GLAST and Dark Matter Substructure in the Milky Way

We discuss the possibility of GLAST detecting gamma-rays from the annihilation of neutralino dark matter in the Galactic halo. We have used "Via Lactea", currently the highest resolution simulation of Galactic cold dark matter substructure, to quantify the contribution of subhalos to the annihilation signal. We present a simulated allsky map of the expected gamma-ray counts from dark matter annihilation, assuming standard values of particle mass and cross section. In this case GLAST should be able to detect the Galactic center and several individual subhalos.Comment: 4 pages, 2 figures, to be published in "The Proceedings of the First International GLAST Symposium", February 5-8, 2007, Stanford University, AIP, Eds. S. Ritz, P.F. Michelson, and C. Meega

Observation of Scaling Violations in Scaled Momentum Distributions at HERA

Charged particle production has been measured in deep inelastic scattering (DIS) events over a large range of $x$ and $Q^2$ using the ZEUS detector. The evolution of the scaled momentum, $x_p$, with $Q^2,$ in the range 10 to 1280 $GeV^2$, has been investigated in the current fragmentation region of the Breit frame. The results show clear evidence, in a single experiment, for scaling violations in scaled momenta as a function of $Q^2$.Comment: 21 pages including 4 figures, to be published in Physics Letters B. Two references adde

Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope

Nearby clusters and groups of galaxies are potentially bright sources of high-energy gamma-ray emission resulting from the pair-annihilation of dark matter particles. However, no significant gamma-ray emission has been detected so far from clusters in the first 11 months of observations with the Fermi Large Area Telescope. We interpret this non-detection in terms of constraints on dark matter particle properties. In particular for leptonic annihilation final states and particle masses greater than ~200 GeV, gamma-ray emission from inverse Compton scattering of CMB photons is expected to dominate the dark matter annihilation signal from clusters, and our gamma-ray limits exclude large regions of the parameter space that would give a good fit to the recent anomalous Pamela and Fermi-LAT electron-positron measurements. We also present constraints on the annihilation of more standard dark matter candidates, such as the lightest neutralino of supersymmetric models. The constraints are particularly strong when including the fact that clusters are known to contain substructure at least on galaxy scales, increasing the expected gamma-ray flux by a factor of ~5 over a smooth-halo assumption. We also explore the effect of uncertainties in cluster dark matter density profiles, finding a systematic uncertainty in the constraints of roughly a factor of two, but similar overall conclusions. In this work, we focus on deriving limits on dark matter models; a more general consideration of the Fermi-LAT data on clusters and clusters as gamma-ray sources is forthcoming.Comment: accepted to JCAP, Corresponding authors: T.E. Jeltema and S. Profumo, minor revisions to be consistent with accepted versio

The Use of Weighting in Periodicity Searches in All-Sky Monitor Data: Applications to the GLAST LAT

The light curves produced by all-sky monitors, such as the Rossi X-ray Timing Explorer All-Sky Monitor and the Swift Burst Alert Telescope (BAT), generally have non-uniform error bars. In searching for periodic modulation in this type of data using power spectra it can be important to use appropriate weighting of data points to achieve the best sensitivity. It was recently demonstrated that for Swift BAT data a simple weighting scheme can actually sometimes reduce the sensitivity of the power spectrum depending on source brightness. Instead, a modified weighting scheme, based on the Cochran semi-weighted mean, gives improved results independent of source brightness. We investigate the benefits of weighting power spectra in period searches using simulated GLAST LAT observations of gamma-ray binaries.Comment: 2 pages. To appear in the Proceedings of the First International GLAST Symposium, Febuary 5-8, 2007, Stanford University, AIP, Eds. S. Ritz, P. F. Michelson, and C. Meega

Trans-Relativistic Supernovae, Circumstellar Gamma-Ray Bursts, and Supernova 1998bw

Supernova (SN) 1998bw and gamma-ray burst (GRB) 980425 offer the first direct evidence that supernovae are the progenitors of some GRBs. However, this burst was unusually dim, smooth and soft compared to other bursts with known afterglows. Whether it should be considered a prototype for cosmological GRBs depends largely on whether the supernova explosion and burst were asymmetrical or can be modeled as spherical. We address this question by treating the acceleration of the supernova shock in the outermost layers of the stellar envelope, the transition to relativistic flow, and the subsequent expansion (and further acceleration) of the ejecta into the surrounding medium. We find that GRB 980425 could plausibly have been produced by a collision between the relativistic ejecta from SN 1998bw and the star's pre-supernova wind; the model requires no significant asymmetry. This event therefore belongs to a dim subclass of GRBs and is not a prototype for jet-like cosmological GRBs.Comment: 5 pages, 2 figures, to appear in Gamma 2001, eds. S. Ritz, N. Gehrels, and C. Shrade

The Origin of Cosmic Rays and the Diffuse Galactic Gamma-Ray Emission

Cosmic-ray interactions with interstellar gas and photons produce diffuse gamma-ray emission. In this talk we will review the current understanding of this diffuse emission and its relationship to the problem of the origin of cosmic rays. We will discuss the open issues and what progress might be possible with GLAST, which is planned for launch in 2006.Comment: 10 pages, 5 figures. Invited talk at the "Gamma 2001" Symp., April 4-6, 2001, Baltimore, MD. AIP Conf. Proc. v.587, eds. S. Ritz, N. Gehrels, & C. R. Shrader, in pres

Discovery of a Pulsar Candidate Associated with the TeV Gamma-ray Source HESS J1813-178

We present a Chandra X-ray observation of G12.82-0.02, a shell-like radio supernova remnant coincident with the TeV gamma-ray source HESS J1813-178. We resolve the X-ray emission from the co-located ASCA source into a compact object surrounded by structured diffuse emission that fills the interior of the radio shell. The morphology of the diffuse emission strongly resembles that of a pulsar wind nebula. The spectrum of the compact source is well-characterized by a power-law with index approx. 1.3, typical of young and energetic rotation-powered pulsars. For a distance of 4.5 kpc, consistent with the X-ray absorption, the 2-10 keV X-ray luminosity of the putative pulsar and nebula is L(PSR) = 3.2E33 erg/s and L(PWN) = 1.4E34 erg/s, respectively. Both the flux ratio of L(PWN)/L(PSR) = 4.3 and the total luminosity of this system imply a pulsar spin-down power greater then 1E37 erg/s, on a par with the top ten most energetic young pulsars in the Galaxy. We associate the putative pulsar with the radio remnant and the TeV source and discuss the origin of the gamma-ray emission.Comment: 3 Pages, 3 Figures. Latex, aipproc.cls. To be published in "The Proceedings of the First International GLAST Symposium" (Held Febuary 5-8, 2007, Stanford Univ., USA), AIP, Eds. S. Ritz, P.F. Michelson, and C. Meegan. Updated coordinate

An AGN Identification for 3EG J2006-2321

We present a multiwavelength analysis of the high-energy gamma-ray source 3EG J2006-2321. The flux of this source above 100 MeV is shown to be variable on time scales of days and months. Optical observations and careful examination of archived radio data indicate that its radio counterpart is PMN J2005-2310, a flat-spectrum radio quasar with a 5-GHz flux density of 260 mJy. Study of the $V=18.7$ optical counterpart indicates a redshift of 0.833 and variable linear polarization. No X-ray source has been detected near the position of PMN J2005-2310, but an X-ray upper limit is derived from ROSAT data. This upper limit provides for a spectral energy distribution with global characteristics similar to those of known gamma-ray blazars. Taken together, these data indicate that 3EG J2006-2321, listed as unidentified in the 3rd EGRET Catalog, is a member of the blazar class of AGN. The 5-GHz radio flux density of this blazar is the lowest of the 68 EGRET-detected AGN. The fact that EGRET has detected such a source has implications for unidentified EGRET sources, particularly those at high latitudes ($|b|>30^{\circ}$), many of which may be blazars.Comment: 22 pages, 6 figures. To appear in ApJ v569 n1, 10 April 200

Gamma-Ray Pulsar Studies with GLAST

Some pulsars have their maximum observable energy output in the gamma-ray band, offering the possibility of using these high-energy photons as probes of the particle acceleration and interaction processes in pulsar magnetospheres. After an extended hiatus between satellite missions, the recently-launched AGILE mission and the upcoming Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) will allow gamma-ray tests of the theoretical models developed based on past discoveries. With its greatly improved sensitivity, better angular resolution, and larger energy reach than older instruments, GLAST LAT should detect dozens to hundreds of new gamma-ray pulsars and measure luminosities, light curves, and phase-resolved spectra with unprecedented resolution. It will also have the potential to find radio-quiet pulsars like Geminga, using blind search techniques. Cooperation with radio and X-ray pulsar astronomers is an important aspect of the LAT team's planning for pulsar studies.Comment: 8 pages, 5 figures. To appear in the proceedings of "40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17, 2007, McGill University, Montreal, Canad