scholarly journals EXTraS discovery of an X-ray superflare from an L dwarf

2020 ◽  
Vol 634 ◽  
pp. L13 ◽  
Author(s):  
Andrea De Luca ◽  
Beate Stelzer ◽  
Adam J. Burgasser ◽  
Daniele Pizzocaro ◽  
Piero Ranalli ◽  
...  
Keyword(s):  
Magnetic Energy ◽  
Plasma Heating ◽  
Detection Threshold ◽  
Plasma Temperature ◽  
X Rays ◽  
M Dwarfs ◽  
Photon Detection ◽  
X Ray ◽  
Dark Energy Survey ◽  
Energy Survey

We present the first detection of an X-ray flare from an ultracool dwarf of spectral class L. The event was identified in the EXTraS database of XMM-Newton variable sources, and its optical counterpart, J0331−27, was found through a cross-match with the Dark Energy Survey Year 3 release. Next to an earlier four-photon detection of Kelu-1, J0331−27 is only the second L dwarf detected in X-rays, and much more distant than other ultracool dwarfs with X-ray detections (photometric distance of 240 pc). From an optical spectrum with the VIMOS instrument at the VLT, we determine the spectral type of J0331−27 to be L1. The X-ray flare has an energy of EX, F ∼ 2 × 1033 erg, placing it in the regime of superflares. No quiescent emission is detected, and from 2.5 Ms of XMM-Newton data we derive an upper limit of LX, qui <  1027 erg s−1. The flare peak luminosity (LX, peak = 6.3 × 1029 erg s−1), flare duration (τdecay ≈ 2400 s), and plasma temperature (≈16 MK) are similar to values observed in X-ray flares of M dwarfs. This shows that strong magnetic reconnection events and the ensuing plasma heating are still present even in objects with photospheres as cool as ∼2100 K. However, the absence of any other flares above the detection threshold of EX, F ∼ 2.5 × 1032 erg in a total of ∼2.5 Ms of X-ray data yields a flare energy number distribution inconsistent with the canonical power law dN/dE ∼ E−2, suggesting that magnetic energy release in J0331−27 – and possibly in all L dwarfs – takes place predominantly in the form of giant flares.

Artifact reduction in the CSPAD detectors used for LCLS experiments

2017 ◽  
Vol 24 (5) ◽  
pp. 1092-1097 ◽  
Author(s):  
Alberto Pietrini ◽  
Carl Nettelblad
Keyword(s):  
False Positive ◽  
Signal To Noise Ratio ◽  
Imaging Techniques ◽  
Detection Threshold ◽  
Photon Detection ◽  
X Ray ◽  
Photon Count ◽  
X Ray Imaging ◽  
Count Distribution ◽  
Linac Coherent Light Source

The existence of noise and column-wise artifacts in the CSPAD-140K detector and in a module of the CSPAD-2.3M large camera, respectively, is reported for the L730 and L867 experiments performed at the CXI Instrument at the Linac Coherent Light Source (LCLS), in low-flux and low signal-to-noise ratio regime. Possible remedies are discussed and an additional step in the preprocessing of data is introduced, which consists of performing a median subtraction along the columns of the detector modules. Thus, we reduce the overall variation in the photon count distribution, lowering the mean false-positive photon detection rate by about 4% (from 5.57 × 10−5to 5.32 × 10−5 photon counts pixel−1frame−1in L867, cxi86715) and 7% (from 1.70 × 10-3to 1.58 × 10−3 photon counts pixel−1frame−1in L730, cxi73013), and the standard deviation in false-positive photon count per shot by 15% and 35%, while not making our average photon detection threshold more stringent. Such improvements in detector noise reduction and artifact removal constitute a step forward in the development of flash X-ray imaging techniques for high-resolution, low-signal and in serial nano-crystallography experiments at X-ray free-electron laser facilities.

scholarly journals X-ray properties of z ≳ 6.5 quasars

2019 ◽  
Vol 491 (3) ◽  
pp. 3884-3890 ◽  
Author(s):  
E Pons ◽  
R G McMahon ◽  
M Banerji ◽  
S L Reed
Keyword(s):  
High Redshift ◽  
Optical Power ◽  
Big Bang ◽  
Mean Value ◽  
Significance Level ◽  
X Ray ◽  
Dark Energy Survey ◽  
Photon Index ◽  
The Big Bang ◽  
Energy Survey

ABSTRACT We present XMM–Newton X-ray observations and analysis of three Dark Energy Survey z &gt; 6.5 quasars (VDES J0020−3653 at z = 6.824, VDES J0244−5008 at z = 6.724, and VDES J0224−4711 at z = 6.526) and six other quasars with 6.438 &lt; z &lt; 6.747 from the XMM–Newton public archive. Two of the nine quasars are detected at a high (&gt;4σ) significance level: VDES J0224−4711(z = 6.53) at 9σ and PSO J159−02 (z = 6.38) at 8σ. They have a photon index of $\Gamma =1.82^{+0.29}_{-0.27}$ and $1.94^{+0.31}_{-0.29}$, respectively, which is consistent with the mean value of ∼1.9 found for quasars at all redshifts. The rest-frame 2–10 keV luminosity of VDES J0224−4711 is $L_{2\!-\!10\, \mathrm{keV}} = (2.92\pm 0.43)\times 10^{45}\,\mathrm{erg\,s^{-1}}$, which makes this quasar one of the most X-ray luminous quasars at z &gt; 5.5 and the most X-ray luminous quasar at z &gt; 6.5, with a luminosity 6 times and 2.5 times larger than ULAS J1120+0641 (z = 7.08) and ULAS J1342+0928 (z = 7.54), respectively. The X-ray-to-optical power-law slopes of the nine quasars are consistent with the previously observed anticorrelation of αox with UV luminosity $L_{2500\, \mathrm{\mathring{\rm A} }}$. We find no evidence for evolution of αox with redshift when the anticorrelation with UV luminosity is taken into account. Similar to previous studies at z ∼ 6, we have found remarkably consistent X-ray spectral properties between low-redshift quasars (z ∼ 1) and high-redshift quasars. Our results add further evidence to the picture that the observable properties of high-luminosity quasars over the UV-to-X-ray spectral region have not evolved significantly from z ∼ 7 to the present day and that quasars comparable to local versions existed 800 Myr after the big bang.

First results of the STIX hard X-ray telescope onboard Solar Orbiter

2021 ◽  
Author(s):  
Andrea Francesco Battaglia ◽  
Jonas Saqri ◽  
Ewan Dickson ◽  
Hualin Xiao ◽  
Astrid Veronig ◽  
...  
Keyword(s):  
Solar Flares ◽  
Magnetic Energy ◽  
Imaging Spectroscopy ◽  
X Rays ◽  
X Ray ◽  
X Ray Imaging ◽  
First Results ◽  
Early Peak ◽  
Accelerated Particles ◽  
Magnetic Energy Release

&lt;p&gt;With the launch and commissioning of Solar Orbiter, the Spectrometer/Telescope for Imaging X-rays (STIX) is the latest hard X-ray telescope to study solar flares over a large range of flare sizes. STIX uses hard X-ray imaging spectroscopy in the range from 4 to 150 keV to diagnose the hottest temperature of solar flare plasma and the related nonthermal accelerated electrons. The unique orbit away from the Earth-Sun line in combination with the opportunity of joint observations with other Solar Orbiter instruments, STIX will provide new inputs into understanding the magnetic energy release and particle acceleration in solar flares. Commissioning observations showed that STIX is working as designed and therefore we report on the first solar microflare observations recorded on June 2020, when the spacecraft was at 0.52 AU from the Sun. STIX&amp;#8217;s measurements are compared with Earth-orbiting observatories, such as GOES and SDO/AIA, for which we investigate and interpret the different temporal evolution. The detected early peak of the STIX profiles relative to GOES is due either by nonthermal X-ray emission of accelerated particles interacting with the dense chromosphere or the higher sensitivity of STIX toward hotter plasma.&lt;/p&gt;

scholarly journals The Radiation Transfer of Soft X-rays

1997 ◽  
Vol 166 ◽  
pp. 337-340 ◽  
Author(s):  
Jürgen Kerp ◽  
Jochen Pietz
Keyword(s):  
Power Law ◽  
Intensity Distribution ◽  
Galactic Halo ◽  
Background Radiation ◽  
Plasma Temperature ◽  
Intensity Variation ◽  
Background Intensity ◽  
X Rays ◽  
Energy Bands ◽  
X Ray

AbstractWe discuss the link between the halo plasma temperature and the power-law spectral index of the extragalactic background radiation. This link is of strong influence for the derivation of the Galactic halo intensity distribution. In principal, we can distinguish between two combinations of Galactic halo plasma temperature and power-law slope. The first combination consists of a halo plasma of Thalo = 106 K and an E−2 approximation of the extragalactic background radiation. The second combination is Thalo = 106.2 K and an E−1.5. Both combinations are in agreement with recent observational results, thus it is not feasible to discriminate between both models on the basis of X-ray data available. But, the soft X-ray background intensity distribution in the ¼ keV and ¾ keV ROSAT energy bands differs significantly. The Thalo = 106 K and an E−2 allows a patchy ¼ keV intensity distribution while the Thalo = 106.2 K and an E−1.5 predicts a much smoother intensity variation since the hotter halo plasma accounts for a significant fraction of the ¾ keV background radiation.

scholarly journals Stellar mass as a galaxy cluster mass proxy: application to the Dark Energy Survey redMaPPer clusters

2020 ◽  
Vol 493 (4) ◽  
pp. 4591-4606 ◽  
Author(s):  
A Palmese ◽  
J Annis ◽  
J Burgad ◽  
A Farahi ◽  
M Soares-Santos ◽  
...  
Keyword(s):  
Dark Energy ◽  
Bayesian Model Averaging ◽  
Galaxy Cluster ◽  
Wide Field ◽  
X Ray ◽  
Mass Scaling ◽  
Cluster Mass ◽  
Dark Energy Survey ◽  
Stellar Masses ◽  
Energy Survey

Abstract We introduce a galaxy cluster mass observable, μ⋆, based on the stellar masses of cluster members, and we present results for the Dark Energy Survey (DES) Year 1 (Y1) observations. Stellar masses are computed using a Bayesian model averaging method, and are validated for DES data using simulations and COSMOS data. We show that μ⋆ works as a promising mass proxy by comparing our predictions to X-ray measurements. We measure the X-ray temperature–μ⋆ relation for a total of 129 clusters matched between the wide-field DES Y1 redMaPPer catalogue and Chandra and XMM archival observations, spanning the redshift range 0.1 &lt; $z$ &lt; 0.7. For a scaling relation that is linear in logarithmic space, we find a slope of α = 0.488 ± 0.043 and a scatter in the X-ray temperature at fixed μ⋆ of $\sigma _{{\rm ln} T_\mathrm{ X}|\mu _\star }= 0.266^{+0.019}_{-0.020}$ for the joint sample. By using the halo mass scaling relations of the X-ray temperature from the Weighing the Giants program, we further derive the μ⋆-conditioned scatter in mass, finding $\sigma _{{\rm ln} M|\mu _\star }= 0.26^{+ 0.15}_{- 0.10}$. These results are competitive with well-established cluster mass proxies used for cosmological analyses, showing that μ⋆ can be used as a reliable and physically motivated mass proxy to derive cosmological constraints.

scholarly journals Quasar lenses in the south: searches over the DES public footprint

2019 ◽  
Vol 489 (2) ◽  
pp. 2525-2535 ◽  
Author(s):  
Adriano Agnello ◽  
Chiara Spiniello
Keyword(s):  
Dark Energy ◽  
Selection Criteria ◽  
High Grade ◽  
X Ray ◽  
Dark Energy Survey ◽  
Public Data ◽  
Data Release ◽  
Energy Survey ◽  
Selection Of

ABSTRACT We have scanned 5000 deg2 of Southern Sky to search for strongly lensed quasars with five methods, all source oriented, but based on different assumptions and selection criteria. We present a list of high-grade candidates from each method (totalling 98 unique, new candidates), to facilitate follow-up spectroscopic campaigns, including two previously unknown quadruplets, WG 210014.9-445206.4 and WG 021416.37-210535.3. We analyse morphological searches based on Gaia multiplet detection and astrometric offsets, fibre-spectroscopic pre-selection, and X-ray and radio pre-selection. The performance and complementarity of the methods are evaluated on a common sample of known lenses in the Dark Energy Survey public Data Release 1 (DR1) footprint. We recovered in total 13 known lenses, of which 8 are quadruplets. Morphological and colour selection of objects, from the WISE andGaia-DR2 surveys, recovers most of those known lenses, but searches in the radio and X-ray cover regimes that are beyond the completeness of Gaia. Given the footprint, pre-selection, and depth limits, the current number of quads indicates that the union of these searches is complete, and the expected purity on high-grade candidates is ${\approx}60{{\ \rm per\ cent}}$. Ongoing, spectroscopic campaigns confirm this estimate.

scholarly journals The next-generation X-ray galaxy survey with eROSITA

2020 ◽  
Vol 498 (2) ◽  
pp. 1651-1667 ◽  
Author(s):  
Antara R Basu-Zych ◽  
Ann E Hornschemeier ◽  
Frank Haberl ◽  
Neven Vulic ◽  
Jörn Wilms ◽  
...  
Keyword(s):  
Generation X ◽  
Simulation Software ◽  
X Ray ◽  
Normal Galaxies ◽  
Dark Energy Survey ◽  
Sky Survey ◽  
Stellar Masses ◽  
Mission Simulation ◽  
The Impact ◽  
Energy Survey

ABSTRACT eROSITA, launched on 2019 July 13, will be completing the first all-sky survey in the soft and medium X-ray band in nearly three decades. This 4-yr survey, finishing in late 2023, will present a rich legacy for the entire astrophysics community and complement upcoming multiwavelength surveys (with, e.g. the Large Synoptic Survey Telescope and the Dark Energy Survey). Besides the major scientific aim to study active galactic nuclei (AGNs) and galaxy clusters, eROSITAwill contribute significantly to X-ray studies of normal (i.e. not AGN) galaxies. Starting from multiwavelength catalogues, we measure star formation rates and stellar masses for 60 212 galaxies constrained to distances of 50–200 Mpc. We chose this distance range to focus on the relatively unexplored volume outside the local Universe, where galaxies will be largely spatially unresolved and probe a range of X-ray luminosities that overlap with the low luminosity and/or highly obscured AGN population. We use the most recent X-ray scaling relations as well as the on-orbit eROSITA instrument performance to predict the X-ray emission from XRBs and diffuse hot gas and to perform both an analytic prediction and an end-to-end simulation using the mission simulation software, sixte. We consider potential contributions from hidden AGN and comment on the impact of normal galaxies on the measurement of the faint end of the AGN luminosity function. We predict that the eROSITA 4-yr survey, will detect ≳15 000 galaxies (3σ significance) at 50–200 Mpc, which is ∼100 × more normal galaxies than detected in any X-ray survey to date.

scholarly journals Long-term soft and hard X-ray investigation of the colliding wind WN+O binary WR 25

2019 ◽  
Vol 487 (2) ◽  
pp. 2624-2638 ◽  
Author(s):  
Bharti Arora ◽  
J C Pandey ◽  
M De Becker
Keyword(s):  
Thermal Emission ◽  
Plasma Temperature ◽  
Background Level ◽  
Archival Data ◽  
X Rays ◽  
X Ray ◽  
Upper Limits ◽  
Post Shock ◽  
Colliding Winds

ABSTRACT We investigated the long-term behaviour in X-rays of the colliding wind binary WR 25, using archival data obtained with Suzaku, Swift, XMM–Newton, and NuSTAR spanning over ∼16 yr. Our analysis reveals phase-locked variations repeating consistently over many consecutive orbits, in agreement with an X-ray emission fully explained by thermal emission from the colliding winds in the 208-d orbit. We report on a significant deviation of the X-ray flux with respect to the 1/D trend (expected for adiabatic shocked winds) close to periastron passage. The absence of a drop in post-shock plasma temperature close to periastron suggests this break in trend cannot be explained in terms of reduced pre-shock velocities in this part of the orbit. Finally, NuSTAR data reveal a lack of hard X-ray emission (above 10.0 keV) above the background level. Upper limits on a putative non-thermal emission strongly suggest that the sensitivity of present hard X-ray observatories is not sufficient to detect non-thermal emission from massive binaries above 10 keV, unless the wind kinetic power is large enough to significantly feed particle acceleration in the wind–wind interaction.

scholarly journals X-ray and ion emission studies from subnanosecond laser-irradiated SiO2 aerogel foam targets

2017 ◽  
Vol 35 (3) ◽  
pp. 505-512 ◽  
Author(s):  
C. Kaur ◽  
S. Chaurasia ◽  
A.A. Pisal ◽  
A.K. Rossall ◽  
D.S. Munda ◽  
...  
Keyword(s):  
Laser Energy ◽  
Laser System ◽  
Line Emission ◽  
Plasma Temperature ◽  
X Rays ◽  
Plasma Parameters ◽  
X Ray ◽  
Spectral Ranges ◽  
Ion Emission

AbstractIn this experiment, a comparative study of ion and X-ray emission from both a SiO2 aerogel foam and a quartz target is performed. The experiment is performed using Nd:glass laser system operated at laser energy up to 15 J with a pulse duration of 500 ps with focusable intensity of 1013–1014 W/cm2 on target. X-ray fluxes in different spectral ranges (soft and hard) are measured by using X-ray diodes covered with Al filters of thickness 5 µm (0.9–1.56 keV) and 20 µm (3.4–16 keV). A 2.5 times enhancement in soft X-ray flux (0.9–1.56 keV) and a decrease of 1.8 times in hard X rays (3.4–16 keV) for 50 mg/cc SiO2 aerogel foam is observed compared with the solid quartz. A decrease in the flux of the K-shell line emission spectrum of soft X rays is noticed in the case of the foam targets. The high-resolution K-shell spectra (He-like) of Si ions in both the cases are analyzed for the determination of plasma parameters by comparing with FLYCHK simulations. The estimated plasma temperature and density are Tc = 180 eV, ne = 7 × 1020 cm−3 and Tc = 190 eV, ne = 4 × 1020 cm−3 for quartz and SiO2 aerogel foam, respectively. To measure the evolution of the plasma moving away from the targets, four identical ion collectors are placed at different angles (22.5, 30, 45, and 67.5°) from target normal. The angular distribution of the thermal ions are scaled as cosnθ with respect to target normal, where n = 3.8 and 4.8 for the foam and quartz, respectively. The experimental plasma volume measured from the ion collectors and shadowgraphy images are verified by a two-dimensional Eulerian radiative–hydrodynamic simulation (POLLUX code).

scholarly journals Electron-Beam Evolution in Partially Ionized Hydrogenic Plasma with Return Currents

1994 ◽  
Vol 142 ◽  
pp. 729-734
Author(s):  
D. V. Syniavskii ◽  
V. V. Zharkova
Keyword(s):  
Electron Beam ◽  
Ohmic Heating ◽  
Plasma Heating ◽  
X Rays ◽  
Ohmic Dissipation ◽  
Lower Corona ◽  
Energetic Electrons ◽  
Coulomb Collisions ◽  
Ambient Plasma ◽  
X Ray

AbstractThis paper presents the kinetic equation solution for beam electrons injected during solar flares from the corona to the chromosphere, consisting of hydrogenic plasma with partial ionization. The electrons are considered to lose their energy both in collisional processes with the charged and neutral species of ambient plasma and in ohmic heating by return currents induced in the plasma by beam electrons. The evolution of the energy and angular distributions of energetic electrons is calculated as functions of the column density. The bulk of the electron-beam energy stored in low-energy electrons is shown to be lost in the ambient plasma heating, less via Coulomb collisions at the lower corona and more via ohmic dissipation at the upper chromosphere. More energetic electrons with energies above 120 keV can reach the chromospheric levels with a weak ionized plasma, where a decrease of the Coulomb collisions and the induced electric field of a return current produce beams as well directed as on the top boundary. The X-ray bremsstrahlung polarization is shown to be positive in the range 5%-10%. It is very sensitive to the emergent photon energies below 40 keV and to angles of view for all of the X-ray radiation range.Subject headings: acceleration of particles — plasmas — Sun: flares — Sun: X-rays, gamma rays

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