Wik D.R.,NASA |
Wik D.R.,Johns Hopkins University |
Lehmer B.D.,NASA |
Lehmer B.D.,Johns Hopkins University |
And 23 more authors.
Astrophysical Journal | Year: 2014
Prior to the launch of NuSTAR, it was not feasible to spatially resolve the hard (E > 10 keV) emission from galaxies beyond the Local Group. The combined NuSTAR data set, comprised of three ∼165 ks observations, allows spatial characterization of the hard X-ray emission in the galaxy NGC 253 for the first time. As a follow up to our initial study of its nuclear region, we present the first results concerning the full galaxy from simultaneous NuSTAR, Chandra, and Very Long Baseline Array monitoring of the local starburst galaxy NGC 253. Above ∼10 keV, nearly all the emission is concentrated within 100″ of the galactic center, produced almost exclusively by three nuclear sources, an off-nuclear ultraluminous X-ray source (ULX), and a pulsar candidate that we identify for the first time in these observations. We detect 21 distinct sources in energy bands up to 25 keV, mostly consisting of intermediate state black hole X-ray binaries. The global X-ray emission of the galaxy - dominated by the off-nuclear ULX and nuclear sources, which are also likely ULXs - falls steeply (photon index ≳3) above 10 keV, consistent with other NuSTAR-observed ULXs, and no significant excess above the background is detected at E > 40 keV. We report upper limits on diffuse inverse Compton emission for a range of spatial models. For the most extended morphologies considered, these hard X-ray constraints disfavor a dominant inverse Compton component to explain the γ-ray emission detected with Fermi and H.E.S.S. If NGC 253 is typical of starburst galaxies at higher redshift, their contribution to theE > 10 keV cosmic X-ray background is <1%. © 2014. The American Astronomical Society. All rights reserved. Source
Lehmer B.D.,Johns Hopkins University |
Lehmer B.D.,NASA |
Tyler J.B.,NASA |
Tyler J.B.,Catholic University of America |
And 19 more authors.
Astrophysical Journal | Year: 2015
We present nearly simultaneous Chandra and NuSTAR observations of two actively star-forming galaxies within 50 Mpc: NGC 3256 and NGC 3310. Both galaxies are significantly detected by both Chandra and NuSTAR, which together provide the first-ever spectra of these two galaxies spanning 0.3-30 keV. The X-ray emission from both galaxies is spatially resolved by Chandra; we find that hot gas dominates the E < 1-3 keV emission while ultraluminous X-ray sources (ULXs) provide majority contributions to the emission at E > 1-3 keV. The NuSTAR galaxy-wide spectra of both galaxies follow steep power-law distributions with Γ ≈ 2.6 at E > 5-7 keV. Using new and archival Chandra data, we search for signatures of heavily obscured or low luminosity active galactic nuclei (AGNs). We find that both NGC 3256 and NGC 3310 have X-ray detected sources coincident with nuclear regions; however, the steep NuSTAR spectra of both galaxies restricts these sources to be either low luminosity AGNs (L2-10 keV/LEdd ≲ 10-5) or non-AGNs in nature (e.g., ULXs or crowded X-ray sources that reach L2-10 keV ∼ 1040 erg s-1 cannot be ruled out). Combining our constraints on the 0.3-30 keV spectra of NGC 3256 and NGC 3310 with equivalent measurements for nearby star-forming galaxies M83 and NGC 253, we analyze the star formation rate (SFR) normalized spectra of these starburst galaxies. The spectra of all four galaxies show sharply declining power-law slopes at energies above 3-6 keV primarily due to ULX populations. Our observations therefore constrain the average spectral shape of galaxy-wide populations of luminous accreting binaries (i.e., ULXs). Interestingly, despite a completely different galaxy sample selection, emphasizing here a range of SFRs and stellar masses, these properties are similar to those of super-Eddington accreting ULXs that have been studied individually in a targeted NuSTAR ULX program. We also find that NGC 3310 exhibits a factor of ≈3-10 elevation of X-ray emission over the other star-forming galaxies due to a corresponding overabundance of ULXs. We argue that the excess of ULXs in NGC 3310 is most likely explained by the relatively low metallicity of the young stellar population in this galaxy, a property that is expected to produce an excess of luminous X-ray binaries for a given SFR. © 2015. The American Astronomical Society. All rights reserved. Source
Lehmer B.D.,Johns Hopkins University |
Lehmer B.D.,NASA |
Wik D.R.,NASA |
Hornschemeier A.E.,NASA |
And 19 more authors.
Astrophysical Journal | Year: 2013
We present results from three nearly simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR) and Chandra monitoring observations between 2012 September 2 and 2012 November 16 of the local star-forming galaxy NGC 253. The 3-40 keV intensity of the inner ∼20 arcsec (∼400 pc) nuclear region, as measured by NuSTAR, varied by a factor of ∼2 across the three monitoring observations. The Chandra data reveal that the nuclear region contains three bright X-ray sources, including a luminous (L2-10 keV ∼ few × 1039 erg s-1) point source located ∼1 arcsec from the dynamical center of the galaxy (within the 3σ positional uncertainty of the dynamical center); this source drives the overall variability of the nuclear region at energies ≳3 keV. We make use of the variability to measure the spectra of this single hard X-ray source when it was in bright states. The spectra are well described by an absorbed (NH ≈ 1.6 × 1023 cm-2) broken power-law model with spectral slopes and break energies that are typical of ultraluminous X-ray sources (ULXs), but not active galactic nuclei (AGNs). A previous Chandra observation in 2003 showed a hard X-ray point source of similar luminosity to the 2012 source that was also near the dynamical center (θ ≈ 0.4 arcsec); however, this source was offset from the 2012 source position by ≈1 arcsec. We show that the probability of the 2003 and 2012 hard X-ray sources being unrelated is ≫99.99% based on the Chandra spatial localizations. Interestingly, the Chandra spectrum of the 2003 source (3-8 keV) is shallower in slope than that of the 2012 hard X-ray source. Its proximity to the dynamical center and harder Chandra spectrum indicate that the 2003 source is a better AGN candidate than any of the sources detected in our 2012 campaign; however, we were unable to rule out a ULX nature for this source. Future NuSTAR and Chandra monitoring would be well equipped to break the degeneracy between the AGN and ULX nature of the 2003 source, if again caught in a high state. © 2013. The American Astronomical Society. All rights reserved.. Source
Ceyhan O.,University of Luxembourg |
Marcolli M.,Mathematics and Astronomy
Advances in Theoretical and Mathematical Physics | Year: 2014
This paper continues our previous study of Feynman integrals in configuration spaces and their algebro-geometric and motivic aspects. We consider here both massless and massive Feynman amplitudes, from the point of view of potential theory. We consider a variant of the wonderful compactification of configuration spaces that works simultaneously for all graphs with a given number of vertices and that also accounts for the external structure of Feynman graph. As in our previous work, we consider two version of the Feynman amplitude in configuration space, which we refer to as the real and complex versions. In the real version, we show that we can extend to the massive case a method of evaluating Feynman integrals, based on expansion in Gegenbauer polynomials, that we investigated previously in the massless case. In the complex setting, we show that we can use algebro-geometric methods to renormalize the Feynman amplitudes, so that the renormalized values of the Feynman integrals are given by periods of a mixed Tate motive. The regularization and renormalization procedure is based on pulling back the form to the wonderful compactification and replace it with a cohomologous one with logarithmic poles. A complex of forms with logarithmic poles, endowed with an operator of pole subtraction, determine a Rota-Baxter algebra on the wonderful compactifications. We can then apply the renormalization procedure via Birkhoff factorization, after interpreting the regularization as an algebra homomorphism from the Connes- Kreimer Hopf algebra of Feynman graphs to the Rota-Baxter algebra. We obtain in this setting a description of the renormalization group. We also extend the period interpretation to the case of Dirac fermions and gauge bosons. © 2014 International Press. Source
The Royal Swedish Academy of Sciences has announced the recipients of the 2016 Crafoord Prizes in Mathematics and Astronomy. The Crafoord Prize in Mathematics has been awarded to Yakov Eliashberg of Stanford University “for the development of contact and symplectic topology and groundbreaking discoveries of rigidity and flexibility phenomena.” The 2016 Crafoord Prize in Astronomy has been awarded to Roy Kerr of the University of Canterbury, Christchurch, New Zealand and to Roger Blandford of Stanford University “for fundamental work on rotating black holes and their astrophysical consequences.” The prize money is 6 million Swedish kronor per prize, and the Crafoord Prize in Astronomy is shared equally between the Laureates. The Royal Swedish Academy of Sciences, founded in 1739, is an independent organization whose overall objective is to promote the sciences and to strengthen their influence in society. The Academy states that it “takes special responsibility for the natural sciences and mathematics, but endeavors to promote the exchange of ideas between various disciplines.” The Academy awarded the Crafoord Prize for the first time in 1982 after receiving “a considerable donation” from the Lund industrialist Holger Crafoord and his wife Anna-Greta in 1980. This donation forms the basis of the Anna-Greta and Holger Crafoord Fund, whose aims are “to promote pure research in mathematics and astronomy, biosciences (in the first place ecology), geosciences and polyarthritis (rheumatoid arthritis).” These disciplines are chosen so as to complement those for which the Nobel Prizes are awarded. The prize sum of SEK 6 million makes the Crafoord one of the world´s largest scientific prizes. The international prize is awarded for one field per year in a fixed order to researchers who have made decisive contributions within their fields: Since 2012, there have been two separate prizes in astronomy and mathematics awarded at the same time. The prize in polyarthritis is awarded only when a special committee has shown that scientific progress in this field has been such that an award is justified. The laureates are announced in mid-January each year, and the prize is presented in April/May on “Crafoord Day." It is received from the hand of His Majesty the King of Sweden. In connection with Crafoord Day, a symposium in the discipline in question is arranged by the Royal Swedish Academy of Sciences. The Academy reports that Russian-American mathematician Yakov Eliashberg is one of the leading mathematicians of our time. For more than 30 years, he has helped to shape and research a field of mathematics known as symplectic geometry, and one of its branches in particular — symplectic topology. Eliashberg has solved many of the most important problems in the field and has found new and surprising results. He has further developed the techniques he used in contact geometry, a twin theory to symplectic geometry. While symplectic geometry deals with spaces with two, four or other even dimensions, contact theory describes spaces with odd dimensions. Both theories are closely related to current developments in modern physics, such as string theory and quantum field theory. Symplectic geometry’s link to physics has old roots. For example, it describes the geometry of a space in a mechanical system, the space phase. For a moving object, its trajectory is determined each moment by its position and velocity. Together, they determine a surface element that is the basic structure of symplectic geometry. The geometry describes the directions in which the system can develop; it describes movement. Physics becomes geometry. One of Eliashberg’s first, and perhaps most surprising, results was the discovery that there are regions where symplectic geometry is rigid and other regions where it is completely flexible. But where the boundary is between the flexible and the rigid regions, and how it can be described mathematically, is still a question awaiting an answer. Yakov Eliashberg was born in 1946 in St. Petersburg, Russia. He receiced his Ph.D. at Leningrad State University 1972. Eliashberg is the Herald L. and Caroline L. Ritch Professor of mathematics at Stanford University. The Academy explains in a background piece for this year’s prize that black holes are the source of the universe’s most powerful radiation, as well as of jets that can stretch many thousands of light years out into space. Roger Blandford’s theoretical work deals with the violent processes behind these phenomena. Roy Kerr laid the foundation for this research early on, when he discovered a mathematical description of rotating black holes. This became one of the most important theoretical discoveries in modern cosmology. The prediction of black holes is one of the perhaps strangest results of the general theory of relativity. When Albert Einstein finally presented his theory, in November 1915, he described gravity as a geometric property of space and time, spacetime. All objects with mass bend spacetime; they create a pit into which smaller objects can fall. The greater the mass, the deeper the pit. The mass of a black hole is so great that nothing that ends up in there can escape, not even light. It was not until 1963 that mathematician Roy Kerr succeeded in solving Einstein’s equations for rotating black holes. That the holes should rotate is feasible because the stars from which they originated should have rotated. At about the same time, astronomers discovered galaxies that emitted light and other electromagnetic radiation that was so strong it outshone several hundred ordinary galaxies. They were named quasars. Nothing other than a black hole could give the quasars their luminosity. So how is the strong light of rotating black holes created? This question was answered by Roger Blandford and his colleagues in the 1970s. Ever since, he has refined and made more realistic models of how gas surrounding a black hole flows towards it, is heated up and transforms some of its gravitational energy to radiation. While this is happening, electrically charged particles are sent millions of kilometers into space in the form of powerful jets. The source of all of this power is the rotational energy of the massive black hole. Roy Kerr was born in 1934 in Gore, New Zeeland. He received his Ph.D. in 1959 at the University of Cambridge. Kerr is an Emeritus Professor at the University of Canterbury, New Zeeland. Roger Blandford was born in 1949 in Grantham, Great Britain. He received his Ph.D. in 1974 at the University of Cambridge. Blandford is Luke Blossom Professor in the School of Humanities and Sciences, at Stanford University.