The X-ray pulsar A0535+26 in hard X-rays - Average spectrum, pulse-phase spectroscopy, and spectral time variability

1988 ◽  
Vol 331 ◽  
pp. 313 ◽  
Author(s):  
D. dal Fiume ◽  
F. Frontera ◽  
E. Morelli
Keyword(s):  
Time Variability ◽  
X Rays ◽  
X Ray ◽  
Pulse Phase ◽  
Average Spectrum

scholarly journals Wide-field Cameras for GRB Observations in X-rays and EUV

1995 ◽  
Vol 151 ◽  
pp. 431-434
Author(s):  
Eugene Moskalenko
Keyword(s):  
Time Scale ◽  
Field Of View ◽  
Time Variability ◽  
Wide Field ◽  
Main Task ◽  
X Rays ◽  
Interstellar Absorption ◽  
X Ray ◽  
Instrumental Approaches ◽  
Stationary Sources

Recent observations of the ASCA satellite resulted in the first identification of a GB source (Murakami et al. 1994). This success confirmed the importance of simultaneous observations in different wavelength bands for GB studies. Besides the ASCA results, there were several observations of GBs in X-ray band with the Ginga (Yoshida et al,.1989), V 78/1 (Laros et al. 1984) and other satellites. It became clear that GBs emit 4 - 8% of their energy in the 2 - 10 keV range. The main task now is to have an equipment which will be able to monitor the sky in X-rays in a mode similar to that of GRO observations, i.e. the telescope should have an all-sky field-of-view (FoV) and should work continuously.A telescope with these features but operating at soft X-ray energies may directly determine the GB distance scale, due to interstellar absorption of the photons with energies less than 2 keV, as was pointed out first by Schaefer (1993). Flaring sources similar to GBs in time scale may be found also in the EUV (hundreds of angstroms) with the help of very wide-field cameras. Of course each such device - in X-ray, soft X-ray and EUV bands - will discover many transient objects, flaring events, will study time variability of bright “stationary” sources etc. In this paper we describe several instrumental approaches in these fields.

scholarly journals Unveiling the Multi-wavelength Phenomenology of Anomalous X-ray Pulsars

2004 ◽  
Vol 218 ◽  
pp. 247-250 ◽  
Author(s):  
GianLuca Israel ◽  
Luigi Stella ◽  
Stefano Covino ◽  
Sergio Campana ◽  
Lorella Angelini ◽  
...  
Keyword(s):  
Energy Spectrum ◽  
Broad Band ◽  
Archival Data ◽  
X Rays ◽  
Spectral Variability ◽  
Band Energy ◽  
X Ray ◽  
Pulse Phase ◽  
Multi Wavelength ◽  
Ir Bands

During 2002–2003 the number of IR-identified counterparts to the Anomalous X-ray Pulsars (AXPs) has grown to four (4U 0142+61, IE 2259+586, IE 1048.1−5937 and RXS J170849−400910) out of the six objects (plus two candidates) known in this class. More importantly, some new common characteristics have been identified, such as IR variability, IR flattening in the broad-band energy spectrum, X-ray spectral variability as a function of pulse phase (which are not predicted by the magnetar model), and X-ray bursts (which cannot be explained in terms of standard accretion models). We present the results obtained from an extensive multi-wavelength observational campaign carried out with the NTT and CFHT for the optical/IR bands, and XMM and Chandra (plus BeppoSAX archival data) in X-rays. Based on these results and those reported in the literature, the IR-to-X-ray emission of AXPs is compared.

The X-ray pulsar A0535 + 26 - Pulse profile and its time variability in hard X-rays

1985 ◽  
Vol 298 ◽  
pp. 585 ◽  
Author(s):  
F. Frontera ◽  
D. dal Fiume ◽  
E. Morelli ◽  
G. Spada
Keyword(s):  
Time Variability ◽  
X Rays ◽  
Pulse Profile ◽  
X Ray

scholarly journals Temporal and spatial variation of synchrotron X-ray stripes in Tycho’s supernova remnant

2020 ◽  
Vol 72 (5) ◽  
Author(s):  
Masamune Matsuda ◽  
Takaaki Tanaka ◽  
Hiroyuki Uchida ◽  
Yuki Amano ◽  
Takeshi Go Tsuru
Keyword(s):  
Surface Brightness ◽  
Supernova Remnant ◽  
Time Variability ◽  
X Rays ◽  
Temporal And Spatial Variation ◽  
Proton Acceleration ◽  
X Ray ◽  
Temporal And Spatial ◽  
Imaging And Spectroscopy ◽  
The Magnetic Field

Abstract The synchrotron X-ray “stripes” discovered in Tycho’s supernova remnant (SNR) have been attracting attention as they may be evidence for proton acceleration up to PeV. We analyzed Chandra data taken in 2003, 2007, 2009, and 2015 for imaging and spectroscopy of the stripes in the southwestern region of the SNR. Comparing images obtained at different epochs, we find that time variability of synchrotron X-rays is not limited to two structures previously reported but is more common in the region. Spectral analysis of nine bright stripes reveals not only their time variabilities but also a strong anti-correlation between the surface brightness and photon indices. The spectra of the nine stripes have photon indices of Γ = 2.1–2.6 and are significantly harder than those of the outer rim of the SNR in the same region with Γ = 2.7–2.9. Based on these findings, we indicate that the magnetic field is substantially amplified, and suggest that particle acceleration through a stochastic process may be at work in the stripes.

scholarly journals Broadband X-ray observations of four gamma-ray narrow-line Seyfert 1 galaxies

2019 ◽  
Vol 632 ◽  
pp. A120 ◽  
Author(s):  
M. Berton ◽  
V. Braito ◽  
S. Mathur ◽  
L. Foschini ◽  
E. Piconcelli ◽  
...  
Keyword(s):  
Accretion Disk ◽  
Gamma Ray ◽  
High Energy ◽  
Time Variability ◽  
X Rays ◽  
Narrow Line ◽  
X Ray ◽  
Relativistic Jet ◽  
Line Region ◽  
Spectrum Radio

Narrow-line Seyfert 1 galaxies (NLS1s) is one of the few classes of active galactic nuclei harboring powerful relativistic jets and detected in γ-rays. NLS1s are well-known X-ray sources. While in non-jetted sources the origin of this X-ray emission may be a hot corona surrounding the accretion disk, in jetted objects, especially beamed ones, the contribution of corona and relativistic jet is difficult to disentangle without a proper sampling of the hard X-ray emission. For this reason, we observed with NuSTAR the first four NLS1s detected at high energy γ-rays. These data, along with XMM-Newton and Swift/XRT observations, confirmed that X-rays originate both in the jet and in the accretion disk corona. Time variability in hard X-rays furthermore suggests that, as observed in flat-spectrum radio quasars, the dissipation region during flares could change its position from source to source, and it can be located both inside and outside the broad-line region. We find that jetted NLS1s, and other blazars as well, seem not to follow the classical fundamental plane of black hole (BH) activity, which therefore should be used as a BH mass estimator in blazars with extreme care only. Our results strengthen the idea according to which γ-NLS1s are smaller and younger version of flat-spectrum radio quasars, in which both a Seyfert and a blazar component co-exist.

scholarly journals Detection of X-ray flares from AX J1714.1−3912, the unidentified source near RX J1713.7−3946

2018 ◽  
Vol 612 ◽  
pp. A32 ◽  
Author(s):  
Marco Miceli ◽  
Aya Bamba
Keyword(s):  
Supernova Remnants ◽  
Time Variability ◽  
X Rays ◽  
Energy Bands ◽  
X Ray ◽  
Nonthermal Emission ◽  
Photon Index ◽  
Unidentified Source

Context. Molecular clouds are predicted to emit nonthermal X-rays when they are close to particle-accelerating supernova remnants (SNRs), and the hard X-ray source AX J1714.1−3912, near the SNR RX J1713.7−3946, has long been considered a candidate for diffuse nonthermal emission associated with cosmic rays diffusing from the remnant to a closeby molecular cloud. Aim. We aim at ascertaining the nature of this source by analyzing two dedicated X-ray observations performed with Suzaku and Chandra. Methods. We extracted images from the data in various energy bands, spectra, and light curves and studied the long-term evolution of the X-ray emission on the basis of the ~4.5 yr time separation between the two observations. Results. We found that there is no diffuse emission associated with AX J1714.1−3912, which is instead the point-like source CXOU J171343.9−391205. We discovered rapid time variability (timescale ~ 103 s), together with a high intrinsic absorption and a hard nonthermal spectrum (power law with photon index Γ ~ 1.4). We also found that the X-ray flux of the source drops down by 1–2 orders of magnitude on a timescale of a few years. Conclusions. Our results suggest a possible association between AX J1714.1−3912 and a previously unknown supergiant fast X-ray transient, although further follow-up observations are necessary to prove this association definitively.

scholarly journals Inner Disk Structure of Dwarf Novae in the Light of X-Ray Observations

2015 ◽  
Vol 2 (1) ◽  
pp. 116-122 ◽  
Author(s):  
S. Balman
Keyword(s):  
White Dwarf ◽  
Spectral Characteristics ◽  
Time Variability ◽  
Time Lags ◽  
X Rays ◽  
Dwarf Novae ◽  
Disk Radius ◽  
X Ray ◽  
Disk Structure ◽  
Band Limited

Diversity of the X-ray observations of dwarf nova are still not fully understood. I review the X-ray spectral characteristics of dwarf novae during the quiescence in general explained by cooling flow models and the outburst spectra that show hard X-ray emission dominantly with few sources that reveal soft X-ray/EUV blackbody emission. The nature of aperiodic time variability of brightness of dwarf novae shows band limited noise, which can be adequately described in the framework of the model of propagating fluctuations. The frequency of the break (1-6 mHz) indicates inner disk truncation of the optically thick disk with a range of radii (3.0-10.0)×109 cm. The RXTE and optical (RTT150) data of SS Cyg in outburst and quiescence reveal that the inner disk radius moves towards the white dwarf and receeds as the outburst declines to quiescence. A preliminary analysis of SU UMa indicates a similar behaviour. In addition, I find that the outburst spectra of WZ Sge shows two component spectrum of only hard X-ray emission, one of which may be fitted with a power law suggesting thermal Comptonization occuring in the system. Cross-correlations between the simultaneous UV and X-ray light curves (XMM −Newton) of five DNe in quiescence show time lags in the X-rays of 96-181 sec consistent with travel time of matter from a truncated inner disk to the white dwarf surface. All this suggests that dwarf novae and other plausible nonmagnetic systems have truncated accretion disks indicating that the disks may be partially evaporated and the accretion may occur through hot (coronal) flows in the disk.

scholarly journals Rosat Observations of Stellar Flares

1994 ◽  
Vol 142 ◽  
pp. 735-742
Author(s):  
J. H. M. M. Schmitt
Keyword(s):  
Time Variability ◽  
X Rays ◽  
Late Type ◽  
X Ray ◽  
Stellar Flares ◽  
Long Duration ◽  
Sky Survey ◽  
Pointed Observation ◽  
Flare Stars ◽  
First Time

AbstractX-ray observations of stellar flares obtained during the ROSAT all-sky survey as well as in the ROSAT pointing program are discussed. The ROSAT all-sky survey allowed—for the first time—an unbiased search for stellar flares among all types of stars. A fundamentally new result obtained is that flares can occur on all types of late-type stars, thus supporting the view that the X-ray emission from these stars is controlled by magnetic processes. Long-duration flares can be studied with the all-sky survey data particularly well, and an especially well-observed long-duration flare event on the flare star EV Lacertae is presented and discussed in detail. Finally, the issue of time variability on the shortest detectable timescales and the question of microflaring is discussed using ROSAT data from a pointed observation of UV Ceti.Subject headings: stars: coronae — stars: flare — stars: late-type — X-rays: stars

scholarly journals Luminous Supersoft X-ray Sources

1996 ◽  
Vol 165 ◽  
pp. 415-424
Author(s):  
S. Rappaport ◽  
R. Di Stefano
Keyword(s):  
Accretion Disks ◽  
Large Magellanic Cloud ◽  
High Energy ◽  
Magellanic Cloud ◽  
Emission Lines ◽  
Time Variability ◽  
X Rays ◽  
X Ray ◽  
Significant Time ◽  
Einstein Observatory

Supersoft X-ray sources exhibit spectra that are remarkably steep, in that the ratio of low-to-high energy X rays is much larger than is characteristic of the spectra associated with the previously known classes of luminous X-ray sources. The first supersoft sources were discovered during a survey of the Large Magellanic Cloud with the EINSTEIN Observatory (Longet al.1981). The all-sky X-ray survey carried out with ROSAT has now established that luminous supersoft X-ray sources constitute a distinct astronomical class (see, e.g., Hasinger 1994). A number of the identified optical counterparts of the supersoft X-ray sources exhibit blue continua with emission lines of H and He II (Smaleet al.1988; Pakullet al.1988; Cowleyet al.1990), which are characteristic of accretion disks. The X-ray emission of some sources is steady, while others exhibit significant time variability. Table 1 briefly summarizes what is known thus far about the numbers and characteristics of supersoft X-ray sources (see Hasinger 1994, and references therein).

scholarly journals Multilayer Mirror Based High-Resolution Solar Soft X-Ray Spectrometer

2021 ◽  
Vol 8 ◽  
Author(s):  
S. S. Panini ◽  
S. Narendranath ◽  
P. Sreekumar ◽  
K. Sankarasubramanian
Keyword(s):  
High Resolution ◽  
Spectral Range ◽  
Spectral Resolution ◽  
High Spectral Resolution ◽  
High Resolution Spectroscopy ◽  
Time Variability ◽  
Type I ◽  
The Sun ◽  
X Rays ◽  
X Ray

Soft X-ray spectroscopy of the Sun is an important tool to understand the coronal dynamics and composition. The solar coronal X-ray spectrum below 1 keV is the least explored with high-resolution spectroscopy. Recent observations with Hinode XRT using coarse spectroscopy along with high-resolution imaging have shown that abundances in the coronae have variability associated with structures on the Sun. Disk averaged abundances with better spectral resolution spectrometers show time variability associated with flares. Both spatial and temporal variabilities seem to be related to changes in the magnetic field topology. Understanding such short term variabilities is necessary to model the underlying dynamics and mixing of material between different layers of the Sun. A Sensitive high-resolution spectrometer that covers the range in plasma temperatures and emission line complexes would uniquely reveal the entire evolution of flares. We are investigating a design of a multi-layer mirror-based X-ray spectrograph in the spectral range from 0.5 to 7 keV. The instrument operates in four asynchronous spectral channels operating one at a time. The multi-layer mirror placed at the focus of a Wolter type I telescope reflects a narrow band X-rays to the CCD which is placed at Nasmyth defocus. Converging X-rays from the front end optics helps to increase the spectral range of each channel while preserving the spectral resolution. This design is estimated to achieve a spectral resolution of 20 eV in the spectral range of 0.5–7 keV. With such high spectral resolution, we can resolve individual spectral features e.g., 6.7 keV Fe complex which can be used to diagnose high-temperature transient plasma during flares. The instrument design estimated performance and the science capabilities of this instrument will be discussed in detail in the paper.

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