## Recursos de colección

#### Caltech Authors (160.010 recursos)

Repository of works by Caltech published authors.

Group = NuSTAR

1. #### First NuSTAR Limits on Quiet Sun Hard X-Ray Transient Events

Marsh, Andrew J.; Smith, David M.; Glesener, Lindsay; Hannah, Iain G.; Grefenstette, Brian W.; Caspi, Amir; Krucker, Säm; Hudson, Hugh S.; Madsen, Kristin K.; White, Stephen M.; Kuhar, Matej; Wright, Paul J.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Hailey, Charles J.; Harrison, Fiona A.; Stern, Daniel; Zhang, William W.
We present the first results of a search for transient hard X-ray (HXR) emission in the quiet solar corona with the Nuclear Spectroscopic Telescope Array (NuSTAR) satellite. While NuSTAR was designed as an astrophysics mission, it can observe the Sun above 2 keV with unprecedented sensitivity due to its pioneering use of focusing optics. NuSTAR first observed quiet-Sun regions on 2014 November 1, although out-of-view active regions contributed a notable amount of background in the form of single-bounce (unfocused) X-rays. We conducted a search for quiet-Sun transient brightenings on timescales of 100 s and set upper limits on emission in...

2. #### 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,...

3. #### 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,...

4. #### 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...

5. #### 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.

6. #### Hard X-ray Emission from the M87 AGN Detected with NuSTAR

Wong, Ka-Wah; Nemmen, Rodrigo S.; Irwin, Jimmy A.; Lin, Dacheng
M87 hosts a 3-6 billion solar mass black hole with a remarkable relativistic jet that has been regularly monitored in radio to TeV bands. However, hard X-ray emission \gtrsim 10 keV expected to primarily come from the jet or the accretion flow had never been detected from its unresolved X-ray core. We report NuSTAR detection up to 40 keV from the the central regions of M87. Together with simultaneous Chandra observations, we have constrained the dominant hard X-ray emission to be from its unresolved X-ray core, presumably in its quiescent state. The core spectrum is well fitted by a power-law with photon index Gamma=2.11 (+0.15 -0.11). The measured...

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. #### Bulk Comptonization: new hints from the luminous blazar 4C+25.05

Kammoun, E. S.; Nardini, E.; Risaliti, G.; Ghisellini, G.; Behar, E.; Celotti, A.
Blazars are often characterized by a spectral break at soft X-rays, whose origin is still debated. While most sources show a flattening, some exhibit a blackbody-like soft excess with temperatures of the order of $\sim$0.1 keV, similar to low-luminosity, non-jetted Seyferts. Here we present the analysis of the simultaneous XMM-Newton and NuSTAR observation of the luminous FSRQ 4C+25.05 ($z=2.368$). The observed 0.3-30 keV spectrum is best described by the sum of a hard X-ray power law ($\Gamma = 1.38_{-0.03}^{+0.05}$) and a soft component, approximated by a blackbody with $kT_{\rm BB} = 0.66_{-0.04}^{+0.05}$ keV (rest frame). If the spectrum of 4C+25.05 is interpreted in the context of bulk Comptonization by...

11. #### Ultra Luminous X-ray sources - new distance indicators?

This paper presents X-ray broad-band spectral observations of the Ultra Luminous X-ray source (ULXs) NGC7793 P13 obtained by NuSTAR and XMM-Newton satellites. Reduced data were successfully fitted with only single spectral emission component from non-spherical system: neutron star plus accretion disk. We obtained the very good fit with the reduced $\chi^2$ per degree of freedom equal 1.08. Furthermore, the normalization of our model constrains the distance to the source. The resulting distance to the ULX source P13, $D=3.41^{+0.11}_{-0.10}$~Mpc, is with perfect agreement with the distance determination based on the Cepheid method to the hosting galaxy NGC7793. Our result shows that the ULX sources may contain central hot neutron star...

12. #### No time for dead time - Use the Fourier amplitude differences to normalize dead time-affected periodograms

Bachetti, Matteo; Huppenkothen, Daniela
Dead time affects many of the instruments used in X-ray astronomy, by producing a strong distortion in power density spectra. This can make it difficult to model the aperiodic variability of the source or look for quasi-periodic oscillations. Whereas in some instruments a simple a-priori correction for dead time-affected power spectra is possible, this is not the case for others such as \nustar, where the dead time is non-constant and long (~2.5 ms). Bachetti et al. 2015 suggested the cospectrum obtained from light curves of independent detectors within the same instrument as a possible way out, but this solution has always only been a partial one: the measured...

13. #### No time for dead time - Use the Fourier amplitude differences to normalize dead time-affected periodograms

Bachetti, Matteo; Huppenkothen, Daniela
Dead time affects many of the instruments used in X-ray astronomy, by producing a strong distortion in power density spectra. This can make it difficult to model the aperiodic variability of the source or look for quasi-periodic oscillations. Whereas in some instruments a simple a-priori correction for dead time-affected power spectra is possible, this is not the case for others such as \nustar, where the dead time is non-constant and long (~2.5 ms). Bachetti et al. 2015 suggested the cospectrum obtained from light curves of independent detectors within the same instrument as a possible way out, but this solution has always only been a partial one: the measured...

14. #### On the Statistical Properties of Cospectra

Huppenkothen, D.; Bachetti, M.
In recent years, the cross spectrum has received considerable attention as a means of characterising the variability of astronomical sources as a function of wavelength. While much has been written about the statistics of time and phase lags, the cospectrum has only recently been understood as means of mitigating instrumental effects dependent on temporal frequency in astronomical detectors, as well as a method of characterizing the coherent variability in two wavelength ranges on different time scales. In this paper, we lay out the statistical foundations of the cospectrum, starting with the simplest case of detecting a periodic signal in the presence of white noise. This case is especially relevant...

15. #### NuSTAR spectral analysis of two bright Seyfert 1 galaxies: MCG +8-11-11 and NGC 6814

Tortosa, A.; Bianchi, S.; Marinucci, A.; Matt, G.; Middei, R.; Piconcelli, E.; Brenneman, L. W.; Cappi, M.; Dadina, M.; De Rosa, A.; Petrucci, P. O.; Ursini, F.; Walton, D. J.
We report on the NuSTAR observations of two bright Seyfert 1 galaxies, namely MCG +8-11-11 (100 ks) and NGC 6814 (150 ks). The main goal of these observations was to investigate the Comptonization mechanisms acting in the innermost regions of AGN which are believed to be responsible for the UV/X-ray emission. The spectroscopic analysis of the NuSTAR spectra of these two sources revealed that although they had different properties overall (black hole masses, luminosity and Eddington ratios) they had very similar coronal properties. Both presented a power law spectrum with a high-energy cutoff at $\sim 150-200$ keV, a relativistically broadened Fe K$\alpha$ line and the associated disk reflection component,...

16. #### NuSTAR hard X-ray data and Gemini 3D spectra reveal powerful AGN and outflow histories in two low-redshift Lyman-α blobs

Kawamuro, Taiki; Schirmer, Mischa; Turner, James E. H.; Davies, Rebecca L.; Ichikawa, Kohei
We have shown that Lyman-$\alpha$ blobs (LABs) may still exist even at $z\sim0.3$, about 7 billion years later than most other LABs known (Schirmer et al. 2016). Their luminous Ly$\alpha$ and [OIII] emitters at $z\sim0.3$ offer new insights into the ionization mechanism. This paper focuses on the two X-ray brightest LABs at $z\sim0.3$, SDSS J0113$+$0106 (J0113) and SDSS J1155$-$0147 (J1155), comparable in size and luminosity to `B1', one of the best-studied LABs at $z \gtrsim$ 2. Our NuSTAR hard X-ray (3--30 keV) observations reveal powerful active galactic nuclei (AGN) with $L_{2-10{\;\rm keV}}=(0.5$--$3)\times10^{44}$ erg cm$^{-2}$ s$^{-1}$. J0113 also faded by a factor of $\sim 5$ between 2014 and 2016, emphasizing...

17. #### 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...

18. #### 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...

19. #### The nature of X-ray spectral variability in MCG-6-30-15

Kammoun, E. S.; Papadakis, I. E.
The flux-flux plot (FFP) method can provide model-independent clues regarding the X-ray variability of active galactic nuclei. To use it properly, the bin size of the light curves should be as short as possible, provided the average counts in the light curve bins are larger than $\sim 200$. We apply the FFP method to the 2013, simultaneous XMM-Newton and NuSTAR observations of the Seyfert galaxy MCG$-$6-30-15, in the 0.3-40 keV range. The FFPs above $\sim 1.6$ keV are well-described by a straight line. This result rules out spectral slope variations and the hypothesis of absorption driven variability. Our results are fully consistent with a power-law component varying in normalization...

20. #### Truncation of the Accretion Disk at One Third of the Eddington Limit in the Neutron Star Low-Mass X-ray Binary Aquila X-1

Ludlam, Renee M.; Miller, Jon M.; Degenaar, Nathalie; Sanna, Andrea; Cackett, Edward M.; Altamirano, Diego; King, Ashley L.
We perform a reflection study on a new observation of the neutron star low-mass X-ray binary Aquila X-1 taken with NuSTAR during the August 2016 outburst and compare with the July 2014 outburst. The source was captured at $\sim32\%\ L_{\mathrm{Edd}}$, which is over four times more luminous than the previous observation during the 2014 outburst. Both observations exhibit a broadened Fe line profile. Through reflection modeling, we determine that the inner disk is truncated $R_{in,\ 2016}=11_{-1}^{+2}\ R_{g}$ (where $R_{g}=GM/c^{2}$) and $R_{in,\ 2014}=14\pm2\ R_{g}$ (errors quoted at the 90% confidence level). Fiducial neutron star parameters (M$_{NS}=1.4$ M$_{\odot}$, $R_{NS}=10$ km) give a stellar radius of $R_{NS}=4.85\ R_{g}$; our measurements rule out a...

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