Related papers: Solar axions cannot explain the XENON1T excess
We review X-ray flux modulation from X-ray binaries on time scales corresponding to the orbital period and those at longer time scales (so called superorbital). Those modulations provide a powerful tool to constrain geometry of the…
Flare occurrence on the Sun is highly variable, exhibiting both short term variation due to the emergence and evolution of active regions, and long-term variation from the solar cycle. On solar-like stars, much larger stellar flares…
X-ray variation is a ubiquitous feature of active galactic nuclei (AGNs), however, its origin is not well understood. In this paper, we show that the X-ray flux variations in some AGNs, and correspondingly the power spectral densities…
Evolved low-mass stars of a wide range of metallicity bear signatures of a non-standard mixing event in their surface abundances of Li, C, and N, and in their 12C/13C ratio. A Na overabundance has also been reported in some giants of open…
Detecting axionic dark matter (DM) could be possible in an X-ray spectrum from strongly magnetized neutron stars (NSs). We examine the possibility of axion-photon conversion in the magnetospheres of strongly magnetized NSs. In the current…
A sudden increase in stellar luminosity may lead to the ejection of a large part of any optically thin gas orbiting the star. Test particles in circular orbits will become unbound, and will escape to infinity (if radiation drag is…
Emission of relativistic axions from transient sources, such as axion star explosions, can lead to observable signatures. We show that axion bursts from collapsing axion stars can be detectable over the wide range of axion masses $10^{-15}…
The disk instability picture gives a plausible explanation for the behavior of soft X-ray transient systems if self-irradiation of the disk is included. We show that there is a simple relation between the peak luminosity (at the start of an…
We perform a comprehensive analysis of the superorbital modulation in the ultracompact X-ray source 4U 1820-303, consisting of a white dwarf accreting onto a neutron star. Based on RXTE data, we measure the fractional amplitude of the…
We show that a consistent fit to observed secondary eclipse data for several strongly irradiated transiting planets demands a temperature inversion (stratosphere) at altitude. Such a thermal inversion significantly influences the…
Recent studies using New Horizons LORRI images have returned the most precise measurement of the cosmic optical background to date, yielding a flux that exceeds that expected from deep galaxy counts by roughly a factor of two. We…
Transmission spectra are differential measurements that utilize stellar illumination to probe transiting exoplanet atmospheres. Any spectral difference between the illuminating light source and the disk-integrated stellar spectrum due to…
Supermassive black holes can experience super-Eddington peak mass fallback rates following the tidal disruption of a star. The theoretical expectation is that part of the infalling material is expelled by means of an accretion disk wind,…
We employ an asteroseismic model of L19-2, a relatively massive ($M_{\star} \sim 0.75 M_{\sun}$) and hot ($T_{\rm eff} \sim 12\,100$ K) pulsating DA (H-rich atmosphere) white dwarf star (DAV or ZZ Ceti variable), and use the observed values…
We investigate a sample of 14 clusters of galaxies observed with XMM-Newton in a search for soft X-ray excess emission. In five of these clusters a significant soft excess is evident. This soft X-ray excess is compared with the thermal…
The diffuse galactic EGRET gamma ray data show a clear excess for energies above 1 GeV in comparison with the expectations from conventional galactic models. The excess is seen with the same spectrum in all sky directions, as expected for…
Solar activity is studied using a cluster analysis of the time-fluctuations of the sunspot number. It is shown that in an Historic period the high activity components of the solar cycles exhibit strong clustering, whereas in a Modern period…
An explanation is presented for the rather strong total surface differential rotation of the observed very young solar-type stars like AB Dor and PZ Tel. Due to its rapid rotation a nonuniform energy flux leaves the stellar core so that the…
In light of the excess in the low-energy electron recoil events reported by XENON1T, many new physics scenarios have been proposed as a possible origin of the excess. One possible explanation is that the excess is a result of a fast moving…
Recent astrophysical transient Swift J1913.1+1946 is possibly associated with the gamma-ray burst GRB 221009A at the redshift z=0.151. The transient was accompanied by very high-energy gamma rays up to 18 TeV observed by LHAASO and a…