Abstract
We present a comprehensive multifrequency study of the high-frequency-peaked BL Lac object 1ES 1959+650 using data from various facilities during the period 2016–2017, including X-ray data ...from AstroSat and Swift during the historically high X-ray flux state of the source observed until 2021 February. The unprecedented quality of X-ray data from high-cadence monitoring with AstroSat during 2016–2017 enables us to establish a detailed description of X-ray flares in 1ES 1959+650. The synchrotron peak shifts significantly between different flux states, in a manner consistent with a geometric (changing Doppler factor) interpretation. A time-dependent leptonic diffusive shock acceleration and radiation transfer model is used to reproduce the spectral energy distributions and X-ray light curves, to provide insight into the particle acceleration during the major activity periods observed in 2016 and 2017. The extensive data of Swift-XRT from 2015 December to 2021 February (exp. = 411.3 ks) reveals a positive correlation between flux and peak position.
Abstract
We carry out detailed spectral and timing analyses of the Chandra X-ray data of HD 179949, a prototypical example of a star with a close-in giant planet with possible star–planet interaction ...(SPI) effects. We find a low coronal abundance
A
(Fe)/
A
H) ≈ 0.2 relative to the solar photospheric baseline of Anders & Grevesse, and significantly lower than the stellar photosphere as well. We further find low abundances of high first ionization potential (FIP) elements
A
(O)/
A
(Fe) ≲ 1,
A
(Ne)/
A
(Fe) ≲ 0.1, but with indications of higher abundances of
A
(N)/
A
(Fe) ≫ 1,
A
(Al)/
A
(Fe) ≲ 10. We estimate a FIP bias for this star in the range ≈ − 0.3 to −0.1, larger than the ≲ −0.5 expected for stars of this type, but similar to stars hosting close-in hot Jupiters. We detect significant intensity variability over timescales ranging from 100 s to 10 ks, and also evidence for spectral variability over timescales of 1–10 ks. We combine the Chandra flux measurements with Swift and XMM-Newton measurements to detect periodicities, and determine that the dominant signal is tied to the stellar polar rotational period, consistent with expectations that the corona is rotational-pole dominated. We also find evidence for periodicity at both the planetary orbital frequency and at its beat frequency with the stellar polar rotational period, suggesting the presence of a magnetic connection between the planet and the stellar pole. If these periodicities represent an SPI signal, it is likely driven by a quasi-continuous form of heating (e.g., magnetic field stretching) rather than sporadic, hot, impulsive flare-like reconnections.
Abstract We report the optical, UV, and soft X-ray observations of the 2017–2022 eruptions of the recurrent nova M31N 2008-12a. We find a cusp feature in the r ′ - and i ′ -band light curves close to ...the peak, which could be related to jets. The geometry of the nova ejecta based on morpho-kinematic modeling of the H α emission line indicates an extended jet-like bipolar structure. Spectral modeling indicates an ejecta mass of 10 −7 –10 −8 M ⊙ during each eruption and an enhanced helium abundance. The supersoft source phase shows significant variability, which is anticorrelated to the UV emission, indicating a common origin. The variability could be due to the reformation of the accretion disk. We infer a steady decrease in the accretion rate over the years based on the intereruption recurrence period. A comparison of the accretion rate with different models on the M WD – M ̇ plane yields the mass of a CO white dwarf, powering the H-shell flashes every ∼1 yr, to be >1.36 M ⊙ and growing with time, making M31N 2008-12a a strong candidate for the single degenerate scenario of the Type Ia supernovae progenitor.
We present a process for thermal forming of thin glass panels of borosilicate glass to produce mirror segments for X-ray telescope optics. The mirror segments are required to be shaped in a parabolic ...and hyperbolic shape in accordance with Wolter-I type design of X-ray telescope optics. Thermal forming of glass is a low-cost method to produce light-weight mirror segments. The process makes use of a semi-cylindrical quartz mold having surface roughness of the order of 1 nm. Flat glass sheets of 0.2 mm and 0.3 mm thickness are placed on the diametric edges of the mold. With a suitable thermal cycle, the glass sheets are thermally formed as per the shape of the mold. The shape of these formed glass sheets was measured using a non-contact optical setup. The surface quality measurements of the formed glass sheets were performed using atomic force microscope and they were found to be in the range of 0.04–0.33 nm. Once tested for acceptance, these glass sheets are coated using sputter deposition of multi-layers of high and low atomic number materials for hard X-ray reflection. Such mirror segments do not require polishing of the surface before being coated with multi-layers.
ABSTRACT
We present the first in-depth study of X-ray emission from a nearby (z ∼ 0.0784) galaxy cluster Abell 1569 using an archival Chandra observation. A1569 consists of two unbound subclusters – ...a northern subcluster (A1569N) hosting a double-lobed radio galaxy 1233+169 at its centre, and a southern subcluster (A1569S) harbouring a wide-angle-tailed (WAT) radio source 1233+168. X-ray emission from A1569N and A1569S extends to a radius r ∼248 kpc and r ∼370 kpc, respectively, indicating that the two gas clumps are group-scale systems. The two subclusters have low X-ray luminosities (∼1042–43 erg s−1), average elemental abundances ∼1/4 Z⊙, low average temperatures (∼2 keV), and lack large (r ≳ 40–50 kpc) cool cores associated with the intracluster gas. We detect a pair of cavities coincident with the radio lobes of 1233+169 in A1569N. The total mechanical power associated with the cavity pair is an order of magnitude larger than the X-ray radiative loss in the cavity-occupied region, providing corroborating evidence for cavity-induced heating of the intragroup gas in A1569N. A1569S exhibits possible evidence for a small-scale cluster-subcluster merger, as indicated by its high central entropy, and the presence of local gas elongation and a density discontinuity in between the bent radio tails of 1233+168. The discontinuity is indicative of a weak merger shock with Mach Number, M ∼ 1.7. The most plausible geometry for the ongoing interaction is a head-on merger occurring between A1569S and a subcluster falling in from the west along the line bisecting the WAT tails.
ABSTRACT
We present a detailed X-ray study of the central subcluster of the nearby ($z\, \sim$0.0368) Hercules cluster (Abell 2151) identified as A2151C that shows a bimodal structure. A bright clump ...of hot gas with X-ray emission extending to radius $r\, \sim$304 kpc and $L_X = 3.03_{-0.04}^{+0.02}\times 10^{43}$ erg s−1 in the 0.4–7.0 keV energy range is seen as a fairly regular subclump towards the west (A2151C(B)). An irregular, fainter and cooler subclump with radius $r\, \sim$364 kpc is seen towards the east (A2151C(F)) and has LX = 1.13 ± 0.02 × 1043 erg s−1 in the 0.4–7.0 keV energy band. The average temperature and elemental abundance of A2151C(B) are 2.01 ± 0.05 keV and 0.43 ± 0.05 Z⊙, respectively, while these values are 1.17 ± 0.04 keV and 0.13 ± 0.02 Z⊙ for A2151C(F). Low temperature (1.55 ± 0.07 keV) and a short cooling time (∼0.81 Gyr) within the central 15 arcsec region confirm the presence of a cool core in A2151C(B). We identify several compact groups of galaxies within A2151C(F). We find that A2151C(F) is a distinct galaxy group in the process of formation and likely not a ram-pressure stripped part of the eastern subcluster in Hercules (A2151E). X-ray emission from A2151C shows a region of overlap between A2151C(B) and A2151C(F) but without any enhancement of temperature or entropy in the two-dimensional (2D) projected thermodynamic maps that could have indicated an interaction due to a merger between the two subclumps.
We present the first in-depth study of X-ray emission from a nearby (z ~ 0.0784) galaxy cluster Abell 1569 using an archival Chandra observation. A1569 consists of two unbound subclusters – a ...northern subcluster (A1569N) hosting a double-lobed radio galaxy 1233+169 at its centre, and a southern subcluster (A1569S) harbouring a wide-angle-tailed (WAT) radio source 1233+168. X-ray emission from A1569N and A1569S extends to a radius r ~248 kpc and r ~370 kpc, respectively, indicating that the two gas clumps are group-scale systems. The two subclusters have low X-ray luminosities (~1042–43 erg s-1), average elemental abundances ~1/4 Z⊙, low average temperatures (~2 keV), and lack large (r ≳ 40–50 kpc) cool cores associated with the intracluster gas. We detect a pair of cavities coincident with the radio lobes of 1233+169 in A1569N. The total mechanical power associated with the cavity pair is an order of magnitude larger than the X-ray radiative loss in the cavity-occupied region, providing corroborating evidence for cavity-induced heating of the intragroup gas in A1569N. A1569S exhibits possible evidence for a small-scale cluster-subcluster merger, as indicated by its high central entropy, and the presence of local gas elongation and a density discontinuity in between the bent radio tails of 1233+168. The discontinuity is indicative of a weak merger shock with Mach Number, M ~ 1.7. The most plausible geometry for the ongoing interaction is a head-on merger occurring between A1569S and a subcluster falling in from the west along the line bisecting the WAT tails.
Jets from active galactic nuclei Singh, Kulinder Pal
Journal of astrophysics and astronomy,
11/2022, Letnik:
43, Številka:
2
Journal Article
Recenzirano
In this article, first the author present a short historical introduction to the discovery of extragalactic jets in active galactic nuclei (AGN), followed by a brief overview of their observational ...properties which lead to their various classifications and a unification scheme based on the viewing geometry of jets in the AGN. The author largely focus on the studies of multi-wavelength emissions and modeling of spectral energy distribution of AGN, which are dominated by emission from jets, namely, blazars. The author present a few new results from the studies of a few blazars based mostly on observations with the AstroSat. The author ends with an overview of the role played by the radio jets in clusters of galaxies in creating various interesting features in the hot gas, and feedback and regulation of heating and cooling in the cores of the hot gas.
AstroSat, India’s first UV and X-ray astronomy satellite, has completed over six years of observations while in orbit around the Earth. It has carried out detailed studies of all kinds of objects in ...the Universe ranging from single stars, stars in clusters, binary stars with compact companions like neutron stars and black holes, star formation in galaxies, supermassive black holes in active nuclei of galaxies, etc. Here, I give a short description of its UV and X-ray telescopes and detectors. Some of the most important results obtained using AstroSat will be described in Part II.
AstroSat, launched in 2015, has observed all kinds of objects in the universe in X-rays and UV light. These objects range from isolated stars to stars in clusters, binary stars with compact ...companions like neutron stars and black holes, star-forming regions in the galaxies, and supermassive black holes in active nuclei of galaxies. In addition, it has carried out deep surveys of certain parts of the sky, reaching the farthest and the faintest objects in those regions. In this second part of the article, I highlight some of the important results obtained using AstroSat in the first five years of its operation.
PDF
