51 results on '"Kaaret, P."'
Search Results
2. Enhanced X-ray emission from candidate Lyman continuum emitting galaxies.
- Author
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Bluem, J, Kaaret, P, Prestwich, A, and Brorby, M
- Subjects
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SUPERNOVA remnants , *X-rays , *GALAXIES , *X-ray binaries , *STAR formation - Abstract
X-ray binaries may have helped reionize the early Universe by enabling Lyman continuum escape. We analysed a set of eight local galaxies that are potential Lyman leaking galaxies, identified by a blue colour and weak emission lines, using Chandra X-ray observations. Five of the galaxies feature X-ray sources, while three galaxies are not significantly detected in X-rays. X-ray luminosities were found for the galaxies and X-ray sources. Four of the galaxies have elevated X-ray luminosity versus what would be expected based on star formation rate and metallicity. The presence of detected X-ray sources within the galaxies is found to correlate with the ratio of the star formation rate estimated from the near-ultraviolet flux to that estimated from the infrared. This implies reduced obscuration due to dust in the galaxies with X-ray sources. These results support the idea that X-ray binaries may be an important part of the process of reionziation. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
3. Resolving the X-ray emission from the Lyman-continuum emitting galaxy Tol 1247-232.
- Author
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Kaaret, P., Brorby, M., Casella, L., and Prestwich, A. H.
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GALAXIES , *LUMINOSITY - Abstract
Chandra observations of the nearby, Lyman-continuum (LyC) emitting galaxy Tol 1247-232 resolve the X-ray emission and show that it is dominated by a point-like source with a hard spectrum (Γ = 1.6 ± 0.5) and a high luminosity [(9 ± 2) × 1040 erg s-1]. Comparison with an earlier XMM-Newton observation shows flux variation of a factor of 2. Hence, the X-ray emission likely arises from an accreting X-ray source: a low-luminosity active galactic nucleus or one or a few X-ray binaries. The Chandra X-ray source is similar to the point-like, hard spectrum (- = 1.2 ± 0.2), high-luminosity (1041 erg s-1) source seen in Haro 11, which is the only other confirmed LyC-emitting galaxy that has been resolved in X-rays. We discuss the possibility that accreting X-ray sources contribute to LyC escape. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
4. An autocollimator alignment system for a Schwarzschild-Couder Cherenkov telescope.
- Author
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Griffiths, S., Kaaret, P., and Smith, E.
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AUTOCOLLIMATOR , *CHERENKOV radiation , *TELESCOPES , *GAMMA rays , *OPTICAL measurements - Abstract
We present a digital autocollimator which will be used in the alignment system of a prototype medium-sized telescope, which is part of the U.S. contribution to the Cherenkov Telescope Array (CTA). The Schwarzschild-Couder optics in the prototype telescope (which is currently under construction) requires the precise alignment of three components: the primary and secondary segmented mirrors, and the gamma-ray camera. The approximately 9 meter separation between the mirrors necessitates remote optical measurement. Our autocollimator will measure the angle of a segment in one mirror relative to the center of the other mirror with a precision better than 5 arcsec over a range of ±0.126 °. We present a detailed description of the instrument and describe its performance in the laboratory. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
5. Enhanced X-ray emission from Lyman break analogues and a possible LX-SFR-metallicity plane.
- Author
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Brorby, M., Kaaret, P., Prestwich, A., and Mirabel, I. F.
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GALAXY formation , *GALACTIC redshift , *X-ray binaries , *STELLAR mass , *STELLAR populations , *PHOTONS , *X-ray emission spectroscopy - Abstract
The source of energetic photons that heated and reionized the early Universe remains uncertain. Early galaxies had low metallicity and recent population synthesis calculations suggest that the number and luminosity of high-mass X-ray binaries are enhanced in star-forming galaxies with low metallicity, offering a potentially important and previously overlooked source of heating and reionization. Lyman break analogue (LBA) galaxies are local galaxies that strongly resemble the high-redshift, star-forming Lyman Break Galaxies and have been suggested as local analogues to these metal-deficient galaxies found in the early Universe. We studied a sample of ten LBAs in order to measure the relation between star formation rate and X-ray luminosity. We found that for LBAs with metallicities in the range 12 + log10(O/H) = 8.15 - 8.80, the LX -SFR relation was log10(LX/SFR[erg s-1 M-1⊙ yr])=39.85(±0.10) in the 0.5 - 8 keV band with a dispersion of σ = 0.25 dex. This is an enhancement of nearly a factor of 2 in the L0.5 - 8keV-SFR relation relative to results for nearby, near-solar metallicity galaxies. The enhancement is significant at the 98.2% level (2.4σ). Our enhanced LX/SFR relation is consistent with the metallicity-dependent predicted value from population synthesis models. We discuss the possibility of a LX-SFR-Metallicity plane for star-forming galaxies. These results are important to our understanding of reionization and the formation of early galaxies. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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6. Searching for X-ray sources in nearby late-type galaxies with low-star formation rates.
- Author
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Chatterjee, K., Kaaret, P., Brorby, M., Kajava, J. J. E., Grisé, F., Farrell, S., and Poutanen, J.
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X-ray astronomy , *STELLAR evolution , *ASTRONOMICAL observations - Abstract
Late-type non-starburst galaxies have been shown to contain X-ray emitting objects, some being ultraluminous X-ray sources. We report on XMM-Newton observations of 11 nearby, late-type galaxies previously observed with the Hubble Space Telescope (HST) in order to find such objects. We found 18 X-ray sources in or near the optical extent of the galaxies, most being point-like. If associated with the corresponding galaxies, the source luminosities range from 2 ? 1037 erg s-1 to 6 ? 1039 erg s-1. We found one ultraluminous X-ray source, which is in the galaxy IC 5052, and one source coincident with the galaxy IC 4662 with a blackbody temperature of 0.166 ± 0.015 keV that could be a quasi-soft source or a quiescent neutron star X-ray binary in the Milky Way. One X-ray source, XMMU J205206.0-691316, is extended and coincident with a galaxy cluster visible on an HST image. The X-ray spectrum of the cluster reveals a redshift of z = 0.25 ± 0.02 and a temperature of 3.6±0.4 keV. The redshiftwas mainly determined by a cluster of Fe XXIV lines between the observed energy range 0.8 - 1.0 keV. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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7. Transition of an X-ray binary to the hard ultraluminous state in the blue compact dwarf galaxy VII Zw 403.
- Author
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Brorby, M., Kaaret, P., and Feng, H.
- Subjects
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X-ray binaries , *DWARF galaxies , *X-ray spectroscopy , *ASTRONOMICAL observations , *STELLAR mass - Abstract
We examine the X-ray spectra of VII Zw 403, a nearby low-metallicity blue compact dwarf (BCD) galaxy. The galaxy has been observed to contain an X-ray source, likely a high-mass X-ray binary (HMXB), with a luminosity of 1.3-23 × 1038 erg s-1 in the 0.3-8 keV energy range. A new Suzaku observation shows a transition to a luminosity of 1.7 × 1040 erg s-1 [0.3-8 keV], higher by a factor of 7-130. The spectra from the high-flux state are hard, best described by a disc plus Comptonization model, and exhibit curvature at energies above 5 keV. This is consistent with many high-quality ultraluminous X-ray source spectra which have been interpreted as stellar mass black holes accreting at super-Eddington rates. However, this lies in contrast to another HMXB in a low-metallicity BCD, I Zw 18, that exhibits a soft spectrum at high flux, similar to Galactic black hole binaries and has been interpreted as a possible intermediate-mass black hole. Determining the spectral properties of HMXBs in BCDs has important implications for models of the Epoch of Reionization. It is thought that the main component of X-ray heating in the early Universe was dominated by HMXBs within the first galaxies. Early galaxies were small, metal-deficient, star-forming galaxies with large HI mass fractions - properties shared by local BCDs we see today. Understanding the spectral evolution of HMXBs in early Universe analogue galaxies, such as BCDs, is an important step in estimating their contribution to the heating of the intergalactic medium during the Epoch of Reionization. The strong contrast between the properties of the only two spectroscopically studied HMXBs within BCDs motivates further study on larger samples of HMXBs in low-metallicity environments in order to properly estimate the X-ray heating in the early Universe. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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8. Spectral state transitions of the Ultraluminous X-ray Source IC 342 X-1.
- Author
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Marlowe, H., Kaaret, P., Lang, C., Feng, H., Grisé, F., Miller, N., Cseh, D., Corbel, S., and Mushotzky, R. F.
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GALACTIC X-ray sources , *PHASE transitions , *RADIO astronomy , *ACCRETION disks , *ASTRONOMICAL observations , *THERMAL analysis - Abstract
We observed the Ultraluminous X-ray Source (ULX) IC 342 X-1 simultaneously in X-ray and radio with Chandra and the JVLA to investigate previously reported unresolved radio emission coincident with the ULX. The Chandra data reveal a spectrum that is much softer than observed previously and is well modelled by a thermal accretion disc spectrum. No significant radio emission above the rms noise level was observed within the region of the ULX, consistent with the interpretation as a thermal state though other states cannot be entirely ruled out with the current data. We estimate the mass of the black hole using the modelled inner disc temperature to be $30 \,\mathrm{M_{{\odot }}} \lesssim M\sqrt{\mathrm{cos}i}\lesssim 200 \,\mathrm{M_{{\odot }}}$ based on a Shakura–Sunyaev disc model. Through a study of the hardness and high-energy curvature of available X-ray observations, we find that the accretion state of X-1 is not determined by luminosity alone. [ABSTRACT FROM PUBLISHER]
- Published
- 2014
- Full Text
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9. The relativistic astrophysics explorer: A new mission for X-ray timing.
- Author
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Kaaret, P., Grindlay, J., Lamb, F. K., Morgan, E. H., Swank, J. H., and Zhang, W.
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ASTROPHYSICS , *SUPERMASSIVE black holes , *NEUTRON stars - Abstract
The great success of the Rossi X-Ray Timing Explorer (RXTE) has given us a new probe to study strong gravitational fields and to measure the physical properties of black holes and neutron stars. Here, we describe a "next-generation" x-ray timing mission, the Relativistic Astrophysics Explorer (RAE), designed to fit within the envelope of a "medium-sized" mission. The main instruments will be a narrow-field x-ray detector array with an area of at least 60,000 cm² equal to ten times that of RXTE, and a wide-field x-ray monitor with good sensitivity and few arcminute position resolution. We describe the design of the instruments and the science which will be possible with a factor of ten increase in collecting area. [ABSTRACT FROM AUTHOR]
- Published
- 2001
10. The compact jet of the black hole candidate XTE J1550-564 during the 2000 X-ray outburst.
- Author
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Corbel, S., Kaaret, P., Jain, R. K., Bailyn, C. D., Fender, R. P., Tomsick, J. A., Kalemci, E., McIntyre, V., Campbell-Wilson, D., Miller, J. M., and McCollough, M. L.
- Subjects
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SUPERMASSIVE black holes , *X-ray bursts , *ASTRONOMICAL observations , *ASTROPHYSICAL jets - Abstract
We report on radio, near-infrared, optical and X-ray observations of the black hole candidate (BHC) XTE J1550-564 performed during its 2000 X-ray outburst. These observations have allowed us to sample the behavior of XTE J1550-564 in the X-ray Low Hard and Intermediate/Very High states. The radio emission in the Low Hard state most likely originates from a compact jet and the synchrotron emission from this jet may extend up to the optical range or beyond, therefore indicating that the total power of the compact jet is a significant fraction of the total luminosity of the system. In the Intermediate/Very High state the radio emission is quenched, implying a suppression of the outflow. We discuss the properties of radio emission in the X-ray states of BHCs. [ABSTRACT FROM AUTHOR]
- Published
- 2001
11. X-ray binary formation in low-metallicity blue compact dwarf galaxies★.
- Author
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Brorby, M., Kaaret, P., and Prestwich, A.
- Subjects
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X-ray binaries , *GALAXY formation , *STAR formation , *STELLAR luminosity function , *COMPARATIVE studies - Abstract
X-rays from binaries in small, metal-deficient galaxies may have contributed significantly to the heating and reionization of the early Universe. We investigate this claim by studying blue compact dwarfs (BCDs) as local analogues to these early galaxies. We constrain the relation of the X-ray luminosity function (XLF) to the star formation rate (SFR) using a Bayesian approach applied to a sample of 25 BCDs. The functional form of the XLF is fixed to that found for near-solar metallicity galaxies and is used to find the probability distribution of the normalization that relates X-ray luminosity to SFR. Our results suggest that the XLF normalization for low-metallicity BCDs (12+log(O/H) < 7.7) is not consistent with the XLF normalization for galaxies with near-solar metallicities, at a confidence level 1-5 × 10− 6. The XLF normalization for the BCDs is found to be $14.5\pm 4.8\ (\rm{M}_{\odot }^{-1}\, {\rm yr})$, a factor of 9.7 ± 3.2 higher than for near-solar metallicity galaxies. Simultaneous determination of the XLF normalization and power-law index result in estimates of $q = 21.2^{+12.2}_{-8.8}\ (\rm{M}_{\odot }^{-1}\, {\rm yr})$ and $\alpha = 1.89^{+0.41}_{-0.30}$, respectively. Our results suggest a significant enhancement in the population of high-mass X-ray binaries in BCDs compared to the near-solar metallicity galaxies. This suggests that X-ray binaries could have been a significant source of heating in the early Universe. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
12. OPTICAL EMISSION OF THE ULTRALUMINOUS X-RAY SOURCE NGC 5408 X-1: DONOR STAR OR IRRADIATED ACCRETION DISK?
- Author
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Grisé, F., Kaaret, P., Corbel, S., Feng, H., Cseh, D., and Tao, L.
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ACCRETION (Astrophysics) , *ACCRETION disks , *BLACK holes , *X-rays , *NEAR infrared spectroscopy , *SPECTRAL energy distribution - Abstract
We obtained three epochs of simultaneous Hubble Space Telescope (HST)/Wide Field Camera 3 and Chandra observations of the ultraluminous X-ray source (ULX) NGC 5408 X-1. The counterpart of the X-ray source is seen in all HST filters, from the UV through the near-IR (NIR), and for the first time, we resolve the optical nebula around the ULX. We identified a small OB association near the ULX that may be the birthplace of the system. The stellar association is young, ~5 Myr, contains massive stars up to 40 M⊙, and is thus similar to associations seen near other ULXs, albeit younger. The UV/optical/NIR spectral energy distribution (SED) of the ULX counterpart is consistent with that of a B0I supergiant star. We are also able to fit the whole SED from the X-rays to the NIR with an irradiated disk model. The three epochs of data show only marginal variability and thus, we cannot firmly conclude on the nature of the optical emission. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
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13. OPTICAL PROPERTIES OF THE ULTRALUMINOUS X-RAY SOURCE HOLMBERG IX X-1 AND ITS STELLAR ENVIRONMENT.
- Author
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GRISÉ, F., KAARET, P., PAKULL, M. W., and MOTCH, C.
- Subjects
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X-ray optics , *OPTICAL disk storage , *FAINT Object Camera , *STAR clusters , *STELLAR mass , *X-ray spectroscopy - Abstract
Holmberg IX X-1 is an archetypal ultraluminous X-ray source (ULX). Here we study the properties of the optical counterpart and of its stellar environment using optical data from SUBARU/Faint Object Camera and Spectrograph, GEMINI/GMOS-N and Hubble Space Telescope (HS7)/Advanced Camera for Surveys, as well as simultaneous Chandra X-ray data. The V ~ 22.6 spectroscopically identified optical counterpart is part of a loose cluster with an age ≲20 Myr. Consequently, the mass upper limit on individual stars in the association is about 20 M.... The counterpart is more luminous than the other stars of the association, suggesting a non-negligible optical contribution from the accretion disk. An observed UV excess also points to non-stellar light similar to X-ray active low-mass X-ray binaries. A broad HeII λ686 emission line identified in the optical spectrum of the ULX further suggests optical light from X-ray reprocessing in the accretion disk. Using stellar evolutionary tracks, we have constrained the mass of the counterpart to be ≳10 M..., even if the accretion disk contributes significantly to the optical luminosity. Comparison of the photometric properties of the counterpart with binary models show that the donor may be more massive, ≳25 M..., with the ULX system likely undergoing case AB mass transfer. Finally, the counterpart exhibits photometric variability of 0.14 mag between two HST observations separated by 50 days which could be due to ellipsoidal variations and/or disk reprocessing of variable X-ray emission. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
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14. Radio observations of NGC 6388: an upper limit on the mass of its central black hole.
- Author
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Cseh, D., Kaaret, P., Corbel, S., Körding, E., Coriat, M., Tzioumis, A., and Lanzoni, B.
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SUPERMASSIVE black holes , *X-rays , *RADIO sources (Astronomy) , *RADIO astronomy , *ASTRONOMY - Abstract
We present the results of deep radio observations with the Australia Telescope Compact Array ( ATCA) of the globular cluster NGC 6388. We show that there is no radio source detected (with an rms noise level of 27 μJy) at the cluster centre of gravity or at the locations of any of the Chandra X-ray sources in the cluster. Based on the fundamental plane of accreting black holes which is a relationship between X-ray luminosity, radio luminosity and black hole mass, we place an upper limit of ∼1500 M on the mass of the putative intermediate-mass black hole located at the centre of NGC 6388. We discuss the uncertainties of this upper limit and the previously suggested black hole mass of based on surface density profile analysis. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
15. Relativistic astrophysics explorer
- Author
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Kaaret, P.
- Subjects
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ASTROPHYSICS , *X-rays , *SUPERMASSIVE black holes , *ASTRONOMY - Abstract
The great success of the Rossi X-Ray Timing Explorer (RXTE) has shown that X-ray timing is an excellent tool for the study of strong gravitational fields and the measurement of fundamental physical properties of black holes and neutron stars. Here, we describe a next-generation X-ray timing mission, the Relativistic Astrophysics Explorer (RAE), designed to fit within the envelope of a medium-sized mission. The instruments will be a narrow-field X-ray detector array with an area of 6 m2 equal to 10 times that of RXTE and a wide-field X-ray monitor. We describe the science made possible with this mission, the design of the instruments, and results on prototype large-area X-ray detectors. [Copyright &y& Elsevier]
- Published
- 2004
- Full Text
- View/download PDF
16. Chandra High-Resolution Camera observations of the luminous X-ray source in the starburst galaxy....
- Author
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Kaaret, P., Prestwich, A.H., Zezas, A., Murray, S.S., Kim, D.-W., Kilgard, R.E., Schlegel, E.M., and Ward, M.J.
- Subjects
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ARTIFICIAL satellites , *GALAXIES , *X-rays - Abstract
Analyzes the Chandra High Resolution Camera observations of the starburst galaxy M82. Position of the X-ray source; Absence of short-term variability on the observations; Compact object mass of the galaxy.
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- 2001
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17. Large-scale X-ray jets from Galactic black holes
- Author
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Kaaret, P., Corbel, S., Tomsick, J.A., Butt, Y., Fender, R.P., Lazendic, J., Miller, J.M., Orosz, J.A., Tzioumis, A.K., and Wijnands, Rudy
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GALAXIES , *ASTRONOMY , *ACTIVE galaxies , *DENSITY wave theory - Abstract
Observations of jets from stellar-mass sources located in our Galaxy offer a unique opportunity to study the dynamical evolution of relativistic jets on time scales inaccessible for active galactic nuclei jets, with implications for our understanding of the dynamics and energetics of relativistic jets from Galactic x-ray binaries and active galactic nuclei. We review recent observations of X-ray jets from Galactic black hole candidates. Spatially resolved X-ray spectra from SS 433 have provided evidence for re-heating in a hadronic jet and may offer an observational probe of jet collimation. A large-scale jet from the now quiescent transient 4U 1755–33 appears to indicate continual jet formation over a period of 10–30 years. Detection of a jet from XTE J1550–564 has provided the first direct measurement of gradual deceleration of a jet from a black hole and strong evidence for the re-energization of jet particles to energies up to 10 TeV at sites far from the jet origin. [Copyright &y& Elsevier]
- Published
- 2004
- Full Text
- View/download PDF
18. The first X-ray polarimetric observation of the black hole binary LMC X-1.
- Author
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Podgorný, J, Marra, L, Muleri, F, Rodriguez Cavero, N, Ratheesh, A, Dovčiak, M, Mikušincová, R, Brigitte, M, Steiner, J F, Veledina, A, Bianchi, S, Krawczynski, H, Svoboda, J, Kaaret, P, Matt, G, García, J A, Petrucci, P-O, Lutovinov, A, Semena, A, and Di Marco, A
- Subjects
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BINARY black holes , *X-ray binaries , *BLACK holes , *X-rays , *ACCRETION disks , *NEUTRON stars - Abstract
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). [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
19. Effects of metallicity on high-mass X-ray binary formation.
- Author
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Ponnada, S, Brorby, M, and Kaaret, P
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INTERSTELLAR medium , *STAR formation , *DWARF galaxies , *GALAXIES , *STELLAR mass , *STARBURSTS , *STATISTICAL significance , *X-ray binaries - Abstract
The heating of the intergalactic medium in the early, metal-poor Universe may have been partly due to radiation from high-mass X-ray binaries (HMXBs). Previous investigations on the effect of metallicity have used galaxies of different types. To isolate the effects of metallicity on the production of HMXBs, we study a sample consisting only of 46 blue compact dwarf galaxies covering metallicity in the range 12+log(O/H) of 7.15–8.66. To test the hypothesis of metallicity dependence in the X-ray luminosity function (XLF), we fix the XLF form to that found for near-solar metallicity galaxies and use a Bayesian method to constrain the XLF normalization as a function of star formation rate for three different metallicity ranges in our sample. We find an increase by a factor of 4.45 ± 2.04 in the XLF normalization between the metallicity ranges 7.1–7.7 and 8.2–8.66 at a statistical significance of 99.79 per cent. Our results suggest that HMXB production is enhanced at low metallicity, and consequently that HMXBs may have contributed significantly to the reheating of the early Universe. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
20. High-resolution imaging of the He iiλ4686 emission line nebula associated with the ultraluminous X-ray source in Holmberg II.
- Author
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Kaaret, P., Ward, M.J., and Zezas, A.
- Subjects
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NEBULAE , *HELIUM , *GALACTIC X-ray sources , *SUPERMASSIVE black holes , *GALAXIES - Abstract
We present Hubble Space Telescope images of the He iii region surrounding the bright X-ray source in the dwarf irregular galaxy Holmberg II. Using Chandra, we find a position for the X-ray source of (J2000) with an uncertainty of 0.6 arcsec. We identify a bright, point-like optical counterpart centred in the nebula with the X-ray source. The optical magnitude and colour of the counterpart are consistent with a star with spectral type between O4V and B3 Ib at a distance of 3.05 Mpc or reprocessed emission from an X-ray illuminated accretion disc. The nebular He ii luminosity is . The morphology of the He ii, Hβ and [O i] emission is consistent with being due to X-ray photoionization and is inconsistent with narrow beaming of the X-ray emission. A spectral model consisting of a multicolour disc blackbody with inverse-Compton emission from a hot corona gives a good fit to X-ray spectra obtained with XMM–Newton. Using the fitted X-ray spectrum, we calculate the relation between the He ii and X-ray luminosity and find that the He ii flux implies a lower bound on the X-ray luminosity in the range 4 to if the extrapolation of the X-ray spectrum between 54 and 300 eV is accurate. A compact object mass of at least 25 to would be required to avoid violating the Eddington limit. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
21. Displacement of X-ray sources from star clusters in starburst galaxies.
- Author
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Kaaret, P., Alonso-Herrero, A., Gallagher, J.S., Fabbiano, G., Zezas, A., and Rieke, M.J.
- Subjects
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STAR clusters , *GALAXIES , *STARBURSTS , *ASTROPHYSICS , *ASTRONOMY , *X-rays - Abstract
We examine the spatial offsets between X-ray point sources and star clusters in three starburst galaxies. We find that the X-ray sources are preferentially located near the star clusters. Because the star clusters are very good tracers of the star formation activity in the galaxies, this indicates that the X-ray sources are young objects associated with current star formation. We find significant displacements of the X-ray sources from the clusters. These displacements are likely due to motion of the X-ray sources and indicates that they are X-ray binaries. We find that brighter X-ray sources preferentially occur closer to clusters. The absence of very bright sources at large displacements from clusters may help constrain models of the sources. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
22. multi-wavelength view of distinct accretion regimes in the pulsating ultraluminous X-ray source NGC 1313 X-2.
- Author
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Sathyaprakash, R, Roberts, T P, Grisé, F, Kaaret, P, Ambrosi, E, Done, C, Gladstone, J C, Kajava, J J E, Soria, R, and Zampieri, L
- Subjects
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X-rays , *X-ray spectra , *ACCRETION disks , *B stars , *ACCRETION (Astrophysics) , *NEUTRON stars , *GALACTIC X-ray sources , *NEAR infrared radiation - Abstract
NGC 1313 X-2 is one of the few known pulsating ultraluminous X-ray sources (PULXs), and so is thought to contain a neutron star that accretes at highly super-Eddington rates. However, the physics of this accretion remains to be determined. Here, we report the results of two simultaneous XMM–Newton and HST observations of this PULX taken to observe two distinct X-ray behaviours as defined from its Swift light curve. We find that the X-ray spectrum of the PULX is best described by the hard ultraluminous regime during the observation taken in the lower flux, lower variability amplitude behaviour; its spectrum changes to a broadened disc during the higher flux, higher variability amplitude epoch. However, we see no accompanying changes in the optical/UV fluxes, with the only difference being a reduction in flux in the near-infrared (NIR) as the X-ray flux increased. We attempt to fit irradiation models to explain the UV/optical/IR fluxes but they fail to provide meaningful constraints. Instead, a physical model for the system leads us to conclude that the optical light is dominated by a companion O/B star, albeit with an IR excess that may be indicative of a jet. We discuss how these results may be consistent with the precession of the inner regions of the accretion disc leading to changes in the observed X-ray properties, but not the optical, and whether we should expect to observe reprocessed emission from ULXs. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
23. Photoelectron Track Length Distributions Measured in a Negative Ion Time Projection Chamber.
- Author
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Prieskorn, Z. R., Hill, J. E., Kaaret, P. E., and Black, J. K.
- Subjects
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PHOTOELECTRONS , *ANIONS , *NITROMETHANE , *X-ray detection , *SYNCHROTRON radiation sources , *LIGHT sources , *NUCLEAR counters - Abstract
We report photoelectron track length distributions between 3 and 8 keV in gas mixtures of Ne + CO_2 + CH3NO_2 (260:80:10 Torr) and CO_2 + CH3NO_2 (197.5: 15 Torr). The measurements were made using a negative ion time projection chamber (NITPC) at the National Synchrotron Light Source (NSLS) at the Brookhaven National Laboratory (BNL). We report the first quantitative analysis of photoelectron track length distributions in a gas. The distribution of track lengths at a given energy is best fit by a lognormal distribution. A powerlaw distribution of the form, f(E) = a(E/Eo)^n, is found to fit the relationship between mean track length and energy. We find n = 1.29\pm 0.07 for Ne + CO_2 + CH3NO_2 and n = 1.20\pm 0.09 for CO_2 + CH3NO_2. Understanding the distribution of photoelectron track lengths in proportional counter gases is important for optimizing the pixel size and the dimensions of the active region in electron-drift time projection chambers (TPCs) and NITPC X-ray polarimeters. [ABSTRACT FROM PUBLISHER]
- Published
- 2014
- Full Text
- View/download PDF
24. A relativistic iron emission line from the neutron star low-mass X-ray binary GX 3+1.
- Author
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Piraino, S., Santangelo, A., Kaaret, P., Mück, B., D'Ai, A., Di Salvo, T., Iaria, R., Robba, N., Burderi, L., and Egron, E.
- Subjects
- *
X-ray binaries , *BINARY stars , *X-ray astronomy , *NEUTRON stars , *COMPACT objects (Astronomy) - Abstract
We present the results of a spectroscopic study of the Fe Kα emission of the persistent neutron-Star atoll low-mass X-ray binary and type TX-ray burster GX 3+1 with the EPIC-PN on board XMM-Newton. The source shows a flux modulation over several years and we observed it during its fainter phase, which corresponds to an X-ray luminosity of Lx -∼ 1037 erg s-1. When fitted with a two-component model, the X-ray spectrum shows broad residuals at -6-7 keV that can be ascribed to an iron K,, fluorescence line, in addition, lower energy features are observed at ∼ 3.3 key, ∼ 3.9 keV and might originate from Ar XVIII and Ca XIX. The broad iron line feature is well fitted with a relativistically smeared profile. This result is robust against possible systematics caused by instrumental pile-up effects. Assuming that the line is produced by reflection from the inner accretion disk, we infer an inner disk radius of ∼25Rg and a disk inclination of 35° < i< 44° [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
25. Revisiting the radio/X-ray flux correlation in the black hole V404 Cyg: from outburst to quiescence.
- Author
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Corbel, S., Koerding, E., and Kaaret, P.
- Subjects
- *
SUPERMASSIVE black holes , *ACCRETION (Astrophysics) , *ASTROPHYSICS , *PHOTONS , *X-ray spectroscopy , *STELLAR luminosity function - Abstract
We report results of Chandra X-ray and Very Large Array (VLA) radio observations of the Galactic accreting black hole V404 Cyg (GS 2023+338) in its quiescent state. V404 Cyg is detected at its faintest level of radio and X-ray emission with a 0.5–10 keV unabsorbed luminosity of (d/3.5 kpc)2 erg s−1. The X-ray spectrum fit with an absorbed power-law model yields a photon index of 2.17 ± 0.13. Contrary to previous findings, this clearly indicates that V404 Cyg undergoes – like most black holes in quiescence – a softening of its X-ray spectrum at very low luminosity compared to the standard hard state. The quiescent radio emission is consistent with the presence of self-absorbed compact jets. We have also re-analysed archival data from the decay of the 1989 outburst of V404 Cyg in order to quantify more precisely the correlation between radio and X-ray emission in the hard state of V404 Cyg. We show that this correlation extends over five decades in X-ray flux and holds down to the quiescent state of V404 Cyg. The index of this correlation (∼0.5) may suggest that synchrotron self-Compton emission is the dominant physical process at high energy in V404 Cyg. However, this index is also consistent with scale invariant jet models coupled to an inefficiently radiating accretion disc. We discuss the properties of the quiescent state of black holes and highlight the fact that some of their properties are different from the standard hard state. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
26. INTEGRAL and XMM–Newton observations of the X-ray pulsar IGR J16320−4751/AX J1631.9−4752.
- Author
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Rodriguez, J., Bodaghee, A., Kaaret, P., Tomsick, J. A., Kuulkers, E., Malaguti, G., Petrucci, P.-O., Cabanac, C., Chernyakova, M., Corbel, S., Deluit, S., Di Cocco, G., Ebisawa, K., Goldwurm, A., Henri, G., Lebrun, F., Paizis, A., Walter, R., and Foschini, L.
- Subjects
- *
ASTRONOMY , *PULSARS , *X-ray binaries , *X-ray astronomy , *SPECTRUM analysis , *X-ray spectroscopy - Abstract
We report on observations of the X-ray pulsar IGR J16320−4751 (also known as AX J1631.9−4752) performed simultaneously with International Gamma-Ray Astrophysics Laboratory ( INTEGRAL) and XMM–Newton. We refine the source position and identify the most likely infrared counterpart. Our simultaneous coverage allows us to confirm the presence of X-ray pulsations at ∼1300 s, that we detect above 20 keV with INTEGRAL for the first time. The pulse fraction is consistent with being constant with energy, which is compatible with a model of polar accretion by a pulsar. We study the spectral properties of IGR J16320−4751 during two major periods occurring during the simultaneous coverage with both satellites, namely a flare and a non-flare period. We detect the presence of a narrow 6.4 keV iron line in both periods. The presence of such a feature is typical of supergiant wind accretors such as Vela X-1 or GX 301−2. We inspect the spectral variations with respect to the pulse phase during the non-flare period, and show that the pulse is solely due to variations of the X-ray flux emitted by the source and not due to variations of the spectral parameters. Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of ∼0.07 keV. We discuss the origin of the X-ray emission in IGR J16320−4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energized cloud in which the compact object is embedded. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
27. HaloSat Observations of Heliospheric Solar Wind Charge Exchange.
- Author
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Ringuette, R., Koutroumpa, D., Kuntz, K. D., Kaaret, P., Jahoda, K., LaRocca, D., Kounkel, M., Richardson, J., Zajczyk, A., and Bluem, J.
- Subjects
- *
CHARGE exchange , *PLASMA astrophysics , *GALACTIC halos , *SOLAR wind , *PLASMA diagnostics , *CUBESATS (Artificial satellites) - Abstract
X-ray emission from solar wind charge exchange (SWCX) produced in interplanetary space contaminates every astrophysical observation, regardless of the line of sight. Unfortunately, the primary SWCX emission lines also happen to be important diagnostics of astrophysical plasmas. Models of SWCX emission are limited by two main uncertainties: the local solar wind fluxes along the line of sight and the charge exchange cross sections. The He cone, a localized density enhancement of helium neutrals, is the only heliospheric SWCX emission feature that is small enough and bright enough to be observationally isolated from the X-ray background and the broader SWCX emission. HaloSat, an X-ray CubeSat mission, has recently completed two series of specialized observations, near and far from the ecliptic plane, during two Earth transits of the He cone. These observations were used to test the predictions of an SWCX emission model against the emission observed at low ecliptic latitude, where the solar wind data are monitored, and at high ecliptic latitude, where the solar wind data are extrapolated. The measured SWCX emission for the set of observations near the ecliptic plane was consistent with the line intensities predicted by the model but underpredicted for the set of observations at high ecliptic latitude near the south ecliptic pole. Additionally, high-temperature Galactic halo emission components are reported for both spectral sets. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
28. A Search for the 3.5 keV Line from the Milky Way's Dark Matter Halo with HaloSat.
- Author
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Silich, E. M., Jahoda, K., Angelini, L., Kaaret, P., Zajczyk, A., LaRocca, D. M., Ringuette, R., and Richardson, J.
- Subjects
- *
DARK matter , *STERILE neutrinos , *GALACTIC center , *GALACTIC halos , *GALACTIC X-ray sources , *GALAXY clusters , *X-ray detection - Abstract
Previous detections of an X-ray emission line near 3.5 keV in galaxy clusters and other dark-matter-dominated objects have been interpreted as observational evidence for the decay of sterile neutrino dark matter. Motivated by this, we report on a search for a 3.5 keV emission line from the Milky Way's galactic dark matter halo with HaloSat. As a single pixel, collimated instrument, HaloSat observations are impervious to potential systematic effects due to grazing incidence reflection and CCD pixelization, and thus may offer a check on possible instrumental systematic errors in previous analyses. We report nondetections of a ∼3.5 keV emission line in four HaloSat observations near the Galactic center. In the context of the sterile neutrino decay interpretation of the putative line feature, we provide 90% confidence level upper limits on the 3.5 keV line flux for a field centered 18.6 degrees from the Galactic center and the corresponding 7.1 keV sterile neutrino mixing angle: F ≤ 0.077 ph cm−2 s−1 sr−1 and. The HaloSat mixing angle upper limit was calculated using a modern parameterization of the Milky Way's dark matter distribution, and in order to compare with previous limits, we also report the limit calculated using a common historical model. The HaloSat mixing angle upper limit places constraints on a number of previous mixing angle estimates derived from observations of the Milky Way's dark matter halo and galaxy clusters, and excludes several previous detections of the line. The upper limits cannot, however, entirely rule out the sterile neutrino decay interpretation of the 3.5 keV line feature. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
29. Evolving morphology of the large-scale relativistic jets from XTE J1550-564.
- Author
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Migliori, Giulia, Corbel, S., Tomsick, J. A., Kaaret, P., Fender, R. P., Tzioumis, A. K., Coriat, M., and Orosz, J. A.
- Subjects
- *
RADIO jets (Astrophysics) , *QUASARS , *ENERGY dissipation , *X-ray emission spectroscopy , *ACCRETION disks , *EXTRAGALACTIC jets (Astrophysics) - Abstract
We present an in-depth study of the large scale, western jet of the microquasar XTEJ1550-564, based on X-ray and radio observations performed in 2002-2003. The jet is spatially resolved in both observing windows. The X-ray jet is expanding in time along the axis of the jet's propagation: we observe the formation of a tail (~2.25 arcsec), which appears to extend backwards with an apparent velocity ~-0.10c. The origin of this feature is discussed in the framework of scenarios of energy dissipation. A single power law adequately describes the broad-band spectra, supporting a synchrotron origin of the X-ray emission. However, a spectral break at ≈1015 Hz is necessary in coincidence with a re-flare at 8.64 GHz in 2002 September. This finding may be indicative of emission from newly accelerated lowenergy particles. The first detection of the jet is in 2001 February (F8.64 GHz =0.25±0.09 mJy) in the flux rising phase. A phase of stable emission is followed by a rapid decay (tdecay =167±5 d). The decay at radio frequencies is significantly shorter than in X-rays (tdecay = 338 ± 14 d). We detected a high fraction (up to ~9 per cent) of linearly polarized radiation at 4.8 and 8.6 GHz. The orientation of the electric vector is consistent with the picture of a shockcompressed magnetic field, and there are hints of variations on month-time-scales, possibly connected with the evolution of the jet structure. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
30. Performance of the PRAXyS X-ray polarimeter.
- Author
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Iwakiri, W.B., Black, J.K., Cole, R., Enoto, T., Hayato, A., Hill, J.E., Jahoda, K., Kaaret, P., Kitaguchi, T., Kubota, M., Marlowe, H., McCurdy, R., Takeuchi, Y., and Tamagawa, T.
- Subjects
- *
X-ray polarization , *TIME projection chambers (Nuclear physics) , *RELATIVISTIC astrophysics , *MONOCHROMATIC light , *POLARISCOPE - Abstract
The performance of the Time Projection Chamber (TPC) polarimeter for the Polarimeter for Relativistic Astrophysical X-ray Sources (PRAXyS) Small Explorer was evaluated using polarized and unpolarized X-ray sources. The PRAXyS mission will enable exploration of the universe through X-ray polarimetry in the 2–10 keV energy band. We carried out performance tests of the polarimeter at the Brookhaven National Laboratory, National Synchrotron Light Source (BNL-NSLS) and at NASA's Goddard Space Flight Center. The polarimeter was tested with linearly polarized, monochromatic X-rays at 11 different energies between 2.5 and 8.0 keV. At maximum sensitivity, the measured modulation factors at 2.7, 4.5 and 8.0 keV are 27%, 43% and 59%, respectively and the measured angle of polarization is consistent with the expected value at all energies. Measurements with a broadband, unpolarized X-ray source placed a limit of less than 1% on false polarization in the PRAXyS polarimeter. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
31. The evolution of a jet ejection of the ultraluminous X-ray source Holmberg II X-1.
- Author
-
Cseh, D., Miller-Jones, J. C. A., Jonker, P. G., Grisé, F., Paragi, Z., Corbel, S., Falcke, H., Frey, S., Kaaret, P., and Körding, E.
- Subjects
- *
STELLAR evolution , *X-ray astronomy , *STELLAR luminosity function , *SYNCHROTRON radiation , *BLACK holes - Abstract
We present quasi-simultaneous, multi-epoch radio and X-ray measurements of Holmberg II X-1 using the European VLBI Network (EVN), the Karl G. Jansky Very Large Array (VLA), and the Chandra and Swift X-ray telescopes. The X-ray data show apparently hard spectra with steady X-ray luminosities four months apart from each other. In the high-resolution EVN radio observations, we have detected an extended milliarcsecond scale source with unboosted radio emission. The source emits non-thermal, likely optically thin synchrotron emission, and its morphology is consistent with a jet ejection. The 9-GHz VLA data show an arcsecond-scale triple structure of Holmberg II X-1 similar to that seen at lower frequencies. However, we find that the central ejection has faded by at least a factor of 7.3 over 1.5 yr. We estimate the dynamical age of the ejection to be higher than 2.1 yr. We show that such a rapid cooling can be explained with simple adiabatic expansion losses. These properties of Holmberg II X-1 imply that ULX radio bubbles may be inflated by ejecta instead of self-absorbed compact jets. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
32. The evolution of a jet ejection of the ultraluminous X-ray source Holmberg II X-1.
- Author
-
Cseh, D., Miller-Jones, J. C. A., Jonker, P. G., Grisé, F., Paragi, Z., Corbel, S., Falcke, H., Frey, S., Kaaret, P., and Körding, E.
- Subjects
- *
VERY long baseline interferometry , *X-ray telescopes , *SOLAR radio emission , *SYNCHROTRONS , *ESTIMATION theory , *JETS (Fluid dynamics) - Abstract
We present quasi-simultaneous, multi-epoch radio and X-ray measurements of Holmberg II X-1 using the European VLBI Network (EVN), the Karl G. Jansky Very Large Array (VLA), and the Chandra and Swift X-ray telescopes. The X-ray data show apparently hard spectra with steady X-ray luminosities four months apart from each other. In the high-resolution EVN radio observations, we have detected an extended milliarcsecond scale source with unboosted radio emission. The source emits non-thermal, likely optically thin synchrotron emission, and its morphology is consistent with a jet ejection. The 9-GHz VLA data show an arcsecond-scale triple structure of Holmberg II X-1 similar to that seen at lower frequencies. However, we find that the central ejection has faded by at least a factor of 7.3 over 1.5 yr. We estimate the dynamical age of the ejection to be higher than 2.1 yr. We show that such a rapid cooling can be explained with simple adiabatic expansion losses. These properties of Holmberg II X-1 imply that ULX radio bubbles may be inflated by ejecta instead of self-absorbed compact jets. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
33. PROBING THE ACTIVE MASSIVE BLACK HOLE CANDIDATE IN THE CENTER OF NGC 404 WITH VLBI.
- Author
-
Paragi, Z., Frey, S., Kaaret, P., Cseh, D., Overzier, R., and Kharb, P.
- Subjects
- *
BLACK holes , *VERY long baseline interferometry , *GALACTIC X-ray sources , *GALAXIES , *DWARF galaxies - Abstract
Recently, Nyland et al. argued that the radio emission observed in the center of the dwarf galaxy NGC 404 originates in a low-luminosity active galactic nucleus powered by a massive black hole (MBH, M ≲ 106M☼). High-resolution radio detections of MBHs are rare. Here we present sensitive, contemporaneous Chandra X-ray, and very long baseline interferometry (VLBI) radio observations with the European VLBI Network. The source is detected in the X-rays, and shows no long-term variability. If the hard X-ray source is powered by accretion, the apparent low accretion efficiency would be consistent with a black hole (BH) in the hard state. Hard state BHs are known to show radio emission compact on the milliarcsecond scales. However, the central region of NGC 404 is resolved out on 10 mas (0.15-1.5 pc) scales. Our VLBI non-detection of a compact, partially self-absorbed radio core in NGC 404 implies that either the BH mass is smaller than M☼, or the source does not follow the fundamental plane of BH activity relation. An alternative explanation is that the central BH is not in the hard state. The radio emission observed on arcsecond (tens of parsecs) scales may originate in nuclear star formation or extended emission due to AGN activity, although the latter would not be typical considering the structural properties of low-ionization nuclear emission-line region galaxies with confirmed nuclear activity. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
34. The Advanced Gamma-ray Imaging System (AGIS) Telescope Optical System Designs.
- Author
-
Bugaev, V., Buckley, J., Diegel, S., Falcone, A., Fegan, S., Finley, J., Guarino, V., Hanna, D., Kaaret, P., Konopelko, A., Krawczynski, H., Ramsey, B., Romani, R., Vassiliev, V., and Weekes, T.
- Subjects
- *
GAMMA rays , *TELESCOPES , *IMAGING systems , *CHERENKOV radiation , *CARBON fibers , *ELECTROFORMING , *ASTRONOMY - Abstract
AGIS is a conceptual design for a future ground-based gamma-ray observatory operating in the energy range 25 GeV–100 TeV, which is based on an array of ∼20–100 imaging atmospheric Cherenkov telescopes (IACTs). The desired improvement in sensitivity, angular resolution, and reliability of operation of AGIS imposes demanding technological and cost requirements on the design of the IACTs. We are considering several options for the optical system (OS) of the AGIS telescopes, which include the traditional Davies-Cotton design as well as novel two-mirror design. Emerging mirror production technologies based on replication processes such as cold and hot glass slumping, cured carbon fiber reinforced plastic (CFRP), and electroforming provide new opportunities for cost-effective solutions for the design of the OS. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
35. POET: POlarimeters for Energetic Transients.
- Author
-
Hill, J. E., McConnell, M. L., Bloser, P., Legere, J., Macri, J., Ryan, J., Barthelmy, S., Angelini, L., Sakamoto, T., Black, J. K., Hartmann, D. H., Kaaret, P., Zhang, B., Ioka, K., Nakamura, T., Toma, K., Yamazaki, R., and Wu, X.
- Subjects
- *
POLARISCOPE , *SPECTRUM analysis , *SOLAR activity , *NEUTRON stars , *RADIATION sources - Abstract
POET (Polarimeters for Energetic Transients) is a Small Explorer mission concept proposed to NASA in January 2008. The principal scientific goal of POET is to measure GRB polarization between 2 and 500 keV. The payload consists of two wide FoV instruments: a Low Energy Polarimeter (LEP) capable of polarization measurements in the energy range from 2–15 keV and a high energy polarimeter (Gamma-Ray Polarimeter Experiment—GRAPE) that will measure polarization in the 60–500 keV energy range. Spectra will be measured from 2 keV up to 1 MeV. The POET spacecraft provides a zenith-pointed platform for maximizing the exposure to deep space. Spacecraft rotation will provide a means of effectively dealing with systematics in the polarization response. POET will provide sufficient sensitivity and sky coverage to measure statistically significant polarization for up to 100 GRBs in a two-year mission. Polarization data will also be obtained for solar flares, pulsars and other sources of astronomical interest. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
36. Transitions of black hole transients to the low/hard state under the microscope.
- Author
-
Kalemci, E., Tomsick, J. A., Rothschild, R. E., Pottschmidt, K., and Kaaret, P.
- Subjects
- *
SUPERMASSIVE black holes , *GALACTIC center , *TRANSIENTS (Dynamics) , *ASTRONOMY , *GALAXIES - Abstract
We characterized the evolution of spectral and temporal properties of several Galactic black hole transients observed between 1996–2001 using the data from well sampled PCA observations close to the transition to the low/hard state. We showed that the changes in temporal properties are much sharper than the changes in the spectral properties, and it is much easier to identify a state transition with the temporal properties. The ratio of the power-law flux to the total flux in the 3–25 keV band increases close to the transition, and the power-law flux shows a sharp increase along with the changes in temporal properties during the transitions. In this work we concentrate on the decay of two recent outbursts, from 4U 1543-47, and H1743-322 and discuss the state transitions by tracking their daily, and sometimes hourly evolution, and interpret results based on the expectations from our earlier observations. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
37. VERITAS: Very energetic radiation imaging telescope array system.
- Author
-
Krennrich, F., Bradbury, S. M., Bond, I. H., Breslin, A. C., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Dingus, B. L., Fegan, D. J., Finley, J. P., Gaidos, J., Grindlay, J., Hillas, A. M., Hermann, G., Kaaret, P., Kieda, D., Knapp, J., LeBohec, S., Lessard, R. W., and Lloyd-Evans, J.
- Subjects
- *
CHERENKOV counters , *GAMMA rays - Abstract
The Very Energetic Radiation Imaging Telescope Array System (VERI-TAS) is a wide energy range (50 GeV–50 TeV) atmospheric Cherenkov detector and will start operation in 2004. The design is driven by a major scientific interest in jets of active galactic nuclei, probing the intergalactic IR fields with TeV γ-ray beams, measuring the high energy spectrum of γ-ray bursts and galactic sources of cosmic rays. Also γ-rays signatures of quantum gravity, neutralinos and primordial black holes constitute the exotic scientific motivations to built a highly versatile detector that can be operated in various modes. The technical concept and design of the seven-telescope array system is described. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 2000
38. The Very Energetic Radiation Imaging Telescope Array System (VERITAS).
- Author
-
Weekes, T. C., Bradbury, S. M., Bond, I. H., Breslin, A. C., Buckley, J. H., Carter-Lewis, D. A., Catanese, M., Dingus, B. L., Fegan, D. J., Finley, J. P., Gaidos, J., Grindlay, J., Hillas, A. M., Hermann, G., Kaaret, P., Kieda, D., Knapp, J., Krennrich, F., LeBohec, S., and Lessard, R.W.
- Subjects
- *
TELESCOPES , *SPECTRAL sensitivity - Abstract
An overview of the current status and scientific goals of VERITAS, a proposed hexagonal array of seven 10 m aperture imaging Cherenkov telescopes, is provided. The selected site is close to Mt. Hopkins, the site of the Whipple Observatory, in Arizona. Each telescope, of 12 m focal length, will be equipped with a 499 element photomultiplier camera covering a 3.5 degree field of view. A central station will initiate the readout of 500 MHz FADCs upon receipt of multiple telescope triggers. The minimum detectable flux sensitivity will be 0.5% of the Crab Nebula flux at 200 GeV. VERITAS will operate primarily as a γ-ray observatory in the 50 GeV to 50 TeV range for the study of active galaxies, supernova remnants, pulsars and gamma-ray bursts. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 2000
39. The black hole candidate MAXI J1659-152 in and towards quiescence in X-ray and radio.
- Author
-
Jonker, P. G., Miller-Jones, J. C. A., Homan, J., Tomsick, J., Fender, R. P., Kaaret, P., Markoff, S., and Gallo, E.
- Subjects
- *
ASTRONOMICAL observations , *BLACK holes , *X-ray binaries , *STELLAR luminosity function , *NEUTRON stars , *VERY large array telescopes - Abstract
ABSTRACT In this paper we report on Expanded Very Large Array radio and Chandra and Swift X-ray observations of the outburst decay of the transient black hole candidate MAXI J1659-152 in 2011. We discuss the distance to the source taking the high inclination into account and conclude that the source distance is probably 6 ± 2 kpc. The lowest observed flux corresponds to a luminosity of erg s−1. This, together with the orbital period of 2.4 h reported in the literature, suggests that the quiescent X-ray luminosity is higher than predicted on the basis of the orbital period-quiescent X-ray luminosity relationship. It is more in line with that expected for a neutron star, although the outburst spectral and timing properties reported in the literature strongly suggest that MAXI J1659-152 harbours a black hole. This conclusion is subject to confirmation of the lowest observed flux as the quiescent flux. The relation between the accretion and ejection mechanisms can be studied using the observed correlation between the radio and X-ray luminosities as these evolve over an outburst. We determine the behaviour of MAXI J1659-152 in the radio-X-ray diagram at low X-ray luminosities using the observations reported in this paper and at high X-ray luminosities using values reported in the literature. At high X-ray luminosities, the source lies closer to the sources that follow a correlation index steeper than 0.6-0.7. However, when compared to other sources that follow a steeper correlation index, the X-ray luminosity in MAXI J1659-152 is also lower. The latter can potentially be explained by the high inclination of MAXI J1659-152 if the X-ray emission comes from close to the source and the radio emission is originating in a more extended region. However, it is probable that the source was not in the canonical low-hard state during these radio observations and this may affect the behaviour of the source as well. At intermediate X-ray luminosities, the source makes the transition from the radio underluminous sources in the direction of the relation traced by the 'standard' correlation similar to what has been reported for H 1743−322 in the literature. However, MAXI J1659-152 remains underluminous with respect to this 'standard' correlation. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
40. The black hole candidate XTE J1752−223 towards and in quiescence: optical and simultaneous X-ray-radio observations.
- Author
-
Ratti, E. M., Jonker, P. G., Miller-Jones, J. C. A., Torres, M. A. P., Homan, J., Markoff, S., Tomsick, J. A., Kaaret, P., Wijnands, R., Gallo, E., Özel, F., Steeghs, D. T. H., and Fender, R. P.
- Subjects
- *
BLACK holes , *ASTRONOMICAL observations , *X-ray astronomy , *PHOTOMETRY , *COMPARATIVE studies , *STELLAR luminosity function , *BINARY stars - Abstract
ABSTRACT We present optical, X-ray and radio observations of the black hole transient (BHT) XTE J1752−223 towards and in quiescence. Optical photometry shows that the quiescent magnitude of XTE J1752−223 is fainter than 24.4 mag in the i′ band. A comparison with measurements of the source during its 2009-2010 outburst shows that the outburst amplitude is more than 8 mag in the i′ band. Known X-ray properties of the source combined with the faintness of the quiescence optical counterpart and the large outburst optical amplitude point towards a short orbital-period system ( Porb≲ 6.8 h) with an M type (or later) mass donor, at a distance of 3.5 ≲ d≲ 8 kpc. Simultaneous X-ray and radio data were collected with Chandra and the Expanded Very Large Array (EVLA), allowing constraints to be placed on the quiescent X-ray and radio flux of XTE J1752−223. Furthermore, using data covering the final stage of the outburst decay, we investigated the low-luminosity end of the X-ray-radio correlation for this source and compared it with other BHTs. We found that XTE J1752−223 adds to the number of outliers with respect to the 'standard' X-ray-radio luminosity relation. Furthermore, XTE J1752−223 is the second source, after the BHT H1743−322, that shows a transition from the region of the outliers towards the 'standard' correlation at low luminosity. Finally, we report on a faint, variable X-ray source we discovered with Chandra at an angular distance of ∼2.9 arcsec to XTE J1752−223 and at a position angle consistent with that of the radio jets previously observed from the BHT. We discuss the possibility that we detected X-ray emission associated with a jet from XTE J1752−223. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
41. The black hole candidate XTE J1752−223 towards and in quiescence: optical and simultaneous X-ray–radio observations.
- Author
-
Ratti, E. M., Jonker, P. G., Miller-Jones, J. C. A., Torres, M. A. P., Homan, J., Markoff, S., Tomsick, J. A., Kaaret, P., Wijnands, R., Gallo, E., Özel, F., Steeghs, D. T. H., and Fender, R. P.
- Subjects
- *
BLACK holes , *ANGULAR distance , *ASTRONOMICAL photometry , *RDS (Radio) - Abstract
We present optical, X-ray and radio observations of the black hole transient (BHT) XTE J1752−223 towards and in quiescence. Optical photometry shows that the quiescent magnitude of XTE J1752−223 is fainter than 24.4 mag in the i′ band. A comparison with measurements of the source during its 2009–2010 outburst shows that the outburst amplitude is more than 8 mag in the i′ band. Known X-ray properties of the source combined with the faintness of the quiescence optical counterpart and the large outburst optical amplitude point towards a short orbital-period system (Porb≲ 6.8 h) with an M type (or later) mass donor, at a distance of 3.5 ≲d≲ 8 kpc. Simultaneous X-ray and radio data were collected with Chandra and the Expanded Very Large Array (EVLA), allowing constraints to be placed on the quiescent X-ray and radio flux of XTE J1752−223. Furthermore, using data covering the final stage of the outburst decay, we investigated the low-luminosity end of the X-ray–radio correlation for this source and compared it with other BHTs. We found that XTE J1752−223 adds to the number of outliers with respect to the ‘standard’ X-ray–radio luminosity relation. Furthermore, XTE J1752−223 is the second source, after the BHT H1743−322, that shows a transition from the region of the outliers towards the ‘standard’ correlation at low luminosity. Finally, we report on a faint, variable X-ray source we discovered with Chandra at an angular distance of ∼2.9 arcsec to XTE J1752−223 and at a position angle consistent with that of the radio jets previously observed from the BHT. We discuss the possibility that we detected X-ray emission associated with a jet from XTE J1752−223. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
42. Evolution of the spectral curvature in the ultraluminous X-ray source Holmberg II X-1.
- Author
-
Kajava, J. J. E., Poutanen, J., Farrell, S. A., Grisé, F., and Kaaret, P.
- Subjects
- *
STELLAR spectra , *STELLAR luminosity function , *GALACTIC X-ray sources , *BLACK holes , *STELLAR mass , *CURVATURE cosmology , *ACCRETION disks , *ASTRONOMICAL observations - Abstract
ABSTRACT Ultraluminous X-ray sources (ULXs) are interesting systems as they can host intermediate-mass black holes. Alternatively, ULXs can represent stellar mass black holes accreting at super-Eddington rates. Recently, spectral curvature or breaks at energies above a few keV have been detected in high-quality ULX spectra. These spectral features have been taken as evidence against the intermediate-mass black hole case. In this paper, we report on a new XMM-Newton observation of the ULX Holmberg II X-1 that also shows a clear spectral break at approximately 4 keV. This observation was performed during a low-luminosity state of the system and by comparing these new data to a high-luminosity state XMM-Newton observation, we can conclude that the spectral break energy increases with luminosity. This behaviour is different from a ULX in the Holmberg IX galaxy, where an opposite trend between the luminosity and the spectral break energy has been claimed. We discuss mechanisms that could explain this complex behaviour. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
43. XMM-NEWTON FINDS THAT SAX J1750.8-2900 MAY HARBOR THE HOTTEST, MOST LUMINOUS KNOWN NEUTRON STAR.
- Author
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LOWELL, A. W., TOMSICK, J. A., HEINKE, C. O., BODAGHEE, A., BOGGS, S. E., KAARET, P., CHATY, S., RODRIGUEZ, J., and WALTER, R.
- Subjects
- *
NEUTRON stars , *X-ray spectra , *POWER law (Mathematics) , *LUMINOSITY , *TEMPERATURE of stars , *THERMODYNAMIC equilibrium - Abstract
We have performed the first sensitive X-ray observation of the low-mass X-ray binary (LMXB) SAX J1750.8 -2900 in quiescence with XMM-Newton. The spectrum was fit to both a classical blackbody model, and a non-magnetized, pure hydrogen neutron star (NS) atmosphere model. A power-law component was added to these models, but we found that it was not required by the fits. The distance to SAX J1750.8-2900 is known to be D = 6.79 kpc from a previous analysis of photospheric radius expansion bursts. This distance implies a bolometric luminosity (as given by the NS atmosphere model) of (1.05 ±0.12) x 1034 (D/6.79 kpc)² erg s-1, which is the highest known luminosity for a NS LMXB in quiescence. One simple explanation for this surprising result could be that the crust and core of the NS were not in thermal equilibrium during the observation. We argue that this was likely not the case, and that the core temperature of the NS in SAX J1750.8-2900 is unusually high. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
44. DISCOVERY AND EVOLUTION OF THE NEW BLACK HOLE CANDIDATE SWIFT J1539.2-6227 DURING ITS 2008 OUTBURST.
- Author
-
KRIMM, H. A., TOMSICK, J. A., MARKWARDT, C. B., BROCKSOPP, C., GRISÉ, F., KAARET, P., and ROMANO, P.
- Subjects
- *
BLACK holes , *OSCILLATIONS , *X-ray spectroscopy , *BINARY stars , *METEOR showers - Abstract
We report on the discovery by the Swift Gamma-Ray Burst Explorer of the black hole (BH) candidate Swift J1539.2-6227 and the subsequent course of an outburst beginning in 2008 November and lasting at least seven months. The source was discovered during normal observations with the Swift Burst Alert Telescope on 2008 November 25. An extended observing campaign with the Rossi X-Ray Timing Explorer and Swift provided near-daily coverage over 176 days, giving us a good opportunity to track the evolution of spectral and timing parameters with fine temporal resolution through a series of spectral states. The source was first detected in a hard state during which strong low-frequency quasi-periodic oscillations (QPOs) were detected. The QPOs persisted for about 35 days and a signature of the transition from the hard- to soft-intermediate states was seen in the timing data. The source entered a short-lived thermal state about 40 days after the start of the outburst. There were variations in spectral hardness as the source flux declined and returned to a hard state at the end of the outburst. The progression of spectral states and the nature of the timing features provide strong evidence that Swift J1539.2-6227 is a candidate BH in a low-mass X-ray binary system. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
45. Results from the first two years of VERITAS observations
- Author
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Krennrich, F., Bautista, M., Beilicke, M., Benbow, W., Boltuch, D., Bradbury, S.M., Cesarini, A., Ciupik, L., Duke, C., Finley, J.P., Finnegan, G., Fortson, L., Gall, D., Guenette, R., Gyuk, G., Hanna, D., Hui, C.M., Humensky, T.B., Kaaret, P., and Karlsson, N.
- Subjects
- *
ASTRONOMICAL observations , *GAMMA rays , *TELESCOPES , *ASTROPHYSICS , *PARTICLES (Nuclear physics) , *COSMIC rays , *SUPERMASSIVE black holes - Abstract
Abstract: The VERITAS observatory is an imaging atmospheric Cherenkov telescope array located in southern Arizona and covers an energy range between 100GeV and 30TeV. The VERITAS collaboration pursues a rigorous observing program that targets a range of key science objectives in astrophysics and particle physics; the understanding of the origin of cosmic rays, the search for supersymmetric dark matter self-annihilation, illuminating the connection between black holes and relativistic jets and constraints to the cosmological diffuse infrared background. We provide a summary of results from the first two years of observations with the full 4-telecope array reported at RICAP09. [Copyright &y& Elsevier]
- Published
- 2011
- Full Text
- View/download PDF
46. Following the 2008 outburst decay of the black hole candidate H 1743-322 in X-ray and radio.
- Author
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Jonker, P. G., Miller-Jones, J., Homan, J., Gallo, E., Rupen, M., Tomsick, J., Fender, R. P., Kaaret, P., Steeghs, D. T. H., Torres, M. A. P., Wijnands, R., Markoff, S., and Lewin, W. H. G.
- Subjects
- *
SUPERMASSIVE black holes , *EINSTEIN-Podolsky-Rosen experiment , *X-ray astronomy , *RADIO sources (Astronomy) , *RADIO astronomy - Abstract
In this paper, we report on radio (Very Large Array and Austrialian Telescope Compact Array) and X-ray ( RXTE, Chandra and Swift) observations of the outburst decay of the transient black hole candidate H 1743-322 in early 2008. We find that the X-ray light curve followed an exponential decay, levelling off towards its quiescent level. The exponential decay time-scale is 4 days and the quiescent flux corresponds to a luminosity of erg s−1. This together with the relation between quiescent X-ray luminosity and orbital period reported in the literature suggests that H 1743-322 has an orbital period longer than ≈10 h. Both the radio and X-ray light curve show evidence for flares. The radio–X-ray correlation can be well described by a power-law with index 0.18. This is much lower than the index of 0.6–0.7 found for the decay of several black hole transients before. The radio spectral index measured during one of the radio flares while the source is in the low–hard state is , which indicates that the radio emission is optically thin. This is unlike what has been found before in black hole sources in the low–hard state. We attribute the radio flares and the low index for the radio–X-ray correlation to the presence of shocks downstream the jet flow, triggered by ejection events earlier in the outburst. We find no evidence for a change in X-ray power-law spectral index during the decay, although the relatively high extinction of limits the detected number of soft photons and thus the accuracy of the spectral fits. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
47. Moving relativistic large-scale X-ray jets in the microquasar XTE J1550−564
- Author
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Corbel, S., Fender, R.P., Tzioumis, A.K., Tomsick, J.A., Orosz, J.A., Miller, J.M., Wijnands, R., and Kaaret, P.
- Subjects
- *
X-rays , *QUASARS , *RADIO sources (Astronomy) , *SYNCHROTRONS , *ASTRONOMY - Abstract
We have discovered large-scale moving X-ray and radio jets from the microquasar XTE J1550
− 564. Using X-ray and radio observations performed between 2000 and 2002, we showed that plasma ejected from XTE J1550− 564 has been able to travel at relativistic velocities during many years, with evidence for gradual deceleration. The broadband spectrum of the jets is consistent with synchrotron emission from high energy particles accelerated in shocks. Full details can be found in Corbel et al. [Science 298 (2002a) 196], Karret et al. [ApJ 582 (2003) 933] and Tomsick et al. [ApJ (2003) 945]. [Copyright &y& Elsevier]- Published
- 2003
- Full Text
- View/download PDF
48. Large-Scale, Decelerating, Relativistic X-ray Jets from the Microquasar XTE J1550-564.
- Author
-
Corbel, S., Fender, R.P., Tzioumis, A.K., Tomsick, J.A., Orosz, J.A., Miller, J.M., Wijnands, R., and Kaaret, P.
- Subjects
- *
PLASMA jets , *ASTRONOMY , *SUPERMASSIVE black holes - Abstract
We have detected, at x-ray and radio wavelengths, large-scale moving jets from the microquasar XTE J1550-564. Plasma ejected from near the black hole traveled at relativistic velocities for at least 4 years. We present direct evidence for gradual deceleration in a relativistic jet. The broadband spectrum of the jets is consistent with synchrotron emission from high-energy (up to 10 tera-electron volts) particles that were accelerated in the shock waves formed within the relativistic ejecta or by the interaction of the jets with the interstellar medium. XTE J1550-564 offers a rare opportunity to study the dynamical evolution of relativistic jets on time scales inaccessible for active galactic nuclei jets, with implications for our understanding of relativistic jets from Galactic x-ray binaries and active galactic nuclei. [ABSTRACT FROM AUTHOR]
- Published
- 2002
- Full Text
- View/download PDF
49. GRB Polarimetry with POET.
- Author
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McConnell, M. L., Angelini, L., Baring, M. G., Barthelmy, S., Black, J. K., Bloser, P. F., Dennis, B., Emslie, A. G., Greiner, J., Hajdas, W., Harding, A. K., Hartmann, D. H., Hill, J. E., Ioka, K., Kaaret, P., Kanbach, G., Kniffen, D., Legere, J. S., Macri, J. R., and Morris, R.
- Subjects
- *
POLARISCOPE , *X-rays , *ARTIFICIAL satellites , *POLARIZATION (Nuclear physics) , *SOLAR flares - Abstract
POET (Polarimeters for Energetic Transients) represents a concept for a Small Explorer (SMEX) satellite mission, whose principal scientific goal is to understand the structure of GRB sources through sensitive X-ray and γ-ray polarization measurements. The payload consists of two wide field-of-view (FoV) instruments: a Low Energy Polarimeter (LEP) capable of polarization measurements in the energy range from 2–15 keV and a high energy polarimeter (Gamma-Ray Polarimeter Experiment or GRAPE) that would measure polarization in the 60–500 keV energy range. The POET spacecraft provides a zenith-pointed platform for maximizing the exposure to deep space. Spacecraft rotation provides a means of effectively dealing with any residual systematic effects in the polarization response. POET provides sufficient sensitivity and sky coverage to measure statistically significant polarization (for polarization levels in excess of 20%) for ∼80 GRBs in a two-year mission. High energy polarization data would also be obtained for SGRs, solar flares, pulsars and other sources of astronomical interest. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
50. Optical counterpart of the ultraluminous X-ray source NGC 1313 X-2
- Author
-
Zampieri, L., Mucciarelli, P., Falomo, R., Kaaret, P., Di Stefano, R., Turolla, R., Chieregato, M., and Treves, A.
- Subjects
- *
OPTICS , *X-rays , *STELLAR luminosity function , *LUMINESCENCE - Abstract
We present new optical and Chandra observations of the field containing the ultraluminous X-ray source NGC1313 X-2. On an ESO 3.6 m image, the Chandra error box embraces a
R=21.6 mag stellar-like object and excludes a previously proposed optical counterpart. The resulting X-ray/optical flux ratio of NGC 1313 X-2 is ∼500. The value offX/fopt , the X-ray variability history and spectral distribution indicate a luminous X-ray binary in NGC 1313 as a likely explanation for NGC 1313 X-2. The inferred optical luminosity (L≈105L◎ ) is consistent with that of a≈10M◎ companion. [Copyright &y& Elsevier]- Published
- 2004
- Full Text
- View/download PDF
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