Existing photometry of the magnetic helium-rich white dwarf Feige 7 is used to derive the parameters $T_\mathrm{eff}=18\,480$ K and log$\;g=8.74$ and a frequency of variability of 10.94192 d$^{-1}$ (period 2.19340 h). New time-series photometry of Feige 7 is presented, covering full cycles of variability in the UBVRI and ugriz filters, which allows the wavelength dependence of the two amplitudes in the double wave light curve to be determined. Amplitudes are virtually constant for wavelengths longer than 5 000 Å, but increase sharply for shorter wavelengths. A simple model consisting of two large cool spots 180$^\circ$ apart on the surface of star provides a reasonable description of the data.

The spin-down law of pulsars is generally perturbed by two types of timing irregularities: glitches and timing noise. Glitches are sudden changes in the rotational frequency of pulsars, while timing noise is a discernible stochastic wandering in the phase, period, or spin-down rate of a pulsar. We present the timing results of a sample of glitching pulsars observed using the Ooty Radio Telescope (ORT) and the upgraded Giant Metrewave Radio Telescope (uGMRT). Our findings include timing noise analysis for 17 pulsars, with seven being reported for the first time. We detected five glitches in four pulsars and a glitch-like event in PSR J1825–0935. The frequency evolution of glitches in pulsars, J0742–2822 and J1740–3015, is presented for the first time. Additionally, we report timing noise results for three glitching pulsars. The timing noise was analysed separately in the pre-glitch and post-glitch regions. We observed an increase in the red noise parameters in the post-glitch regions, where exponential recovery was considered in the noise analysis. Timing noise can introduce ambiguities in the correct evaluation of glitch observations. Hence, it is important to consider timing noise in glitch analysis. We propose an innovative glitch verification approach designed to discern between a glitch and strong timing noise. The novel glitch analysis technique is also demonstrated using the observed data.

We present a comprehensive analysis of simultaneous, long-term observations of blazar S5 0716+714, covering optical/UV, X-ray, and $\gamma$-ray wavelengths. All available observations of the source by Swift-UVOT/XRT and Fermi-LAT till January 2023 were used, and the spectra were fitted using power-law/log-parabola functions. A detailed correlation study between the best-fit parameters were performed, and our results suggest that the spectral changes observed during high flux states could be associated with the spectral energy distribution shifting towards the blue end. The flux distribution predominantly shows a log-normal/double log-normal behaviour, whereas the index distribution indicates a Gaussian or double Gaussian nature. As a Gaussian variation in the index of a power-law spectrum will result in a log-normal variation in the flux, the observed log-normal variability in blazars may be associated with Gaussian variation in the spectral indices. The observed normal/log-normal variations in indices/fluxes can again be interpreted through bluer when brighter behaviour of the source. Furthermore, the broadband SED during two distinct flux states can be successfully fitted by considering synchrotron, synchrotron self-Compton, and external Compton emission processes. The flux enhancement of the source is predominantly associated with an increase in the bulk Lorentz factor. Additionally, we find that the model curves corresponding to variations in the Lorentz factor have the potential to explain the observed correlations between the spectral parameters. Our study thereby concludes that the spectral variations of blazar S5 0716+714 are primarily associated with changes in the bulk Lorentz factor of the jet.

Neutral and singly ionised states of the magnesium (Mg) are the origin of several spectral lines that are useful for solar diagnostic purposes. An important element in modelling such solar lines is collisional data of the Mg with different perturbers abundant in the Sun, specially with neutral hydrogen. This work aims at providing complete depolarisation and polarisation and population transfer data for Mg II due to collisions with hydrogen atoms. For this purpose, a general formalism is employed to calculate the needed rates of MgII due to collisions with hydrogen atoms. The resulting collisional rates are then employed to investigate the impact of collisions on the polarisation of 25 Mg II lines relevant to solar applications by solving the governing statistical equilibrium equations within multi-level and multi-term atomic models. We find that the polarisation of some Mg II lines starts to be sensitive to collisions for hydrogen density $n_H \!\gtrsim\!$ 10$^{14}$ cm$^{-3}$.

We present spectroscopic properties of 22 Ly$\alpha$ emitters (LAEs) at $z = 5.5 - 6.6$ with Ly$\alpha$ luminosity $\mathrm{log}( L_{\mathrm{Ly}\alpha} \, [\mathrm{erg} \, \mathrm{s}^{-1}]) = 42.4 - 43.5 $, obtained using VLT/MUSE as part of the Middle Ages Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey. Additionally, we incorporate broad-band photometric data from the Subaru Hyper Suprime-Cam (HSC) Wide layer for 17 LAEs in our sample. The HSC-y band magnitudes show that our LAEs are UV-bright, with rest-frame absolute UV magnitudes $ -19.74 \leq \mathrm{M}_{\mathrm{UV}} \leq -23.27$. We find that the Ly$\alpha$ line width increases with Ly$\alpha$ luminosity, and this trend becomes more prominent at $z \gt 6$ where Ly$\alpha$ lines become significantly broadened ($\gtrsim+260 \, \mathrm{km}\, \mathrm{s}^{-1}$) at luminosities $\mathrm{log}( L_{\mathrm{Ly}\alpha} \, [\mathrm{erg} \, \mathrm{s}^{-1}]) \gt 43 $. This broadening is consistent with previous studies, suggesting that these sources are located inside larger ionised bubbles. We observe a slightly elevated ionising photon production efficiency estimated for LAEs at $z \gt 6$, which indicates that younger galaxies could be producing more ionising photons per UV luminosity. A tentative anti-correlation between ionising photon production efficiency and Ly$\alpha$ rest-frame equivalent width is noticed, which could indicate a time delay between production and escape of ionising photon primarily due to supernovae activity. Furthermore, we find a positive correlation between radius of ionised regions and Ly$\alpha$ line width, which again suggests that large ionised bubbles are created around these LAEs, which are allowing them to self-shield from the scattering effects of the intergalactic medium (IGM). We also detect two very closely separated LAEs at $z = 6.046$ (projected spatial distance between the cores is 15.92 kpc). This is the LAE pair with the smallest separation ever discovered in the reionisation epoch. The size of their respective bubbles suggests that they likely sit inside a common large ionised region. Such a closely separated LAE pair increases the size of ionised bubble, potentially allowing a boosted transmission of Ly$\alpha$ through neutral IGM and also supports an accelerated reionisation scenario.

We report a novel pilot project to characterise intra-night optical variability (INOV) of an extremely rare type of quasar, which has recently been caught in the act of transiting from a radio-quiet to radio-loud state, on a decadal time scale. Such rare transitions may signify a recurrence, or conceivably the first switch-on of jet activity in optically luminous quasars. The newly formed jet could well be jittery and unsteady, both in power and direction. The optically brightest among such radio-state transition candidates, the quasar J0950+5128 ($z = 0.2142$), was monitored by us with dense sampling in the R-band, during 2020-21 in 6 sessions, each lasting $ \gt $ 4 hours. This is the first attempt to characterise the INOV properties associated with this recently discovered, extremely rarely observed phenomenon of quasar radio-state transition. The non-detection of INOV in any of the 6 sessions, down to the 1-2% level, amounts to a lack of evidence for a blazar-like optical activity, $\sim$ 2 years after its transition to radio-loud state was found. The only INOV feature detected in J0950+5128 during our observational campaign was a $\sim$ 0.15-mag spike lasting < 6 minutes, seen at 13.97 UT on 18-March-2021. We also report the available optical light curves of this quasar from the Zwicky Transient Facility survey, which indicate that it had experienced a phase of INOV activity around the time its transition to the radio-loud state was detected, however that phase did not sustain until the launch of our INOV campaign $\sim$ 2 years later.

New time series photometry of WISE J152614.95-111326.4, an eclipsing binary candidate, has been obtained. Full cycles of variation were covered in five filters, ranging from B to z. Archival time series photometry is also available from several sources. The phased light curve shape changes from a double wave form in the red, to a single wave at shorter wavelengths. Analysis of the spectral energy distribution and SALT spectra shows the presence of a cool ($\sim$7 250–7 900 K) white dwarf and an M6 star. The light curves can be explained by a hot spot on the opposing hemisphere of the white dwarf. The star may be in a pre-cataclysmic variable phase with a very low rate of mass flow from the red dwarf to the white dwarf, such that no flickering is evident. Evidence in favour of this hypothesis is that the period of the system (2.25 h) is in the cataclysmic variable period gap. It is speculated that a weak magnetic field associated with the white dwarf funnels accreted material onto a magnetic pole. Amplitudes of the W1 and W2 WISE light curves are anomalously large. The possibility is discussed that variability in this spectral region is primarily driven by electron cyclotron radiation.

Fast radio bursts (FRBs) are short-duration radio transients that occur at random times in host galaxies distributed all over the sky. Large field of view instruments can play a critical role in the blind search for rare FRBs. We present a concept for an all-sky FRB monitor using a compact all-sky phased array (CASPA), which can efficiently achieve an extremely large field of view of $\sim10^4$ square degrees. Such a system would allow us to conduct a continuous, blind FRB search covering the entire southern sky. Using the measured FRB luminosity function, we investigate the detection rate for this all-sky phased array and compare the result to a number of other proposed large field-of-view instruments. We predict a rate of a few FRB detections per week and determine the dispersion measure and redshift distributions of these detectable FRBs. This instrument is optimal for detecting FRBs in the nearby Universe and for extending the high-end of the FRB luminosity function through finding ultraluminous events. Additionally, this instrument can be used to shadow the new gravitational-wave observing runs, detect high-energy events triggered from Galactic magnetars and search for other bright, but currently unknown transient signals.

A key objective for upcoming surveys, and when re-analysing archival data, is the identification of variable stellar sources. However, the selection of these sources is often complicated by the unavailability of light curve data. Utilising a self-organising map (SOM), we demonstrate the selection of diverse variable source types from a catalogue of variable and non-variable SDSS Stripe 82 sources whilst employing only the median $u-g$, $g-r$, $r-i$, and $i-z$ photometric colours for each source as input, without using source magnitudes. This includes the separation of main sequence variable stars that are otherwise degenerate with non-variable sources ($u-g$,$g-r$) and ($r-i$,$i-z$) colour-spaces. We separate variable sources on the main sequence from all other variable and non-variable sources with a purity of $80.0\%$ and completeness of $25.1\%$, figures which can be modified depending on the application. We also explore the varying ability of the same method to simultaneously select other types of variable sources from the heterogeneous sample, including variable quasars and RR-Lyrae stars. The demonstrated ability of this method to select variable main sequence stars in colour-space holds promise for application in future survey reduction pipelines and for the analysis of archival data, where light curves may not be available or may be prohibitively expensive to obtain.

The Gaia optical astrometric mission has measured the precise positions of millions of objects in the sky, including extragalactic sources also observed by Very Long Baseline Interferometry (VLBI). In the recent Gaia EDR3 release, an effect of negative parallax with a magnitude of approximately $-17$ $\mu$as was reported, presumably due to technical reasons related to the relativistic delay model. A recent analysis of a 30-yr set of geodetic VLBI data (1993–2023) revealed a similar negative parallax with an amplitude of $-15.8 \pm 0.5$ $\mu$as. Since both astrometric techniques, optical and radio, provide consistent estimates of this negative parallax, it is necessary to investigate the potential origin of this effect.

We developed the extended group relativistic delay model to incorporate the additional parallactic effect for radio sources at distances less than 1 Mpc and found that the apparent annual signal might appear due the non-orthogonality of the fundamental axes, which are defined by the positions of the reference radio sources themselves. Unlike the conventional parallactic ellipse, the apparent annual effect in this case appears as a circular motion for all objects independently of their ecliptic latitude. The measured amplitude of this circular effect is within a range of 10–15 $\mu$as that is consistent with the ICRF3 stability of the fundamental axis. This annual circular effect could also arise if a Gödel-type cosmological metric were applied, suggesting that, in the future, this phenomenon could be used to indicate global cosmic rotation.

We present a re-discovery of G278.94+1.35a as possibly one of the largest known Galactic supernova remnants (SNRs) – that we name Diprotodon. While previously established as a Galactic SNR, Diprotodon is visible in our new Evolutionary Map of the Universe (EMU) and GaLactic and Extragalactic All-sky MWA (GLEAM) radio continuum images at an angular size of $3{{{{.\!^\circ}}}}33\times3{{{{.\!^\circ}}}}23$, much larger than previously measured. At the previously suggested distance of 2.7 kpc, this implies a diameter of 157$\times$152 pc. This size would qualify Diprotodon as the largest known SNR and pushes our estimates of SNR sizes to the upper limits. We investigate the environment in which the SNR is located and examine various scenarios that might explain such a large and relatively bright SNR appearance. We find that Diprotodon is most likely at a much closer distance of $\sim$1 kpc, implying its diameter is 58$\times$56 pc and it is in the radiative evolutionary phase. We also present a new Fermi-LAT data analysis that confirms the angular extent of the SNR in gamma rays. The origin of the high-energy emission remains somewhat puzzling, and the scenarios we explore reveal new puzzles, given this unexpected and unique observation of a seemingly evolved SNR having a hard GeV spectrum with no breaks. We explore both leptonic and hadronic scenarios, as well as the possibility that the high-energy emission arises from the leftover particle population of a historic pulsar wind nebula.

In this study, the results obtained using GOES satellite X-ray data and MWO and WSO measurements of the solar magnetic field between 1976 and 2022 are compared and discussed. By analysing GOES satellite X-ray data in 47 different time periods of one month long, 7 500 solar flares are obtained, the flare equivalent duration distributions against the total duration of the flare are statistically modelled, and then their variation via time is examined. The variations of the model parameters such as the Plateau, which is considered as an indicator of the stellar saturation level in an observation season, and the flare timescales via time are examined. We noticed that the variation found in the solar magnetic field and the variation determined in the flare saturation levels are very similar. As a result, it is well known that the solar magnetic dipole moment measured from the solar poles steadily decreased from 1976 to 2022. We revealed that the solar X-ray flare energies are also generally decreasing in the same trend. This decrease is also evident in flare timescales, indicating that the geometry of solar magnetic loops is getting smaller over time.

The bright radio source, GLEAM J091734$-$001243 (hereafter GLEAM J0917$-$0012), was previously selected as a candidate ultra-high redshift ($z \gt 5$) radio galaxy due to its compact radio size and faint magnitude ($K(\mathrm{AB})=22.7$). Its redshift was not conclusively determined from follow-up millimetre and near-infrared spectroscopy. Here we present new HST WFC3 G141 grism observations which reveal several emission lines including [NeIII]$\lambda$3867, [NeV]$\lambda$3426 and an extended ($\approx 4.8\,$kpc), [OII]$\lambda$3727 line which confirm a redshift of $3.004\pm0.001$. The extended component of the [OII]$\lambda$3727 line is co-spatial with one of two components seen at 2.276 GHz in high resolution ($60\times 20\,$mas) Long Baseline Array data, reminiscent of the alignments seen in local compact radio galaxies. The BEAGLE stellar mass ($\approx 2\times 10^{11}\,\textit{M}_\odot$) and radio luminosity ($L_{\mathrm{500MHz}}\approx 10^{28}\,$W Hz$^{-1}$) put GLEAM J0917$-$0012 within the distribution of the brightest high-redshift radio galaxies at similar redshifts. However, it is more compact than all of them. Modelling of the radio jet demonstrates that this is a young, $\approx 50\,$kyr old, but powerful, $\approx 10^{39}\,$W, compact steep spectrum radio source. The weak constraint on the active galactic nucleus bolometric luminosity from the [NeV]$\lambda$3426 line combined with the modelled jet power tentatively implies a large black hole mass, $\ge 10^9\,\textit{M}_\odot$, and a low, advection-dominated accretion rate, i.e. an Eddington ratio $\le 0.03$. The [NeV]$\lambda$3426/[NeIII]$\lambda$3867 vs [OII]$\lambda$3727/[NeIII]$\lambda$3867 line ratios are most easily explained by radiative shock models with precursor photoionisation. Hence, we infer that the line emission is directly caused by the shocks from the jet and that this radio source is one of the youngest and most powerful known at cosmic noon. We speculate that the star-formation in GLEAM J0917$-$0012 could be on its way to becoming quenched by the jet.

Galaxy Zoo is an online project to classify morphological features in extra-galactic imaging surveys with public voting. In this paper, we compare the classifications made for two different surveys, the Dark Energy Spectroscopic Instrument (DESI) imaging survey and a part of the Kilo-Degree Survey (KiDS), in the equatorial fields of the Galaxy And Mass Assembly (GAMA) survey. Our aim is to cross-validate and compare the classifications based on different imaging quality and depth. We find that generally the voting agrees globally but with substantial scatter, that is, substantial differences for individual galaxies. There is a notable higher voting fraction in favour of ‘smooth’ galaxies in the DESI+zoobot classifications, most likely due to the difference between imaging depth. DESI imaging is shallower and slightly lower resolution than KiDS and the Galaxy Zoo images do not reveal details such as disc features and thus are missed in the zoobot training sample. We check against expert visual classifications and find good agreement with KiDS-based Galaxy Zoo voting. We reproduce the results from Porter-Temple+ (2022), on the dependence of stellar mass, star formation, and specific star formation on the number of spiral arms. This shows that once corrected for redshift, the DESI Galaxy Zoo and KiDS Galaxy Zoo classifications agree well on population properties. The zoobot cross-validation increases confidence in its ability to compliment Galaxy Zoo classifications and its ability for transfer learning across surveys.