385 research outputs found
A Search for Aperiodic Millisecond Variability in Cygnus X-1
No full textWe discuss a search for aperiodic millisecond variability in the integrated 1 to 25 keV X-ray region of Cyg X-1. We have examined HEAO A-1 archival data and RXTE guest observer data for indications of excess power above the Poisson noise #oor using the relative integral power analysis and the Fourier transform method. We present results that are in disagreement with the results of Meekins et al. #1984#. We attribute the discrepancy to an instrumental e#ect for which Meekins et al. #1984# did not apply a correction. With the correction we see no evidence for excess power above 25 Hz. Our analysis of RXTE data is in agreement with previously published results of di#erent data sets and shows no sign of excess power above 30 Hz. Submitted to Astrophysical Journal # Work supported by Department of Energy contract DE#AC03#76SF00515. A Search for Aperiodic Millisecond Variability in Cygnus X-1 C. Chaput 1 ,E.Bloom 1 , L. Cominsky 1;2 , G. Godfrey 1 , P. Hertz 3 ,J.Scargle 4 , ..
Constraining the p-Mode-g-Mode Tidal Instability with GW170817
No full textWe analyze the impact of a proposed tidal instability coupling p modes and g modes within neutron stars on GW170817. This nonresonant instability transfers energy from the orbit of the binary to internal modes of the stars, accelerating the gravitational-wave driven inspiral. We model the impact of this instability on the phasing of the gravitational wave signal using three parameters per star: An overall amplitude, a saturation frequency, and a spectral index. Incorporating these additional parameters, we compute the Bayes factor (lnB!pgpg) comparing our p-g model to a standard one. We find that the observed signal is consistent with waveform models that neglect p-g effects, with lnB!pgpg=0.03-0.58+0.70 (maximum a posteriori and 90% credible region). By injecting simulated signals that do not include p-g effects and recovering them with the p-g model, we show that there is a ≃50% probability of obtaining similar lnB!pgpg even when p-g effects are absent. We find that the p-g amplitude for 1.4 MâŠneutron stars is constrained to less than a few tenths of the theoretical maximum, with maxima a posteriori near one-Tenth this maximum and p-g saturation frequency ∼70 Hz. This suggests that there are less than a few hundred excited modes, assuming they all saturate by wave breaking. For comparison, theoretical upper bounds suggest a103 modes saturate by wave breaking. Thus, the measured constraints only rule out extreme values of the p-g parameters. They also imply that the instability dissipates a1051 erg over the entire inspiral, i.e., less than a few percent of the energy radiated as gravitational waves
Constraining the p-Mode–g-Mode tidal instability with GW170817
No full textWe analyze the impact of a proposed tidal instability coupling p modes and g modes within neutron stars on GW170817. This nonresonant instability transfers energy from the orbit of the binary to internal modes of the stars, accelerating the gravitational-wave driven inspiral. We model the impact of this instability on the phasing of the gravitational wave signal using three parameters per star: an overall amplitude, a saturation frequency, and a spectral index. Incorporating these additional parameters, we compute the Bayes factor (ln B pg !pg) comparing our p-g model to a standard one. We find that the observed signal is consistent with waveform models that neglect p-g effects, with ln B pg !pg = 0.03 +0.70 -0.58 (maximum a posteriori and 90% credible region). By injecting simulated signals that do not include p-g effects and recovering them with the p-g model, we show that there is a ?50% probability of obtaining similar ln B pg !pg even when p-g effects are absent. We find that the p-g amplitude for 1.4 ?M? neutron stars is constrained to less than a few tenths of the theoretical maximum, with maxima a posteriori near one-tenth this maximum and p-g saturation frequency ~70 Hz. This suggests that there are less than a few hundred excited modes, assuming they all saturate by wave breaking. For comparison, theoretical upper bounds suggest ?103 modes saturate by wave breaking. Thus, the measured constraints only rule out extreme values of the p-g parameters. They also imply that the instability dissipates ?10^51 erg over the entire inspiral, i.e., less than a few percent of the energy radiated as gravitational waves
Echoes from the companion star in Sco X-1
No full textWe present simultaneous X-ray (RXTE) and optical (ULTRACAM) narrow-band ( Bowen blend/He II and nearby continuum) observations of Sco X-1 at 2-10 Hz time resolution. We find that the Bowen/He II emission lags the X-ray light curves with a light traveltime of similar to 11-16 s which is consistent with reprocessing in the companion star. The echo from the donor is detected at orbital phase similar to 0.5 when Sco X-1 is at the top of the flaring branch (FB). Evidence of echoes is also seen at the bottom of the FB but with time-lags of 5-10 s which are consistent with reprocessing in an accretion disc with a radial temperature profile. We discuss the implication of our results for the orbital parameters of Sco X-1
Studies in the preparation of alkyl substituted thioxanthones and thioxanthenes
No full textIt has been the purpose of this investigation to study the Bethods of preparation of ethyl substituted thioxanthene. It was found that this compound cannot be prepared by application of the Friedel-Crafts Reaction at average experimental conditions. However, fusion of thiosalicylic acid with ethyl bengene under the dehydrating influence of concentrated sulfuric acid yields ethyl thioxanthone. By subsequent reduction of this keto compound, ethyl thioxanthene results. As a consequence of the failure to apply a substitution type reaction in order to synthesise etlyl thioxanthene, it can be said that thiaxanthene does not exhibit sronatio properties, at least not as far as the Friedel-Crafte Reaction is concerned.Chemistry, Department o
Compact objects in active galactic nuclei and X-ray binaries
No full textIn this thesis I study the inner-most regions of Active Galactic Nuclei (AGN) using
the reverberation mapping technique, and neutron star low-mass X-ray binaries in
quiescence using X-ray observations.
Using the 13-year optical monitoring data for the AGN NGC 5548, the luminosity dependence
of the Hβ emitting radius was modelled using a delay map, finding that
the radius scales with luminosity as predicted by recent theoretical models. Time-delays
between the continuum at different wavelengths in AGN can be used to probe the accretion
disc. Here, continuum time-delays in a sample of 14 AGN were used to measure the radial
temperature profile of the accretion discs, determine the nuclear extinction, and measure
distances to the objects. However, the distances measured correspond to a value for
Hubble's constant that is a factor of ~2 lower than the accepted value. The implications
of this on the thermal disc reprocessing model are discussed.
I present two Chandra observations of the neutron star transient in the globular
cluster NGC 6440 in quiescence, where the power-law component to the spectrum is seen
to be variable between the observations, suggesting that there is ongoing residual accretion.
From a Chandra observation of the globular cluster Terzan 1, I have identifed the likely
quiescent counterpart to a transient previously observed in outburst, and discuss the other
sources within the cluster. Using Chandra and XMM-Newton monitoring observations of
two neutron star transients (KS 1731-260 and MXB 1659-29) in quiescence I have found
that the neutron star crusts in both sources have now returned to thermal equilibrium
with the core. These observations also indicate that the crusts in both sources may have
a high thermal conductivity and that enhanced neutrino emission may be occurring in the
core. Finally, the discovery of an X-ray transient with XMM-Newton is presented, and the
other sources in this observation discussed
Very high energy cosmic gamma rays from radio and x-ray pulsars
No full textThis thesis is concerned with the detection of very high energy cosmic gamma-rays from isolated pulsars and X-ray binary sources using the atmospheric Cerenkov technique. A general introduction to gamma ray detection techniques is followed by adscription of the properties of atmospheric Cerenkov radiation and a discussion of the principles of the atmospheric Cerenkov technique. The Mark I and Mark II gamma-ray telescopes operated in Dugway, Utah by the University of Durham between 1981 and 1984 are briefly described. There follows a discussion of the results from observations at many different wavelengths of Cygnus X-3. This object was observed by the Durham group between 1981 and 1983 in Dugway Utah and also in Durham during autumn 1985. The detection in the Dugway data of the 4.8 hr X-ray period and the possible detection of a19.2 day intensity variation are considered. The discovery of a 12.59 ms pulsar in data taken on Cygnus X-3 in 1983 is described. Evidence is presented which suggests this periodicity is also present at a weaker level in earlier data and also in the data taken in Durham in 1985.Results from observations of PSR1937+21 , PSR1953+29and six radio pulsars , are presented. The design and construction of the Mark III telescope, now operating in Narrabri , N.S.W. , is described in detail. Preliminary results from observations with the Mark III telescope of three objects, LMC X-4, the Vela pulsar and CentaurusX-3, are presented, with particular reference to periodicities inherent in the sources. An observation of the supernova in the Large Magellanic Cloud is discussed. A brief discussion of the mechanisms by which V.H.E. gamma-rays may be produced in isolated pulsars and X-ray binary pulsars is given, followed by a description of the future prospects for the Mark III and Mark IV telescopes
High time resolution optical/X-ray cross-correlations for X-ray binaries : anticorrelations and rapid variability
No full textUsing simultaneous observations in X-rays and optical, we have performed a homogeneous analysis of the cross-correlation behaviours of four X-ray binaries: SWIFT J1753.5-0127, GX339-4, Sco X-1 and CygX-2. With high-time-resolution observations using ULTRACAM and RXTE, we concentrate on the short time-scale, delta t < 20 s, variability in these sources. Here we present our data base of observations, with three simultaneous energy bands in both the optical and the X-ray, and multiple epochs of observation for each source, all with similar to second or better time resolution. For the first time, we include a dynamical cross-correlation analysis, i.e. an investigation of how the cross-correlation function changes within an observation. We describe a number of trends which emerge. We include the full data set of results, and pick a few striking relationships from among them for further discussion.
We find, that the surprising form of X-ray/optical cross-correlation functions, a positive correlation signal preceded by an anticorrelation signal, is seen in all the sources at least some of the time. Such behaviour suggests a mechanism other than reprocessing as being the dominant driver of the short-term variability in the optical emission. This behaviour appears more pronounced when the X-ray spectrum is hard. Furthermore, we find that the cross-correlation relationships themselves are not stable in time, but vary significantly in strength and form. This all hints at dynamic interactions between the emitting components which could be modelled through non-linear or differential relationships
The Fermi Gamma Ray Space Telescope discovers the Pulsar in the Young Galactic Supernova-Remnant CTA 1
No full textA. A. Abdo, M. Ackermann, W. B. Atwood, L. Baldini, J. Ballet, G. Barbiellini, M. G. Baring, D. Bastieri, B. M. Baughman, K. Bechtol, R. Bellazzini, B. Berenji, R. D. Blandford, E. D. Bloom, G. Bogaert, E. Bonamente, A. W. Borgland, J. Bregeon, A. Brez, M. Brigida, P. Bruel, T. H. Burnett, G. A. Caliandro, R. A. Cameron, P. A. Caraveo, P. Carlson, J. M. Casandjian, C. Cecchi, E. Charles, A. Chekhtman, C. C. Cheung, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, L. R. Cominsky, J. Conrad, S. Cutini, D. S. Davis, C. D. Dermer, A. de Angelis, F. de Palma, S. W. Digel, M. Dormody, E. do Couto e Silva, P. S. Drell, R. Dubois, D. Dumora, Y. Edmonds, C. Farnier, W. B. Focke, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, D. Gasparrini, N. Gehrels, S. Germani, B. Giebels, N. Giglietto, F. Giordano, T. Glanzman, G. Godfrey, I. A. Grenier, M.-H. Grondin, J. E. Grove, L. Guillemot, S. Guiriec, A. K. Harding, R. C. Hartman, E. Hays, R. E. Hughes, G. Jóhannesson, A. S. Johnson, R. P. Johnson, T. J. Johnson, W. N. Johnson, T. Kamae, Y. Kanai, G. Kanbach, H. Katagiri, N. Kawai, M. Kerr, T. Kishishita, B. Kızıltan, J. Knödlseder, M. L. Kocian, N. Komin, F. Kuehn, M. Kuss, L. Latronico, M. Lemoine-Goumard, F. Longo, V. Lonjou, F. Loparco, B. Lott, M. N. Lovellette, P. Lubrano, M. Marelli, M. N. Mazziotta, J. E. McEnery, S. McGlynn, C. Meurer, P. F. Michelson, T. Mineo, W. Mitthumsiri, T. Mizuno, A. A. Moiseev, C. Monte, M. E. Monzani, A. Morselli, I. V. Moskalenko, S. Murgia, T. Nakamori, P. L. Nolan, E. Nuss, M. Ohno, T. Ohsugi, A. Okumura, N. Omodei, E. Orlando, J. F. Ormes, M. Ozaki, D. Paneque, J. H. Panetta, D. Parent, V. Pelassa, M. Pepe, M. Pesce-Rollins, G. Piano, L. Pieri, F. Piron, T. A. Porter, S. Rainò, R. Rando, P. S. Ray, M. Razzano, A. Reimer, O. Reimer, T. Reposeur, S. Ritz, L. S. Rochester, A. Y. Rodriguez, R. W. Romani, M. Roth, F. Ryde, H. F.-W. Sadrozinski, D. Sanchez, A. Sander, P. M. Saz Parkinson, T. L. Schalk, A. Sellerholm, C. Sgrò, E. J. Siskind, D. A. Smith, P. D. Smith, G. Spandre, P. Spinelli, J.-L. Starck, M. S. Strickman, D. J. Suson, H. Tajima, H. Takahashi, T. Takahashi, T. Tanaka, J. B. Thayer, J. G. Thayer, D. J. Thompson, S. E. Thorsett, L. Tibaldo, D. F. Torres, G. Tosti, A. Tramacere, T. L. Usher, A. Van Etten, N. Vilchez, V. Vitale, P. Wang, K. Watters, B. L. Winer, K. S. Wood, H. Yasuda, T. Ylinen, M. Ziegler
Contact authors: G. Kanbach, K. Wood, M. ZieglerEnergetic young pulsars and expanding blast waves (supernova remnants, SNRs) are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 ms, a period derivative of 3.614 x 10⁻¹³ s s⁻¹ . Its characteristic age of 104 years is comparable to that estimated for the SNR. It is conjectured that most unidentified Galactic gamma ray sources associated with star-forming regions and SNRs are such young pulsars.The Fermi LAT Collaboration acknowledges the generous support of a number of agencies and institutes that have supported the Fermi LAT Collaboration. These include the National Aeronautics and Space Administration and the Department of Energy in the
United States, the Commissariat à l'Energie Atomique and the Centre National de la echerche Scientifique / Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica
Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation and the
Swedish National Space Board in Sweden.https://escholarship.org/uc/item/1397g37
2FHL: THE SECOND CATALOG OF HARD FERMI-LAT SOURCES
No full textM. Ackermann, M. Ajello, W. B. Atwood, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, J. Becerra Gonzalez, R. Bellazzini, E. Bissaldi, R. D. Blandford, E. D. Bloom, R. Bonino, E. Bottacini, T. J. Brandt, J. Bregeon, P. Bruel, R. Buehler, S. Buson, G. A. Caliandro, R. A. Cameron, R. Caputo, M. Caragiulo, P. A. Caraveo, E. Cavazzuti, C. Cecchi, E. Charles, A. Chekhtman, C. C. Cheung, J. Chiang, G. Chiaro, S. Ciprini, J. M. Cohen, J. Cohen-Tanugi, L. R. Cominsky, J. Conrad, A. Cuoco, S. Cutini, F. D’Ammando, A. de Angelis, F. de Palma, R. Desiante, M. Di Mauro, L. Di Venere, A. Dominguez ́, P. S. Drell, C. Favuzzi, S. J. Fegan, E. C. Ferrara, W. B. Focke, P. Fortin, A. Franckowiak, Y. Fukazawa, S. Funk, A. K. Furniss, P. Fusco, F. Gargano, D. Gasparrini, N. Giglietto, P. Giommi, F. Giordano, M. Giroletti, T. Glanzman, G. Godfrey, I. A. Grenier, M.H. Grondin, L. Guillemot, S. Guiriec, A. K. Harding, E. Hays, J. W. Hewitt, A. B. Hill, D. Horan, G. Iafrate, Dieter Hartmann, T. Jogler, G. JÓhannesson, A. S. Johnson, T. Kamae, J. Kataoka, J. Knödlseder, M. Kuss, G. La Mura, S. Larsson, L. Latronico, M. Lemoine-Goumard, J. Li, L. Li,
F. Longo, F. Loparco, B. Lott, M. N. Lovellette, P. Lubrano, G. M. Madejski, S. Maldera, A. Manfreda, M. Mayer, M. N. Mazziotta, P. F. Michelson, N. Mirabal, W. Mitthumsiri, T. Mizuno, A. A. Moiseev, M. E. Monzani, A. Morselli, I. V. Moskalenko, S. Murgia, E. Nuss, T. Ohsugi, N. Omodei, M. Orienti, E. Orlando, J. F. Ormes, D. Paneque, J. S. Perkins, M. Pesce-Rollins, V. Petrosian, F. Piron, G. Pivato, T. A. Porter, S. Rainò, R. Rando, M. Razzano, S. Razzaque, A. Reimer, O. Reimer, T. Reposeur, R. W. Romani, M. Sánchez-Conde, P. M. Saz Parkinson, J. Schmid, A. Schulz, C. Sgrò, E. J. Siskind, F. Spada, G. Spandre, P. Spinelli, D. J. Suson, H. Tajima, H. Takahashi, M. Takahashi, T. Takahashi, J. B. Thayer, D. J. Thompson, L. Tibaldo, D. F. Torres, G. Tosti, E. Troja, G. Vianello, K. S. Wood, M. Wood, M. Yassine, G. Zaharijas, and S. Zimmer.We present a catalog of sources detected above 50 GeV by the Fermi-Large Area Telescope (LAT) in 80 months of data. The newly delivered Pass 8 event-level analysis allows the detection and characterization of sources in the 50 GeV–2 TeV energy range. In this energy band, Fermi-LAT has detected 360 sources, which constitute the second catalog of hard Fermi-LAT sources (2FHL). The improved angular resolution enables the precise localization of point sources (~1farcm7 radius at 68% C. L.) and the detection and characterization of spatially extended sources. We find that 86% of the sources can be associated with counterparts at other wavelengths, of which the majority (75%) are active galactic nuclei and the rest (11%) are Galactic sources. Only 25% of the 2FHL sources have been previously detected by Cherenkov telescopes, implying that the 2FHL provides a reservoir of candidates to be followed up at very high energies. This work closes the energy gap between the observations performed at GeV energies by Fermi-LAT on orbit and the observations performed at higher energies by Cherenkov telescopes from the ground.The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l’Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d’Études Spatiales in France. This research has made
use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.https://iopscience.iop.org/article/10.3847/0067-0049/222/1/5http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/ApJS/222/
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