Spectral energy distribution of 1ES 2344+514. The high flux spectrum (triangles) are from VERITAS data on December 7, 2007 and Swift UVOT and XRT data on December 8, 2007. The time-averaged VERITAS spectrum and near-average flux level X-ray spectrum from Swift XRT and RXTE PCA data on January 1, 2008 are represented by circles. Non-contemporaneous VHE gamma-ray spectra are shown from MAGIC data in August to December 2005 (open squares) and from Whipple 10 m data on the flare night of December 20, 1995 (open triangles). All VHE gamma-ray spectra are corrected for absorption by the extragalactic background light (Franceschini et al. 2008). Archival millimeter fluxes (open diamonds) are from SCUBA data (Stevens & Gear 1999). The broadband curves are from synchrotron self-Compton (SSC) modeling to the contemporaneous data (Krawczynski et al. 2004).

1ES 2344+514

1ES 2344+514 is a nearby (z = 0.044) blazar , and was discovered at very high energy (VHE) gamma-rays energies ( >350 GeV) by the Whipple 10 m telescope during a 1 day flare on December 20, 1995. Blazars are active galactic nuclei (AGN) with a relativistic plasma jet oriented close to the line of sight. These objects exhibit rapid variability and have broadband spectral energy distributions (SEDs) characterized, in a νFν representation, by a synchrotron component extending from radio to X-ray frequencies, and a second component peaking at gamma-ray frequencies due to either inverse-Compton radiation or from hadronic processes.

VERITAS observed 1ES 2344+514 for 18 hours spread over 37 nights between October 4, 2007 and January 11, 2008. The total VERITAS signal has a statistical significance of >20 sigma. A strong VHE gamma-ray flare on December 7, 2007 was measured at F(>300 GeV) = (6.76 ± 0.62) * 10^-11 cm^-2 s¹, corresponding to 48% of the Crab Nebula flux. Excluding this flaring episode, nightly variability at lower fluxes was observed with a time-averaged mean of 7.6% of the Crab Nebula flux.

During the full period of VERITAS observations contemporaneous X-ray and UV data were taken with Swift and RXTE. Variability by a factor of ~7 is evident in the 2–10 keV flux between nightly observations. On December 8, 2007 the highest ever observed X-ray flux from 1ES 2344+514 was measured by Swift XRT. Evidence for a correlation between the X-ray flux and VHE gamma-ray flux on nightly time-scales is indicated with a Pearson correlation coefficient of r = 0.60 ± 0.11. Contemporanous spectral energy distributions (SEDs) of 1ES 2344+514 are presented for two distinct flux states. A one-zone synchrotron self-Compton (SSC) model describes both SEDs well.

For more information on the science of this object please contact Jeffrey Grube .

Very-high-energy gamma-ray emission from M87 during 2007-2008 (H.E.S.S, MAGIC & VERITAS). The regular gaps in the light curve correspond to phases of full moon during which no observations are possible. The vertical grey box indicates the time period of the strong flaring activity. Lower panel: Radio flux as measured with the VLBA from a region very close to the supermassive black hole in M87.

γ-rays from the Edge of a Supermassive Black Hole

High-resolution radio and gamma-ray observations reveal the site of relativistic particle acceleration in the galaxy M87

An international collaboration of 390 scientists reports the discovery of an outburst of very-high-energy (VHE) gamma radiation from the giant radio galaxy Messier 87 (M87), accompanied by a strong rise of the radio flux measured from the direct vicinity of its super-massive black hole. The combined results give first experimental evidence that particles are accelerated to extremely high energies of tera electron Volt (one electron Volt is the energy an electron or proton gains when it is accelerated by a voltage of one Volt) in the immediate vicinity of a supermassive black hole and then emit the observed gamma rays. The gamma rays have energies a trillion times higher than the energy of visible light. The large collaborative effort involved three arrays of 12-meter to 17-meter telescopes (VERITAS, MAGIC and H.E.S.S. ) that detect very high-energy gamma rays and the Very Long Baseline Array (VLBA) that detects radio waves with high spatial precision. The results will appear in the July 2 Science Express, the advance online publication of the journal Science.

"We had scheduled gamma-ray observations of M87 in a close cooperative effort with the three major gamma-ray observatories VERITAS, H.E.S.S. and MAGIC, and we were lucky that an extraordinary gamma-ray flare happened just when the source was observed with the VLBA and its impressive spatial resolving power," says Beilicke, working with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). "Only combining the high-resolution radio observations with the VHE gamma-ray observations allowed us to locate the site of the gamma-ray production," says Craig Walker, staff scientist at the National Radio Astronomy Observatory in Socorro, New Mexico.

For more information on the science of this object, please see Acciari et al., Science, 325, 444 (full text, http://arxiv.org/abs/0908.0511 ). You may also contact Matthias Beilicke.  

Light curve above 1 TeV from HESS J0632+057 is shown assuming a spectral shape of dn/dE ~ E^-Gamma with Gamma = 2.5. The downward pointing arrows show the 99% confidence limits derived here from the VERITAS data. The HESS fluxes are taken from Aharonian et al.(2007). The X-ray fluxes measured by XMM-Newton and Swift are indicated by open symbols.

HESS J0632+057

HESS J0632+057 is one of only two unidentified very-high-energy gamma-ray sources which appear to be point-like within experimental resolution. It is possibly associated with the massive Be star MWC 148 and has been suggested to resemble known TeV binary systems like LS I +61 303 or LS 5039 .

HESS J0632+057 was observed by VERITAS for 31 hours in 2006, 2008 and 2009. During these observations, no significant signal in gamma rays with energies above 1 TeV was detected from the direction of HESS J0632+057. A flux upper limit corresponding to 1.1% of the flux of the Crab Nebula has been derived from the VERITAS data. The non-detection by VERITAS excludes with a probability of 99.993% that HESS J0632+057 is a steady gamma-ray emitter. Contemporaneous X-ray observations with Swift XRT reveal a factor of 1.8 ± 0.4 higher flux in the 1-10 keV range than earlier X-ray observations of HESS J0632+057.

Point-like gamma-ray sources stand out among the many galactic VHE objects with spatially extended gamma-ray emission. The latter are usually associated with either pulsar wind nebulae or supernova remnants. High-mass X-ray binaries constitute the only known class of galactic objects with variable point-like VHE emission (see e.g., the VERITAS results on the TeV binary LS I +61 303). TeV binaries show variable emission of gamma rays, likely connected to changes in physical parameters associated with the orbital movement. While there has been no compact companion discovered for MWC 148, the point-like nature of the VHE emission combined with the variable X-ray emission can easily be explained by a production scenario similar to those in TeV binaries. Future multiwavelength observations combined with results from ground-based and space-based gamma-ray observatories will provide a deeper understanding of the true nature of HESS J0632+057.

For more information on the science of this object please see V.A.Acciari et al, The Astrophysical Journal, 698, L94, 2009 (ArXiv:0905.3139).  You may also contact Gernot Maier.

Upper limits on the thermally averaged cross section of the WIMP as a function of its mass calculated using the VHE flux limits and DM density models for Draco (solid line), Ursa Minor (dashed line), and M15 (dotted line). Note that the limits derived from M15 represent a scenario in which the DM halo has been adibatically compressed by the infall of baryonic matter. Shown as open circles are MSSM models that fall within three standard deviations of the relic DM density measured in the three-year WMAP data set.

A Search for Dark Matter

One of the leading candidates for dark matter (DM) is a weakly interacting massive particle (WIMP) that was in thermal equilibrium with baryons and photons in the early universe and decoupled as the universe expanded.  The mass of the WIMP is expected to be on the scale of 50 GeV - 10 TeV based on the known relic density of DM and the results of accelerator searches.  Particle physics models such as the minimal supersymmetric extension to the standard model (MSSM) can naturally accomodate a particle with these properties, for example the lightest supersymmetric particle, usually the neutralino.  The self-annihilation of WIMPs in astrophysical environments is predicted to generate stable secondary particles including very-high-energy (VHE) gamma-rays with energies up to the mass of the WIMP particle. Ground- and satellite- based VHE gamma-ray observatories can potentially detect gamma-ray fluxes from DM annihilations in regions of especially high DM density such as the Galactic Center and the cores of nearby galaxies.  The detection of the gamma-ray emission from such regions with the unique spectral characteristics of DM annihilations would provide a compelling case for the identification of the particle physics counterpart to astrophysical DM.

The Whipple 10m telescope conducted a search for VHE gamma-ray emission from DM self-annihilations in five astrophysical targets: the dwarf galaxies Draco and Ursa Minor, the local group galaxies M32 and M33, and the globular cluster M15.  These data comprise approximately 50 hours of observations taken over the course of the 2002-2004 observing seasons.  No sources of significant VHE emission were detected, and upper limits were derived on the thermally averaged product of velocity and cross-section of the WIMP as a function of its mass (see Figure).  To interpret the VHE flux upper limits as constraints on properties of the WIMP, the DM distribution of each source modeled with input from stellar and gas kinematics as well as cold dark matter (CDM) simulations.  For some sources, such as dwarf galaxies, the present-day distribution of DM is likely well described by collisionless CDM simulations and can be directly inferred from existing kinematic data.  Sources in which baryonic matter dominates the central gravitational potential such as globular clusters and local group galaxies are more challenging to model but may have a significantly larger annihilation signal augmented by the adiabatic compression of DM in the core by infalling baryonic matter.  Future measurements by current generation instruments such as VERITAS should improve on the sensitivity of the limits presented here by at least an order of magnitude.

For more information on the science of this object please see M.Wood et al, The Astrophysical Journal, Volume 678, Issue 2, pp. 594-605 (arXiv:0801.1708 ).  You may also contact Matthew Wood.