Fermi Science Support Center

Papers Relevant to Fermi Science - Week of March 14, 2011

Title: Constraining the Milky Way Dark Matter Density Profile with Gamma-Rays with Fermi-LAT
Authors: Nicolas Bernal (Bonn U.), Sergio Palomares-Ruiz (Lisbon, CFTP-IST)
Comments: 28 pages, 7 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

We study the abilities of the Fermi-LAT instrument on board of the Fermi mission to simultaneously constrain the Milky Way dark matter density profile and some dark matter particle properties, as annihilation cross section, mass and branching ratio into dominant annihilation channels. A single dark matter density profile is commonly assumed to determine the capabilities of gamma-ray experiments to extract dark matter properties or to set limits on them. However, our knowledge of the Milky Way halo is far from perfect, and thus in general, the obtained results are too optimistic. Here, we study the effect these astrophysical uncertainties would have on the determination of dark matter particle properties and conversely, we show how gamma-ray searches could also be used to learn about the structure of the Milky Way halo, as a complementary tool to other type of observational data that study the gravitational effect caused by the presence of dark matter. In addition, we also show how these results would improve if external information on the annihilation cross section and on the local dark matter density were included and compare our results with the predictions from numerical simulations.

arXiv: 1103.2377

Title: The bright unidentified gamma-ray source 1FGL J1227.9-4852: Can it be associated with an LMXB?
Authors: A. B. Hill, A. Szostek, S. Corbel, F. Camilo, R. H. D. Corbet, R. Dubois, G. Dubus, P. G. Edwards, E. C. Ferrara, M. Kerr, E. Koerding, D. Kozieł, Ł. Stawarz
Comments: Accepted for publication in MNRAS; 9 pages, 8 figures, 2 tables
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

We present an analysis of high energy (HE; 0.1-300 GeV) γ-ray observations of 1FGL J1227.9-4852 with the Fermi Gamma-ray Space Telescope, follow-up radio observations with the Australia Telescope Compact Array, Giant Metrewave Radio Telescope and Parkes radio telescopes of the same field and follow-up optical observations with the ESO VLT. We also examine archival XMM-Newton and INTEGRAL X-ray observations of the region around this source. The γ-ray spectrum of 1FGL J1227.9-4852 is best fit with an exponentially cutoff power-law, reminiscent of the population of pulsars observed by Fermi. A previously unknown, compact radio source within the 99.7% error circle of 1FGL J1227.9-4852 is discovered and has a morphology consistent either with an AGN core/jet structure or with two roughly symmetric lobes of a distant radio galaxy. A single bright X-ray source XSS J12270-4859, a low-mass X-ray binary, also lies within the 1FGL J1227.9-4852 error circle and we report the first detection of radio emission from this source. The potential association of 1FGL J1227.9-4852 with each of these counterparts is discussed. Based upon the available data we find the association of the γ-ray source to the compact double radio source unlikely and suggest that XSS J12270-4859 is a more likely counterpart to the new HE source. We propose that XSS J12270-4859 may be a millisecond binary pulsar and draw comparisons with PSR J1023+0038.

arXiv: 1103.2637

Title: Constraining pulsar gap models with the light-curve and flux properties of the gamma-ray pulsar population
Authors: Marco Pierbattista, Isabelle Grenier, Alice Harding, Peter L. Gonthier
Comments: 4 pages, 3 figures, to appear in the proceedings of the Pulsar 2010 Conference, Italy, 10 - 15 October 2010
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

We compare population synthesis results for inner and outer magnetosphere emission models with the various characteristics measured in the first LAT pulsar catalogue for both the radio-loud and radio-weak or radio-quiet γ-ray pulsars. We show that all models fail to reproduce the observations: for each model there is a lack of luminous and energetic objects that suggest a non dipolar magnetic field structure or spin-down evolution. The large dispersion that we find in the simulated gamma-ray luminosity versus spin-down power relation does not allow to use the present trend seen in the Fermi data to distinguish among models. For each model and each Fermi detected pulsar, we have generated light curves as a function of obliquity and inclination angles. The theoretical curves were fitted to the observed one, using a maximum-likelihood approach, to derive the best-fit orientations and to compare how well each model can reproduce the data. Including the radio light-curve gives an additional key constraint to restrict the orientation space

arXiv: 1103.2682

Title: WMAP7 and future CMB constraints on annihilating dark matter: implications on GeV-scale WIMPs
Authors: Gert Hütsi, Jens Chluba, Andi Hektor, Martti Raidal
Comments: 10 pages, 5 figures, will be submitted to A&A
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

Context We calculate constraints from current and future cosmic microwave background (CMB) measurements on annihilating dark matter (DM) with masses below the electroweak scale: mDM = 5-100 GeV. In particular, we focus our attention on the lower end of this mass range, as DM particles with masses mDM ~ 10 GeV have been recently claimed to be consistent with the CoGeNT and DAMA/LIBRA results, while also providing viable DM candidates to explain the measurements of Fermi and WMAP haze.
Aims We study the model (in)dependence of CMB spectrum on particle physics DM models, large scale structure formation and cosmological uncertainties. We attempt to find a simple and practical recipe for estimating current and future CMB bounds on a broad class of DM annihilation models.
Results We show that in the studied DM mass range the CMB signal of DM annihilations is independent of the details of large scale structure formation, distribution and profile of DM halos and other cosmological uncertainties. All particle physics models of DM annihilation can be described with only one parameter, the fraction of energy carried away by neutrinos in DM annihilation. As the main result we provide a simple and rather generic fitting formula for calculating CMB constraints on the annihilation cross section of light WIMPs. We show that thermal relic DM in the CoGeNT, DAMA favoured mass range is in a serious conflict with present CMB data for the annihilation channels with few neutrinos, and will definitely be tested by the Planck mission for all possible DM annihilation channels. Also, our findings strongly disfavor the claim that thermal relic DM annihilations with mDM ~ 10 GeV and ⟨σAυ⟩ ~ 9x10-25 cm3 s-1 could be a cause for Fermi and WMAP haze.

arXiv: 1103.2766

Title: Discovery of GeV gamma-ray emission from PSR B1259-63/SS 2883
Authors: P. H. Thomas Tam, Regina H. H. Huang, Jumpei Takata, C. Y. Hui, Albert K. H. Kong, K. S. Cheng
Comments: submitted to ApJ Letters
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The binary system PSR B1259-63/SS 2883 consists of a 47.8 ms radio pulsar that orbits the companion Be star with a period of 3.4 years in a highly eccentric orbit. The system is well sampled in radio, X-rays, and TeV γ-rays, and shows orbital-phase-dependent variability in all observed frequencies. Here we report on the discovery of >100 MeV γ-rays from PSR B1259-63/SS 2883 through the 2010 pariastron passage. Using data collected with the Large Area Telescope aboard Fermi from 33 days before pariastron to 75 days after pariastron, PSR B1259-63/SS 2883 is detected at a significance of 13.6 standard deviations. The γ-ray light curve is highly variable over the above period, with changing photon index that correlates with γ-ray flux. In particular, two major flares that occur after the pariastron passage were observed. The onset of γ-ray emission occurs close to, but not at the same orbital phases as, the two disk passages that occur ~1 month before and ~1 month after the pariastron passage. The fact that the GeV orbital light curve is different from that of the X-ray and TeV light curves strongly suggests that GeV γ-ray emission originates from a different component. We speculate that the observed GeV flares may be resulting from Doppler boosting effects.

arXiv: 1103.3129

Title: Gamma-ray observations of the Be/pulsar binary 1A 0535+262 during a giant X-ray outburst
Authors: VERITAS collaboration: V. A. Acciari, E. Aliu, M. Araya, T. Arlen, T. Aune, M. Beilicke, W. Benbow, S. M. Bradbury, J. H. Buckley, V. Bugaev, K. Byrum, A. Cannon, A. Cesarini, L. Ciupik, E. Collins-Hughes, W. Cui, R. Dickherber, C. Duke, A. Falcone, J. P. Finley, L. Fortson, A. Furniss, N. Galante, D. Gall, S. Godambe, S. Griffin, R. Guenette, G. Gyuk, D. Hanna, J. Holder, G. Hughes, C. M. Hui, T. B. Humensky, A. Imran, P. Kaaret, M. Kertzman, H. Krawczynski, F. Krennrich, A. S. Madhavan, G. Maier, P. Majumdar, S. McArthur, P. Moriarty, R. A. Ong, A. N. Otte, D. Pandel, N. Park, J. S. Perkins, M. Pohl, H. Prokoph, J. Quinn, K. Ragan, L. C. Reyes, P. T. Reynolds, E. Roache, H. J. Rose, D. B. Saxon, G. H. Sembroski, G. Demet Senturk, A. W. Smith, G. Tešić, M. Theiling, S. Thibadeau, et al. (12 additional authors not shown)
Comments: 28 pages, 4 figures; accepted by The Astrophysical Journal
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Giant X-ray outbursts, with luminosities of about 1037 erg s-1, are observed roughly every 5 years from the nearby Be/pulsar binary 1A 0535+262. In this article, we present observations of the source with VERITAS at very-high energies (VHE; E>100 GeV) triggered by the X-ray outburst in December 2009. The observations started shortly after the onset of the outburst, and they provided comprehensive coverage of the episode, as well as the 111-day binary orbit. No VHE emission is evident at any time. We also examined data from the contemporaneous observations of 1A 0535+262 with the Fermi/LAT at high energy photons (HE; E>0.1 GeV) and failed to detect the source at GeV energies. The X-ray continua measured with the Swift/XRT and the RXTE/PCA can be well described by the combination of blackbody and Comptonized emission from thermal electrons. Therefore, the gamma-ray and X-ray observations suggest the absence of a significant population of non-thermal particles in the system. This distinguishes 1A~0535+262 from those Be X-ray binaries (such as PSR B1259-63 and LS I +61°303) that have been detected at GeV-TeV energies. We discuss the implications of the results on theoretical models.

arXiv: 1103.3250

Title: Extragalactic Very-High-Energy gamma-ray background
Authors: A.Neronov, D.V.Semikoz
Comments: 8 pages, 6 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

We study extragalactic very-high-energy (VHE) diffuse gamma-ray background in 10-400 GeV energy range using the data of Fermi telescope. To estimate the background level, we count VHE photons at high Galactic latitudes |b| > 60°. Subtracting photons associated to known sources and the residual cosmic ray and Galactic diffuse backgrounds, we estimate the VHE Extragalactic Gamma-ray Background (EGB) flux. We find that the spectrum of VHE EGB closely follows the stacked spectrum of BL Lacs. LAT data reveal positive (1+z)k, 1<k<4 cosmological evolution of BL Lac source population consistent with that of their parent population, FR I radio galaxies. We show that EGB at E>10 GeV could be completely explained by emission from unresolved BL Lacs if k~3.

arXiv: 1103.3484

Title: Constraining emissivity of ultrahigh energy cosmic rays in the distant universe with the diffuse gamma-ray emission
Authors: Xiang-Yu Wang, Ruo-Yu Liu, Felix Aharnonian
Comments: 8 pages, 8 figures, submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Ultra-high cosmic rays (UHECRs) with energies >1019 eV emitted at cosmological distances will be attenuated by cosmic microwave and infrared background radiation through photohadronic processes. Lower energy extra-galactic cosmic rays (~1018-1019 eV) can only travel a linear distance smaller than ~Gpc in a Hubble time due to the diffusion if the extra-galactic magnetic fields are as strong as nano Gauss. These prevent us from directly observing most of the UHECRs in the universe, and thus the observed UHECR intensity reflects only the emissivity in the nearby universe within hundreds of Mpc. However, UHECRs in the distant universe, through interactions with the cosmic background photons, produce UHE electrons and gamma-rays that in turn initiate electromagnetic cascades on cosmic background photons. This secondary cascade radiation forms part of the extragalactic diffuse GeV-TeV gamma-ray radiation and, unlike the original UHECRs, is observable. Motivated by new measurements of extragalactic diffuse gamma-ray background radiation by Fermi/LAT, we obtained upper limits placed on the UHECR emissivity in the distant universe by requiring that the cascade radiation they produce not exceed the observed levels. By comparison with the gamma-ray emissivity of candidate UHECR sources (such as GRBs and AGNs) at high-redshifts, we find that the obtained upper limit for a flat proton spectrum is ~101.5 times larger than the gamma-ray emissivity in GRBs and ~10 times smaller than the gamma-ray emissivity in BL Lac objects. In the case of iron nuclei composition, the derived upper limits of UHECR emissivity is a factor of 3-5 times higher. Robust upper limit on the cosmogenic neutrino flux is further obtained, which is marginally reachable by the Icecube detector and the next-generation detector JEM-EUSO.

arXiv: 1103.3574