Search Publications
Peak of spectral energy distribution plays an important role in intra-day variability of blazars?
Gupta, Alok C.; Kalita, Nibedita; Gaur, Haritma +1 more
Blazars can be divided into two sub-classes namely high energy and low energy peaked blazars. In spectral energy distribution, the first synchrotron hump of the former class peaks in UV/X-rays and in IR/optical bands for the latter class. The peak of the spectral energy distribution seems to be responsible for variability properties of these class…
A pair of O VI and broad Ly α absorbers probing warm gas in a galaxy group environment at z ∼ 0.4
Savage, Blair D.; Wakker, Bart P.; Muzahid, Sowgat +4 more
We report the detection of two O VI absorbers at z = 0.416 14 and 0.419 50 (|Δv| = 710 km s-1), towards SBS 0957+599. Both absorbers are multiphase systems tracing substantial reservoirs of warm baryons. The low- and intermediate-ionization metals in the z = 0.416 14 absorber are consistent with an origin in photoionized gas. O VI has a…
Origin and evolution of two-component debris discs and an application to the q1 Eridani system
Kirchschlager, Florian; Booth, Mark; Krivov, Alexander V. +3 more
Many debris discs reveal a two-component structure, with an outer Kuiper-belt analogue and a warm inner component whose origin is still a matter of debate. One possibility is that warm emission stems from an `asteroid belt' closer in to the star. We consider a scenario in which a set of giant planets is formed in an initially extended planetesimal…
X-ray, UV and optical analysis of supergiants: ɛ Ori
Hillier, D. John; Leutenegger, Maurice A.; Cohen, David H. +2 more
We present a multi-wavelength (X-ray to optical) analysis, based on non-local thermodynamic equilibrium photospheric+wind models, of the B0 Ia-supergiant: ɛ Ori. The aim is to test the consistency of physical parameters, such as the mass-loss rate and CNO abundances, derived from different spectral bands. The derived mass-loss rate is {dot {M}} / …
Ne X X-ray emission due to charge exchange in M82
Liu, L.; Cumbee, R. S.; Lyons, D. +4 more
Recent X-ray observations of star-forming galaxies such as M82 have shown the Ly β/Ly α line ratio of Ne X to be in excess of predictions for thermal electron impact excitation. Here, we demonstrate that the observed line ratio may be due to charge exchange and can be used to constrain the ion kinetic energy to be ≲ 500 eV/u. This is accomplished …
X-ray/UV variability and the origin of soft X-ray excess emission from II Zw 177
Dewangan, Gulab C.; Pal, Main; Misra, Ranjeev +1 more
We study X-ray and UV emission from the narrow-line Seyfert 1 galaxy II Zw 177 using a 137 ks long and another 13 ks short XMM-Newton observation performed in 2012 and 2001, respectively. Both observations show soft X-ray excess emission contributing 76.9 ± 4.9 per cent in 2012 and 58.8 ± 10.2 per cent in 2001 in the 0.3-2 keV band. We find that b…
Where are all of the nebulae ionized by supersoft X-ray sources?
Gilfanov, M.; Woods, T. E.
Accreting, steadily nuclear-burning white dwarfs are associated with so-called close-binary supersoft X-ray sources (SSSs), observed to have temperatures of a few × 105 K and luminosities on the order of 1038 erg s-1. These and other types of SSSs are expected to be capable of ionizing their surrounding circumstell…
Insights into the location and dynamics of the coolest X-ray emitting gas in clusters of galaxies
Zhang, Y. -Y.; Finoguenov, A.; de Plaa, J. +10 more
We extend our previous study of the cool gas responsible for the emission of O VII X-ray lines in the cores of clusters and groups of galaxies. This is the coolest X-ray emitting phase and connects the 10 000 K H α emitting gas to the million degree phase, providing a useful tool to understand cooling in these objects. We study the location of the…
The ATCA REXCESS Diffuse Emission Survey (ARDES) - I. Detection of a giant radio halo and a likely radio relic
Pratt, G. W.; Johnston-Hollitt, M.; Shakouri, S.
We present the results of the radio halo survey of 16 REXCESS southern clusters up to a redshift of 0.2 with the Australia Telescope Compact Array (ATCA) at 1.4 and 2.1 GHz. This cluster sample called the ATCA REXCESS Diffuse Emission Survey (ARDES) includes clusters in a wide range of X-ray luminosities and is morphologically unbiased. We find tw…
On the properties of the interstellar medium in extremely metal-poor blue compact dwarf galaxies. A VIMOS-IFU study of the cometary galaxy and Ly α absorber Tol 65
Demarco, R.; Humphrey, A.; Roche, N. +5 more
In this study, we present high-resolution VIsible Multi-Object Spectrograph integral field unit spectroscopy (VIMOS-IFU) of the extremely metal-poor H II/blue compact dwarf (BCD) galaxy Tol 65. The optical appearance of this galaxy shows clearly a cometary morphology with a bright main body and an extended and diffuse stellar tail. We focus on the…