analysis, we highly suggest that the secondary of EY Cyg is a K-type star.

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arXiv2017

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 [Puebla et al 2007]. 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 ($\dot{M} \sim $ a few $10^{-9}M_{\odot}$/yr). For V592 Cas, the slightly modified disk ($\dot{M} \sim 6 \times 10^{-9}M_{\odot}$/yr) completely dominates the UV. These results are consistent with Swift X-ray observations of these systems [Balman et al 2014], 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 (IUE) spectra UV slope decreases in the same order as the ratio of the X-ray flux to optical/UV flux: from SU UMa's, to U Gem's, Z Cam's, UX UMa's, and VY Scl's.

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arXiv2016

A Reanalysis of High Resolution XMM-Newton Data of V2491 Cyg Using Collisionally Ionized Hot Absorber Models

We present a reanalysis of XMM-Newton Reflection Grating Spectrometer data of the classical nova V2491 Cyg obtained from two different pointings, 40 d and 50 d after outburst utilizing the SRON software SPEX version 2.05.04. We aim to model absorption components using hot collisionally ionized absorber models along with interstellar absorption (of gas and dust origin separately). We find blackbody temperatures in a range 61-91 eV for the continuum yielding a white dwarf mass of 1.15-1.3 M_sun. We derive two different hot absorber components with blueshifts yielding 2900-3800 km/s for the first (day 40) and 2600-3600 km/s for the second observation 50 days after outburst consistent with ejecta/wind speeds. The two collisionally ionized hot absorption components have temperatures kT_1 =1.0-3.6 keV and kT_2 =0.4-0.87 keV with rms velocities (sigma_v) 872 km/s and 56 km/s. These are consistent with shock temperatures in the X-ray wavelengths. V2491 Cyg shows signature of H-burning with underabundant carbon C/C_sun=0.3-0.5, and enhanced nitrogen N/N_sun=5-7 and oxygen O/O_sun=16-43. We find the equivalent hydrogen column density of the hot collisionally ionized absorbers in a range (0.6-18.0)x10^{23} cm^{-2} and (2.0-5.3)x10^{23} cm^{-2} on days 40 and 50 after outburst, respectively. Our fits yield the most adequate redchisq (range 1.8-2.9) up-to-date obtained for the modeling of high resolution X-ray data of V2491 Cyg. An additional photoionized absorber (third intrinsic absorber component) originating in the shell/ejecta improves the model fits with redchisq in a range 1.7-2.5, but shows only (1-0.1)% of the absorption by the collisionaly-ionized hot gas. Our analysis reveals a second blackbody component on day 50 with effective temperature 120-131 eV and effective radius about 10% of the WD which may indicate the onset of magnetic accretion.

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arXiv2016

X-ray spectral and optical properties of a ULX in NGC 4258 (M106)

We study the X-ray and optical properties of the ultraluminous X-ray source (ULX) X-6 in the nearby galaxy NGC 4258 (M106) based on the archival {\it XMM-Newton}, {\it Chandra}, {\it Swift}, and {\it Hubble Space Telescope} ({\it HST}) observations. The source has a peak luminosity of $L_{\mathrm{X}} \sim 2 \times 10^{39}$ erg s$^{-1}$ in the {\it XMM-Newton} observation of 2004 June. Consideration of the hardness ratios and spectral model parameters shows that the source seems to exhibit possible spectral variations throughout the X-ray observations. In the images from the {\it HST}/Advanced Camera for Surveys (ACS), three optical sources have been identified as counterpart candidates within the 1$σ$ error radius of 0$\arcsec$.3. The brightest one has an absolute magnitude of $M_{V} \approx$ $-$7.0 and shows extended structure. The remaining two sources have absolute magnitudes of $M_{V} \approx$ $-$5.8 and $-$5.3 mag. The possible spectral types of the candidates from brightest to dimmest were determined as B6$-$A5, B0$-$A7, and B2$-$A3, respectively. The counterparts of the X-ray source possibly belong to a young star cluster. Neither the standard disk model nor the slim disk model provides firm evidence to determine the spectral characteristics of ULX X-6. We argue that the mass of the compact object lies in the range $10-15M_{\sun}$ indicating that the compact source is most likely a stellar-mass black hole.

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arXiv2014

Pre-outburst $Chandra$ Observations of the Recurrent Nova T Pyxidis

I present a total of 98.8 ksec ($\sim$ 3$\times$30 ksec) observation of T Pyx with the ACIS-S3 detector on-board the $Chandra$ Observatory obtained during the quiescent phase, about 2-3 months before its outburst in April 2011. The total $Chandra$ spectrum of the source T Pyx gives a maximum temperature kT$_{max}$$>$ 37.0 keV with (0.9-1.5)$\times 10^{-13}$ erg s$^{-1}$ cm$^{-2}$ and (1.3-2.2)$\times$10$^{32}$ erg s$^{-1}$ (at 3.5 kpc) in the 0.1-50 keV range using a multi-temperature plasma emission model (i.e., CEVMKL in XSPEC). I find a ratio of (L$_{x}$/L$_{disk}$)$\simeq$(2-7)$\times$10$^{-4}$ indicating considerable inefficiency of emission in the boundary layer. There is no blackbody emission with 2$σ$ upper limits kT$_{BB}$$<$ 25 eV and L$_{soft}$$<$ 2.0$\times$10$^{33}$ erg s$^{-1}$ in the 0.1-10.0 keV band. All fits yield only interstellar N${\rm _H}$ during quiescence. I suggest that T Pyx has an optically thin boundary layer (BL) merged with an ADAF-like flow (Advection-Dominated Flow) and/or X-ray corona in the inner disk indicating ongoing quasi-spherical accretion at (very) high rates during quiescent phases. Such a BL structure may be excessively heating the WD, influencing the thermonuclear runaway leading to the recurrent nova events. The central source (i.e., the binary system) emission and its spectrum is deconvolved with a detailed procedure at the sub-pixel level revealing an extended emission with S/N $\sim$6-10. The derived shape looks like an elliptical nebula with a semi-major axis $\sim$1.0 arc sec and a semi-minor axis $\sim$0.5 arc sec. The calculated approximate count rate of the extended emission is 0.0013-0.0025 c s$^{-1}$. The luminosity of the nebula is $\sim$(0.6-30.0)$\times$10$^{31}$ erg s$^{-1}$. The nebulosity seems consistent with an interaction of the outflow/ejecta from the 1966 outburst.

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arXiv2014

SWIFT XRT Observations of the Nova-like Cataclysmic Variables MV Lyr, BZ Cam and V592 Cas

We present a total of ~ 45 ksec (3$\times$15 ksec) of SWIFT XRT observations for three non-magnetic nova-like (NL) Cataclysmic Variables (CVs) (MV Lyr, BZ Cam, V592 Cas) in order to study characteristics of Boundary Layers (BL) in CVs. The nonmagnetic NLs are found mostly in a state of high mass accretion rate ($\ge$1$\times$10$^{-9}$ Msun 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 boundary layers 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 up-scattering of the soft disk photons. The X-ray luminosities of the (multi-temperature) thermal plasma emission in the 0.1-50.0 keV range are (0.9-5.0)$\times$10$^{32}$ erg/sec. The ratio of the X-ray and disk luminosities (calculated from the UV-optical wavelengths) yield an efficiency (L$_{x}$/L$_{disk}$) ~ 0.01-0.001. Given this non-radiative ratio for the X-ray emitting boundary layers 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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arXiv2013

Discovery of an X-ray Emitting Nebula around the Recurrent Nova T Pyxidis

I resolved and detected an X-ray nebulosity around the recurrent nova T Pyx using a 98.8 ksec observation with the ACIS-S detector on-board the Chandra Observatory during the quiescent phase of the nova before its outburst in 2011. The nebula shows an elliptical shape with an inner semi-major axis $\sim$ 0.45 arc sec and an outer semi-major axis $\sim$ 0.9 arc sec which indicates a torus-like or a ring-like shell structure around the nova. There is also a (conical) elongation towards the southern direction of about 1.85 arc sec. This structure may be part of a bipolar outflow from the source/nova. The count rate of the nebulosity is 0.0025$\pm$0.0010 c s$^{-1}$ and that of the the central binary is $\sim$ 0.003 c s$^{-1}$ over the 0.2-9.0 keV energy range. The best fitted spectrum of the X-ray nebula is a two-component plasma model (e.g., a double MEKAL) with $\sim$ 0.6 keV and $\sim$ 2.2 keV along with two different neutral hydrogen column densities of (0.2-0.9)$\times 10^{22}$ cm$^{-2}$ and (3.0-26.0)$\times 10^{22}$ cm$^{-2}$ for the two temperatures, respectively. I calculate an absorbed X-ray flux of (0.6-10.0)$\times10^{-14}$ erg cm$^{-2}$ s$^{-1}$ with a luminosity of (0.08-2.0)$\times10^{32}$ erg s$^{-1}$ (at 3.5 kpc) for the X-ray nebula. The estimated shocked mass is $\le1.8\times10^{-5}$ M$_{\odot}$. The central source spectrum can be fitted by a single MEKAL model with a temperature 9.2$^{<}_{-5.4}$ keV yielding a luminosity of about 5.2$\times10^{31}$ erg s$^{-1}$. The orbital period of the system is detected in the Chandra light curve.

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arXiv2012

X-ray variations in the inner accretion flow of Dwarf Novae

We show for five DN systems, SS Cyg, VW Hyi, RU Peg, WW Cet and T Leo 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 (10-3)$\times10^{9}$ 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 XMM-Newton data obtained in the quiescence and find X-ray time lags of 96-181 sec. This can be explained by the travel time of matter from a truncated inner disk to the white dwarf surface. 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 a 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 $α\sim0.25$ in the innermost parts of the accretion flow of DN systems.

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arXiv2012

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(ξ) = 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.

astro-ph.SR↗

arXiv2009

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 LMXBs in the 3--10 keV and 20--40 keV energy ranges. The spectral parameters derived from the fits to the INTEGRAL 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 flux between 4--200 keV are 5.9$\times 10^{-10}$ erg s$^{-1}$ cm$^{-2}$ for XB 1916-053, 3.3$\times 10^{-10}$ erg s$^{-1}$ cm$^{-2}$ for XB 1323-619, 21.6$\times 10^{-10}$ erg s$^{-1}$ cm$^{-2}$ for X 1624-490 and 11.0$\times 10^{-10}$ 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$\times 10^{15}$ 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 photo-ionized absorber model for the two sources show that XB 1916-053 has the highest ionized absorber amoung the two.

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arXiv2006

The Detection of a 3.5-h 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 (N 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) d (3.5 h). 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 magnitude) 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 which 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.

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