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We present multiwavelength temporal and spectral characteristics of a magnetic cataclysmic variable (MCV) Swift J0503.7-2819, using far ultraviolet and X-ray data from AstroSat , supplemented with optical data from the Southern African Large Telescope and X-ray data from the XMM-Newton and Swift observatories. The X-ray modulations at 4897.6657 s and 3932.0355 s are interpreted as the orbital (P Ω) and spin (P ω) period, respectively, and are consistent with prior reports. With a spin-orbit period ratio of 0.8 and P Ω falling below the period gap (2–3 h) of CVs, Swift J0503.7-2819 would be the newest addition to the growing population of nearly synchronous MCVs, which we call EX Hya-like systems. Hard X-ray luminosity of <2.5 × 1032 erg s−1, as measured with the Swift Burst Alert Telescope, identifies it to be a low-luminosity intermediate polar, similar to other EX Hya-like systems. The phenomenology of the light curves and the spectral characteristics rule out a purely disc-fed/stream-fed model and instead reveal the presence of complex accretion structures around the white dwarf. We propose a ring-like accretion flow, akin to EX Hya, using period ratio, stability arguments, and observational features. An attempt is made to differentiate between the asynchronous polar/nearly synchronous intermediate polar nature of Swift J0503.7-2819. Further, we note that with the advent of sensitive surveys, a growing population of MCVs that exhibit characteristics of both polars and intermediate polars is beginning to be identified, likely forming a genealogical link between the two conventional classes of MCVs. [ABSTRACT FROM AUTHOR]

We present the first Bayesian method for tomographic decomposition of the plane-of-sky orientation of the magnetic field with the use of stellar polarimetry and distance. This standalone tomographic inversion method presents an important step forward in reconstructing the magnetized interstellar medium (ISM) in three dimensions within dusty regions. We develop a model in which the polarization signal from the magnetized and dusty ISM is described by thin layers at various distances, a working assumption which should be satisfied in small-angular circular apertures. Our modeling makes it possible to infer the mean polarization (amplitude and orientation) induced by individual dusty clouds and to account for the turbulence-induced scatter in a generic way. We present a likelihood function that explicitly accounts for uncertainties in polarization and parallax. We develop a framework for reconstructing the magnetized ISM through the maximization of the log-likelihood using a nested sampling method. We test our Bayesian inversion method on mock data, representative of the high Galactic latitude sky, taking into account realistic uncertainties from Gaia and as expected for the optical polarization survey PASIPHAE according to the currently planned observing strategy. We demonstrate that our method is effective at recovering the cloud properties as soon as the polarization induced by a cloud to its background stars is higher than ~0.1% for the adopted survey exposure time and level of systematic uncertainty. The larger the induced polarization is, the better the method's performance, and the lower the number of required stars. Our method makes it possible to recover not only the mean polarization properties but also to characterize the intrinsic scatter, thus creating new ways to characterize ISM turbulence and the magnetic field strength. Finally, we apply our method to an existing data set of starlight polarization with known line-of-sight decomposition, demonstrating agreement with previous results and an improved quantification of uncertainties in cloud properties. [ABSTRACT FROM AUTHOR]

Polarization offers a unique view in the physical processes of astrophysical jets. We report on optical circular polarization (CP) observations of two famous blazars, namely 3C 279 and PKS 1510−089, at high linearly polarized states. This is the first time PKS 1510−089 is observed in optical CP. While only upper limits can be extracted from our observing campaign, the non-detection of optical CP allows us to provide meaningful constraints on their magnetic field strength and jet composition. We find that high-energy emission models requiring high magnetic field strength and a low positron fraction can be excluded. [ABSTRACT FROM AUTHOR]

We present an overview of the ongoing observational, theoretical and modelling work on magnetically controlled accretion phenomena in magnetic cataclysmic variables. With SAAO's high speed polarimeter, HIPPO, we have discovered polarized Quasi-Periodic Oscillations, on a timescale of several minutes. We have investigated various scenarios in which such QPOs can be created, all of them requiring some interaction between the ballistic accretion flow and the magnetic field of the accreting white dwarf. With high speed photometry, including observations with SALT, we are investigating the nature of high frequency QPOs (~sub-few seconds) from the accretion shocks in mCVs. We also present some high speed photometric observations revealing the magnetic accretion spots on the accreting White Dwarfs. Developments in the use of Doppler tomography are also presented. Our new "inside-out" visualization gives an alternative way of calculating Doppler tomograms that can better emphasize the ballistic and magnetically confined accretion flows.

It was recently proposed that the cataclysmic variable (CV) LAMOST J024048.51+195226.9 may be a twin to the unique magnetic propeller system AE Aqr. If this is the case, two predictions are that it should display a short period white dwarf spin modulation, and that it should be a bright radio source. We obtained follow-up optical and radio observations of this CV, in order to see if this holds true. Our optical high-speed photometry does not reveal a white dwarf spin signal, but lacks the sensitivity to detect a modulation similar to the 33 s spin signal seen in AE Aqr. We detect the source in the radio, and measure a radio luminosity similar to that of AE Aqr and close to the highest so far reported for a CV. We also find good evidence for radio variability on a time-scale of tens of minutes. Optical polarimetric observations produce no detection of linear or circular polarization. While we are not able to provide compelling evidence, our observations are all consistent with this object being a propeller system. [ABSTRACT FROM AUTHOR]

We present phase-resolved optical spectroscopy of the eclipsing nova-like cataclysmic variable EC 21178−5417 obtained between 2002 and 2013. The average spectrum of EC 21178−5417 shows broad double-peaked emission lines from He  ii 4686 Å (strongest feature) and the Balmer series. The high-excitation feature, C  iii /N  iii at 4640–4650 Å, is also present and appears broad in emission. A number of other lines, mostly He  i , are clearly present in absorption and/or emission. The average spectrum of EC 21178−5417 taken at different months and years shows variability in spectral features, especially in the Balmer lines beyond Hγ, from pure line emission, mixed line absorption, and emission to pure absorption lines. Doppler maps of the He  ii 4686 Å emission reveal the presence of a highly inclined asymmetric accretion disc and a two spiral arm-like structure, whereas that of the Balmer lines (Hα and Hβ) reveal a more circular accretion disc. There is no evidence of a bright-spot in the Doppler maps of EC 21178−5417 and no emission from the secondary star is seen in the tomograms of the He  ii 4686 Å and Balmer lines. Generally, the emission in EC 21178−5417 is dominated by emission from the accretion disc. We conclude that EC 21178−5417 is a member of the RW Tri or UX UMa subtype of nova-like variables based on these results and because it shows different spectral characteristics at different dates. This spectral behaviour suggests that EC 21178−5417 undergoes distinct variations in mass transfer rate on the observed time-scales of months and years. [ABSTRACT FROM AUTHOR]

We present phase-resolved spectroscopy, photometry, and circular spectropolarimetry of the eclipsing polar UZ Fornacis. Doppler tomography of the strongest emission lines using the inside-out projection revealed the presence of three emission regions: from the irradiated face of the secondary star, the ballistic stream and the threading region, and the magnetically confined accretion stream. The total intensity spectrum shows broad emission features and a continuum that rises in the blue. The circularly polarized spectrum shows the presence of three cyclotron emission harmonics at ∼4500, 6000, and 7700 Å, corresponding to harmonic numbers 4, 3, and 2, respectively. These features are dominant before the eclipse and disappear after the eclipse. The harmonics are consistent with a magnetic field strength of ∼57 MG. We also present phase-resolved circular and linear photopolarimetry to complement the spectropolarimetry around the times of eclipse. MeerKAT radio observations show a faint source that has a peak flux density of 30.7 ± 5.4 |$\mu$| Jy beam−1 at 1.28 GHz at the position of UZ For. [ABSTRACT FROM AUTHOR]

We report the discovery of the first transient with MeerKAT, MKT J170456.2–482100, discovered in ThunderKAT images of the low-mass X-ray binary GX339–4. MKT J170456.2–482100 is variable in the radio, reaching a maximum flux density of |$0.71\pm 0.11\, \mathrm{mJy}$| on 2019 October 12, and is undetected in 15 out of 48 ThunderKAT epochs. MKT J170456.2–482100 is coincident with the chromospherically active K-type sub-giant TYC 8332-2529-1, and |$\sim 18\, \mathrm{yr}$| of archival optical photometry of the star shows that it varies with a period of |$21.25\pm 0.04\, \mathrm{d}$|⁠. The shape and phase of the optical light curve changes over time, and we detect both X-ray and UV emission at the position of MKT J170456.2–482100, which may indicate that TYC 8332-2529-1 has large star spots. Spectroscopic analysis shows that TYC 8332-2529-1 is in a binary, and has a line-of-sight radial velocity amplitude of |$43\, \mathrm{km\, s^{-1}}$|⁠. We also observe a spectral feature in antiphase with the K-type sub-giant, with a line-of-sight radial velocity amplitude of |$\sim 12\pm 10\, \mathrm{km\, s^{-1}}$|⁠ , whose origins cannot currently be explained. Further observations and investigation are required to determine the nature of the MKT J170456.2–482100 system. [ABSTRACT FROM AUTHOR]

We report the discovery of a new eclipsing polar, MASTER OT J061451.70–272535.5, detected as an optical transient by MASTER auto-detection software at the recently commissioned MASTER-SAAO telescope. Time resolved (10–20 s) photometry with the SAAO 1.9-m and 1.0-m telescopes, utilizing the SHOC EM-CCD cameras, revealed that the source eclipses, with a period of 2.08 h (7482.9 |$\pm 3.5\,$| s). The eclipse light curve has a peculiar morphology, comprising an initial dip, where the source brightness drops to 50 per cent of the pre-eclipse level before gradually increasing again in brightness. A second rapid ingress follows, where the brightness drops by 60–80 per cent, followed by a more gradual decrease to zero flux. We interpret the eclipse profile as the result of an initial obscuration of the accretion hot-spot on the magnetic white dwarf by the accretion stream, followed by an eclipse of both the hotspot and partially illuminated stream by the red dwarf donor star. This is similar to what has been observed in other eclipsing polars such as HU Aqr, but here the stream absorption is more pronounced. The object was subsequently observed with South African Large Telescope (SALT) using the Robert Stobie Spectrograph (RSS). This revealed a spectrum with all of the Balmer lines in emission, a strong He  ii 4686 Å line with a peak flux greater than that of H β, as well as weaker He  i lines. The spectral features, along with the structure of the light curve, suggest MASTER OT J061451.70–272535.5 is a new magnetic cataclysmic variable, most likely of the synchronized Polar subclass. [ABSTRACT FROM AUTHOR]

We present 33 new mid-eclipse times spanning approximately eight years of the eclipsing polar UZ Fornacis. We have used our new observations to test the two-planet model previously proposed to explain the variations in its eclipse times measured over the past ~35 yr. We find that the proposed model does indeed follow the general trend of the new eclipse times, however, there are significant departures. In order to accommodate the new eclipse times, the two-planet model requires that one or both of the planets require highly eccentric orbits, that is, e ≥ 0.4. Such multiple planet orbits are considered to be unstable. Whilst our new observations are consistent with two cyclic variations as previously predicted, significant residuals remain. We conclude that either additional cyclic terms, possibly associated with more planets, or other mechanisms, such as the Applegate mechanism are contributing to the eclipse time variations. Further long-term monitoring is required. [ABSTRACT FROM AUTHOR]

The blue continuum of the eclipsing polar UZ For is dominated by single- or double-peaked emission from He ii, He i and the Balmer lines. The red spectrum shows weak emission from the Na i doublet at λ 8183 and 8194 Å and strong emission from the Ca ii lines at λ 8498 and 8542 Å. Doppler tomography of the strongest emission features reveals the presence of emission from the irradiated face of the secondary star, the threading region, and the ballistic and magnetically confined accretion stream. We have obtained 28 new eclipse times of UZ For during 2011–2016 as part of our eclipse timing follow-up programme to test the two-planet model proposed to explain variations in the eclipse times of UZ For. [ABSTRACT FROM AUTHOR]

The Advanced LIGO observatory recently reported the first direct detection of the gravitational waves (GWs) predicted by Einstein & Sitzungsber. We report on the first optical observations of the GW source GW150914 error region with the Global MASTER Robotic Net. Between the optical telescopes of electromagnetic support, the covered area is dominated by MASTER with an unfiltered magnitude up to 19.9 mag (5σ). We detected several optical transients, which proved to be unconnected with the GW event. The main input to investigate the final error box of GW150914 was made by the MASTER-SAAO robotic telescope, which covered 70 per cent of the final GW error box and 90 per cent of the common localization area of the LIGO and Fermi events. Our result is consistent with the conclusion (Abbott et al. 2016a) that GWs from GW150914 were produced in a binary black hole merger. At the same time, we cannot exclude that MASTER OT J040938.68-541316.9 exploded on 2015 September 14. [ABSTRACT FROM AUTHOR]

We present photometric and spectroscopic follow-up observations of short-period variables discovered in the OmegaWhite survey, a wide-field high-cadence g-band synoptic survey targeting the Galactic Plane. We have used fast photometry on the SAAO 1.0- and 1.9-m telescopes to obtain light curves of 27 variables, and use these results to validate the period and amplitude estimates from the OmegaWhite processing pipeline. Furthermore, 57 sources (44 unique, 13 with newlight curves) were selected for spectroscopic follow-up using either the SAAO 1.9-m telescope or the Southern African Large Telescope. We find that many of these variables have spectra which are consistent with being δ Scuti-type pulsating stars. At higher amplitudes, we detect four possible pulsating white dwarf/subdwarf sources and an eclipsing cataclysmic variable. Due to their rarity, these targets are ideal candidates for detailed follow-up studies. From spectroscopy, we confirm the symbiotic binary star nature of two variables identified as such in the SIMBAD database. We also report what could possibly be the first detection of the 'Bump Cepheid' phenomena in a δ Scuti star, with OWJ175848.21-271653.7 showing a pronounced 22 per cent amplitude dip lasting 3 min during each pulsational cycle peak. However, the precise nature of this target is still uncertain as it exhibits the spectral features of a B-type star. [ABSTRACT FROM AUTHOR]

We present the results of UBVRI polarimetry of the TeV γ-ray binary HESS J0632+057 obtained on 2015 March 24 (JD 245 7106) and 2015 December 12 (JD 245 7369). The detected polarization values of HESS J0632+057, just after periastron passage (March 24), are higher than all previously published values (pV ~ 4.2 per cent), and the position angle (⊖obs ~ 171°-172°) is also different by ~6°-10° from previously published values. The data obtained just before the subsequent periastron passage (December 12) show a statistically lower polarization in all photometric bands (pV ~3.9 per cent) and a different position angle ⊖obs ~ 167°-168°. From observations of a nearby field star, the interstellar component of the measured polarization was estimated as pisV ~ 0.65 per cent and ⊖is ~ 153°. This estimate was used with the previous 'V'-band estimation by the 'field-stars method' (pisV is ~ 2 per cent and ⊖ is ~ 165°) of Yudin to identify the wavelength dependence of the intrinsic polarization in HESS J0632+057. It was found that after subtraction of the interstellar component (for both pis estimates), the wavelength dependence of the intrinsic polarization in HESS J0632+057 is essentially flat. We propose that the formation of an additional source of polarization or some perturbation of circumstellar material at this orbital phase can explain the changes in the level of polarization in HESS J0632+057 close to periastron passage. [ABSTRACT FROM AUTHOR]

Context. Doppler tomography is a technique that has revolutionised the interpretation of the phase-resolved spectroscopic observations of interacting binary systems. Aims. We present the results of our investigation of reversing the velocity axis to create an inside-out Doppler coordinate framework with the intent to expose overly compacted and enhance washed out emission details in the standard Doppler framework. Methods. The inside-out tomogram is constructed independently of the standard tomogram by directly projecting phase-resolved spectra onto an inside-out velocity coordinate frame. For the inside-out framework, the zero-velocity origin is transposed to the outer circumference and the maximum velocities to the origin of the velocity space. We test the technique on a simulated system and two real systems with easily identifiable features, namely the accretion disc and bright spot in WZ Sge, and spiral shocks in IP Peg. Results. Our tests show that there is a redistribution of the relative brightness of emission components throughout the tomograms, i.e., where the standard framework tends to concentrate and enhance lower velocity features towards the origin, the inside-out velocity framework tends to concentrate and enhance higher velocity features towards the origin. Conversely, the standard framework disperses and smears the higher velocities farther away from the origin whereas the inside-out framework disperses and smears the lower velocities. In addition, the projection of the accretion disc in velocity space now appears correctly orientated with the inner edge close to the maximum velocity origin and its outer edge closer to the zero-velocity outer circumference. Furthermore, the gas stream and secondary star are projected on the outside of the disc with the bright spot of the stream-disc impact region on the disc's outer edge in the inside-out velocity space. Conclusions. We conclude that inside-out Doppler tomography complements the already powerful tomographic techniques in the analysis of spectroscopic emissions from interacting binary systems. [ABSTRACT FROM AUTHOR]

We report on the detection of an ~5900 s quasi-periodic variation in the extensive photometry of TX Col spanning 12 yr. We discuss five different models to explain this period. We favour a mechanism where the quasi-periodic variation results from the beating of the Keplerian frequency of the ‘blobs’ orbiting in the outer accretion disc with the spin frequency and from modulated accretion of these ‘blobs’ taking place in a shocked region near the disc/magnetosphere boundary. [ABSTRACT FROM AUTHOR]

We present optical spectroscopy of EX Hya during its 1991 outburst. This outburst is characterized by strong irradiation of the front face of the secondary star by the white dwarf, an overflowing stream which is seen strongly in He iiλ4686 and by a dip in the light curves, which extends from 0.1 to 0.6 in the binary and spin phases. Strong irradiation of the accretion curtain and that of the inner regions of the disc led to strong emission of He iiλ4686 and to the suppression of the Hγ and Hβ emission. Disc overflow was observed in quiescence in earlier studies, where the overflow stream material was modulated at high velocities close to 1000 km s−1. In outburst, the overflowing material is modulated at even higher velocities (∼1500 km s−1). These are streaming velocities down the field lines close to the white dwarf. Evidence for material collecting near the outer edge of the disc and corotating with the accretion curtain was observed. In decline, this material and the accretion curtain obscured almost all the emission near binary phase 0.4, causing a dip. The dip minimum nearly corresponds with spin pulse minimum. This has provided additional evidence for an extended accretion curtain, and for the corotation of material with the accretion curtain at the outer edge of the disc. From these observations we suggest that a mechanism similar to that of Spruit and Taam, where outbursts result due to the storage and release of matter outside the magnetosphere, triggers the outbursts of EX Hya. This is followed by the irradiation of the secondary star due to accretion induced radiation. [ABSTRACT FROM AUTHOR]

Results from spectroscopic observations of the intermediate polar (IP) EX Hya in quiescence during 1991 and 2001 are presented. Spin-modulated radial velocities consistent with an outer disc origin were detected for the first time in an IP. The spin pulsation was modulated with velocities near . These velocities are consistent with those of the material circulating at the outer edge of the accretion disc, suggesting co-rotation of the accretion curtain with the material near the Roche lobe radius. Furthermore, spin Doppler tomograms have revealed evidence of the accretion curtain emission extending from velocities of ∼500 to ∼1000 km s−1. These findings have confirmed the theoretical model predictions for EX Hya, which predict large accretion curtains that extend to a distance close to the Roche lobe radius in this system. Evidence for overflow stream of material falling on to the magnetosphere was observed, confirming the result of Belle et al. that disc overflow in EX Hya is present during quiescence as well as outburst. It appears that the Hβ and Hγ spin radial velocities originated from the rotation of the funnel at the outer disc edge, while those of Hα were produced due to the flow of the material along the field lines far from the white dwarf (narrow component) and close to the white dwarf (broad-base component), in agreement with the accretion curtain model. [ABSTRACT FROM AUTHOR]

We present a densely sampled map of visual polarimetry of stars in the direction of the Southern Coalsack dark cloud. Our sample consists of new polarimetric observations of 225 stars drawn from the spectrophotometric survey of Seidensticker, and an additional 173 stars, covering the surrounding areas of the cloud, taken from the literature. Because all the target stars have at least spectroscopic parallaxes, we can reliably investigate the spatial origins of the polarization, in three dimensions. We decompose the polarization into three components, due to (i) the wall of the local hot bubble, (ii) the Coalsack cloud and (iii) material in the Carina spiral arm. The polarization due to the Coalsack varies, both in alignment efficiencyand in the dispersion in polarization angle, across the cloud. Using a simplified radiative transfer treatment we show that the measured polarization in background gas is significantly affected by foreground polarization, and specifically that the analysis of the Coalsack polarization must take the effects of the local hot bubble wall into consideration. Correcting for this effect as well as for the internal line-of-sight averaging in the Coalsack, we find, based on a Chandrasekhar–Fermi analysis, a plane-of-the-sky magnetic field for the Coalsack cloud of. A systematic error, best described by a multiplicative factor between 0.5 and 1.5, additionally arises from radiative transfer effect uncertainties. We propose that this high value for the magnetic field in the cloud envelope is due to the fact that the Coalsack cloud is embedded in the hot interior of the Upper Centaurus–Lupus superbubble. [ABSTRACT FROM AUTHOR]