Fermi Gamma-ray Space Telescope

Papers Relevant to Fermi Science - Week of July 11, 2011

Title: Where will supersymmetric dark matter first be seen?
Authors: L. Gao, C. S. Frenk, A. Jenkins, V. Springel, S. D. M. White
Comments: 6 pages, 3 figure, submitted to MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

If the dark matter consists of supersymmetric particles, γ-ray observatories such as the Fermi satellite may detect annihilation radiation from the haloes of galaxies and galaxy clusters. Much recent effort has been devoted to searching for this signal around the Milky Way's dwarf satellites. Using a new suite of high-resolution simulations of galaxy cluster haloes (the Phoenix Project), together with the Aquarius simulations of Milky-Way-like galaxy haloes, we show that higher signal-to-noise and equally clean signals are, in fact, predicted to come from nearby rich galaxy clusters. Most of the cluster emission is produced by small subhaloes with masses less than that of the Sun. The large range of mass scales covered by our two sets of simulations allows us to deduce a physically motivated extrapolation to these small (and unresolved) masses. Since tidal effects destroy subhaloes in the dense inner regions of haloes, most cluster emission is then predicted to come from large radii, implying that the nearest and brightest systems should be much more extended than Fermi's angular resolution limit. The most promising targets for detection are clusters such as Coma and Fornax, but detection algorithms must be tuned to the predicted profile of the emission if they are to maximize the chance of finding this weak signal.

arXiv: 1107.1916
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Title: Fermi/GBM Observations of SGR J0501+4516 Bursts
Authors: Lin Lin, Chryssa Kouveliotou, Matthew G. Baring, Alexander J. van der Horst, Sylvain Guiriec, Peter M. Woods, Ersin Gogus, Yuki Kaneko, Jeffrey Scargle, Jonathan Granot, Robert Preece, Andreas von Kienlin, Vandiver Chaplin, Anna L. Watts, Ralph A.M.J. Wijers, Shuang Nan Zhang, Narayan Bhat, Mark H. Finger, Neil Gehrels, Alice Harding, Lex Kaper, Victoria Kaspi, Julie Mcenery, Charles A. Meegan, William S. Paciesas, Asaf Pe'er, Enrico Ramirez-Ruiz, Michiel van der Klis, Stefanie Wachter, Colleen Wilson-Hodge
Comments: accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present our temporal and spectral analyses of 29 bursts from SGR J0501+4516, detected with the Gamma-ray Burst Monitor onboard the Fermi Gamma-ray Space Telescope during the 13 days of the source activation in 2008 (August 22 to September 3). We find that the T90 durations of the bursts can be fit with a log-normal distribution with a mean value of ~ 123 ms. We also estimate for the first time event durations of Soft Gamma Repeater (SGR) bursts in photon space (i.e., using their deconvolved spectra) and find that these are very similar to the T90s estimated in count space (following a log-normal distribution with a mean value of ~ 124 ms). We fit the time-integrated spectra for each burst and the time-resolved spectra of the five brightest bursts with several models. We find that a single power law with an exponential cutoff model fits all 29 bursts well, while 18 of the events can also be fit with two black body functions. We expand on the physical interpretation of these two models and we compare their parameters and discuss their evolution. We show that the time-integrated and time-resolved spectra reveal that Epeak decreases with energy flux (and fluence) to a minimum of ~30 keV at F=8.7x10-6 erg cm-2 s-1, increasing steadily afterwards. Two more sources exhibit a similar trend: SGRs J1550-5418 and 1806-20. The isotropic luminosity, Liso corresponding to these flux values is roughly similar for all sources (0.4-1.5x1040 erg s-1).

arXiv: 1107.2121
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Title: Quasi -Periodic Pulsations in Solar Flares: new clues from the Fermi Gamma-Ray Burst Monitor
Authors: D. Gruber, P. Lachowicz, E. Bissaldi, M.S. Briggs, V. Connaughton, J. Greiner, A. J. van der Horst, G. Kanbach, A. Rau, P. N. Bhat, R. Diehl, A. von Kienlin, R. M. Kippen, C. A. Meegan, W. S. Paciesas, R. D. Preece, C. Wilson-Hodge
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In the last four decades it has been observed that solar flares show quasi-periodic pulsations (QPPs) from the lowest, i.e. radio, to the highest, i.e. gamma-ray, part of the electromagnetic spectrum. To this day, it is still unclear which mechanism creates such QPPs. In this paper, we analyze four bright solar flares which show compelling signatures of quasi-periodic behavior and were observed with the Gamma-Ray Burst Monitor (GBM) onboard the Fermi satellite. Because GBM covers over 3 decades in energy (8 keV to 40 MeV) it can be a key instrument to understand the physical processes which drive solar flares. We tested for periodicity in the time series of the solar flares observed by GBM by applying a classical periodogram analysis. However, contrary to previous authors, we did not detrend the raw light curve before creating the power spectral density spectrum (PSD). To assess the significance of the frequencies we made use of a method which is commonly applied for X-ray binaries and Seyfert galaxies. This technique takes into account the underlying continuum of the PSD which for all of these sources has a P(f) ~ f-α dependence and is typically labeled red-noise. We checked the reliability of this technique by applying it to a solar flare which was observed by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) which contains, besides any potential periodicity from the Sun, a 4 s rotational period due to the rotation of the spacecraft around its axis. While we do not find an intrinsic solar quasi-periodic pulsation we do reproduce the instrumental periodicity. Moreover, with the method adopted here, we do not detect significant QPPs in the four bright solar flares observed by GBM. We stress that for the purpose of such kind of analyses it is of uttermost importance to appropriately account for the red-noise component in the PSD of these astrophysical sources.

arXiv: 1107.2399
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Title: Constraints on Enhanced Dark Matter Annihilation from IceCube Results
Authors: Ivone F.M. Albuquerque, Leandro J. Beraldo e Silva, Carlos Pérez de los Heros
Comments: 10 pages, 4 figures
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Experiment (hep-ex)

Excesses on electromagnetic fluxes measured by ATIC, and the PAMELA and Fermi-LAT telescopes can be explained by dark matter annihilation in our Galaxy. However, this requires large boosts on the dark matter annihilation rate. There are many possible enhancement mechanisms, such as the Sommerfeld effect or the existence of dark matter clumps in our halo. If such enhancements are taking place, the dark matter annihilation in the core of the Earth should also be enhanced. Here we use IceCube 40 strings results in order to constrain large boosts. These constraints do not depend on the enhancement mechanism. We also determine the boost range that can be probed by the full IceCube telescope. Dark matter models which require annihilation enhancements of 100 or more and that annihilate significantly into neutrinos are excluded as the explanation for these excesses.

arXiv: 1107.2408
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Title: Dense DM clumps seeded by cosmic string loops and DM annihilation
Authors: V.S. Berezinsky, V.I. Dokuchaev, Yu.N. Eroshenko
Comments: 10 pages, 2 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The annihilation of the dark matter in clumps around cosmic string loops is studied. These clumps form at the radiation dominated stage and may have densities >>ρeq. We conclude that 100 GeV neutralino DM is incompatible with the range of the strings' tension 5x10-10 < Gμ/c2 < 5.1x10-9 because the gamma-ray signal exceeds the Fermi-LAT limit in this case.

arXiv: 1107.2751
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Title: Identification of γ-ray emission from 3C345 and NRAO512
Authors: F.K. Schinzel, K.V. Sokolovsky, F. D'Ammando, T.H. Burnett, W. Max-Moerbeck, C.C. Cheung, S.J. Fegan, J.M. Casandjian, L.C. Reyes, M. Villata, C.M. Raiteri, I. Agudo, O.J.A. Bravo Calle, D. Carosati, R. Casas, J.L. Gomez, M.A. Gurwell, H.Y. Hsiao, S.G. Jorstad, G. Kimeridze, T.S. Konstantinova, E.N. Kopatskaya, E. Koptelova, O.M. Kurtanidze, S.O. Kurtanidze, V.M. Larionov, E.G. Larionova, L.V. Larionova, A.P. Marscher, D.A. Morozova, M.G. Nikolashvili, M. Roca-Sogorb, J.A. Ros, L.A. Sigua, O. Spiridonova, I.S. Troitsky, V.V. Vlasyuk, A.P. Lobanov, J.A. Zensus
Comments: 11 pages, 5 figures, 5 tables, accepted for publication in A&A
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

For more than 15 years, since the days of the Energetic Gamma-Ray Experiment Telescope (EGRET) on board the Compton Gamma-Ray Observatory (CGRO; 1991-2000), it has remained an open question why the prominent blazar 3C 345 was not reliably detected at γ-ray energies ≥20 MeV. Recently a bright γ-ray source (0FGL J1641.4+3939/1FGL J1642.5+3947), potentially associated with 3C 345, was detected by the Large Area Telescope (LAT) on Fermi. Multiwavelength observations from radio bands to X-rays (mainly GASP-WEBT and Swift) of possible counterparts (3C 345, NRAO 512, B3 1640+396) were combined with 20 months of Fermi-LAT monitoring data (August 2008 - April 2010) to associate and identify the dominating γ-ray emitting counterpart of 1FGL J1642.5+3947. The source 3C 345 is identified as the main contributor for this γ-ray emitting region. However, after November 2009 (15 months), a significant excess of photons from the nearby quasar NRAO 512 started to contribute and thereafter was detected with increasing γ-ray activity, possibly adding flux to 1FGL J1642.5+3947. For the same time period and during the summer of 2010, an increase of radio, optical and X-ray activity of NRAO 512 was observed. No γ-ray emission from B3 1640+396 was detected.

arXiv: 1107.2926
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