Recursos de colección

Caltech Authors (157.532 recursos)

Repository of works by Caltech published authors.

Group = Space Radiation Laboratory

Mostrando recursos 1 - 20 de 640

  1. NuSTAR Hard X-ray Observation of the Gamma-ray Binary Candidate HESS J1832-093

    Mori, Kaya; Gotthelf, E. V.; Hailey, Charles J.; Hord, Ben J.; de Ona Wilhelmi, Emma; Rahoui, Farid; Tomsick, John A.; Zhang, Shuo; Hong, Jaesub; Garvin, Amani M.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Harrison, Fiona A.; Stern, Daniel; Zhang, William W.
    We present a hard X-ray observation of the TeV gamma-ray binary candidate HESS J1832-093 coincident with supernova remnant (SNR) G22.7-0.2 using the Nuclear Spectroscopic Telescope Array (NuSTAR). Non-thermal X-ray emission from XMMU J183245-0921539, the X-ray source associated with HESS J1832-093, is detected up to ~30 keV and is well-described by an absorbed power-law model with the best-fit photon index $\Gamma = 1.5\pm0.1$. A re-analysis of archival Chandra and XMM-Newton data finds that the long-term X-ray flux increase of XMMU J183245-0921539 is $50^{+40}_{-20}$% (90% C.L.), much less than previously reported. A search for a pulsar spin period or binary orbit modulation yields no significant signal to a pulse fraction limit...

  2. NuSTAR + XMM-Newton monitoring of the neutron star transient AX J1745.6-2901

    Ponti, G.; Bianchi, S.; Munos-Darias, T.; Mori, K.; De, K.; Rau, A.; De Marco, B.; Hailey, C.; Tomsick, J.; Madsen, K. K.; Clavel, M.; Rahoui, F.; Lal, D. V.; Roy, S.; Stern, D.
    AX J1745.6-2901 is a high-inclination (eclipsing) transient neutron star (NS) Low Mass X-ray Binary (LMXB) showcasing intense ionised Fe K absorption. We present here the analysis of 11 XMM-Newton and 15 NuSTAR new data-sets (obtained between 2013-2016), therefore tripling the number of observations of AX J1745.6-2901 in outburst. Thanks to simultaneous XMM-Newton and NuSTAR spectra, we greatly improve on the fitting of the X-ray continuum. During the soft state the emission can be described by a disk black body ($kT\sim1.1-1.2$ keV and inner disc radius $r_{DBB}\sim14$ km), plus hot ($kT\sim2.2-3.0$ keV) black body radiation with a small emitting radius ($r_{BB}\sim0.5-0.8$ km) likely associated with the boundary layer or NS...

  3. NuSTAR + XMM-Newton monitoring of the neutron star transient AX J1745.6-2901

    Ponti, G.; Bianchi, S.; Munos-Darias, T.; Mori, K.; De, K.; Rau, A.; De Marco, B.; Hailey, C.; Tomsick, J.; Madsen, K. K.; Clavel, M.; Rahoui, F.; Lal, D. V.; Roy, S.; Stern, D.
    AX J1745.6-2901 is a high-inclination (eclipsing) transient neutron star (NS) Low Mass X-ray Binary (LMXB) showcasing intense ionised Fe K absorption. We present here the analysis of 11 XMM-Newton and 15 NuSTAR new data-sets (obtained between 2013-2016), therefore tripling the number of observations of AX J1745.6-2901 in outburst. Thanks to simultaneous XMM-Newton and NuSTAR spectra, we greatly improve on the fitting of the X-ray continuum. During the soft state the emission can be described by a disk black body ($kT\sim1.1-1.2$ keV and inner disc radius $r_{DBB}\sim14$ km), plus hot ($kT\sim2.2-3.0$ keV) black body radiation with a small emitting radius ($r_{BB}\sim0.5-0.8$ km) likely associated with the boundary layer or NS...

  4. Development of the Thirty-Meter Telescope project

    Stone, Edward; Bolte, Michael
    The Thirty-Meter Telescope (TMT) project is a welladvanced effort to construct one of the first of the next generation of extremely large telescopes with primary mirror diameter larger than 25 m. When used with an adaptive optics systems capable of producing diffraction- limited images, the science reach of a 30 m telescope is extraordinary with improvements in sensitivity over existing telescopes by as much as a factor of 80 for some kinds of observations. The TMT design extends that of the twin Keck 10 m telescopes now in operation and uses the same close-packed segmented primary mirror. The partnership that will finish the design, construct...

  5. The Mass Function of GX 339–4 from Spectroscopic Observations of Its Donor Star

    Heida, M.; Jonker, P. G.; Torres, M. A. P.; Chiavassa, A.
    We obtained 16 VLT/X-shooter observations of GX 339−4 in quiescence during the period 2016 May–September and detected absorption lines from the donor star in its NIR spectrum. This allows us to measure the radial velocity curve and projected rotational velocity of the donor for the first time. We confirm the 1.76 day orbital period and we find that K_2 = 219 ± 3 km s^(−1), γ = 26 ± 2 km s^(−1), and v sin i = 64 ± 8 km s^(−1). From these values we compute a mass function f(M) = 1.91 ± 0.08 M_⊙, a factor ~3 lower...

  6. The NuSTAR Serendipitous Survey: Hunting for the Most Extreme Obscured AGN at >10 keV

    Lansbury, G. B.; Baloković, M.; Brightman, M.; Harrison, F. A.; Walton, D. J.
    We identify sources with extremely hard X-ray spectra (i.e., with photon indices of Γ ≾ 0.6) in the 13 deg^2 NuSTAR serendipitous survey, to search for the most highly obscured active galactic nuclei (AGNs) detected at > 10 keV. Eight extreme NuSTAR sources are identified, and we use the NuSTARdata in combination with lower-energy X-ray observations (from Chandra, Swift XRT, and XMM-Newton) to characterize the broadband (0.5–24 keV) X-ray spectra. We find that all of the extreme sources are highly obscured AGNs, including three robust Compton-thick (CT; N_H > 1.5 x 10^(24) cm^(−2)) AGNs at low redshift (z < 0.1)...

  7. Relationship between solar activity and Δ^(14)C peaks in AD 775, AD 994, and 660 BC

    Park, Junghun; Southon, John; Fahrni, Simon; Creasman, Pearce Paul; Mewaldt, Richard
    Since the AD 775 and AD 994 Δ^(14)C peak (henceforth M12) was first measured by Miyake et al. (2012, 2013), several possible production mechanisms for these spike have been suggested, but the work of Mekhaldi et al. (2015) shows that a very soft energy spectrum was involved, implying that a strong solar energetic particle (SEP) event (or series of events) was responsible. Here we present Δ^(14)C values from AD 721–820 Sequoiadendron giganteum annual tree-ring samples from Sequoia National Park in California, USA, together with Δ^(14)C in German oak from 650–670 BC. The AD 721–820 measurements confirm that a sharp Δ^(14)C...

  8. Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013

    Baloković, M.; Forster, K.; Grefenstette, B.; Harrison, F. A.; Madsen, K. K.; Mao, P. H.; Miyasaka, H.; Rana, V.; Hovatta, T.; Readhead, A. C. R.
    We present coordinated multiwavelength observations of the bright, nearby BL Lacertae object Mrk 421 taken in 2013 January–March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, VERITAS, and other collaborations and instruments, providing data from radio to very high energy (VHE) γ-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3–79 keV range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep Γ ≈ 3 power law, with no evidence for an exponential cutoff or additional hard components up to ~80 keV. For the first time, we observed both the synchrotron and...

  9. Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013

    Baloković, M.; Forster, K.; Grefenstette, B.; Harrison, F. A.; Madsen, K. K.; Mao, P. H.; Miyasaka, H.; Rana, V.; Hovatta, T.; Readhead, A. C. R.
    We present coordinated multiwavelength observations of the bright, nearby BL Lacertae object Mrk 421 taken in 2013 January–March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, VERITAS, and other collaborations and instruments, providing data from radio to very high energy (VHE) γ-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3–79 keV range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep Γ ≈ 3 power law, with no evidence for an exponential cutoff or additional hard components up to ~80 keV. For the first time, we observed both the synchrotron and...

  10. The composition and distribution of anomalous cosmic rays

    Stone, E. C.
    The composition of anomalous cosmic rays (ACR), is thought to reflect that of the neutral atoms in the very local interstellar medium, such as helium, nitrogen and neon. Recent observations in the outer heliosphere have provided the first unambiguous evidence for ACR argon, carbon and hydrogen, as well, and a method has been developed to relate the ACR abundances to those of the interstellar medium. The observations also indicate persistent negative latitudinal gradients, opposite to that observed by Pioneer 11 during the previous minimum in solar activity. These and other results are consistent with the presence of gradient and curvature...

  11. Characteristics of Solar Energetic Ions as a Function of Longitude

    Cohen, C. M. S.; Mason, G. M.; Mewaldt, R. A.
    Since the 2006 launch of STEREO, multi-spacecraft studies have yielded several surprising results regarding the spread of solar energetic particles (SEPs) within the inner heliosphere. We have investigated the role of energy and ridigity, using ACE and STEREO 10 MeV n^(−1) oxygen data to identify 41 large SEP events observed by two or three spacecraft. We calculated fluence spectra from ~0.1 to >10 MeV n^(−1) for H, He, O, and Fe for each event at the observing spacecraft (including SOHO and GOES). The particle fluences at 0.3, 1, and 10 MeV n^(−1) were examined as a function of the distance...

  12. A Systematic Search for Near-Infrared Counterparts of Nearby Ultraluminous X-ray sources (II)

    López, K. M.; Heida, M.; Jonker, P. G.; Torres, M. A. P.; Roberts, T. P.; Walton, D. J.; Moon, D.-S.; Harrison, F. A.
    We present the results of our continued systematic search for near-infrared (NIR) candidate counterparts to ultraluminous X-ray sources (ULXs) within 10 Mpc. We observed 42 ULXs in 24 nearby galaxies and detected NIR candidate counterparts to 15 ULXs. Fourteen of these ULXs appear to have a single candidate counterpart in our images and the remaining ULX has two candidate counterparts. Seven ULXs have candidate counterparts with absolute magnitudes in the range between −9.26 and −11.18 mag, consistent with them being red supergiants (RSGs). The other eight ULXs have candidate counterparts with absolute magnitudes too bright to be a single stellar...

  13. A Systematic Search for Near-Infrared Counterparts of Nearby Ultraluminous X-ray sources (II)

    López, K. M.; Heida, M.; Jonker, P. G.; Torres, M. A. P.; Roberts, T. P.; Walton, D. J.; Moon, D.-S.; Harrison, F. A.
    We present the results of our continued systematic search for near-infrared (NIR) candidate counterparts to ultraluminous X-ray sources (ULXs) within 10 Mpc. We observed 42 ULXs in 24 nearby galaxies and detected NIR candidate counterparts to 15 ULXs. Fourteen of these ULXs appear to have a single candidate counterpart in our images and the remaining ULX has two candidate counterparts. Seven ULXs have candidate counterparts with absolute magnitudes in the range between −9.26 and −11.18 mag, consistent with them being red supergiants (RSGs). The other eight ULXs have candidate counterparts with absolute magnitudes too bright to be a single stellar...

  14. Broadband X-ray spectral analysis of the Seyfert 1 galaxy GRS 1734-292

    Tortosa, A.; Marinucci, A.; Matt, G.; Bianchi, S.; La Franca, F.; Ballantyne, D. R.; Boorman, P. G.; Fabian, A. C.; Farrah, D.; Fuerst, F.; Gandhi, P.; Harrison, F. A.; Koss, M. J.; Ricci, C.; Stern, D.; Ursini, F.; Walton, D. J.
    We discuss the broad-band X-ray spectrum of GRS 1734−292 obtained from non-simultaneous XMM–Newton and NuSTAR (Nuclear Spectroscopic Telescope Array) observations, performed in 2009 and 2014, respectively. GRS1734−292 is a Seyfert 1 galaxy, located near the Galactic plane at z = 0.0214. The NuSTAR spectrum (3–80 keV) is dominated by a primary power-law continuum with Γ = 1.65 ± 0.05 and a high-energy cut-off E_c=53^(+11)_(−8) keV, one of the lowest measured by NuSTAR in a Seyfert galaxy. Comptonization models show a temperature of the coronal plasma of kT_e=11.9^(+1.2)_(−0.9) keV and an optical depth, assuming a slab geometry, τ=2.98^(+0.16)_(−0.19) or a similar...

  15. Broadband X-ray spectral analysis of the Seyfert 1 galaxy GRS 1734-292

    Tortosa, A.; Marinucci, A.; Matt, G.; Bianchi, S.; La Franca, F.; Ballantyne, D. R.; Boorman, P. G.; Fabian, A. C.; Farrah, D.; Fuerst, F.; Gandhi, P.; Harrison, F. A.; Koss, M. J.; Ricci, C.; Stern, D.; Ursini, F.; Walton, D. J.
    We discuss the broad-band X-ray spectrum of GRS 1734−292 obtained from non-simultaneous XMM–Newton and NuSTAR (Nuclear Spectroscopic Telescope Array) observations, performed in 2009 and 2014, respectively. GRS1734−292 is a Seyfert 1 galaxy, located near the Galactic plane at z = 0.0214. The NuSTAR spectrum (3–80 keV) is dominated by a primary power-law continuum with Γ = 1.65 ± 0.05 and a high-energy cut-off E_c=53^(+11)_(−8) keV, one of the lowest measured by NuSTAR in a Seyfert galaxy. Comptonization models show a temperature of the coronal plasma of kT_e=11.9^(+1.2)_(−0.9) keV and an optical depth, assuming a slab geometry, τ=2.98^(+0.16)_(−0.19) or a similar...

  16. > 25 MeV Proton Events Observed by the High Energy Telescopes on the STEREO A and B Spacecraft and/or at Earth During the First ∼ Seven Years of the STEREO Mission

    Richardson, I. G.; von Rosenvinge, T. T.; Cane, H. V.; Christian, E. R.; Cohen, C. M. S.; Labrador, A. W.; Leske, R. A.; Mewaldt, R. A.; Wiedenbeck, M. E.; Stone, E. C.
    Using observations from the High Energy Telescopes (HETs) on the STEREO A and B spacecraft and similar observations from near-Earth spacecraft, we summarize the properties of more than 200 individual > 25 MeV solar proton events, some detected by multiple spacecraft, that occurred from the beginning of the STEREO mission in October 2006 to December 2013, and provide a catalog of these events and their solar sources and associations. Longitudinal dependencies of the electron and proton peak intensities and delays to onset and peak intensity relative to the solar event have been examined for 25 three-spacecraft particle events. Expressed as Gaussians,...

  17. Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields

    Pogorelov, N. V.; Fichtner, H.; Czechowski, A.; Lazarian, Alex; Lembege, B.; Le Roux, J. A.; Potgieter, M. S.; Scherer, K.; Stone, E. C.; Strauss, R. D.; Wiengarten, T.; Wurz, Peter; Zank, G. P.; Zhang, M.
    This paper summarizes the results obtained by the team “Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Mag- netic Fields” supported by the International Space Science Institute (ISSI) in Bern, Switzerland. We focus on the physical processes occurring in the outer heliosphere, especially at its boundary called the heliopause, and in the local interstellar medium. The importance of magnetic field, charge exchange between neutral atoms and ions, and solar cycle on the heliopause topology and observed heliocentric distances to different heliospheric disconti- nuities are discussed. It is shown that time-dependent, data-driven boundary conditions are necessary to...

  18. Disentangling the Complex Broadband X-ray Spectrum of IRAS 13197-1627 with NuSTAR, XMM-Newton and Suzaku

    Walton, D. J.; Brightman, M.; Risaliti, G.; Fabian, A. C.; Fürst, F.; Harrison, F. A.; Lohfink, A. M.; Matt, G.; Miniutti, G.; Parker, M. L.; Stern, D.
    We present results from a coordinated XMM-Newton+NuSTAR observation of the type 1.8 Seyfert galaxy IRAS 13197-1627. This is a highly complex source, with strong contributions from relativistic reflection from the inner accretion disk, neutral absorption and further reprocessing by more distant material, and ionised absorption from an outflow. We undertake a detailed spectral analysis combining the broadband coverage provided by XMMNewton+NuSTAR with a multi-epoch approach incorporating archival observations performed by XMM-Newton and Suzaku. Our focus is on characterising the reflection from the inner accretion disk, which previous works have suggested may dominate the AGN emission, and constraining the black hole spin. Using lamppost disk reflection models, we find...

  19. Disentangling the Complex Broadband X-ray Spectrum of IRAS 13197-1627 with NuSTAR, XMM-Newton and Suzaku

    Walton, D. J.; Brightman, M.; Risaliti, G.; Fabian, A. C.; Fürst, F.; Harrison, F. A.; Lohfink, A. M.; Matt, G.; Miniutti, G.; Parker, M. L.; Stern, D.
    We present results from a coordinated XMM-Newton+NuSTAR observation of the type 1.8 Seyfert galaxy IRAS 13197-1627. This is a highly complex source, with strong contributions from relativistic reflection from the inner accretion disk, neutral absorption and further reprocessing by more distant material, and ionised absorption from an outflow. We undertake a detailed spectral analysis combining the broadband coverage provided by XMMNewton+NuSTAR with a multi-epoch approach incorporating archival observations performed by XMM-Newton and Suzaku. Our focus is on characterising the reflection from the inner accretion disk, which previous works have suggested may dominate the AGN emission, and constraining the black hole spin. Using lamppost disk reflection models, we find...

  20. X-ray bolometric corrections for Compton-thick active galactic nuclei

    Brightman, M.; Baloković, M.; Ballantyne, D. R.; Bauer, F. E.; Boorman, P. G.; Buchner, J.; Brandt, W. N.; Comastri, A.; Del Moro, A.; Farrah, D.; Gandhi, P.; Harrison, F. A.; Koss, M.; Lanz, L.; Masini, A.; Ricci, C.; Stern, D.; Vasudevan, R.; Walton, D. J.
    We present X-ray bolometric correction factors, κ_(Bol) (≡L_(Bol)/LX), for Compton-thick (CT) active galactic nuclei (AGN) with the aim of testing AGN torus models, probing orientation effects, and estimating the bolometric output of the most obscured AGN. We adopt bolometric luminosities, L_(Bol), from literature infrared (IR) torus modeling and compile published intrinsic 2–10 keV X-ray luminosities, L_X, from X-ray torus modeling of NuSTAR data. Our sample consists of 10 local CT AGN where both of these estimates are available. We test for systematic differences in κ_(Bol) values produced when using two widely used IR torus models and two widely used X-ray...

Aviso de cookies: Usamos cookies propias y de terceros para mejorar nuestros servicios, para análisis estadístico y para mostrarle publicidad. Si continua navegando consideramos que acepta su uso en los términos establecidos en la Política de cookies.