Recursos de colección

Caltech Authors (160.918 recursos)

Repository of works by Caltech published authors.

Group = Space Radiation Laboratory

Mostrando recursos 1 - 20 de 940

  1. The Voyagers

    Stone, Ed
    Forty years ago, the two Voyager spacecraft left Earth to begin one of the most rewarding voyages of human discovery ever to have been undertaken. Project Scientist Ed Stone recounts his treasured moments from the mission.

  2. Investigating the Evolution of the Dual AGN System ESO 509-IG066

    Kosec, P.; Brightman, M.; Stern, D.; Müller-Sánchez, F.; Koss, M.; Oh, K.; Assef, R. J.; Gandhi, P.; Harrison, F. A.; Jun, H.; Masini, A.; Ricci, C.; Walton, D. J.; Treister, E.; Comerford, J.; Privon, G.
    We analyze the evolution of the dual active galactic nucleus (AGN) in ESO 509-IG066, a galaxy pair located at z = 0.034 whose nuclei are separated by 11 kpc. Previous observations with XMM-Newtonon this dual AGN found evidence for two moderately obscured (N_H ~ 10^(22) cm^(−2)) X-ray luminous (L_X ~ 10^(43) erg s^(−1)) nuclear sources. We present an analysis of subsequent Chandra, NuSTAR, and Swift/XRT observations that show one source has dropped in flux by a factor of 10 between 2004 and 2011, which could be explained by either an increase in the absorbing column or an intrinsic fading of...

  3. Inversion of the decay of the cyclotron line energy in Hercules X-1

    Staubert, R.; Klochkov, D.; Fürst, F.; Wilms, J.; Rothschild, R. E.; Harrison, F.
    Recent observations of Her X-1 with NuSTAR and INTEGRAL in 2016 have provided evidence that the 20-year decay of the cyclotron line energy found between 1996 and 2015 has ended and that an inversion with a new increase, possibly similar to the one observed around 1990–1993, has started. We consider this a strong motivation for further observations and for enhanced efforts to significantly improve our theoretical understanding of the accretion process in binary X-ray pulsars. We speculate about the physics behind the long-term decay and its inversion, a possible cyclic behavior, and correlations with other variable observables.

  4. The NuSTAR Extragalactic Survey: Average Broadband X-Ray Spectral Properties of the NuSTAR-detected AGNs

    Del Moro, A.; Alexander, D. M.; Aird, J. A.; Bauer, F. E.; Civano, F.; Mullaney, J. R.; Ballantyne, D. R.; Brandt, W. N.; Comastri, A.; Gandhi, P.; Harrison, F. A.; Lansbury, G. B.; Lanz, L.; Luo, B.; Marchesi, S.; Puccetti, S.; Ricci, C.; Saez, C.; Stern, D.; Treister, E.; Zappacosta, L.
    We present a study of the average X-ray spectral properties of the sources detected by the NuSTARextragalactic survey, comprising observations of the Extended Chandra Deep Field South (E-CDFS), Extended Groth Strip (EGS), and the Cosmic Evolution Survey (COSMOS). The sample includes 182 NuSTAR sources (64 detected at 8–24 keV), with 3–24 keV fluxes ranging between f_(3-24 kev) ≈ 10^(-14) and 6 × 10^(−13) erg cm^(−2) s^(−1) (f_(8-24 kev) ≈ 3 x 10^(-14)-3 x 10^(-13) erg cm^(−2) s^(−1)) and redshifts in the range of z = 0.04-3.21. We produce composite spectra from the Chandra + NuSTAR data (E ≈ 2-40 keV,...

  5. An elevation of 0.1 light-seconds for the optical jet base in an accreting Galactic black hole system

    Gandhi, P.; Harrison, F. A.
    Relativistic plasma jets are observed in many systems that host accreting black holes. According to theory, coiled magnetic fields close to the black hole accelerate and collimate the plasma, leading to a jet being launched. Isolating emission from this acceleration and collimation zone is key to measuring its size and understanding jet formation physics. But this is challenging because emission from the jet base cannot easily be disentangled from other accreting components. Here, we show that rapid optical flux variations from an accreting Galactic black-hole binary are delayed with respect to X-rays radiated from close to the black hole by...

  6. Inversion of the decay of the cyclotron line energy in Her X-1

    Staubert, R.; Klochkov, D.; Fürst, F.; Wilms, J.; Rothschild, R. E.; Harrison, F. A.
    Recent observations of Her X-1 with NuSTAR and INTEGRAL in 2016 have provided evidence that the 20-year decay of the cyclotron line energy found between 1996 and 2015 has ended and that an inversion with a new increase, possibly similar to the one observed around 1990-1993, has started. We consider this a strong motivation for further observations and for enhanced efforts to significantly improve our theoretical understanding of the accretion process in binary X-ray pulsars. We speculate about the physics behind the long-term decay and its inversion, a possible cyclic behavior, and correlations with other variable observables.

  7. Swift and NuSTAR observations of GW170817: detection of a blue kilonova

    Evans, P. A.; Madsen, K. K.; Harrison, F. A.; Xu, Y.; Forster, K.; Garcia, J.; Grefenstette, B.; Heida, M.; Miyasaka, H.; Pike, S.; Rosswog, S.
    With the first direct detection of merging black holes in 2015, the era of gravitational wave (GW) astrophysics began. A complete picture of compact object mergers, however, requires the detection of an electromagnetic (EM) counterpart. We report ultraviolet (UV) and x-ray observations by Swift and the Nuclear Spectroscopic Telescope ARray (NuSTAR) of the EM counterpart of the binary neutron star merger GW 170817. The bright, rapidly fading ultraviolet emission indicates a high mass (≈ 0.03 solar masses) wind-driven outflow with moderate electron fraction (Y_e ≈ 0.27). Combined with the x-ray limits, we favor an observer viewing angle of ≈30° away...

  8. 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...

  9. 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 Oña 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, which is coincident with the supernova remnant G22.7−0.2, using the Nuclear Spectroscopic Telescope Array. 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 a best-fit photon index Γ = 1.5 ± 0.1. A re-analysis of archival Chandra and XMM-Newtondata 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...

  10. 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...

  11. 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...

  12. 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...

  13. 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...

  14. 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)...

  15. 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...

  16. 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...

  17. 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...

  18. 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...

  19. 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...

  20. 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...

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