arXiv subjects

Martina Veresvarska

Publications and source records attributed to Martina Veresvarska.

11 recordsLinked to original sources

arXiv2026

The X-ray and optical emission of the intermediate polar Swift J0614.0+1709

We present the first detailed X-ray and optical study of the intermediate polar Swift J0614.0+1709 based on a pointed XMM-Newton observation complemented by long-term optical photometry from TESS. A strong coherent modulation at the white dwarf spin period was detected in X-rays, with a period of $\sim$1411 s, confirming the magnetic nature of the system. The X-ray spin pulse exhibits a pronounced energy dependence, with the modulation amplitude decreasing towards higher energies, consistent with phase-dependent absorption in the accretion flow. Phase-resolved spectroscopy further shows that the spin variability is primarily driven by changes in the covering fraction of the partial-covering absorber. The broadband X-ray spectrum is well described by a partially absorbed thermal plasma model with a temperature of $\sim$12 keV and a soft blackbody component at $\sim$63 eV. The inferred bolometric luminosity of $\sim$5$\times$10$^{34}$ erg s$^{-1}$ places the source among the more luminous intermediate polars. The TESS observations reveal substantial sector-to-sector variability in the relative strengths of the orbital and spin modulations. While the spin signal remains persistently dominant, the beat modulation varies significantly and disappears entirely in one Sector, suggesting temporal changes in the contribution of the reprocessing region(s). The orbital and, to a lesser extent, spin modulation amplitudes show some tendency to be stronger during brighter optical states, suggesting that changes in the mass transfer rate may influence the optical emission and modulation amplitudes. Overall, Swift J0614.0+1709 is a comparatively X-ray luminous intermediate polar exhibiting complex optical variability characterised by changes in pulse morphology and recurrent brightening events, making it a valuable target for future simultaneous optical and X-ray studies.

astro-ph.HE↗

arXiv2026

On the frequency-dependent time lags of the intermediate polar V709 Cas

Cataclysmic variables (CVs) are binary systems in which a white dwarf (WD) primary accretes material from a late-type secondary, typically via a disc. To date, only six CVs, all of which are non-magnetic, have been found to exhibit lags (delayed variability in one band with respect to another). In all six cases, these lags are ``red'' (i.e., red lags blue) with a time lag of order seconds. While there is no generally accepted mechanism for producing red lags in CVs, current theories suggest reprocessing in the disc, either on the thermal or recombination time-scales, or inside-out shocks propagating through the disc. Using $g$-, $r$-, and $i$-band data from the OPtical TIming CAMera (OPTICAM), we report the discovery of frequency-dependent red lags from V709 Cas: a magnetic CV of the intermediate polar (IP) subclass. These red lags reach a maximum of $\sim$4--6 s on time-scales of 7.4--13.0 min, similar to previously-reported lags in non-magnetic CVs. The detection of lags in an IP is significant as the WD's magnetic field truncates the accretion disc, limiting disc-based lag mechanisms to large radii; as a result, characteristic accretion disc time-scales cannot explain the observed lags. However, recombination can occur on second time-scales, even in systems with truncated discs. For example, we show that recombination in the disc's bright spot, where overflowing material from the secondary meets the outer-edge of the disc, plausibly explains V709 Cas's optical spectrum, the prominence of optical spin-orbit beat pulsations, and the red lags found in this work.

astro-ph.SR↗

arXiv2026

COPAS: Compact Objects and the Physics of Accretion Survey I. Accreting Binaries with P < 83 Minutes

We present the first results from the Compact Objects and the Physics of Accretion Survey (COPAS), a high-cadence photometric survey focused on the detection of accreting white dwarf binaries mainly through their outbursts using TESS. From an initial sample of 2,054 cataclysmic variable (CV) candidates observed during TESS Cycle 6 and 7, we identify 11 systems with periods below 83 minutes. This includes 7 AM CVns and 4 CVs. Our Gemini spectroscopic data confirm ZTF18aaxuusk and ASASSN-21eo as AM CVns, while Gaia21akb is confirmed as a CV. We provide the first period measurements for 6 out of the 11 systems. Complementing our TESS data with ground-based observations, we measured superoutburst recurrence times of approximately one year for the AM CVn systems ASASSN-21in and ZTF18aaxuusk, and 1.8-2.0 years for the short-period CVs ASASSN-18rd and ASASSN-15ev. Using TESS, we also estimate the mass-ratio for ASASSN-19ct (q = 0.05 +/- 0.02), which is consistent with a highly evolved low-mass donor star. Though the number of ultracompact systems detected among the total sample is low (0.54%), and likely the result of observational biases and intrinsic population rareness, the reclassification of 5 systems as AM CVns highlights the importance of continuous monitoring to identify more systems through their outbursts and short periods.

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arXiv2026

The Long-Period Radio Transient and Cataclysmic Variable ASKAP J1745-5051: Evidence for a 15,000 K White Dwarf and a Sub-Stellar Donor

Long-period transients (LPTs) are radio sources that exhibit polarized periodic radio bursts on time-scales of minutes to hours. At least some LPTs are associated with white dwarfs (WDs) in close binary systems. However, the evolutionary connection between LPTs and accreting WDs (aka ``cataclysmic variables'' [CVs]) has been unclear. The recent discovery of ASKAP J1745-5051 has been a breakthrough: this system is a bona-fide LPT that is also an X-ray emitting magnetic CV (mCV) with P_orb ~ 1.3 hrs. Here, we construct the broad-band far-UV through near-IR SED for the system and show that it is well described by two components: a 15,000 K WD (which dominates the far-UV through optical bands) and a sub-stellar (M_2 ~ 0.05~M_sun, T_eff ~ 1800 K) donor star (which dominates in the K_s band). Our SED-fitting results differ from those in the discovery paper for four reasons: (i) we fix an issue with the treatment of reddening/extinction; (ii) we discard photometric measurements that are irreparably contaminated by an unrelated star located just 0.9" from the target; (iii) we add near-infrared brightness measurements obtained from PSF-fitting photometry on archival VISTA/VHS observations; (iv) we fit the data with synthetic spectra based on model atmospheres (rather than with blackbodies). The inferred WD temperature is reasonable for an accretion-heated primary in a short-period mCV. The sub-stellar nature of the donor suggests that the system is a "period bouncer" that has already evolved past the CV period minimum. The SED fit also yields a distance of d ~ 320 pc, only ~4x larger than that to the nearest confirmed mCV. Since the fraction of the sky swept out by the radio beam is likely to be small, systems like ASKAP J1745-5051 could make up a large percentage of mCVs. This may point towards a connection between LPTs and the ``missing'' population of period bouncers among CVs.

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arXiv2026

A Systematic Search for Optical Outbursts in IPs Using ASAS-SN

Cataclysmic variables can show rapid increases in optical flux. Intermediate polars (IPs), a subset with strong magnetic fields that disrupt the inner accretion disc, have been thought to possess truncated discs that rarely undergo the disc-instability outbursts seen in dwarf novae. However, the discovery of micronovae and magnetic-gating bursts suggests that such events may occur even without a fully developed disc. Using data from the All-Sky Automated Survey for Supernovae (ASAS-SN), we identify a previously unrecognised population of short-timescale optical outbursts in IPs. Initial energy estimates indicate that at least half of these bursts may be consistent with micronovae, though limited cadence reduces our ability to classify each event with high confidence. These detections should therefore be regarded as evidence of short outbursts in IPs rather than definitive micronova identifications. Our results show that such bursts are more common in IPs than assumed and may include a substantial fraction of micronovae. Simulations reveal that if micronovae occur once per year at regular intervals, up to 30\% of the shortest bursts could be missed over a 10-year observing baseline. Under the same assumptions, and assuming all IPs display micronovae, we would expect 50--70\% of IPs to show these bursts, yet only 14\% of known IPs in our sample do so. This discrepancy suggests that not all IPs undergo micronovae. Overall, this work establishes the first comprehensive set of short burst detections in IPs, providing a foundation for future investigations and a list of candidate micronova systems for follow-up analysis.

astro-ph.HE↗

arXiv2026

A Catalogue of Orbital Periods of Cataclysmic Variables and Candidates from TESS Observations

We present a systematic analysis of 2544 cataclysmic variable systems and related candidates observed by the Transiting Exoplanet Survey Satellite (TESS), with the aim of compiling a comprehensive catalogue of orbital periods. Using 2-minute photometric time-series data, we applied an automated algorithm to generate Lomb-Scargle periodograms and identify the most significant coherent periodic signals, which were subsequently verified through visual inspection. This process yielded a confident sample of 910 sources exhibiting at least one periodic signal, hereafter referred to as the Cataclysmic Variable Confident Catalogue (CCC). For each object, we report the most likely orbital period together with additional periodic features such as spin modulations and/or superhump signals when present. To assess consistency with previously published measurements, we cross-matched the CCC with the Ritter \& Kolb catalogue, identifying 300 overlapping systems, of which 215 showed full agreement with the R\&K orbital periods, while 39 displayed discrepancies for which the R\&K values were revised based on our TESS measurements and supporting evidence from the literature. Overall, the CCC provides a means to validate known orbital periods, propose corrections where necessary, and offer new determinations for systems with previously unknown periods, thereby supporting a more complete and reliable characterisation of the cataclysmic variable population.

astro-ph.SR↗

arXiv2026

The Inner and Outer Shock Layers of Bow Shocks in Cataclysmic Variables

Bow shocks around cataclysmic variables (CVs) have traditionally been identified with a single bright optical arc. This feature has been interpreted as the bow shock formed by the interaction between a sustained outflow and the interstellar medium (ISM). We show that this interpretation is incomplete. Generic wind-ISM interaction theory predicts a two-shock configuration consisting of an inner terminal wind (reverse) shock and an outer forward shock, separated by a hot, low-density shocked wind cavity. Using archival ultraviolet, optical, and infrared imaging of the nova-like systems BZ Cam and V341 Ara, and the polar 1RXS J052832.5+283824, we find that the nebulae around all three systems exhibit this layered structure. In each case, the previously identified bow shock bright in Halpha and [OIII] corresponds to a compact inner arc, while additional emission components reveal a more extended morphology. Specifically, each system shows an outer arc detected in mid-infrared images, and the region between the optical and infrared arcs is filled with faint Halpha emission and, where available, far ultraviolet emission. We identify this infrared arc, reported here for the first time in these systems, as the sweep-up boundary of the forward shock, while the bright inner optical arc corresponds to the terminal wind shock rather than the forward shock as previously assumed. These results reveal that the true extent and layered structure of bow shocks around CVs only become apparent when observations extend beyond the optical band.

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arXiv2026

A persistent bow shock in a diskless magnetised accreting white dwarf

Stellar bow shocks are formed when an outflow interacts with the interstellar medium. In white dwarfs accreting from a binary companion, outflows are associated with either strong winds from the donor star, the accretion disk, or a thermonuclear runaway explosion on the white dwarf surface. To date, only six accreting white dwarfs are known to harbour disk-wind driven bow shocks that are not associated to thermonuclear explosions. Here, we report the discovery of a bow shock associated with a high-proper-motion disk-less accreting white dwarf, 1RXS J052832.5+283824. We show that the white dwarf has a strong magnetic field in the range B~42-45 MG, making RXJ0528+2838 the a bonafide known polar-type cataclysmic variable harbouring a bow shock. The resolved bow shock is shown to be inconsistent with a past thermonuclear explosion, or being inflated by a donor wind, ruling out all accepted scenarios for inflating a bow shock around this system. Modelling of the energetics reveals that the observed bow shock requires a persistent power source with a luminosity significantly exceeding the system accretion energy output. This implies the presence of a powerful, previously unrecognized energy loss mechanism - potentially tied to magnetic activity - that may operate over sufficiently long timescales to influence the course of binary evolution.

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arXiv2025

How Mass Flows Through Accretion Discs: A Spectral-Timing Vision for the 2040s

Understanding how mass and angular momentum flow through accretion discs remains a fundamental unsolved problem in astrophysics. Accreting white dwarfs offer an ideal laboratory for addressing this question: their variability occurs on accessible timescales of seconds to minutes, and their optical spectra contain continuum and emission-line components that trace distinct disc regions. Broad-band timing studies have revealed time-lags similar to those observed in X-ray binaries and active galactic nuclei, suggesting propagating fluctuations and possible coupling to an inner hot flow. However, the blending of line and continuum light in broad filters prevents a physical interpretation of these signals. The 2040s will bring an unprecedented number of disc-accreting systems discovered by Rubin-LSST, space-based gravitational-wave observatories, and third-generation ground and space-based detectors. To extract disc physics from these sources, high-cadence optical spectral-timing, simultaneously resolving continuum and individual lines, is essential. Such measurements would directly map how variability propagates through discs, determine how the outer disc responds to changes in the inner flow, and test whether accretion physics is scale-invariant from white dwarfs to supermassive black holes. This white paper outlines the scientific motivation and observational capabilities required to realise this vision. It highlights the opportunity for ESO to enable a transformative new window on accretion physics in the coming decade.

astro-ph.IM↗

arXiv2025

Evolution of the inner accretion flow and the white-dwarf spin pulse during the 2023 outburst in GK Persei

We present our X-ray and optical observations performed by NICER, NuSTAR, and Tomo-e Gozen during the 2023 outburst in the intermediate polar GK Persei. The X-ray spectrum consisted of three components: blackbody emission of several tens of eVs from the irradiated white-dwarf surface, a source possibly including several emission lines around 1 keV, and multi-temperature bremsstrahlung emission from the accretion column. The 351.3-s white-dwarf spin pulse was detected in X-rays, and the observable X-ray flux from the column drastically decreased at the off-pulse phase, which suggests that the absorption of the column by the accreting gas called the curtain was the major cause of the pulse. As the system became brighter in optical, the column became fainter, the pulse amplitude became higher, and the energy dependence of pulses became weaker at $<$8~keV. These phenomena could be explained by the column's more pronounced absorption by the denser curtain as mass accretion rates increased. The blackbody and line fluxes rapidly decreased at the optical decline, which suggests the expansion of the innermost disk edge with decreasing accretion rates. The electron scattering or the column geometry may be associated with almost no energy dependence of high-energy pulses. The irradiated vertically-thick structure at the disk may generate optical QPOs with a period of $\sim$5700 s.

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arXiv2024

Classifying optical (out)bursts in cataclysmic variables: the distinct observational characteristics of dwarf novae, micronovae, stellar flares and magnetic gating

Cataclysmic variables can experience short optical brightenings, which are commonly attributed to phenomena such as dwarf novae outbursts, micronovae, donor flares or magnetic gating bursts. Since these events exhibit similar observational characteristics, their identification has often been ambiguous. In particular, magnetic gating bursts and micronovae have been suggested as alternative interpretations of the same phenomena. Here we show that the timescales and energies separate the optical brightenings into separate clusters consistent with their different classifications. This suggest that micronovae and magnetic gating bursts are in fact separate phenomena. Based on our finding we develop diagnostic diagrams that can distinguish between these bursts/flares based on their properties. We demonstrate the effectiveness of this approach on observations of a newly identified intermediate polar, CTCV J0333-4451, which we classify as a magnetic gating system. CTCV J0333-4451 is the third high spin-to-orbital period ratio intermediate polar with magnetic gating, suggesting that these bursts are common among these rare systems.

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