235 results on '"Grefenstette, Brian W"'
Search Results
202. First hard X-ray detection of the non-thermal emission around the Arches cluster: morphology and spectral studies with NuSTAR
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Krivonos, Roman A., Tomsick, John A., Bauer, Franz E., Baganoff, Frederick K., Barriere, Nicolas M., Bodaghee, Arash, Boggs, Steven E., Christensen, Finn E., Craig, William W., Grefenstette, Brian W., Hailey, Charles J., Harrison, Fiona A., Hong, JaeSub, Madsen, Kristin K., Mori, Kaya, Nynka, Melania, Stern, Daniel, Zhang, William W., Krivonos, Roman A., Tomsick, John A., Bauer, Franz E., Baganoff, Frederick K., Barriere, Nicolas M., Bodaghee, Arash, Boggs, Steven E., Christensen, Finn E., Craig, William W., Grefenstette, Brian W., Hailey, Charles J., Harrison, Fiona A., Hong, JaeSub, Madsen, Kristin K., Mori, Kaya, Nynka, Melania, Stern, Daniel, and Zhang, William W.
- Abstract
The Arches cluster is a young, densely packed massive star cluster in our Galaxy that shows a high level of star formation activity. The nature of the extended non-thermal X-ray emission around the cluster remains unclear. The observed bright Fe K_alpha line emission at 6.4 keV from material that is neutral or in a low ionization state can be produced either by X-ray photoionization or by cosmic-ray particle bombardment or both. In this paper we report on the first detection of the extended emission around the Arches cluster above 10 keV with the NuSTAR mission, and present results on its morphology and spectrum. The spatial distribution of the hard X-ray emission is found to be consistent with the broad region around the cluster where the 6.4 keV line is observed. The interpretation of the hard X-ray emission within the context of the X-ray reflection model puts a strong constraint on the luminosity of the possible illuminating hard X-ray source. The properties of the observed emission are also in broad agreement with the low-energy cosmic-ray proton excitation scenario., Comment: 15 pages, 9 figures, accepted for publication in ApJ
- Published
- 2013
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203. The smooth cyclotron line in her x-1 as seen with nuclear spectroscopic telescope array
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Fuerst, Felix, Grefenstette, Brian W., Staubert, Ruediger, Tomsick, John A., Bachetti, Matteo, Barret, Didier, Bellm, Eric C., Boggs, Steven E., Chenevez, Jérôme, Christensen, Finn Erland, Craig, William W., Hailey, Charles J., Harrison, Fiona, Klochkov, Dmitry, Madsen, Kristin K., Pottschmidt, Katja, Stern, Daniel, Walton, Dominic J., Wilms, Joern, Zhang, William, Fuerst, Felix, Grefenstette, Brian W., Staubert, Ruediger, Tomsick, John A., Bachetti, Matteo, Barret, Didier, Bellm, Eric C., Boggs, Steven E., Chenevez, Jérôme, Christensen, Finn Erland, Craig, William W., Hailey, Charles J., Harrison, Fiona, Klochkov, Dmitry, Madsen, Kristin K., Pottschmidt, Katja, Stern, Daniel, Walton, Dominic J., Wilms, Joern, and Zhang, William
- Abstract
Her X-1, one of the brightest and best studied X-ray binaries, shows a cyclotron resonant scattering feature (CRSF) near 37 keV. This makes it an ideal target for detailed study with the Nuclear Spectroscopic Telescope Array (NuSTAR), taking advantage of its excellent hard X-ray spectral resolution. We observed Her X-1 three times, coordinated with Suzaku, during one of the high flux intervals of its 35d super-orbital period. This paper focuses on the shape and evolution of the hard X-ray spectrum. The broad-band spectra can be fitted with a powerlaw with a high-energy cutoff, an iron line, and a CRSF. We find that the CRSF has a very smooth and symmetric shape, in all observations and at all pulse-phases. We compare the residuals of a line with a Gaussian optical depth profile to a Lorentzian optical depth profile and find no significant differences, strongly constraining the very smooth shape of the line. Even though the line energy changes dramatically with pulse phase, we find that its smooth shape does not. Additionally, our data show that the continuum is only changing marginally between the three observations. These changes can be explained with varying amounts of Thomson scattering in the hot corona of the accretion disk. The average, luminosity-corrected CRSF energy is lower than in past observations and follows a secular decline. The excellent data quality of NuSTAR provides the best constraint on the CRSF energy to date.
- Published
- 2013
204. Pushing the limits of NuSTARdetectors
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Holland, Andrew D., Beletic, James, Grefenstette, Brian W., Cook, W. Rick, Harrison, Fiona A., Kitaguchi, Takao, Madsen, Kristin K., Miyasaka, Hiromasa, and Pike, Sean N.
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- 2018
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205. Characterization of Redlen CZT detectors for x-ray astronomy
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Holland, Andrew D., Beletic, James, Pike, Sean N., Harrison, Fiona A., Burnham, Jill A., Cook, Walter W., Grefenstette, Brian W., Madsen, Kristin K., and Miyasaka, Hiromasa
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- 2018
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206. NuSTARDISCOVERY OF A LUMINOSITY DEPENDENT CYCLOTRON LINE ENERGY IN VELA X-1
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Fürst, Felix, primary, Pottschmidt, Katja, additional, Wilms, Jörn, additional, Tomsick, John A., additional, Bachetti, Matteo, additional, Boggs, Steven E., additional, Christensen, Finn E., additional, Craig, William W., additional, Grefenstette, Brian W., additional, Hailey, Charles J., additional, Harrison, Fiona, additional, Madsen, Kristin K., additional, Miller, Jon M., additional, Stern, Daniel, additional, Walton, Dominic J., additional, and Zhang, William, additional
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- 2013
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207. THE REFLECTION COMPONENT FROM CYGNUS X-1 IN THE SOFT STATE MEASURED BYNuSTARANDSUZAKU
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Tomsick, John A., primary, Nowak, Michael A., additional, Parker, Michael, additional, Miller, Jon M., additional, Fabian, Andy C., additional, Harrison, Fiona A., additional, Bachetti, Matteo, additional, Barret, Didier, additional, Boggs, Steven E., additional, Christensen, Finn E., additional, Craig, William W., additional, Forster, Karl, additional, Fürst, Felix, additional, Grefenstette, Brian W., additional, Hailey, Charles J., additional, King, Ashley L., additional, Madsen, Kristin K., additional, Natalucci, Lorenzo, additional, Pottschmidt, Katja, additional, Ross, Randy R., additional, Stern, Daniel, additional, Walton, Dominic J., additional, Wilms, Jörn, additional, and Zhang, William W., additional
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- 2013
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208. NuSTARANDINTEGRALOBSERVATIONS OF A LOW/HARD STATE OF 1E1740.7-2942
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Natalucci, Lorenzo, primary, Tomsick, John A., additional, Bazzano, Angela, additional, Smith, David M., additional, Bachetti, Matteo, additional, Barret, Didier, additional, Boggs, Steven E., additional, Christensen, Finn E., additional, Craig, William W., additional, Fiocchi, Mariateresa, additional, Fürst, Felix, additional, Grefenstette, Brian W., additional, Hailey, Charles J., additional, Harrison, Fiona A., additional, Krivonos, Roman, additional, Kuulkers, Erik, additional, Miller, Jon M., additional, Pottschmidt, Katja, additional, Stern, Daniel, additional, Ubertini, Pietro, additional, Walton, Dominic J., additional, and Zhang, William W., additional
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- 2013
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209. The Nuclear Spectroscopic Telescope Array (NuSTAR)
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Arnaud, Monique, Murray, Stephen S., Takahashi, T., Harrison, Fiona A., Bhalereo, Varun, Cook, W. Rick, Grefenstette, Brian W., Kitaguchi, Takeo, Madsen, Kristin Kruse, Mao, Peter H., Miyasaka, Hiromasa, Rana, Vikram, Arnaud, Monique, Murray, Stephen S., Takahashi, T., Harrison, Fiona A., Bhalereo, Varun, Cook, W. Rick, Grefenstette, Brian W., Kitaguchi, Takeo, Madsen, Kristin Kruse, Mao, Peter H., Miyasaka, Hiromasa, and Rana, Vikram
- Abstract
The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the rst focusing hard X-ray (6 - 80 keV) telescope to orbit. NuSTAR will oer a factor 50 - 100 sensitivity improvement compared to previous collimated or coded mask imagers that have operated in this energy band. In addition, NuSTAR provides sub-arcminute imaging with good spectral resolution over a 12-arcminute eld of view. After launch, NuSTAR will carry out a two-year primary science mission that focuses on four key programs: studying the evolution of massive black holes through surveys carried out in elds with excellent multiwavelength coverage, understanding the population of compact objects and the nature of the massive black hole in the center of the Milky Way, constraining the explosion dynamics and nucleosynthesis in supernovae, and probing the nature of particle acceleration in relativistic jets in active galactic nuclei. A number of additional observations will be included in the primary mission, and a guest observer program will be proposed for an extended mission to expand the range of scientic targets. The payload consists of two co-aligned depth-graded multilayer coated grazing incidence optics focused onto a solid state CdZnTe pixel detectors. To be launched in early 2012 on a Pegasus rocket into a low-inclination Earth orbit, NuSTAR largely avoids SAA passage, and will therefore have low and stable detector backgrounds. The telescope achieves a 10.14-meter focal length through on-orbit deployment of an extendable mast. An aspect and alignment metrology system enable reconstruction of the absolute aspect and variations in the telescope alignment resulting from mast exure during ground data processing. Data will be publicly available at GSFC's High Energy Archive Research Center (HEASARC) following validation at the science operations center located at Caltech.
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- 2010
210. High dynamic range techniques for astronomical applications of CMOS devices.
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Earnshaw, Hannah P., Greffe, Timothee, Smith, Roger M., Grefenstette, Brian W., Harrison, Fiona A., Hennessy, John J., Nikzad, Shouleh, and Shapiro, Charles A.
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- 2022
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211. THE SMOOTH CYCLOTRON LINE IN HER X-1 AS SEEN WITH NUCLEAR SPECTROSCOPIC TELESCOPE ARRAY
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Fürst, Felix, primary, Grefenstette, Brian W., additional, Staubert, Rüdiger, additional, Tomsick, John A., additional, Bachetti, Matteo, additional, Barret, Didier, additional, Bellm, Eric C., additional, Boggs, Steven E., additional, Chenevez, Jerome, additional, Christensen, Finn E., additional, Craig, William W., additional, Hailey, Charles J., additional, Harrison, Fiona, additional, Klochkov, Dmitry, additional, Madsen, Kristin K., additional, Pottschmidt, Katja, additional, Stern, Daniel, additional, Walton, Dominic J., additional, and Wilms, Jörn, additional
- Published
- 2013
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212. THE ULTRALUMINOUS X-RAY SOURCES NGC 1313 X-1 AND X-2: A BROADBAND STUDY WITHNuSTARANDXMM-Newton
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Bachetti, Matteo, primary, Rana, Vikram, additional, Walton, Dominic J., additional, Barret, Didier, additional, Harrison, Fiona A., additional, Boggs, Steven E., additional, Christensen, Finn E., additional, Craig, William W., additional, Fabian, Andrew C., additional, Fürst, Felix, additional, Grefenstette, Brian W., additional, Hailey, Charles J., additional, Hornschemeier, Ann, additional, Madsen, Kristin K., additional, Miller, Jon M., additional, Ptak, Andrew F., additional, Stern, Daniel, additional, Webb, Natalie A., additional, and Zhang, William W., additional
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- 2013
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213. NuSTARDETECTION OF HARD X-RAY PHASE LAGS FROM THE ACCRETING PULSAR GS 0834–430
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Miyasaka, Hiromasa, primary, Bachetti, Matteo, additional, Harrison, Fiona A., additional, Fürst, Felix, additional, Barret, Didier, additional, Bellm, Eric C., additional, Boggs, Steven E., additional, Chakrabarty, Deepto, additional, Chenevez, Jerome, additional, Christensen, Finn E., additional, Craig, William W., additional, Grefenstette, Brian W., additional, Hailey, Charles J., additional, Madsen, Kristin K., additional, Natalucci, Lorenzo, additional, Pottschmidt, Katja, additional, Stern, Daniel, additional, Tomsick, John A., additional, Walton, Dominic J., additional, Wilms, Jörn, additional, and Zhang, William, additional
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- 2013
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214. NuSTAR DISCOVERY OF A 3.76 s TRANSIENT MAGNETAR NEAR SAGITTARIUS A*
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Mori, Kaya, primary, Gotthelf, Eric V., additional, Zhang, Shuo, additional, An, Hongjun, additional, Baganoff, Frederick K., additional, Barrière, Nicolas M., additional, Beloborodov, Andrei M., additional, Boggs, Steven E., additional, Christensen, Finn E., additional, Craig, William W., additional, Dufour, Francois, additional, Grefenstette, Brian W., additional, Hailey, Charles J., additional, Harrison, Fiona A., additional, Hong, Jaesub, additional, Kaspi, Victoria M., additional, Kennea, Jamie A., additional, Madsen, Kristin K., additional, Markwardt, Craig B., additional, Nynka, Melania, additional, Stern, Daniel, additional, Tomsick, John A., additional, and Zhang, William W., additional
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- 2013
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215. THENUCLEAR SPECTROSCOPIC TELESCOPE ARRAY(NuSTAR) HIGH-ENERGY X-RAY MISSION
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Harrison, Fiona A., primary, Craig, William W., additional, Christensen, Finn E., additional, Hailey, Charles J., additional, Zhang, William W., additional, Boggs, Steven E., additional, Stern, Daniel, additional, Cook, W. Rick, additional, Forster, Karl, additional, Giommi, Paolo, additional, Grefenstette, Brian W., additional, Kim, Yunjin, additional, Kitaguchi, Takao, additional, Koglin, Jason E., additional, Madsen, Kristin K., additional, Mao, Peter H., additional, Miyasaka, Hiromasa, additional, Mori, Kaya, additional, Perri, Matteo, additional, Pivovaroff, Michael J., additional, Puccetti, Simonetta, additional, Rana, Vikram R., additional, Westergaard, Niels J., additional, Willis, Jason, additional, Zoglauer, Andreas, additional, An, Hongjun, additional, Bachetti, Matteo, additional, Barrière, Nicolas M., additional, Bellm, Eric C., additional, Bhalerao, Varun, additional, Brejnholt, Nicolai F., additional, Fuerst, Felix, additional, Liebe, Carl C., additional, Markwardt, Craig B., additional, Nynka, Melania, additional, Vogel, Julia K., additional, Walton, Dominic J., additional, Wik, Daniel R., additional, Alexander, David M., additional, Cominsky, Lynn R., additional, Hornschemeier, Ann E., additional, Hornstrup, Allan, additional, Kaspi, Victoria M., additional, Madejski, Greg M., additional, Matt, Giorgio, additional, Molendi, Silvano, additional, Smith, David M., additional, Tomsick, John A., additional, Ajello, Marco, additional, Ballantyne, David R., additional, Baloković, Mislav, additional, Barret, Didier, additional, Bauer, Franz E., additional, Blandford, Roger D., additional, Brandt, W. Niel, additional, Brenneman, Laura W., additional, Chiang, James, additional, Chakrabarty, Deepto, additional, Chenevez, Jerome, additional, Comastri, Andrea, additional, Dufour, Francois, additional, Elvis, Martin, additional, Fabian, Andrew C., additional, Farrah, Duncan, additional, Fryer, Chris L., additional, Gotthelf, Eric V., additional, Grindlay, Jonathan E., additional, Helfand, David J., additional, Krivonos, Roman, additional, Meier, David L., additional, Miller, Jon M., additional, Natalucci, Lorenzo, additional, Ogle, Patrick, additional, Ofek, Eran O., additional, Ptak, Andrew, additional, Reynolds, Stephen P., additional, Rigby, Jane R., additional, Tagliaferri, Gianpiero, additional, Thorsett, Stephen E., additional, Treister, Ezequiel, additional, and Urry, C. Megan, additional
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- 2013
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216. Spectral calibration and modeling of the NuSTAR CdZnTe pixel detectors
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Kitaguchi, Takao, primary, Grefenstette, Brian W., additional, Harrison, Fiona A., additional, Miyasaka, Hiromasa, additional, Bhalerao, Varun B., additional, Cook III, Walter R., additional, Mao, Peter H., additional, Rana, Vikram R., additional, Boggs, Steven E., additional, and Zoglauer, Andreas C., additional
- Published
- 2011
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217. Characteristics of broadband lightning emissions associated with terrestrial gamma ray flashes
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Lu, Gaopeng, primary, Cummer, Steven A., additional, Li, Jingbo, additional, Han, Feng, additional, Smith, David M., additional, and Grefenstette, Brian W., additional
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- 2011
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218. High-energy electron beams launched into space by thunderstorms
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Dwyer, Joseph R., primary, Grefenstette, Brian W., additional, and Smith, David M., additional
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- 2008
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219. Getting NuSTARon target: predicting mast motion
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Peck, Alison B., Seaman, Robert L., Benn, Chris R., Forster, Karl, Madsen, Kristin K., Miyasaka, Hiromasa, Craig, William W., Harrison, Fiona A., Rana, Vikram R., Markwardt, Craig B., and Grefenstette, Brian W.
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- 2016
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220. NuSTAR DISCOVERY OF A LUMINOSITY DEPENDENT CYCLOTRON LINE ENERGY IN VELA X-1.
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Fürst, Felix, Pottschmidt, Katja, Wilms, Jörn, Tomsick, John A., Bachetti, Matteo, Boggs, Steven E., Christensen, Finn E., Craig, William W., Grefenstette, Brian W., Hailey, Charles J., Harrison, Fiona, Madsen, Kristin K., Miller, Jon M., Stern, Daniel, Walton, Dominic J., and Zhang, William
- Subjects
X-ray binaries ,CYCLOTRON radiation ,NEUTRON stars ,STAR observations ,STELLAR luminosity function ,ACCRETION (Astrophysics) ,SCATTERING (Physics) - Abstract
We present NuSTAR observations of Vela X-1, a persistent, yet highly variable, neutron star high-mass X-ray binary (HMXB). Two observations were taken at similar orbital phases but separated by nearly a year. They show very different 3-79 keV flux levels as well as strong variability during each observation, covering almost one order of magnitude in flux. These observations allow, for the first time ever, investigations on kilo-second time-scales of how the centroid energies of cyclotron resonant scattering features (CRSFs) depend on flux for a persistent HMXB. We find that the line energy of the harmonic CRSF is correlated with flux, as expected in the sub-critical accretion regime. We argue that Vela X-1 has a very narrow accretion column with a radius of around 0.4 km that sustains a Coulomb interaction dominated shock at the observed luminosities of L
x ∼ 3 × 1036 erg s–1 . Besides the prominent harmonic line at 55 keV the fundamental line around 25 keV is clearly detected. We find that the strengths of the two CRSFs are anti-correlated, which we explain by photon spawning. This anti-correlation is a possible explanation for the debate about the existence of the fundamental line. The ratio of the line energies is variable with time and deviates significantly from 2.0, also a possible consequence of photon spawning, which changes the shape of the line. During the second observation, Vela X-1 showed a short off-state in which the power-law softened and a cut-off was no longer measurable. It is likely that the source switched to a different accretion regime at these low mass accretion rates, explaining the drastic change in spectral shape. [ABSTRACT FROM AUTHOR]- Published
- 2014
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221. NuSTAR Hard X-ray Survey of the Galactic Center Region II: X-ray Point Sources
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Hong, Jaesub, Mori, Kaya, Hailey, Charles J., Nynka, Melania, Zhang, Shuo, Gotthelf, Eric, Fornasini, Francesca M., Krivonos, Roman, Bauer, Franz, Perez, Kerstin, Tomsick, John A., Bodaghee, Arash, Chiu, Jeng-Lun, Clavel, Maïca, Stern, Daniel, Grindlay, Jonathan E., Alexander, David M., Aramaki, Tsuguo, Baganoff, Frederick K., Barret, Didier, Barrière, Nicolas, Boggs, Steven E., Canipe, Alicia M., Christensen, Finn E., Craig, William W., Desai, Meera A., Forster, Karl, Giommi, Paolo, Grefenstette, Brian W., Harrison, Fiona A., Hong, Dooran, Hornstrup, Allan, Kitaguchi, Takao, Koglin, Jason E., Madsen, Kristen K., Mao, Peter H., Miyasaka, Hiromasa, Perri, Matteo, Pivovaroff, Michael J., Puccetti, Simonetta, Rana, Vikram, Westergaard, Niels J., Zhang, William W., and Zoglauer, Andreas
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Galaxy: center ,X-rays: binaries ,X-rays: diffuse background ,X-rays: general - Abstract
We present the first survey results of hard X-ray point sources in the Galactic Center (GC) region by NuSTAR. We have discovered 70 hard (3–79 keV) X-ray point sources in a 0.6 deg${}^{2}$ region around Sgr A* with a total exposure of 1.7 Ms, and 7 sources in the Sgr B2 field with 300 ks. We identify clear Chandra counterparts for 58 NuSTAR sources and assign candidate counterparts for the remaining 19. The NuSTAR survey reaches X-ray luminosities of ~4× and ~8 × 10${}^{32}$ erg s${}^{-1}$ at the GC (8 kpc) in the 3–10 and 10–40 keV bands, respectively. The source list includes three persistent luminous X-ray binaries (XBs) and the likely run-away pulsar called the Cannonball. New source-detection significance maps reveal a cluster of hard (>10 keV) X-ray sources near the Sgr A diffuse complex with no clear soft X-ray counterparts. The severe extinction observed in the Chandra spectra indicates that all the NuSTAR sources are in the central bulge or are of extragalactic origin. Spectral analysis of relatively bright NuSTAR sources suggests that magnetic cataclysmic variables constitute a large fraction (>40%–60%). Both spectral analysis and logN–logS distributions of the NuSTAR sources indicate that the X-ray spectra of the NuSTAR sources should have kT > 20 keV on average for a single temperature thermal plasma model or an average photon index of Γ = 1.5–2 for a power-law model. These findings suggest that the GC X-ray source population may contain a larger fraction of XBs with high plasma temperatures than the field population., Astronomy
- Published
- 2016
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222. The First Survey of Quiet Sun Features Observed in Hard X-Rays with NuSTAR.
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Paterson, Sarah, Hannah, Iain G., Grefenstette, Brian W., Hudson, Hugh S., Krucker, Säm, Glesener, Lindsay, White, Stephen M., and Smith, David M.
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SOLAR atmosphere , *HARD X-rays , *FOCUS (Optics) , *ISOTHERMAL temperature , *SPECTRAL imaging , *SUN , *SOFT X rays - Abstract
We present the first survey of quiet Sun features observed in hard X-rays (HXRs), using the Nuclear Spectroscopic Telescope ARray (NuSTAR), a HXR focusing optics telescope. The recent solar minimum, combined with NuSTAR's high sensitivity, has presented a unique opportunity to perform the first HXR imaging spectroscopy on a range of features in the quiet Sun. By studying the HXR emission of these features, we can detect or constrain the presence of high temperature (> 5 MK) or non-thermal sources, to help understand how they relate to larger, more energetic solar phenomena, and determine their contribution to heating the solar atmosphere. We report on several features observed in the 28 September 2018 NuSTAR full-disk quiet Sun mosaics, the first of the NuSTAR quiet Sun observing campaigns, which mostly include steady features of X-ray bright points and an emerging flux region, which later evolved into an active region, as well as a short-lived jet. We find that the features' HXR spectra are well fitted with isothermal models with temperatures ranging between 2.0 – 3.2 MK. Combining the NuSTAR data with softer X-ray emission from Hinode/XRT and EUV from SDO/AIA, we recover the differential emission measures, confirming little significant emission above 4 MK. The NuSTAR HXR spectra allow us to constrain the possible non-thermal emission that would still be consistent with a null HXR detection. We found that for only one of the features (the jet) was there a potential non-thermal upper limit capable of powering the heating observed. However, even here, the non-thermal electron distribution had to be very steep (effectively mono-energetic) with a low energy cut-off between 3 – 4 keV. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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223. NuSTAR Hard X-ray Survey of the Galactic Center Region I: Hard X-ray Morphology and Spectroscopy of the Diffuse Emission
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Mori, Kaya, Hailey, Charles J., Krivonos, Roman, Hong, Jaesub, Ponti, Gabriele, Bauer, Franz, Perez, Kerstin, Nynka, Melania, Zhang, Shuo, Tomsick, John A., Alexander, David M., Baganoff, Frederick K., Barret, Didier, Barrière, Nicolas, Boggs, Steven E., Canipe, Alicia M., Christensen, Finn E., Craig, William W., Forster, Karl, Giommi, Paolo, Grefenstette, Brian W., Grindlay, Jonathan E., Harrison, Fiona A., Hornstrup, Allan, Kitaguchi, Takao, Koglin, Jason E., Luu, Vy, Madsen, Kristen K., Mao, Peter H., Miyasaka, Hiromasa, Perri, Matteo, Pivovaroff, Michael J., Puccetti, Simonetta, Rana, Vikram, Stern, Daniel, Westergaard, Niels J., Zhang, William W., and Zoglauer, Andreas
- Subjects
Galaxy: center ,radiation mechanisms: non-thermal ,X-rays: general ,X-rays: ISM - Abstract
We present the first sub-arcminute images of the Galactic Center above 10 keV, obtained with NuSTAR. NuSTAR resolves the hard X-ray source IGR J17456–2901 into non-thermal X-ray filaments, molecular clouds, point sources, and a previously unknown central component of hard X-ray emission (CHXE). NuSTAR detects four non-thermal X-ray filaments, extending the detection of their power-law spectra with Γ ~ 1.3–2.3 up to ~50 keV. A morphological and spectral study of the filaments suggests that their origin may be heterogeneous, where previous studies suggested a common origin in young pulsar wind nebulae (PWNe). NuSTAR detects non-thermal X-ray continuum emission spatially correlated with the 6.4 keV Fe Kα fluorescence line emission associated with two Sgr A molecular clouds: MC1 and the Bridge. Broadband X-ray spectral analysis with a Monte-Carlo based X-ray reflection model self-consistently determined their intrinsic column density (~1023 cm−2), primary X-ray spectra (power-laws with Γ ~ 2) and set a lower limit of the X-ray luminosity of Sgr A* flare illuminating the Sgr A clouds to LX gsim 1038 erg s−1. Above ~20 keV, hard X-ray emission in the central 10 pc region around Sgr A* consists of the candidate PWN G359.95–0.04 and the CHXE, possibly resulting from an unresolved population of massive CVs with white dwarf masses MWD ~ 0.9 M⊙. Spectral energy distribution analysis suggests that G359.95–0.04 is likely the hard X-ray counterpart of the ultra-high gamma-ray source HESS J1745–290, strongly favoring a leptonic origin of the GC TeV emission., Astronomy
- Published
- 2015
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224. First joint X-ray solar microflare observations with NuSTAR and Solar Orbiter/STIX.
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Bajnoková, Natália, Hannah, Iain G, Cooper, Kristopher, Krucker, Säm, Grefenstette, Brian W, Smith, David M, Jeffrey, Natasha L S, and Duncan, Jessie
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- *
SOLAR corona , *HARD X-rays , *SPECTRAL imaging , *X-ray imaging , *X-ray telescopes - Abstract
We present the first joint spectral and imaging analysis of hard X-ray (HXR) emission from three microflares observed by the Nuclear Spectroscopic Telescope ARray (NuSTAR) and Solar Orbiter/Spectrometer/Telescope for Imaging X-rays (STIX). We studied 5 joint spectra from GOES A7, B1, and B6 class microflares from active region AR12765 on 2020 June 6 and 7. As these events are very bright for NuSTAR, resulting in extremely low (<1 per cent) livetime, we introduce a pile-up correction method. All five joint spectra were fitted with an isothermal model finding temperatures in the 9–11 MK range. Furthermore, three joint spectra required an additional non-thermal thick-target model finding non-thermal powers of |$10^{25}$| – |$10^{26}$| erg s |$^{-1}$|. All the fit parameters were within the ranges expected for HXR microflares. The fit results give a relative scaling of STIX and NuSTAR mostly between 6 and 28 per cent (one outlier at 52 per cent) suggesting each instrument are well calibrated. In addition to spectral analysis, we performed joint HXR imaging of the June 6 and one of the June 7 microflares. In NuSTAR's field of view (FOV), we observed two separate non-thermal sources connected by an elongated thermal source during the June 6 microflares. In STIX's FOV (44 |$^{\circ }$| W with respect to NuSTAR), we imaged thermal emission from the hot flare loops which when reprojected to an Earth viewpoint matches the thermal sources seen with NuSTAR and in the hotter EUV channels with the Solar Dynamic Observatory's Atmospheric Imaging Assembly. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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225. Reconstruction of the NuSTAR point spread function using single-laser metrology
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Earnshaw, Hannah P., Madsen, Kristin K., Forster, Karl, Grefenstette, Brian W., Brightman, Murray, Zoglauer, Andreas, and Harrison, Fiona
- Published
- 2021
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226. The smooth cyclotron line in Her X-1 as seen with NuSTAR
- Author
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Fuerst, Felix, Grefenstette, Brian W., Staubert, Ruediger, Tomsick, John A., Matteo Bachetti, Barret, Didier, Bellm, Eric C., Boggs, Steven E., Chenevez, Jerome, Christensen, Finn E., Craig, William W., Hailey, Charles J., Harrison, Fiona, Klochkov, Dmitry, Madsen, Kristin K., Pottschmidt, Katja, Stern, Daniel, Walton, Dominic J., Wilms, Joern, and Zhang, William
- Subjects
High Energy Astrophysical Phenomena (astro-ph.HE) ,Accretion ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,neutron [Stars] ,Astrophysics - High Energy Astrophysical Phenomena ,individual (Her X-1) [Pulsars] ,binaries [X-ray] - Abstract
Her X-1, one of the brightest and best studied X-ray binaries, shows a cyclotron resonant scattering feature (CRSF) near 37 keV. This makes it an ideal target for detailed study with the Nuclear Spectroscopic Telescope Array (NuSTAR), taking advantage of its excellent hard X-ray spectral resolution. We observed Her X-1 three times, coordinated with Suzaku, during one of the high flux intervals of its 35d super-orbital period. This paper focuses on the shape and evolution of the hard X-ray spectrum. The broad-band spectra can be fitted with a powerlaw with a high-energy cutoff, an iron line, and a CRSF. We find that the CRSF has a very smooth and symmetric shape, in all observations and at all pulse-phases. We compare the residuals of a line with a Gaussian optical depth profile to a Lorentzian optical depth profile and find no significant differences, strongly constraining the very smooth shape of the line. Even though the line energy changes dramatically with pulse phase, we find that its smooth shape does not. Additionally, our data show that the continuum is only changing marginally between the three observations. These changes can be explained with varying amounts of Thomson scattering in the hot corona of the accretion disk. The average, luminosity-corrected CRSF energy is lower than in past observations and follows a secular decline. The excellent data quality of NuSTAR provides the best constraint on the CRSF energy to date., Comment: 13 pages, 13 figures, accepted for publication in ApJ
227. Detecting non-thermal emission in a solar microflare using nested sampling.
- Author
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Cooper, Kristopher, Hannah, Iain G, Glesener, Lindsay, and Grefenstette, Brian W
- Subjects
- *
PARTICLE acceleration , *SOLAR atmosphere , *SOLAR flares , *PLASMA heating , *X-ray spectra , *PROCESS heating , *ELECTRON density - Abstract
Microflares are energetically smaller versions of solar flares, demonstrating the same processes of plasma heating and particle acceleration. However, it remains unclear down to what energy scales this impulsive energy release continues, which has implications for how the solar atmosphere is heated. The heating and particle acceleration in microflares can be studied through their X-ray emission, finding predominantly thermal emission at lower energies; however, at higher energies it can be difficult to distinguish whether the emission is due to hotter plasma and/or accelerated electrons. We present the first application of nested sampling to solar flare X-ray spectra, an approach that provides a quantitative degree of confidence for one model over another. We analyse Nuclear Spectroscopic Telescope Array X-ray observations of a small active region microflare (A0.02 GOES/XRS class equivalent) that occurred on 2021 November 17, with a new python package for spectral fitting, sunkit-spex , to compute the parameter posterior distributions and the evidence of different models representing the higher energy emission as due to thermal or non-thermal sources. Calculating the Bayes factor, we show that there is significantly stronger evidence for the higher energy microflare emission to be produced by non-thermal emission from flare-accelerated electrons than by an additional hot thermal source. Qualitative confirmation of this non-thermal source is provided by the lack of hotter (10 MK) emission in Solar Dynamic Observatory's Atmospheric Imaging Assembly's extreme ultraviolet data. The nested sampling approach used in this paper has provided clear support for non-thermal emission at the level of 3 × 1024 erg s−1 in this tiny microflare. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
228. The high energy X-ray probe (HEX-P): instrument and mission profile.
- Author
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Madsen, Kristin K., García, Javier A., Stern, Daniel, Amini, Rashied, Basso, Stefano, Coutinho, Diogo, Grefenstette, Brian W., Kenyon, Steven, Moretti, Alberto, Morrissey, Patrick, Nandra, Kirpal, Pareschi, Giovanni, Predehl, Peter, Rau, Arne, Spiga,, Daniele, Wilms, Jörn, Zhang, William W., Marshall, Herman, and Rothschild, Richard
- Subjects
- *
X-ray telescopes , *PERFORMANCE technology , *TELESCOPES - Abstract
The High Energy X-ray Probe (HEX-P) is a proposed NASA probe-class mission that combines the power of high angular resolution with a broad X-ray bandpass to provide the necessary leap in capabilities to address the important astrophysical questions of the next decade. HEX-P achieves breakthrough performance by combining technologies developed by experienced international partners. To meet the science goals, the payload consists of a suite of co-aligned X-ray telescopes designed to cover the 0.2-80 keV bandpass. The High Energy Telescope (HET) has an effective bandpass of 2-80 keV, and the Low Energy Telescope (LET) has an effective bandpass of 0.2-20 keV. HEX-P will be launched into L1 to enable high observing efficiency, and the combination of bandpass and high observing efficiency delivers a powerful platform for broad science to serve a wide community. The baseline mission is 5 years, with 30% of the observing time dedicated to the PI-led program and 70% to a General Observer (GO) program. The General Observer program will be executed along with the PI-led program. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
229. NuSTAR Observation of Energy Release in 11 Solar Microflares.
- Author
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Duncan, Jessie, Glesener, Lindsay, Grefenstette, Brian W., Vievering, Juliana, Hannah, Iain G., Smith, David M., Krucker, Säm, White, Stephen M., and Hudson, Hugh
- Subjects
- *
SOLAR flares , *BLOOD volume , *HARD X-rays , *NON-thermal plasmas , *OPTICS - Abstract
Solar flares are explosive releases of magnetic energy. Hard X-ray (HXR) flare emission originates from both hot (millions of Kelvin) plasma and nonthermal accelerated particles, giving insight into flare energy release. The Nuclear Spectroscopic Telescope ARray (NuSTAR) utilizes direct-focusing optics to attain much higher sensitivity in the HXR range than that of previous indirect imagers. This paper presents 11 NuSTAR microflares from two active regions (AR 12671 on 2017 August 21 and AR 12712 on 2018 May 29). The temporal, spatial, and energetic properties of each are discussed in context with previously published HXR brightenings. They are seen to display several "large flare" properties, such as impulsive time profiles and earlier peak times in higher-energy HXRs. For two events where the active region background could be removed, microflare emission did not display spatial complexity; differing NuSTAR energy ranges had equivalent emission centroids. Finally, spectral fitting showed a high-energy excess over a single thermal model in all events. This excess was consistent with additional higher-temperature plasma volumes in 10/11 microflares and only with an accelerated particle distribution in the last. Previous NuSTAR studies focused on one or a few microflares at a time, making this the first to collectively examine a sizable number of events. Additionally, this paper introduces an observed variation in the NuSTAR gain unique to the extremely low livetime (<1%) regime and establishes a correction method to be used in future NuSTAR solar spectral analysis. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
230. Ground calibration of the spatial response and quantum efficiency of the CdZnTe hard x-ray detectors for NuSTAR
- Author
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Burger, Arnold, James, Ralph B., Fiederle, Michael, Franks, Larry, Payne, Stephen A., Grefenstette, Brian W., Bhalerao, Varun, Cook, W. Rick, Harrison, Fiona A., Kitaguchi, Takao, Madsen, Kristin K., Mao, Peter H., Miyasaka, Hiromasa, and Rana, Vikram
- Published
- 2017
- Full Text
- View/download PDF
231. THE BROADBAND XMM-NEWTON AND NuSTAR X-RAY SPECTRA OF TWO ULTRALUMINOUS X-RAY SOURCES IN THE GALAXY IC 342.
- Author
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Rana, Vikram, Harrison, Fiona A., Bachetti, Matteo, Walton, Dominic J., Furst, Felix, Barret, Didier, Miller, Jon M., Fabian, Andrew C., Boggs, Steven E., Christensen, Finn C., Craig, William W., Grefenstette, Brian W., Hailey, Charles J., Madsen, Kristin K., Ptak, Andrew F., Stern, Daniel, Webb, Natalie A., and Zhang, William W.
- Subjects
GALAXIES ,ACCRETION disks ,ACCRETION (Astrophysics) ,BLACK holes ,BINARY stars - Abstract
We present results for two ultraluminous X-ray sources (ULXs), IC 342 X-1 and IC 342 X-2, using two epochs of XMM-Newton and NuSTAR observations separated by ∼7 days. We observe little spectral or flux variability above 1 keV between epochs, with unabsorbed 0.3-30 keV luminosities being erg s
–1 for IC 342 X-1 and 7.40 ± 0.20 × 1039 erg s–1 for IC 342 X-2, so that both were observed in a similar, luminous state. Both sources have a high absorbing column in excess of the Galactic value. Neither source has a spectrum consistent with a black hole binary in low/hard state, and both ULXs exhibit strong curvature in their broadband X-ray spectra. This curvature rules out models that invoke a simple reflection-dominated spectrum with a broadened iron line and no cutoff in the illuminating power-law continuum. X-ray spectrum of IC 342 X-1 can be characterized by a soft disk-like blackbody component at low energies and a cool, optically thick Comptonization continuum at high energies, but unique physical interpretation of the spectral components remains challenging. The broadband spectrum of IC 342 X-2 can be fit by either a hot (3.8 keV) accretion disk or a Comptonized continuum with no indication of a seed photon population. Although the seed photon component may be masked by soft excess emission unlikely to be associated with the binary system, combined with the high absorption column, it is more plausible that the broadband X-ray emission arises from a simple thin blackbody disk component. Secure identification of the origin of the spectral components in these sources will likely require broadband spectral variability studies. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
232. Constraints on Axionlike Particles from a Hard X-Ray Observation of Betelgeuse.
- Author
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Mengjiao Xiao, Perez, Kerstin M., Giannotti, Maurizio, Straniero, Oscar, Mirizzi, Alessandro, Grefenstette, Brian W., Roach, Brandon M., and Nynka, Melania
- Subjects
- *
HARD X-rays , *GALACTIC magnetic fields , *X-rays , *MAGNETIC fields , *PARTICLES - Abstract
We use the first observation of Betelgeuse in hard x rays to perform a novel search for axionlike particles (ALPs). Betelgeuse is not expected to be a standard source of x rays, but light ALPs produced in the stellar core could be converted back into photons in the Galactic magnetic field, producing a detectable flux that peaks in the hard x-ray band (Eγ>10 keV). Using a 50 ks observation of Betelgeuse by the NuSTAR satellite telescope, we find no significant excess of events above the expected background. Using models of the regular Galactic magnetic field in the direction of Betelgeuse, we set a 95% C.L. upper limit on the ALP-photon coupling of gaγ<(0.5-1.8)×10-11 GeV-1 (depending on magnetic field model) for ALP masses ma<(5.5-3.5)×10-11 eV. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
233. THE NUCLEAR SPECTROSCOPIC TELESCOPE ARRAY (NuSTAR) HIGH-ENERGY X-RAY MISSION
- Author
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Fiona A. Harrison, William W. Craig, Finn E. Christensen, Charles J. Hailey, William W. Zhang, Steven E. Boggs, Daniel Stern, W. Rick Cook, Karl Forster, Paolo Giommi, Brian W. Grefenstette, Yunjin Kim, Takao Kitaguchi, Jason E. Koglin, Kristin K. Madsen, Peter H. Mao, Hiromasa Miyasaka, Kaya Mori, Matteo Perri, Michael J. Pivovaroff, Simonetta Puccetti, Vikram R. Rana, Niels J. Westergaard, Jason Willis, Andreas Zoglauer, Hongjun An, Matteo Bachetti, Nicolas M. Barrière, Eric C. Bellm, Varun Bhalerao, Nicolai F. Brejnholt, Felix Fuerst, Carl C. Liebe, Craig B. Markwardt, Melania Nynka, Julia K. Vogel, Dominic J. Walton, Daniel R. Wik, David M. Alexander, Lynn R. Cominsky, Ann E. Hornschemeier, Allan Hornstrup, Victoria M. Kaspi, Greg M. Madejski, Giorgio Matt, Silvano Molendi, David M. Smith, John A. Tomsick, Marco Ajello, David R. Ballantyne, Mislav Baloković, Didier Barret, Franz E. Bauer, Roger D. Blandford, W. Niel Brandt, Laura W. Brenneman, James Chiang, Deepto Chakrabarty, Jerome Chenevez, Andrea Comastri, Francois Dufour, Martin Elvis, Andrew C. Fabian, Duncan Farrah, Chris L. Fryer, Eric V. Gotthelf, Jonathan E. Grindlay, David J. Helfand, Roman Krivonos, David L. Meier, Jon M. Miller, Lorenzo Natalucci, Patrick Ogle, Eran O. Ofek, Andrew Ptak, Stephen P. Reynolds, Jane R. Rigby, Gianpiero Tagliaferri, Stephen E. Thorsett, Ezequiel Treister, C. Megan Urry, Massachusetts Institute of Technology. Department of Physics, MIT Kavli Institute for Astrophysics and Space Research, Chakrabarty, Deepto, Harrison Fiona, A., Craig William, W., Christensen Finn, E., Hailey Charles, J., Zhang William, W., Boggs Steven, E., Stern, Daniel, Cook W., Rick, Forster, Karl, Giommi, Paolo, Grefenstette Brian, W., Kim, Yunjin, Kitaguchi, Takao, Koglin Jason, E., Madsen Kristin, K., Mao Peter, H., Miyasaka, Hiromasa, Mori, Kaya, Perri, Matteo, Pivovaroff Michael, J., Puccetti, Simonetta, Rana Vikram, R., Westergaard Niels, J., Willis, Jason, Zoglauer, Andrea, An, Hongjun, Bachetti, Matteo, Barriere Nicolas, M., Bellm Eric, C., Bhalerao, Varun, Brejnholt Nicolai, F., Fuerst, Felix, Liebe Carl, C., Markwardt Craig, B., Nynka, Melania, Vogel Julia, K., Walton Dominic, J., Wik Daniel, R., Alexander David, M., Cominsky Lynn, R., Hornschemeier Ann, E., Hornstrup, Allan, Kaspi Victoria, M., Madejski Greg, M., Matt, Giorgio, Molendi, Silvano, Smith David, M., Tomsick John, A., Ajello, Marco, Ballantyne David, R., Balokovic, Mislav, Barret, Didier, Bauer Franz, E., Blandford Roger, D., Brandt W., Niel, Brenneman Laura, W., Chiang, Jame, Chenevez, Jerome, Comastri, Andrea, Dufour, Francoi, Elvis, Martin, Fabian Andrew, C., Farrah, Duncan, Fryer Chris, L., Gotthelf Eric, V., Grindlay Jonathan, E., Helfand David, J., Krivonos, Roman, Meier David, L., Miller Jon, M., Natalucci, Lorenzo, Ogle, Patrick, Ofek Eran, O., Ptak, Andrew, Reynolds Stephen, P., Rigby Jane, R., Tagliaferri, Gianpiero, Thorsett Stephen, E., Treister, Ezequiel, and Urry C., Megan
- Subjects
media_common.quotation_subject ,Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Collimated light ,law.invention ,Telescope ,X-rays ,Primary (astronomy) ,Observatory ,law ,Spectral resolution ,Astrophysics::Galaxy Astrophysics ,media_common ,Physics ,Spacecraft ,business.industry ,Astrophysics::Instrumentation and Methods for Astrophysics ,Astronomy ,Astronomy and Astrophysics ,Space vehicles ,Space and Planetary Science ,Sky ,Astrophysics::Earth and Planetary Astrophysics ,Orbit (control theory) ,business ,Instruments - Abstract
The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 2012 June 13, is the first focusing high-energy X-ray telescope in orbit. NuSTAR operates in the band from 3 to 79 keV, extending the sensitivity of focusing far beyond the ~10 keV high-energy cutoff achieved by all previous X-ray satellites. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than 100-fold improvement in sensitivity over the collimated or coded mask instruments that have operated in this bandpass. Using its unprecedented combination of sensitivity and spatial and spectral resolution, NuSTAR will pursue five primary scientific objectives: (1) probe obscured active galactic nucleus (AGN) activity out to the peak epoch of galaxy assembly in the universe (at z[< over ~]2) by surveying selected regions of the sky; (2) study the population of hard X-ray-emitting compact objects in the Galaxy by mapping the central regions of the Milky Way; (3) study the non-thermal radiation in young supernova remnants, both the hard X-ray continuum and the emission from the radioactive element [superscript 44]Ti; (4) observe blazars contemporaneously with ground-based radio, optical, and TeV telescopes, as well as with Fermi and Swift, to constrain the structure of AGN jets; and (5) observe line and continuum emission from core-collapse supernovae in the Local Group, and from nearby Type Ia events, to constrain explosion models. During its baseline two-year mission, NuSTAR will also undertake a broad program of targeted observations. The observatory consists of two co-aligned grazing-incidence X-ray telescopes pointed at celestial targets by a three-axis stabilized spacecraft. Deployed into a 600 km, near-circular, 6° inclination orbit, the observatory has now completed commissioning, and is performing consistent with pre-launch expectations. NuSTAR is now executing its primary science mission, and with an expected orbit lifetime of 10 yr, we anticipate proposing a guest investigator program, to begin in late 2014., United States. National Aeronautics and Space Administration (Contract NNG08FD06C)
- Published
- 2013
234. 3C 273 WITHNuSTAR: UNVEILING THE ACTIVE GALACTIC NUCLEUS
- Author
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Dominic J. Walton, Karl Forster, William W. Craig, Andrew C. Fabian, Giorgio Matt, Fiona A. Harrison, Charles J. Hailey, Brian W. Grefenstette, Greg Madejski, S. E. Boggs, Laura Brenneman, Finn Erland Christensen, Matteo Guainazzi, Felix Fürst, Daniel Stern, Kristin K. Madsen, Krzysztof Nalewajko, William W. Zhang, Roland Walter, David R. Ballantyne, Madsen, Kristin K., Fürst, Felix, Walton, Dominic J., Harrison, Fiona A., Nalewajko, Krzysztof, Ballantyne, David R., Boggs, Steve E., Brenneman, Laura W., Christensen, Finn E., Craig, William W., Fabian, Andrew C., Forster, Karl, Grefenstette, Brian W., Guainazzi, Matteo, Hailey, Charles J., Madejski, Greg M., Matt, Giorgio, Stern, Daniel, Walter, Roland, and Zhang, William W.
- Subjects
Physics ,Nuclear and High Energy Physics ,Photon ,Active galactic nucleus ,Astrophysics::High Energy Astrophysical Phenomena ,Extrapolation ,Astronomy and Astrophysics ,Quasar ,Astrophysics ,individual (3C 273) [X-rays] ,Power law ,Accretion (astrophysics) ,Spectral line ,Space and Planetary Science ,individual (3C 273) [quasars] ,Fermi Gamma-ray Space Telescope - Abstract
We present results from a 244 ks NuSTAR observation of 3C 273 obtained during a cross-calibration campaign with the Chandra, INTEGRAL, Suzaku, Swift, and XMM-Newton observatories. We show that the spectrum, when fit with a power-law model using data from all observatories except INTEGRAL over the 1-78 keV band, leaves significant residuals in the NuSTAR data between 30 and 78 keV. The NuSTAR 3-78 keV spectrum is well. described by an exponentially cutoff power law (Γ = 1.646± 0.006, Ecutoff = 202-34 +51 keV) with a weak reflection component from cold, dense material. There is also evidence for a weak (EW = 23 ± 11 eV) neutral iron line. We interpret these features as arising from coronal emission plus reflection off an accretion disk or distant material. Beyond 80 keV INTEGRAL data show clear excess flux relative to an extrapolation of the active galactic nucleus model fit to NuSTAR. This high-energy power. law is consistent with the presence of a beamed jet, which begins to dominate over emission from the inner accretion flow at 30-40 keV. Modeling the jet locally (in the NuSTAR + INTEGRAL band) as a power. law, we find that the coronal component is fit by ΓAGN = 1.638 ± 0.045, Ecutoff = 47 ± 15 keV, and jet photon index by Γjet = 1.05 ± 0.4. We also consider Fermi/LAT observations of 3C 273, and here the broadband spectrum of the jet can be described by a log-parabolic model, peaking at ∼ 2 MeV. Finally, we investigate the spectral variability in the NuSTAR band and find an inverse correlation between flux and Gamma.
- Published
- 2015
235. New Star Observations with NuSTAR : Flares from Young Stellar Objects in the ρ Ophiuchi Cloud Complex in Hard X-Rays.
- Author
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Vievering JT, Glesener L, Grefenstette BW, and Smith DM
- Abstract
We study the structure and dynamics of extreme flaring events on young stellar objects (YSOs) observed in hard X-rays by the Nuclear Spectroscopic Telescope Array ( NuSTAR ). During 2015 and 2016, NuSTAR made three observations of the star-forming region ρ Ophiuchi, each with an exposure ~50 ks. NuSTAR offers unprecedented sensitivity above ~7 keV, making this data set the first of its kind. Through improved coverage of hard X-rays, it is finally possible to directly measure the high-energy thermal continuum for hot plasmas and to sensitively search for evidence of nonthermal emission from YSO flares. During these observations, multiple flares were observed, and spectral and timing analyses were performed on three of the brightest flares. By fitting an optically thin thermal plasma model to each of these events, we found flare plasma heated to high temperatures (~40-80 MK) and determined that these events are ~1000 times brighter than the brightest flares observed on the Sun. Two of the studied flares showed excess emission at 6.4 keV, and this excess may be attributable to iron fluorescence in the circumstellar disk. No clear evidence for a nonthermal component was observed, but upper limits on nonthermal emission allow for enough nonthermal energy to account for the estimated thermal energy in the flare on protostar IRS 43, which is consistent with the standard model for solar and stellar flares.
- Published
- 2019
- Full Text
- View/download PDF
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