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At least 181 records · Page 10

X-ray imaging observations of active galactic nuclei and quasars

After discussing the X-ray properties of active galactic nuclei and quasars which have been ascertained by means of Einstein Observatory imaging observations, the observation of X-ray jets coincident with the optical and radio jets in 3C 273 and M87 is considered. The sensitivity of the Einstein Observatory makes possible the search for variability in Seyfert galaxies on time scales shorter than one day. It is noted that if such short time scale variability occurs in all Seyferts, X-ray emission lines due to Compton smearing are unlikely, as is borne out by observations. It appears that integrated emission from quasars makes up a large fraction of the X-ray background in the 1-3 keV band, with the observational consequence that the average value of many quasar spectra should be the same as the background spectrum.

Henry, J. P.↗

Electron-beam-based Compton scattering x-ray source for probing high-energy-density physics

The physics basis for an electron-beam-based Compton scattering x-ray source is investigated for single-shot experiments at the major high-energy-density facilities, such as the Omega Laser Facility, National Ignition Facility, and Z pulsed power facility. A source of monoenergetic ( δ ε / ε < 5 % ) 10- to 50-keV x rays can be produced by scattering of a short-pulse optical laser by a 23- to 53-MeV electron beam and collimating the scattered photons. The number and spectrum of scattered photons are calculated as a function of electron packet charge, electron and laser pulse duration, laser intensity, and collision geometry. A source delivering greater than 10 10 photons in a 1-mm-radius spot and 100-ps time resolution is plausible with the available electron gun and laser technology. Applications of this source for x-ray diffraction, x-ray imaging, x-ray absorption fine structure, and x-ray absorption spectroscopy in high-energy-density physics experiments are described, demonstrating significant advancements compared to the present state of the art. Published by the American Physical Society 2024

47 OTHER INSTRUMENTATION↗

Potential origin of the state-dependent hard tail in the black hole microquasar Cygnus X-1 as seen with INTEGRAL

Context.0.1–10 MeV observations of the black hole microquasar Cygnus X-1 have shown the presence of a spectral feature in the form of a power law in addition to the standard black body (0.1–10 keV) and Comptontonization (10–200 keV) components usually seen in all black hole X-ray binaries. This so-called “high-energy tail” has recently been shown to be strong in the hard spectral state and has been interpreted as high-energy part of the emission from a compact jet. Aims. This result was, however, obtained from a data set largely dominated by hard state observations. In the soft state, only upper limits on the presence and hence the potential parameters of a hard tail could be derived. Using an extended data set we aim at obtaining better constraints on the properties of this spectral component in both states. Methods. We make use of data obtained from about 15 years of observations with the INTEGRAL satellite. The data set is separated into the different states and we analyse stacked state-resolved spectra obtained from both the gamma-ray Imager and the Spectrometer onboard. Results. A high-energy component is detected in both states, confirming its earlier detection in the hard state and its suspected presence in the soft state as seen in a much smaller SPI data set. We first characterize the hard tail components in the two states through a model-independent, phenomenological analysis. We then apply physical models based on hybrid Comptonization (eqpair and belm). The spectra are well modeled in all cases, with a similar goodness of the fit. The spectral properties of the tails in the two states are, however, quite different. This might indicate that the emission originates from different media in the two cases. Our results are compatible with a compact jet origin in the hard state and hybrid Comptonization in the soft state.

F. Cangemi↗

X-Ray Polarization From the Atoll 4U 1735−44 Suggests a Low Inclination

X-ray polarimetry is a new tool capable of probing the geometry of accretion onto weakly magnetized neutron stars. Here we present the first X-ray spectro-polarimetric results from coordinated observations of the atoll source 4U 1735−44, conducted with the Imaging X-ray Polarimetry Explorer (IXPE), NICER, and NuSTAR . Over the 2–8 keV energy range, we obtained a marginal detection of polarization with the polarization degree of 1.4% ± 0.7% and polarization angle of −29◦ ± 14◦, corresponding to a 3σ upper limit on the polarization degree of 3.5%. The best-fit model to describe the spectrum comprises a thermal component associated with the accretion disk, a Comptonized black body component, and a relativistic reflection component. From the reflection model, we infer a disk inclination of ∼40◦. The spectroscopic and polarimetric properties of 4U 1735−44 are consistent with those observed in other atoll sources studied by IXPE, with its low polarization likely due to its low inclination

X-rays: binaries↗

Exploring baryon resonances with transition generalized parton distributions: status and perspectives

QCD gives rise to a rich spectrum of excited baryon states. Understanding their internal structure is important for many areas of nuclear physics, such as nuclear forces, dense matter, and neutrino-nucleus interactions. Generalized parton distributions (GPDs) are an established tool for characterizing the QCD structure of the ground-state nucleon. They are used to create 3D tomographic images of the quark/gluon structure and quantify the mechanical properties such as the distribution of mass, angular momentum, and forces in the system. Transition GPDs extend these concepts to N → N* transitions and can be used to characterize the 3D structure and mechanical properties of baryon resonances. They can be probed in high-momentum-transfer exclusive electroproduction processes with resonance transitions e + N → e' + M + N*, such as deeply-virtual Compton scattering (M = γ) or meson production (M = π, K, etc.), and in related photon/hadron-induced processes. This White Paper describes a research program aiming to explore baryon resonance structure with transition GPDs. This includes the properties and interpretation of the transition GPDs, theoretical methods for structures and processes, first experimental results from JLab 12 GeV, future measurements with existing and planned facilities (JLab detector and energy upgrades, COMPASS/AMBER, EIC, EicC, J-PARC, LHC ultraperipheral collisions), and the theoretical and experimental developments needed to realize this program.

Experimental Nuclear Physics↗

Measurement of the Deeply Virtual Compton Scattering Cross Section from the Proton at 10.6 GeV using the CLAS12 Detector

Deeply Virtual Compton Scattering (DVCS) is an exclusive process that produces a real photon when a lepton scatters from a quark inside a nucleon or a nucleus. Measurement of the DVCS cross section enables the study of the Generalized Parton Distributions (GPD), which plays a central role in understanding the QCD dynamics inside a hadron. Thus, the quark and gluon origin of the nucleon spin and mass can be probed and three-dimensional images of the target nucleon or nucleus can be realized. This thesis presents a cross section analysis of DVCS from the proton in the presence of its background, Bethe-Heitler (BH) process. The CEBAF Large Acceptance Spectrometer for operation at 12 GeV beam energy (CLAS12) collaboration has taken electron-proton scattering data in fall 2018 using a liquid hydrogen target and the 10.6 GeV polarized electron beam from the Continuous Electron Beam Accelerator Facility (CEBAF). The CLAS12 detector is a nearly hermetic fixed-target detector, located in Hall B, Jefferson Lab at Newport News, Virginia. The experimentally determined BH-DVCS cross section is in good agreement with a phenomenological-model based theoretical prediction. The kinematic dependence of the cross section is reported over a wide range. The short-term plan to utilize the results presented here for a thorough tomography study and the long-term plan for GPD studies at future facilities such as the Electron-Ion Collider (EIC) are discussed.

Lee, Sangbaek↗

Rapid X-ray variability from the Seyfert 1 Galaxy NGC 4051

Strong variable X-ray emission from the nearby low luminosity Seyfert 1 galaxy NGC 4051 was discovered during observations with the imaging proportional counter of the Einstein Observatory. During one 2304 second observation, the X-ray flux more than doubled in an approximately linear fashion, and a 70% increase for 150 seconds was seen during another 968 second observation. Evidence is presented which demonstrates that the X-ray spectrum of NGC 4051 is unusually soft compared to Seyfert 1 galaxies or QSOs. The emission mechanism is probably not synchrotron or synchrotron self-Compton, but the emission can be plausibly explained by various black hole accretion models.

Marshall, F. E.↗

Results from the Advanced Scintillator Compton Telescope (ASCOT) Balloon Payload

The Advanced Scintillator Compton Telescope (ASCOT) is a medium-energy gamma-ray Compton telescope flown on NASA’s high-altitude scientific balloon from Palestine, TX on 5th July 2018. It uses commercially available highperformance scintillators like Cerium Bromide (CeBr3) and p-terphenyl along with compact readout devices - silicon photomultipliers (SiPMs) - for an improved instrument response. ASCOT was built to address the existing need for observations in the gamma-ray energy range of 0.4 - 20 MeV. Operating stably throughout the mission, it reached an altitude of 120,000 ft and observed the Crab Nebula at MeV energies for ~5 hours. Built on the legacy of COMPTEL (onboard CGRO), along with the hardware advancement ASCOT also makes use of the Time-of-Flight (ToF) background rejection technique for effective imaging. Presented here is the Energy and ToF calibrated flight data with optimal data cuts (Earth Horizon Cut, Pulse Shape Discrimination Cut). The growth curves generated using this data from 5 to 100 g/cm2 of residual atmosphere in conjunction with the Monte Carlo simulations of the instrument response have been used to obtain the Cosmic Diffuse Gamma-ray (CDG) flux value of (1.28 ± 0.37)×10 -5 photons/cm 2 /s/sr/keV for 0.4 – 0.7 MeV energy range. The 3σ upper limit for CDG flux is 1.8×10-5 photons/cm 2 /s/sr/keV for 0.7-1.5 MeV and 2×10-6 photons/cm2/s/sr/keV for 1.5-2.5 MeV. The analysis of the Crab Nebula from flight observation is underway

79 ASTRONOMY AND ASTROPHYSICS↗

Einstein observations of the X-ray structure of Centaurus A - Evidence for the radio-lobe energy source

The X-ray source at the center of the radio galaxy Centaurus A has been resolved into the following components with the imaging detectors on board the Einstein X-ray Observatory: (1) a point source coincident with the infrared nucleus; (2) diffuse X-ray emission coinciding with the inner radio lobes; (3) a 4-arcmin extended region of emission about the nucleus; and (4) an X-ray jet between the nucleus and the NE inner radio lobe. The 2 x 10 to the 39th ergs/s detected from the radio lobes probably arises from inverse Compton scattering of the microwave background. The average magnetic field in the SW lobe is determined to be not less than 4 microgauss. The extended region may be due to emission by a cloud of hot gas, cosmic-ray scattering, or stellar sources. The jet provides strong evidence for the continuous resupply of energy to the lobes from the nucleus.

Schreier, E. J.↗

Rapid X-ray variability from the Seyfert 1 galaxy NGC 4051

Strong variable X-ray emission from the nearby low luminosity Seyfert 1 galaxy NGC 4051 was discovered during observations with the imaging proportional counter of the Einstein Observatory. During one 2304 second observation, the X-ray flux more than doubled in an approximately linear fashion, and a 70 percent increase for 150 seconds was seen during another 968 second observation. Evidence is presented which demonstrates that the X-ray spectrum of NGC 4051 is unusually soft compared to Seyfert 1 galaxies or QSOs. The emission mechanism is probably not synchrotron or synchrotron self-Compton, but the emission can be plausibly explained by various black hole accretion models. Previously announced in STAR as N83-23265

Marshall, F. E.↗

Measurement of the Deeply Virtual Neutral Pion Electroproduction Cross Section off the Proton at 10.6 GeV using the CLAS12 Detector

Deeply virtual exclusive reactions provide unique channels to study both transverse and longitudinal properties of the nucleon simultaneously, allowing for a 3D image of nucleon substructure. This presentation will discuss work towards extracting an absolute cross section for one such exclusive process, deeply virtual neutral pion production, using 10.6 GeV electron scattering data off a proton target from the CLAS12 experiment in Jefferson Lab Hall B. This measurement is important as exclusive meson production has unique access to the chiral odd Generalized Parton Distributions, and is also a background for other exclusive processes such as Deeply Virtual Compton Scattering, making the determination of this cross section crucial for other exclusive analyses.

Johnston, Robert↗

The First X-Ray Polarimetric Observation of the Black Hole Binary LMC X-1

We report on an X-ray polarimetric observation of the high-mass X-ray binary LMC X-1 in the high/soft state, obtained by the Imaging X-ray Polarimetry Explorer ( IXPE ) in 2022 October. The measured polarization is below the minimum detectable polarization of 1.1 per cent (at the 99 per cent confidence level). Simultaneously, the source was observed with the Neutron Star Interior Composition Explorer (NICER), Nuclear Spectroscopic Telescope Array ( NuSTAR ), and Spectrum-Rontgen-Gamma ( SRG )/Astronomical Roentgen Telescope – X-ray Concentrator (ART-XC) instruments, which enabled spectral decomposition into a dominant thermal component and a Comptonized one. The low 2–8 keV polarization of the source did not allow for strong constraints on the black hole spin and inclination of the accretion disc. However, if the orbital inclination of about 36◦ is assumed, then the upper limit is consistent with predictions for pure thermal emission from geometrically thin and optically thick discs. Assuming the polarization degree of the Comptonization component to be 0, 4, or 10 per cent, and oriented perpendicular to the polarization of the disc emission (in turn assumed to be perpendicular to the large-scale ionization cone orientation detected in the optical band), an upper limit to the polarization of the disc emission of 1.0, 0.9, or 0.9 per cent, respectively, is found (at the 99 per cent confidence level).

LMC X-1↗

Space Archeology Overview at Gordion: 2010 to 2012

In fiscal years 2010, 2011, and 2012, Compton Tucker was the principal investigator of a NASA Space Archaeology project that worked at Gordion, in Central Turkey. Tucker was assisted by an excellent team of co-workers including Joseph Nigro and Daniel Slayback of Science Systems Applications Incorporated, Jenny Strum of the University of New Mexico, and Karina Yager, a post doctoral fellow at NASA/GSFC. This report summaries their research activities at Gordion for the field seasons of 2010, 2011, and 2012. Because of the possible use of our findings at Gordion for tomb robbing there and/or the encouragement of potential tomb robbers using our geophysical survey methods to locate areas to loot, we have not published any of our survey results in the open literature nor placed any of these results on any web sites. These 2010- 2012 survey results remain in the confidential archives of the University of Pennsylvania's University Museum of Archaeology and Anthropology, the group that leads the Gordion Excavation and Research Project. Excavations are planned for 2013 at Gordion, including several that will be based upon the research results in this report. The site of Gordion in central Turkey, famous as the home of King Midas, whose father's intricately tied knot gave the site its name, also served as the center of the Phrygian kingdom that ruled much of Central Anatolia in Asia Minor during the early first millennium B.C. Gordion has been a University of Pennsylvania Museum of Archaeology and Anthropology excavation project since 1950, yet the site is incompletely published despite six decades of research. The primary obstacles related to the site and its preservation were two problems that NASA technology could address: (1) critical survey errors in the hundreds of maps and plans produced by the earlier excavators, most of which used mutually incompatible geospatial referencing systems, that prevented any systematic understanding of the site; and (2) agricultural encroachment upon the site that was compromising its archaeological integrity. Our NASA Space Archaeology proposal was written to address both of these problems. When we started working at Gordion in 2010, we added a third objective, (3) ground penetrating radar and magnetic geophysical surveys of threatened areas. The first objective our NASA Space Archaeology Project was to provide the University of Pennsylvania's Museum of Archaeology and Anthropology a system to rectify and incorporate all existing survey data from Gordion, including previous aerial photographs of the site, detailed site surveys, maps, and excavation plans, into a common mapping system. This was accomplished with a Geographic Information System (GIS) based upon a 60 cm Quickbird satellite image ortho-rectified using Shuttle Radar Topographic Mission (SRTM) 30 m digital elevation data and tied to a known datum at Gordion. This enabled the first accurate, multi-layer plan of this complex site, occupied almost continuously from the Bronze Age to the 1st millennium CE, and made possible Gordion's three-dimensional development for the first time.

Gordion↗

Detection of X-rays during the outburst of supernova 1980k

X-ray emission from SN 1980k in NGC 6946 was detected about 35 days after maximum light using the imaging proportional counter on the Einstein Observatory. The absorption corrected X-ray flux of SN 1980k was about 0.03 micro-Jy at 0.24 x 10 to the 18th Hz (1 keV), which corresponds to a luminosity of about 2 x 10 to the 39th ergs/s (0.2-4 keV) at 10 Mpc. This detection of radio emission suggests the presence of relativistic electrons and a magnetic field strength of not greater than about 1 gauss. Inverse Compton scattering of the optical photons on the electrons can explain the X-ray emission without additional ad hoc assumptions, although other emission mechanisms are possible.

Canizares, C. R.↗

A review of recent results in gamma-ray astronomy obtained from high-altitude balloons

This paper reviews recent results in gamma-ray astronomy obtained from experiments flown on high-altitude balloons. New generation balloon-borne imaging experiments have produced the first gamma-ray maps of the Galactic center (GC) region. Balloon flights of new gamma-ray spectrometers with improved sensitivity have provided important new information on the GC annihilation line. For the first time, the narrow 511 keV line as been resolved (FWHM approx. = 3 keV). A very interesting spectral feature at approximately 170 keV has been attributed to backscattered annihilation, probably from the vicinity of a compact object. New results from the Compton Gamma-Ray Observatory (CGRO)/OSSE and Granat/SIGMA experiments on the annihilation line, when considered together with the recent balloon results, have added greatly to our knowledge and understanding of the origin and distribution of this emission. Balloon-borne instruments have made important measurements of gamma-ray continuum and line emission from SN 1987A. The GRIS spectrometer unambiguously resolved the 847 and 1238 keV line emission from radioactive Co-56 synthesized during the explosion. This data indicated that simple spherically symmetric and homogeneous models did not provide an adequate description of the expanding SN shell.

Teegarden, B. J.↗

Multiwavelength Investigation of γ-Ray Source MGRO J1908+06 Emission Using Fermi-LAT, VERITAS and HAWC

This paper investigates the origin of the γ-ray emission from MGRO J1908+06 in the GeV–TeV energy band. By analyzing the data collected by the Fermi Large Area Telescope, the Very Energetic Radiation Imaging Telescope Array System, and High Altitude Water Cherenkov, with the addition of spectral data previously reported by LHAASO, a multiwavelength study of the morphological and spectral features of MGRO J1908+06 provides insight into the origin of the γ-ray emission. The mechanism behind the bright TeV emission is studied by constraining the magnetic field strength, the source age, and the distance through detailed broadband modeling. Both spectral shape and energy-dependent morphology support the scenario that inverse Compton emission of an evolved pulsar wind nebula associated with PSR J1907+0602 is responsible for the MGRO J1908+06 γ-ray emission with a best-fit true age of T = 22 ± 9 kyr and a magnetic field of B = 5.4 ± 0.8 μG, assuming the distance to the pulsar d PSR = 3.2 kpc.

Gamma-ray astronomy↗

Precision Fe K-Alpha and Fe K-Beta Line Spectroscopy of the Seyfert 1.9 Galaxy NGC 2992 with Suzaku

We present detailed time-averaged X-ray spectroscopy in the 0.5-10 keV band of the Seyfert 1.9 galaxy NGC 2992 with the Suzaku X-ray Imaging Spectrometers (XIS). The source had a factor approximately 3 higher 2-10 keV flux (approximately 1.2 x l0(exp -11) erg per square cm per s) than the historical minimum and a factor approximately 7 less than the historical maximum. The XIS spectrum of NGC 2992 can be described by several components. There is a primary continuum, modeled as a power-law with a photon index of Gamma = 1.57(sup +0.06) (sup -0.03) that is obscured by a Compton-thin absorber with a column density of 8.01(sup +0.6) (sup -0.5)x l0 (exp 21) per square cm. . There is another, weaker, unabsorbed power-law component (modeled with the same slope as the primary), that is likely to be due to the primary continuum being electron-scattered into our line-of-sight by a region extended on a scale of hundreds of parsecs. We measure the Thomson depth of the scattering zone to be Tau = 0.072 +/- 0.021. An optically-thin thermal continuum emission component, which probably originates in the same extended region, is included in the model and yields a temperature and luminosity of KT = 0.656(sup +0.088) (sup -0.0.61) keV and approximately 1.2 +/- 0.4 x l0 (exp 40) erg per s respectively. We detect an Fe K emission complex which we model with broad and narrow lines and we show that the intensities of the two components are decoupled at a confidence level > 3 sigma. The broad Fe K alpha line has an equivalent width of 118(sup +32) (sup -61) eV and could originate in an accretion disk (with inclination angle greater than approximately 30 deg) around the putative central black hole. The narrow Fe K alpha line has an equivalent width of 1632(sup +47) (sup -26) eV and is unresolved (FWHM < 4630 km per s) and likely originates in distant matter. The absolute flux in the narrow line implies that the column density out of the line-of-sight could be much higher than measured in the line-of-sight, and that the mean (historically-averaged) continuum luminosity responsible for forming the line could be a factor of several higher than that measured from the data. We also detect the Fe K Beta line (corresponding to the narrow Fe K alpha line) with a high signal-to-noise ratio and describe a new robust method to constrain the ionization state of Fe responsible for the Fe K alpha and Fe K Beta lines that does not require any knowledge of possible gravitational and Doppler energy shifts affecting the line energies. For the distant line-emitting matter (e. g. the putative obscuring torus) we deduce that the predominant ionization state is lower than Fe VIII (at 99% confidence), conservatively taking into account residual calibration uncertainties in the XIS energy scale and theoretical and experimental uncertainties in the Fe K fluorescent line energies. From the limits on a possible Compton-reflection continuum it is likely that the narrow Fe K alpha and Fe K Beta lines originate in a Compton-thin structure.

Yaqoob, Tahir↗

Discovery of a bright extended X-ray jet in RGB J1512+020A

ABSTRACT We report the discovery of a bright, extended X-ray jet in the quasar RGB J1512+020A (z = 0.22). Chandra observations show the X-ray core and 13 arcsec (∼45 kpc projected) extended emission coincident with the radio jet. The jet stands out as one of brightest X-ray jets (LX ∼ 7 × 1043 erg s−1) at low redshift (z < 0.5) discovered so far, with remarkably large X-ray to radio luminosity ratios (LX/Lr up to ∼50). We identified four main components, two unresolved knots and two extended structures, one being the jet brightest feature (JBF). All jet features are also detected in ALMA archival observations. The radio, sub-mm to X-ray spectra of the two knots can be modelled with a single synchrotron component. For the two resolved structures, the ALMA data unveil a turnover of the low-energy continuum at ∼460 GHz. External Comptonization of cosmic microwave background photons can account for the observed X-ray emission if the jet speed remains highly relativistic, with bulk motion Γbulk > 15, up to tens of kiloparsec from the core. However, the comparison with the spectral energy distribution of similar X-ray detected jets shows that the alternative hypothesis of synchrotron emission from an additional population of ultra-high-energy electrons is also possible. We report a tentative (≳2σ) optical detection of the JBF in images of the Dark Energy Camera Legacy Survey. If confirmed, the optical emission should be either the low-energy tail of the radiative component responsible for the X-ray emission or a third, separate component.

79 ASTRONOMY AND ASTROPHYSICS↗