Fermi Science Support Center

Papers Relevant to Fermi Science - Week of October 18, 2010

Title: Cosmic Ray e+/(e- + e+) and pbar/p Ratios Explained by an Injection Model Based on Gamma-ray Observations
Authors: T. Kamae (1), S.-H. Lee (1), L. Baldini (2), F. Giordano (3,4), M.-H. Grondin (5), L. Latronico (2), M. Lemoine-Goumard (5), C. Sgró (2), T. Tanaka (1), Y. Uchiyama (1) ((1) KIPAC and SLAC National Accelerator Laboratory, Stanford University, (2) Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, (3) Dipartimento di Fisica "M. Merlin" dell'Universita e del Politecnico di Bari, (4) Istituto Nazionale di Fisica Nucleare, Sezione di Bari, (5) Université Bordeaux 1, CNRS/IN2p3, Centre d'Études Nucleaires de Bordeaux Gradignan)
Comments: Submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present a model of cosmic ray injection into the Galactic space based on recent γ-ray observations of supernova remnants (SNRs) and pulsar wind nebulae (PWNe) by the Fermi Large Area Telescope and atmospheric Cherenkov telescopes. Steady-state (SS) injection of nuclear particles and electrons (e-) from the Galactic ensemble of SNRs, and electrons and positrons (e+) from the Galactic ensemble of PWNe are assumed, with their spectra deduced from γ-ray observations and recent evolution models. The ensembles of SNRs and PWNe are assumed to share the same spatial distributions and the secondary CR production in dense molecular clouds interacting with SNRs is incorporated in the model. Propagation of CRs to Earth is calculated using GALPROP with 2 source distributions and 2 Galaxy halo sizes. We show that this observation-based model reproduces the positron fraction e+/(e- + e+) and antiproton-to-proton ratio reported by PAMELA reasonably well without calling for new sources. Significant discrepancy is found, however, between our model and the e- + e+ spectrum measured by Fermi below ∼ 20GeV. Important quantities for Galactic CRs, including their energy injection, average lifetime, and mean gas density along their typical propagation path are also presented.

arXiv: 1010.3477

Title: X-ray pulsations from the radio-quiet gamma-ray pulsar in CTA 1
Authors: P.A. Caraveo, A. De Luca, M. Marelli, G.F. Bignami, P.S. Ray, P.M. Saz-Parkinson, G. Kanbach
Comments: 19 pages, 4 figures. Accepted for publication in ApJ Letters
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Prompted by the Fermi LAT discovery of a radio-quiet gamma-ray pulsar inside the CTA 1 supernova remnant, we obtained a 130 ks XMM-Newton observation to assess the timing behavior of this pulsar. Exploiting both the unprecedented photon harvest and the contemporary Fermi LAT timing measurements, a 4.7σ single peak pulsation is detected, making PSR J0007+7303 the second example, after Geminga, of a radio-quiet gamma-ray pulsar also seen to pulsate in X-rays. Phase-resolved spectroscopy shows that the off-pulse portion of the light curve is dominated by a power-law, non-thermal spectrum, while the X-ray peak emission appears to be mainly of thermal origin, probably from a polar cap heated by magnetospheric return currents, pointing to a hot spot varying throughout the pulsar rotation.

arXiv: 1010.4167

Title: Cosmic rays of leptons from Pulsars and Supernova Remnants
Authors: Roberto A. Lineros (University of Torino and INFN/Torino)
Comments: 6 pages, 1 figures, Proceeding for the Conference on Cosmic Rays for Particle and Astroparticle Physics, CRICATPP 2010, Como, Italy
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

The latest results from PAMELA and FERMI experiments confirm the necessity to improve theoretical models of production and propagation of galactic electrons and positrons. There are many possible explanations for the positron excess observed at energies larger than 10 GeV and for some features around 1 TeV in the total flux of electrons and positrons. Supernovae are astrophysical objects with the potential to explain these observations. In this work, we present an updated study of the astrophysical sources of lepton cosmic rays and the possible and the possible explanation of the anomalies in terms of astrophysical sources.

arXiv: 1010.4200

Title: PSRs J0248+6021 and J2240+5832: Young Pulsars in the Northern Galactic Plane. Discovery, Timing, and Gamma-ray observations
Authors: G. Theureau, D. Parent, I. Cognard, G. Desvignes, D. A. Smith, J. M. Casandjian, C. C. Cheung, H. A. Craig, D. Donato, R. Foster, L. Guillemot, A. K. Harding, J.-F. Lestrade, P. S. Ray, R. W. Romani, D. J. Thompson, W. W. Tian, K. Watters
Comments: 13 pages, Accepted to Astronomy & Astrophysics
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Pulsars PSR J0248+6021 (rotation period P=217 ms and spin-down power Edot = 2.13E35 erg s-1) and PSR J2240+5832 (P=140 ms, Edot = 2.12E35 erg s-1) were discovered in 1997 with the Nancay radio telescope during a northern Galactic plane survey, using the Navy-Berkeley Pulsar Processor (NBPP) filter bank. GeV gamma-ray pulsations from both were discovered using the Fermi Large Area Telescope. Twelve years of radio and polarization data allow detailed investigations. The two pulsars resemble each other both in radio and in gamma-ray data. Both are rare in having a single gamma-ray pulse offset far from the radio peak. The high dispersion measure for PSR J0248+6021 (DM = 370 pc cm-3) is most likely due to its being within the dense, giant HII region W5 in the Perseus arm at a distance of 2 kpc, not beyond the edge of the Galaxy as obtained from models of average electron distributions. Its high transverse velocity and the low magnetic field along the line-of-sight favor this small distance. Neither gamma-ray, X-ray, nor optical data yield evidence for a pulsar wind nebula surrounding PSR J0248+6021. The gamma-ray luminosity for PSR J0248+6021 is Lγ = (1.4 ± 0.3) x 1034 erg s-1. For PSR J2240+5832, we find either Lγ = (7.9 ± 5.2) x 1034 erg s-1 if the pulsar is in the Outer arm, or Lγ = (2.2 ± 1.7) x 1034 erg s-1 for the Perseus arm. These luminosities are consistent with an Lγ ∝ √Edot rule. Comparison of the gamma-ray pulse profiles with model predictions, including the constraints obtained from radio polarization data, favor emission in the far magnetosphere. These two pulsars differ mainly in their inclination angles and acceleration gap widths, which in turn explains the observed differences in the gamma-ray peak widths.

arXiv: 1010.4230

Title: Evidence for gamma-ray emission from the low-mass X-ray binary system FIRST J102347.6+003841
Authors: P.H. Thomas Tam, Chung-Yue Hui, Regina H.H. Huang, Albert K.H. Kong, Jumpei Takata, Lupin C.C. Lin, Y.J. Yang, K.S. Cheng, Ronald E. Taam
Comments: 10 pages, 3 figures, 2 tables, ApJ Letters, in press
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The low-mass X-ray binary (LMXB) system FIRST J102347.6+003841 hosts a newly born millisecond pulsar (MSP) PSR J1023+0038 that was revealed as the first and only known rotation-powered MSP in a quiescent LMXB. While the system is shown to have an accretion disk before 2002, it remains unclear how the accretion disk has been removed in order to reveal the radio pulsation in 2007. In this Letter, we report the discovery of γ-rays spatially consistent with FIRST J102347.6+003841, at a significance of 7 standard deviations, using data obtained by the Fermi Gamma-ray Space Telescope. The γ-ray spectrum can be described by a power law (PL) with a photon index of 2.9±0.2, resulting in an energy flux above 200 MeV of 5.3+3.0-2.0x10-12 erg cm-2 s-1. The γ-rays likely originate from the MSP PSR J1023+0038, but also possibly from an intrabinary shock between the pulsar and its companion star. To complement the γ-ray study, we also re-investigate the XMM-Newton data taken in 2004 and 2008. Our X-ray spectral analysis suggests that a broken PL with two distinct photon indices describes the X-ray data significantly better than a single PL. This indicates that there exists two components and that both components appear to vary with the orbital phase. The evidence for γ-ray emission conforms with a recent suggestion that γ-rays from PSR J1023+0038 may be responsible for ejecting the disk material out of the system.

arXiv: 1010.4311

Title: The first gamma-ray outburst of a Narrow-Line Seyfert 1 Galaxy: the case of PMN J0948+0022 in July 2010
Authors: L. Foschini, G. Ghisellini, Y.Y. Kovalev, M.L. Lister, F. D'Ammando, D.J. Thompson, A. Tramacere, E. Angelakis, D. Donato, A. Falcone, L. Fuhrmann, M. Hauser, Yu.A. Kovalev, K. Mannheim, L. Maraschi, W. Max-Moerbeck, I. Nestoras, V. Pavlidou, T.J. Pearson, A.B. Pushkarev, A.C.S. Readhead, J.L. Richards, M.A. Stevenson, G. Tagliaferri, O. Tibolla, F. Tavecchio, S. Wagner
Comments: 8 pages, 7 figures, 2 tables. Submitted to MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

We report on a multiwavelength campaign on the radio-loud Narrow-Line Seyfert 1 (NLS1) Galaxy PMN J0948+0022 (z=0.5846) performed in 2010 July-September and triggered by a high-energy γ-ray outburst observed by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. The peak flux in the 0.1-100 GeV energy band exceeded, for the first time in this type of source, the value of ∼ 10-6 ph cm-2 s-1, corresponding to an observed luminosity of ∼ 1048 erg s-1. Although the source was too close to the Sun position to organize a densely sampled follow-up, it was possible to gather some multiwavelength data that confirmed the state of high activity across the sampled electromagnetic spectrum. The comparison of the spectral energy distribution of the NLS1 PMN J0948+0022 with that of a typical blazar – like 3C 273 – shows that the power emitted at γ rays is extreme.

arXiv: 1010.4434

Title: Detection of a Thermal Spectral Component in the Prompt Emission of GRB 100724B
Authors: Sylvain Guiriec, Valerie Connaughton, Michael S. Briggs, Michael Burgess, Felix Ryde, Frédéric Daigne, Peter Mészáros, Adam Goldstein, Julie McEnery, Nicola Omodei, P.N. Bhat, Elisabetta Bissaldi, Ascensión Camero-Arranz, Vandiver Chaplin, Roland Diehl, Gerald Fishman, Suzanne Foley, Melissa Gibby, Misty M. Giles, Jochen Greiner, David Gruber, Andreas von Kienlin, Marc Kippen, Chryssa Kouveliotou, Sheila McBreen, Charles A. Meegan, William Paciesas, Robert Preece, Arne Rau, Dave Tierney, Alexander J. van der Horst, Colleen Wilson-Hodge
Comments: 6 pages, 3 figures, 1 table, Submitted for publication in the Astrophysical Journal Letters, October 20, 2010
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Observations of GRB 100724B with the Fermi Gamma-Ray Burst Monitor (GBM) find that the spectrum is dominated by the typical Band functional form, which is usually taken to represent a non-thermal emission component, but also includes a very significant thermal spectral contribution. The simultaneous observation of the thermal and non-thermal components allows us to confidently identify the two emission components. The fact that these seem to vary independently favors the idea that the thermal component is of photospheric origin while the dominant non-thermal emission occurs at larger radii. Our results imply either a very high efficiency for the non-thermal process, or a very small size of the region at the base of the flow, both quite challenging for the standard fireball model. These problems are resolved if the jet is initially highly magnetized and has a substantial Poynting flux.

arXiv: 1010.4601