Circular polarization survey of intermediate polars  I. Northern targets
 in the range 17 h &lt; RA &lt; 23 h

Aims. We aim at characterizing a sample of nine new hard X-ray selected cataclysmic variable (CVs), to unambiguously identify them as magnetic systems of the intermediate polar (IP) type. Methods. We performed detailed timing and spectral analysis by using X-ray, and simultaneous UV and optical data collected by XMM-Newton, complemented with hard X-ray data provided by INTEGRAL and Swift. The pulse arrival time were used to estimate the orbital periods. The broad band X-ray spectra were fitted using composite models consisting of different absorbing columns and emission components. Results. Strong X-ray pulses at the white dwarf (WD) spin period are detected and found to decrease with energy. Most sources are spin-dominated systems in the X-rays, though four are beat dominated at optical wavelengths. We estimated the orbital period in all system (except for IGR J16500-3307), providing the first estimate for IGR J08390-4833, IGR J18308-1232, and IGR J18173-2509. All X-ray spectra are multi-temperature. V2069 Cyg and RX J0636+3535 posses a soft X-ray optically thick component at kT ∼ 80 eV. An intense K α Fe line at 6.4 keV is detected in all sources. An absorption edge at 0.76 keV from OVII is detected in IGR J08390-4833. The WD masses and lower limits to the accretion rates are also estimated. Conclusions. We found all sources to be IPs. IGR J08390-4833, V2069 Cyg, and IGR J16500-3307 are pure disc accretors, while IGR J18308-1232, IGR J1509-6649, IGR J17195-4100, and RX J0636+3535 display a disc-overflow accretion mode. All sources show a temperature gradient in the post-shock regions and a highly absorbed emission from material located in the pre-shock flow which is also responsible for the X-ray pulsations. Reflection at the WD surface is likely the origin of the fluorescent iron line. There is an increasing evidence for the presence of a warm absorber in IPs, a feature that needs future exploration. The addition of two systems to the subgroup of soft X-ray IPs confirms a relatively large (∼30%) incidence.

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“…3.1.3 for its interpretation). Butters et al (2009) by using RXTE data of IGR J1509 found a signal at 809.7 ± 0.6 s, consistent with our results.…”

Section: Referencessupporting

confidence: 92%

“…asynchronously rotating WDs (P ω P Ω ) and except for a few cases (Piirola et al 1993;Potter et al 1997;Katajainen et al 2007;Butters et al 2009;Potter et al 2012), they do not show polarization. These systems are believed to possess weakly magnetized WDs (B < 10 MG).…”

Section: Introductionmentioning

confidence: 99%

Characterization of new hard X-ray cataclysmic variables

Bernardini

Martino

Falanga

et al. 2012

A&A

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“…The inferred magnetic field strengths are quite uncertain for most systems, being 9−21 MG for PQ Gem (Potter et al 1997), 9−27 MG for V2400 Oph (Vaeth 1997) and ∼30 MG for V405 Aur (Piirola et al 2008). A 20 MG field was proposed for RX J2133 (Katajainen et al 2007), while no field estimate is given for 1RXS J173021.5-055933 (Butters et al 2009). To really test the proposal made by Anzolin et al (2008), spectro-polarimetric measures of the magnetic field strengths are essential for all soft systems.…”

Section: Rx J2133mentioning

confidence: 99%

“…Lower temperatures would indicate higher field systems because of larger irradiated WD areas by cyclotron radiation. However, the recent detection of significant polarized emission in RX J2133 (Katajainen et al 2007) and 1RXS J173021.5-055933 (Butters et al 2009) adds them to the subset of soft X-ray and polarized IPs together with V2400 Oph, PQ Gem and V405 Aur. While the degree of polarization could also be affected by the accretion geometry, these five polarized systems possess soft blackbody components that span a wide range of temperatures, with three out of five displaying hot blackbodies.…”

Section: Rx J2133mentioning

confidence: 99%

Broad-band properties of the hard X-ray cataclysmic variables IGR J00234+6141 and 1RXS J213344.1+510725

Anzolin

Martino

Falanga

et al. 2009

A&A

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Context. A significant number of cataclysmic variables have been detected as hard X-ray sources in the INTEGRAL survey, most of them of the magnetic intermediate polar type. Aims. We present a detailed X-ray broad-band study of two new sources, IGR J00234+6141 and 1RXS J213344.1+510725, that allow us to classify them as secure members of the intermediate polar class. Methods. Timing and spectral analysis of IGR J00234+6141 are based on an XMM-Newton observation and INTEGRAL publicly available data. For 1RXS J213344.1+510725, we use XMM-Newton and Suzaku observations at different epochs, as well as INTEGRAL publicly available data. Results. We determine a spin period of 561.64 ± 0.56 s for the white dwarf in IGR J00234+6141. The X-ray pulses are observed up to ∼2 keV. From XMM-Newton and Suzaku observations of 1RXS J213344.1+510725, we find a rotational period of 570.862 ± 0.034 s. The observations span three epochs where the pulsation is observed to change at different energies both in amplitude and shape. In both objects, the spectral analysis spanned over a wide energy range, from 0.3 to 100 keV, shows the presence of multiple emission components absorbed by dense material. The X-ray spectrum of IGR J00234+6141 is consistent with a multi-temperature plasma with a maximum temperature of ∼50 keV. In 1RXS J213344.1+510725, multiple optically thin components are inferred, as well as an optically thick (blackbody) soft X-ray emission with a temperature of ∼100 eV. This adds 1RXS J213344.1+510725 to the growing group of soft X-ray intermediate polars.Conclusions. Though showing similar rotational periods and being hard X-ray sources, these two intermediate polars appear different in several respects, among which the presence of a soft X-ray component in 1RXS J213344.1+510725. This source also emits circularly polarized light in the optical band, thus joining the group of soft and polarized intermediate polars as a fifth member. How the hard X-ray and polarized emission are thermalized in these systems is a timely question.

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“…In the low state, one expects the mass-transfer rate to be reduced by about a factor 10 from the high state. -Magnetic moment: Butters et al (2009) found some evidence for circular polarisation in the I band, and variation of this with spin phase. This detection is marginal, however, and assuming a surface magnetic field of a few MG as for other intermediate polars for which circular polarisation has been detected, one obtains a magnetic moment of a few 10 32 -10 33 G cm 3 for a 0.7 M white dwarf.…”

Section: Introductionmentioning

confidence: 99%

The disappearance and reformation of the accretion disc during a low state of FO Aquarii

Hameury

Lasota

2017

A&A

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Context. FO Aquarii, an asynchronous magnetic cataclysmic variable (intermediate polar) went into a low state in 2016, from which it slowly and steadily recovered without showing dwarf nova outbursts. This requires explanation since in a low state, the mass-transfer rate is in principle too low for the disc to be fully ionised and the disc should be subject to the standard thermal and viscous instability observed in dwarf novae. Aims. We investigate the conditions under which an accretion disc in an intermediate polar could exhibit a luminosity drop of two magnitudes in the optical band without showing outbursts. Methods. We use our numerical code for the time evolution of accretion discs, including other light sources from the system (primary, secondary, hot spot). Results. We show that although it is marginally possible for the accretion disc in the low state to stay on the hot stable branch, the required mass-transfer rate in the normal state would then have to be extremely high, of the order of 10 19 g s −1 or even larger. This would make the system so intrinsically bright that its distance should be much larger than allowed by all estimates. We show that observations of FO Aqr are well accounted for by the same mechanism that we have suggested as explaining the absence of outbursts during low states of VY Scl stars: during the decay, the magnetospheric radius exceeds the circularisation radius, so that the disc disappears before it enters the instability strip for dwarf nova outbursts. Conclusions. Our results are unaffected, and even reinforced, if accretion proceeds both via the accretion disc and directly via the stream during some intermediate stages; the detailed process through which the disc disappears still requires investigation.

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Circular polarization survey of intermediate polars I. Northern targets in the range 17 h < RA < 23 h

Cited by 24 publications

References 46 publications

Characterization of new hard X-ray cataclysmic variables

Characterization of new hard X-ray cataclysmic variables

Broad-band properties of the hard X-ray cataclysmic variables IGR J00234+6141 and 1RXS J213344.1+510725

The disappearance and reformation of the accretion disc during a low state of FO Aquarii

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