Search Publications
Three-year Swift-BAT Survey of Active Galactic Nuclei: Reconciling Theory and Observations?
Greiner, J.; Merloni, A.; Comastri, A. +3 more
It is well accepted that unabsorbed as well as absorbed active galactic nuclei (AGNs) are needed to explain the nature and shape of the Cosmic X-ray background (CXB), even if the fraction of highly absorbed objects (dubbed Compton-thick sources) still substantially escapes detection. We derive and analyze the absorption distribution using a comple…
When a Standard Candle Flickers
Kouveliotou, Chryssa; Krimm, Hans A.; Kuulkers, Erik +28 more
The Crab Nebula is the only hard X-ray source in the sky that is both bright enough and steady enough to be easily used as a standard candle. As a result, it has been used as a normalization standard by most X-ray/gamma-ray telescopes. Although small-scale variations in the nebula are well known, since the start of science operations of the Fermi …
The Brightest Gamma-Ray Flaring Blazar in the Sky: AGILE and Multi-wavelength Observations of 3C 454.3 During 2010 November
Maraschi, L.; Sakamoto, T.; Pian, E. +84 more
Since 2005, the blazar 3C 454.3 has shown remarkable flaring activity at all frequencies, and during the last four years it has exhibited more than one γ-ray flare per year, becoming the most active γ-ray blazar in the sky. We present for the first time the multi-wavelength AGILE, Swift, INTEGRAL, and GASP-WEBT data collected in order to explain t…
Diffuse Emission Measurement with the SPectrometer on INTEGRAL as an Indirect Probe of Cosmic-Ray Electrons and Positrons
Jourdain, Elisabeth; Roques, Jean-Pierre; Bouchet, Laurent +3 more
Significant advances have been made in the understanding of the diffuse Galactic hard X-ray continuum emission using data from the INTEGRAL observatory. The diffuse hard power-law component seen with the SPectrometer on INTEGRAL (SPI) has been identified with inverse-Compton emission from relativistic (GeV) electrons on the cosmic microwave backgr…
Lifting the Veil on Obscured Accretion: Active Galactic Nuclei Number Counts and Survey Strategies for Imaging Hard X-Ray Missions
Rigby, J. R.; Treister, E.; Ballantyne, D. R. +2 more
Finding and characterizing the population of active galactic nuclei (AGNs) that produces the X-ray background (XRB) is necessary to connect the history of accretion to observations of galaxy evolution at longer wavelengths. The year 2012 will see the deployment of the first hard X-ray imaging telescope which, through deep extragalactic surveys, wi…
PTF 10bzf (SN 2010ah): A Broad-line Ic Supernova Discovered by the Palomar Transient Factory
Cenko, S. B.; Mitrofanov, I.; Bloom, J. S. +26 more
We present the discovery and follow-up observations of a broad-line Type Ic supernova (SN), PTF 10bzf (SN 2010ah), detected by the Palomar Transient Factory (PTF) on 2010 February 23. The SN distance is cong218 Mpc, greater than GRB 980425/SN 1998bw and GRB 060218/SN 2006aj, but smaller than the other SNe firmly associated with gamma-ray bursts (G…
Observation of Diffuse Cosmic and Atmospheric Gamma Rays at Balloon Altitudes with an Electron-tracking Compton Camera
Okada, Yoko; Hattori, Kaori; Nagayoshi, Tsutomu +13 more
We observed diffuse cosmic and atmospheric gamma rays at balloon altitudes with the Sub-MeV gamma-ray Imaging Loaded-on-balloon Experiment I (SMILE-I) as the first step toward a future all-sky survey with a high sensitivity. SMILE-I employed an electron-tracking Compton camera comprised of a gaseous electron tracker as a Compton-scattering target …
Eclipses during the 2010 Eruption of the Recurrent Nova U Scorpii
Maehara, Hiroyuki; Schaefer, Bradley E.; Worters, Hannah L. +34 more
The eruption of the recurrent nova U Scorpii on 2010 January 28 is now the all-time best observed nova event. We report 36,776 magnitudes throughout its 67 day eruption, for an average of one measure every 2.6 minutes. This unique and unprecedented coverage is the first time that a nova has had any substantial amount of fast photometry. With this,…
Discovery of an Energetic 38.5 ms Pulsar Powering the Gamma-ray Source IGR J18490-0000/HESS J1849-000
Gotthelf, E. V.; Terrier, R.; Halpern, J. P. +1 more
We report the discovery of a 38.5 ms X-ray pulsar in observations of the soft γ-ray source IGR J18490-0000 with the Rossi X-ray Timing Explorer (RXTE). PSR J1849-0001 is spinning down rapidly with period derivative 1.42 × 10-14 s s-1, yielding a spin-down luminosity \dot{E} = 9.8 × 1036 erg s-1, characte…
A Statistical Model for the γ-ray Variability of the Crab Nebula
Yuan, Qiang; Zhang, Bing; Wu, Xue-Feng +3 more
A statistical scenario is proposed to explain the γ-ray variability and flares of the Crab Nebula, which were observed recently by the Fermi/LAT. In this scenario electrons are accelerated in a series of knots, whose sizes follow a power-law distribution. These knots presumably move outward from the pulsar and have a distribution in the Doppler bo…