Magnetic CV Research Articles

Classifying IGR J15038−6021 as a magnetic CV with a massive white dwarf

ABSTRACT Cataclysmic variables (CVs) are binary systems consisting of a white dwarf (WD) accreting matter from a companion star. Observations of CVs provide an opportunity to learn about accretion discs, the physics of compact objects, classical novae, and the evolution of the binary and the WD that may ultimately end in a Type Ia supernova (SN). As Type Ia SNe involve a WD reaching the Chandrasekhar limit or merging WDs, WD mass measurements are particularly important for elucidating the path from CV to Type Ia SN. For intermediate polar (IP) type CVs, the WD mass is related to the bremsstrahlung temperature of material in the accretion column, which typically peaks at X-ray energies. Thus, the IPs with the strongest hard X-ray emission, such as those discovered by the INTEGRAL satellite, are expected to have the highest masses. Here, we report on XMM–Newton, Nuclear Spectroscopic Telescope Array (NuSTAR), and optical observations of IGR J15038−6021. We find an X-ray periodicity of 1678 ± 2 s, which we interpret as the WD spin period. From fitting the 0.3–79 keV spectrum with a model that uses the relationship between the WD mass and the post-shock temperature, we measure a WD mass of $1.36^{+0.04}_{-0.11}$ M⊙. This follows an earlier study of IGR J14091−6108, which also has a WD with a mass approaching the Chandrasekhar limit. We demonstrate that these are both outliers among IPs in having massive WDs and discuss the results in the context of WD mass studies as well as the implications for WD mass evolution.

XMM-Newton and TESS observations of the highly variable polar V496 UMa

Aims. We studied the temporal and spectral behavior of V496 UMa from the optical to the X-ray regimes. Methods. We used archival XMM-Newton and TESS observations obtained in 2017 and 2019, respectively, to perform a spectral and timing analysis of the highly variable magnetic CV. Results. The light curves of the TESS and XMM-Newton satellites reveal a double-humped pattern modulated with the periodicity of 91.058467 ± 0.00001 min. V496 UMa displays a two-pole accretion geometry in the high accretion state. X-ray spectra from these regions are composed of thermal plasma radiation and soft blackbody components with almost identical temperatures and a total accretion rate of Ṁ = 1.4(8) × 10−11 M⊙ yr−1. The X-ray centers of the humps show longitudinal shifts of −18° and 4°, and shifts around photometric phase zero of −172° and −186°, for the main hump and second hump, respectively. The long-term ZTF light curves reveal high and low accretions states. Low-state ZTF and SDSS photometric data are consistent with an 0.8 M⊙ white dwarf at 10 000 K and a main-sequence donor star with a spectral type of M5.0 at a Gaia determined distance of 758 pc. Conclusions. V496 UMa is a very bright polar in X-rays when it is in the high state. Due to its unusual geometric structure, mass accretion onto the second accretion pole is interrupted occasionally. This discontinuous behavior does not follow a certain pattern in time and has been observed so far only in the high state. The X-ray light curves display clear evidence of an accretion stream at the photometric phase of ϕ = 0.81, which does not show up in optical light curves. An accurate period was derived using the combined TESS and XMM-Newton data, which differs by 3.8σ from published results.

Circular polarimetry of suspect wind-accreting magnetic pre-polars

ABSTRACT We present results from a circular polarimetric survey of candidate detached magnetic white dwarf – M dwarf binaries obtained using the Nordic Optical Telescope, La Palma. We obtained phase resolved spectropolarimetry and imaging polarimetry of seven systems, five of which show clearly variable circular polarisation. The data indicate that these targets have white dwarfs with magnetic field strengths >80 MG. Our study reveals that cyclotron emission can dominate the optical luminosity at wavelengths corresponding to the cyclotron emission harmonics, even in systems where the white dwarfs are only wind-accreting. This implies that a very significant fraction of the stellar wind of the companion star is captured by the magnetic white dwarf reducing the magnetic braking in pre-cataclysmic variables (CVs). Furthermore, the polarimetric confirmation of several detached, wind-accreting magnetic systems provides observational constraints on the models of magnetic CV evolution and white dwarf magnetic field generation. We also find that the white dwarf magnetic field configuration in at least two of these systems appears to be very complex.

A Systematic Search for Outbursting AM CVn Systems with the Zwicky Transient Facility

Abstract AM CVn systems are a rare type of accreting binary that consists of a white dwarf and a helium-rich, degenerate donor star. Using the Zwicky Transient Facility (ZTF), we searched for new AM CVn systems by focusing on blue, outbursting stars. We first selected outbursting stars using the ZTF alerts. We cross matched the candidates with Gaia and Pan-STARRS catalogs. The initial selection of candidates based on the Gaia BP-RP contains 1751 unknown objects. We used the Pan-STARRS g-r and r-i color in combination with the Gaia color to identify 59 strong AM CVn candidates. We obtained identification spectra of 35 sources, of which 18 are high-priority candidates, and discovered nine new AM CVn systems and one magnetic CV that shows only He-ii lines. Using the outburst recurrence time, we estimate the orbital periods of the nine new AM CVn systems that are in the range of 29–50 minutes. We conclude that targeted follow up of blue, outbursting sources is an efficient method to find new AM CVn systems and we plan to follow up all candidates we identified to systematically study the population of outbursting AM CVn systems.

Spectral characterization of tetradentate Schiff base complexes of N2O2 donor groups

Copper(II) complexes of tetra dentate Schiff bases N, N’ – disalicylidene – 1, 2 – phenylenediamine(H2dsp), N, N’ – disalicylidene – 3, 4 – diaminotoluene(H2dst), 4 – nitro - N, N’ – disalicylidene – 1, 2 – phenylenediamine(H2ndsp), N, N’ – disalicylideneethylenediamine(H2salen) have been synthesized and characterized by elemental analysis, electronic spectra, IR spectra, magnetic susceptibility measurement, EPR, CV and thermal studies. TG studies show that Cu(dsp) and Cu(ndsp) complexes thermally degrade in two steps and Cu(dst) and Cu(salen) in one step. Kinetic and thermodynamic parameters were computed from thermal decomposition data. The activation energies of both the thermal degradation step lie in between 52 – 74 kJ/mol .

XMM-Newton observations of eleven intermediate polars and possible candidates

Aims. We aim to identify new intermediate polars (IPs) in XMM-Newton observations from a list of promising candidates. By selecting targets not previously known to be X-ray bright, we aim to uncover evidence for an X-ray underluminous IP subpopulation. Methods. We performed period searches on the XMM-Newton X-ray and optical data of our targets to seek both the spin and orbital periods, which differ in IPs. We also investigated the X-ray spectra to find the hot plasma emission shown by these objects. With archival Swift data we coarsely investigated the long-term X-ray variability, and with archival optical data from a variety of catalogues, we compared the optical to X-ray luminosity to identify X-ray faint objects. This paper presents the first XMM-Newton observation of the prototype IP, DQ Her. Results. We find firm evidence for HZ Pup, V349 Aqr, and IGR J18151-1052 being IPs, with likely white dwarf spin periods of 1552, 390, and 390 s, respectively. The former two have luminosities typical of IPs, and the latter is strongly absorbed and with unknown distance. GI Mon and V1084 Her are apparently non-magnetic CVs with interesting short-term variability unrelated to WD spin. V533 Her is probably a magnetic CV and remains a good IP candidate, while V1039 Cen is possibly a polar. The remaining candidates were too faint to allow for any firm conclusions.

Electrochemical behavior, structural, morphological, Calf Thymus-DNA interaction and in-vitro antimicrobial studies of synthesized Schiff base transition metal complexes

New tetradentate Schiff base transition metal complexes have been derived from salicylidene-4-imino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one and histidine were characterized by CHN analysis, magnetic susceptibility measurements, molar conductance, FAB-MS, IR, 1H-NMR, UV, CV, EPR, Fluorescence emission, AFM and Powder XRD techniques. AFM images and Powder XRD data endure that the complexes are nano-size grains with polycrystalline structure. The spectral evidences showed that all the metal chelates are square planar geometry except [VOL] complex which exist square-pyramidal geometry. Electrochemical data (CV) for [CuL] and [VOL] complexes in acetonitrile solution indicates that the redox potential of metal ions is affected by the coordinated ligand. Electron Spin Resonance (ESR) spectra of [CuL] and [VOL] complexes were well coinciding with proposed geometries and other reported complexes. CT-DNA interaction studies of [CuL] complex reveals that an intercalation binding mode occurs between complex and DNA base pairs. The in vitro antimicrobial activity of complexes has been tested against the growth of some fungal and bacterial species persist that chelates have better control than ligand.

The true nature of Swift J0746.3-1608: a possible Intermediate Polar showing accretion state changes

Optical and X-ray observations suggested that the 9.38 h binary, SWIFT J0746.3- 1608 could be a Cataclysmic Variable of the magnetic or nova-like type, or a low mass X-ray binary. Its optical, UV, and X-ray light curves are strongly variable over years. We report on a recent XMM-Newton observation (28 April 2018), when the source had recovered from a deep low state that likely begun mid-late 2011. We detect for the first time a signal at about 38 min that we interpret as the rotation of the accreting white dwarf primary. Its amplitude decreases with increasing energy, indicating localised photoelectric absorption from cold material. The X-ray spectrum shows optically thin thermal emission with excess at the iron complex, absorbed by a dense medium partially covering the X-ray source. Based on these features, we propose that SWIFT J0746.3-1608 is a magnetic CV of the Intermediate Polar (IP) type. The long-term light curves at different wavelengths show high and low states, a rare phenomenon in the IP subclass and observed so far in only three other systems. The long orbital period, the peculiar long term variability, and its proposed magnetic nature, makes SWIFT J0746.3-1608 an interesting evolutionary test case.

IGR J14257−6117, a magnetic accreting white dwarf with a very strong strong X-ray orbital modulation

IGR J14257-6117 is an unclassified source in the hard X-ray catalogues. Optical follow-ups suggest it could be a Cataclysmic Variable of the magnetic type. We present the first high S/N X-ray observation performed by \XMM\ at 0.3--10 keV, complemented with 10--80 keV coverage by \Swift/BAT, aimed at revealing the source nature. We detected for the first time a fast periodic variability at 509.5\,s and a longer periodic variability at 4.05\,h, ascribed to the white dwarf (WD) spin and binary orbital periods, respectively. These unambiguously identify IGR J14257-6117 as a magnetic CV of the Intermediate Polar (IP) type. The energy resolved light curves at both periods reveal amplitudes decreasing with increasing energy, with the orbital modulation reaching $\sim100\%$ in the softest band. The energy spectrum shows optically thin thermal emission with an excess at the iron complex, absorbed by two dense media (${\rm N_{H}\sim10^{22-23}\,cm^{-2}}$), partially covering the X-ray source. These are likely localised in the magnetically confined accretion flow above the WD surface and at the disc rim, producing the energy dependent spin and orbital variabilities, respectively. IGR J14257-6117, joins the group of strongest orbitally modulated IPs now counting four systems. Drawing similarities with low-mass X-ray binaries displaying orbital dips, these IPs should be seen at large orbital inclinations allowing azimuthally extended absorbing material fixed in the binary frame to intercept the line of sight. For IGR J14257-6117, we estimate ($50^o\,\lesssim\,i\,\lesssim\,70^o$). Whether also the mass accretion rate plays a role in the large orbital modulations in IPs cannot be established with the present data.

Identifying IGR J14091−6108 as a magnetic CV with a massive white dwarf using X-ray and optical observations

IGR J14091-6108 is a Galactic X-ray source known to have an iron emission line, a hard X-ray spectrum, and an optical counterpart. Here, we report on X-ray observations of the source with XMM-Newton and NuSTAR as well as optical spectroscopy with ESO/VLT and NOAO/SOAR. In the X-rays, this provides data with much better statistical quality than the previous observations, and this is the first report of the optical spectrum. Timing analysis of the XMM data shows a very significant detection of 576.3+/-0.6 s period. The signal has a pulsed fraction of 30%+/-3% in the 0.3-12 keV range and shows a strong drop with energy. The optical spectra show strong emission lines with significant variability in the lines and continuum, indicating that they come from an irradiated accretion disk. Based on these measurements, we identify the source as a magnetic Cataclysmic Variable of Intermediate Polar (IP) type where the white dwarf spin period is 576.3 s. The X-ray spectrum is consistent with the continuum emission mechanism being due to thermal Bremsstrahlung, but partial covering absorption and reflection are also required. In addition, we use the IP mass (IPM) model, which suggests that the white dwarf in this system has a high mass, possibly approaching the Chandrasekhar limit.

ENIGMAS FROM THE SLOAN DIGITAL SKY SURVEY DR7 KLEINMAN WHITE DWARF CATALOG

We report results from a continuation of our searches for high field magnetic white dwarfs paired in a detached binary with non degenerate companions. We made use of the Sloan Digital Sky Survey DR7 catalog of Kleinman et al. (2013) with 19,712 spectroscopically-identified white dwarfs. These include 1,735 white dwarf plus M dwarf detached pairs (almost 10\% of the Kleinman at al.'s list). No new pairs were found, although we did recover the polar (AM~Herculis system) ST\,LMi in a low state of accretion. With the larger sample the original situation reported ten years ago remains intact now at a much higher level of statistical significance: in the selected SDSS sample, high field magnetic white dwarfs are not found in an apparently-detached pairing with an M dwarf, unless they are a magnetic CV in a low state of accretion. This finding strengthens the case that the fields in the isolated high field magnetic white dwarfs are generated by stellar mergers but also raises questions on the nature of the progenitors of the magnetic CVs.

Suzaku View of Magnetic Cataclysmic Variables

Results of magnetic cataclysmic variable studies performed with the Suzaku satellite are reviewed in this article. Particular emphasis is placed on the recent update of X-ray spectral model of intermediate polars, possible kinematically redshifted fluorescent Fe K emission lines, and the magnetic CV contribution to the Galactic ridge X-ray emission.

Modified Phenyl Groups on Pyrazin Groups to Synthesized Cobalt String Complexes

In the literature, ligand such as oligo-α-pyridylamines and oligo-naphthyridylamine are usually used in the linear metal string complex. In addition to all of the above, another series of ligand is synthesized by mixing two types of ligands. In other words, the type of ligand contains pyridyl and naphthyridyl groups. Permuting the possible permutation, we can find that symmetrical and the shortest ligand is 2,7-bis(α-pyridylamino)-1,8-naphthyridine (H2bpyany). Complexes contain bpyany2-, hexa-nickel or hexa-cobalt, axial ligands such as chloride and thiocyanate, and anions such as hexafluorophosphate and tetrafluoroborate were published1, 2. Another similar ligand that H2bpyany replaces pyridyl groups by pyrimidyl group is 2,7-bis(α-pyrimidylamino)-1,8-naphthyridine (H2bpmany). Hexanickel complexes with bpmany2- were also published3. According to the above, if we replace pyridyl group by pyrazin group, properties of complexes such as magnetic property, CV and resistance make a change. 2,7-bis(α-pyrazinamino)-1,8-naphthyridine (H2bpzany) and nickel or cobalt ions were reacted. We can get the signal in MALDI, but we cannot isolate the target. Because of this, we modified phenyl groups on pyrazin groups. By 2,7-bis(5-phenyl)-α-pyrazinamino-1,8-naphthyridine (H2bphpzany), [Co5(bphpzany)4(NCS)2] (1), [Co6(bphpzany)4(NCS)2](PF6)n (n=1 (2), n=2 (3)) have been synthesized and the crystal structures for complex 1–3 have been determined by X-ray crystallography. Three complexes are the similar component of four ligands, five or six cobalt ions, two thiocyanates as axial ligands, and hexafluorophosphate as counterions. The structural characterization is that the cobalt chain is helically wrapped by four bphpzany2–. Complex 1–3 have Co510+, Co612+ configurations, and all are air-stable.

Identification of 23 accreting binaries in the Galactic Bulge Survey

(Abridged:) We present the identification of optical counterparts to 23 Galactic Bulge Survey X-ray sources. We report their accurate coordinates and optical spectra acquired at the VLT and Magellan. All sources are classified as accreting binaries according to their emission line characteristics. To distinguish accreting binaries from chromospherically active objects we develop and explain criteria based on Halpha and HeI 5786,6678 emission line properties available in the literature. The spectroscopic properties and photometric variability of all the objects are discussed and a classification of the source is given where possible. Among the 23 systems, at least 9 of them show an accretion-dominated optical spectrum (CX28, CX63, CX70, CX128, CX142, CX207, CX522, CX794, CX1011) and another 6 show photospheric lines from a late-type donor star in addition to accretion disc emission (CX44, CX93, CX137, CX154, CX377 and CX1004) indicating that they are probably accreting binaries in quiescence or in a low accretion rate state. Two sources are confirmed to be eclipsing: CX207 and CX794. CX207 shows a broad asymmetric Halpha profile blue-shifted by >300 km/s. Such line profile characteristics are consistent with a magnetic (Polar) CV. CX794 is an eclipsing nova-like CV in the period gap. Time-resolved photometry and the large broadening of the Halpha emission lines in CX446 (2100 km/s FWHM) suggest that this is also an eclipsing or high-inclination accreting binary. Finally, the low-accretion rate source CX1004 shows a double-peaked Halpha profile with a FWHM of 2100 km/s. This supports a high inclination or even eclipsing system. Whether the compact object is a white dwarf in an eclipsing CV or a black hole primary in a high-inclination LMXB remains to be established.

Life after eruption - I. Spectroscopic observations of 10 nova candidates★

We have started a project to investigate the connection of post-novae with the population of cataclysmic variables. Our first steps in this concern improving the sample of known post-novae and their properties. Here we present the recovery and/or confirmation of the old novae MT Cen, V812 Cen, V655 CrA, IL Nor, V2109 Oph, V909 Sgr, V2572 Sgr, and V728 Sco. Principal photometric and spectroscopic properties of these systems are discussed. We find that V909 Sgr is a probable magnetic CV, and that V728 Sco is a high-inclination system. We furthermore suggest that the two candidate novae V734 Sco and V1310 Sgr have been misclassified and instead are Mira variables.

Paloma (RX J0524+42): the missing link in magnetic CV evolution?

Decent optical photometry of the candidate magnetic CV Paloma has uncovered three persistent periods at 157, 146, and 136 min, which we interpret as the manifestation of the orbital motion of the system, the white dwarf’s spin, and a related side-band frequency of the other two. All three periodicities are caused by a double-humped modulation of about 1 mag appearing only at certain fractions of the beat cycle, and it probably originates from one or two accretion spots. Our data is consistent with two plausible solutions, with the spin period being either 146 or 136 min. The appearance of a corresponding spin-folded light curve suggests two different scenarios, for which either pole switching between two diametrically opposed accretion regions (for Pspin = 146 min) or pole migration of one single spot (with Pspin = 136 min) is the preferred accretion mode. Complementary ROSAT X-ray observations and low-resolution spectroscopy provide supporting evidence of the magnetic nature of the object. Depending on the choice of the spin period, the degree of asynchronism with respect to the orbital period is 7% or 14%, implying a beat period of 0.7 or 1.4 days. Thus, the source populates the gap between the near-synchronous polars (<2%) and the DQ Herculis stars with long spin periods (e.g. EX Hya, V1025 Cen, DW Cnc). With an orbital period right within the period gap, Paloma is a key object for magnetic CV evolution: it might be the first bona fide transition object between the DQ Her and AM Her system with a white dwarf currently in the process of synchronisation.

20-100 keV properties of cataclysmic variables detected in the INTEGRAL/IBIS survey

Analysis of INTEGRAL/IBIS survey observations has revealed that the rare intermediate polar and asynchronous polar cataclysmic variables are consistently found to emit in the 20-100 keV energy band, whereas synchronous polars and the common non-magnetic CVs rarely do so. From the correlation of a candidate INTEGRAL/IBIS survey source list with a CV catalogue, 15 CV detections by IBIS have been established including a new INTEGRAL source IGR J06253+7334. The properties of these sources and 4 additional CV candidates are discussed in the context of their 20-100 keV emission characteristics and we conclude that the INTEGRAL mission is an important tool in the detection of new magnetic CV systems. Furthermore, analysis of the time-averaged spectra of CVs detected by INTEGRAL indicate that although there is little difference between the spectral slopes of the different sub-types, intermediate polars may be considerably more luminous than polars in the soft gamma-ray regime. We also present the detection of an unusual high-energy burst from V1223 Sgr discovered by inspection of the IBIS light-curve. Additionally, we have compared the IBIS and optical AAVSO light-curves of SS Cyg and extracted IBIS spectra during single periods of optical outburst and quiescence. We find that the 20-100 keV flux is an order of magnitude greater during optical quiescence. This is in agreement with previous studies which show that the hard X-ray component of SS Cyg is suppressed during high accretion states

Density Diagnostics of the Hot Plasma in AE Aquarii withXMM‐Newton

We report on XMM-Newton observations of the magnetic CV AE Aqr. High-resolution spectroscopy of the He-like triplet of N and O with the RGS has enabled us to measure the electron number density of the plasma as ~1011 cm-3. Incorporating this with the emission measure, we estimate the geometrical scale of the plasma emitting these lines to be lp (2-3) × 1010 cm. Since the density and the scale are both incompatible with the standard postshock accretion column of an mCV, the plasma cannot be a product of mass accretion onto the white dwarf. The widths of the H-like Kα emission lines of N and O (=1250-1600 km s-1) are of similar magnitude to the thermal velocity dispersion of the hottest part of the plasma, where kTmax is 4.6 keV. It is known that Balmer series and UV emission lines also show a similar velocity dispersion. In addition, like these lines, the X-ray emission lines are found to show dramatic flaring activity. These facts strongly suggest that all these broad emission lines from X-ray to optical wave bands are produced in the course of adiabatic cooling of the plasma once heated up to Tmax in the deep gravitational potential of the white dwarf. This interpretation can resolve the problem of the absence of the high-velocity component in the Hα emission line spectrum by a scenario where the plasma that is expelled due to the propeller action is still too hot to emit the Hα line within a region of r < lp (roughly equal to the Roche lobe size) from the white dwarf where the high-velocity component is expected to originate.

Three dimensional hydrogen-bonding network in a copper complex of 2-hydroxy-1,4-naphthoquinone: structural, spectroscopic and magnetic properties

Abstract Supramolecular [Cu(II)(ONQ)2(H2O)2]n (1) a complex of the 2-hydroxy-1,4-naphthoquinone ligand (2HNQ), has been synthesized using CuCl2 · 2H2O. ONQ is the deprotonated oxidized form of the ligand (viz. 2-oxido-1,4-naphthoquinone). The complex has been characterised by X-ray crystallography, variable temperature magnetic susceptibility measurements (SQUID), EPR and CV studies. The crystal structure of 1 has been solved at 295 and 161 K. The cell volume decreases from 435.3(6) A3 at 295 K to 427.9(6) A3 at 161 K. The monomeric units of 1 are linked by three types of intermolecular hydrogen bondings through coordinated ONQ ligands and water molecules, which results in a supramolecular three dimensional hydrogen bonding network. The magnetic susceptibility data of 1 were best fitted with the Bonner Fisher equation with the coupling parameter J = −3.2 cm−1, indicating a weak antiferromagnetic interaction along the chain.

Mononuclear and homobinuclear vanadium(IV), chromium(III), molybdenum(III), and uranium(VI) chelates with ortho-cresolphthalein complexone

Mononuclear and homobinuclear o-cresolphthalein complexone complexes with VO2+, Cr3+, MoO+, and UO2 2+ have been prepared and their structures investigated. The empirical formulas, the mode of bonding, and the geometry of the complexes were obtained from elemental and thermal analyses, IR, electronic and ESR spectra, magnetic moment determinations, DC and CV polarographic studies.