The uGMRT Observations of Three New Gigahertz-peaked Spectra Pulsars

Using the Giant Metrewave Radio Telescope, we report the detailed spectral measurements over a wide frequency range of three pulsars (J1741−3016, J1757−2223, and J1845−0743), which allow us to identify them as new gigahertz-peaked spectra pulsars. Our results indicate that their spectra show turnovers at the frequencies of 620 MHz, 640 MHz, and 650 MHz, respectively. Our analysis proves that wideband observations improve estimations of spectral nature using a free–free thermal absorption model, and thus allow for a more accurate approximation of the maximum energy in the spectrum. While there is no evidence as yet that these objects are associated with a supernova remnant or pulsar wind nebula, they will make good targets when looking for interesting environments in the future, or when conducting more sensitive sky surveys.

Observational cosmology

The main strands of observation in cosmology are presented. These are redshift surveys using standard candles; galaxy distributions; age estimates drawing on a number of strands of evidence; and the CMB radiation. The chapter begins with a discussion of systemtic and statistical error in measurements, and explains the terminology of “Lambda CDM” model. Observations are combined with the Friedman equation in order to constrain the density parameters in a LCDM model. Data from supernova surveys are used to obtain the Hubble parameter and the deceleration parameter, and hence evidence of an accelerating expansion. Evidence of the BAO process is deduced from sky surveys, and used to constrain the spatial curvature. The CMB radiation is discussed at length. The Sachs-Wolfe effect is obtained by a simple calculation,. The method to deduce spatial curvature from the position of the acoustic peaks is outlined. Further features such as spectal index and polarization are briefly discussed.

Observations of Her X-1 in low states during SRG/eROSITA all-sky survey

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) instrument onboard the Russian-German ‘Spectrum-Roentgen-Gamma’ (SRG) mission observed the Her X-1/HZ Her binary system in multiple scans over the source during the first and second SRG all-sky surveys. Both observations occurred during a low state of the X-ray source when the outer parts of the accretion disk blocked the neutron star from view. The orbital modulation of the X-ray flux was detected during the low states. We argue that the detected X-ray radiation results from scattering of the emission of the central source by three distinct regions: (a) an optically thin hot corona with temperature ~(2−4) × 106 K above the irradiated hemisphere of the optical star; (b) an optically thin hot halo above the accretion disk; and (c) the optically thick cold atmosphere of the optical star. The latter region effectively scatters photons with energies above 5–6 keV.

Evidence that short-period AM CVn systems are diverse in outburst behaviour

ABSTRACT We present results of our analysis of up to 15 yr of photometric data from eight AM CVn systems with orbital periods between 22.5 and 26.8 min. Our data have been collected from the GOTO, ZTF, Pan-STARRS, ASAS-SN, and Catalina all-sky surveys and amateur observations collated by the AAVSO. We find evidence that these interacting ultracompact binaries show a similar diversity of long-term optical properties as the hydrogen accreting dwarf novae. We found that AM CVn systems in the previously identified accretion disc instability region are not a homogenous group. Various members of the analysed sample exhibit behaviour reminiscent of Z Cam systems with long superoutbursts (SOs) and standstills, SU UMa systems with regular, shorter SOs, and nova-like systems that appear only in a high state. The addition of TESS full frame images of one of these systems, KL Dra, reveals the first evidence for normal outbursts appearing as a precursor to SOs in an AM CVn system. Our results will inform theoretical modelling of the outbursts of hydrogen deficient systems.