arXiv subjects

H. J. Rose

Publications and source records attributed to H. J. Rose.

At least 37 records · Page 2Linked to original sources

arXiv2010

The Discovery of gamma-Ray Emission From The Blazar RGB J0710+591

The high-frequency-peaked BL Lacertae object RGB J0710+591 was observed in the very high-energy (VHE; E > 100 GeV) wave band by the VERITAS array of atmospheric Cherenkov telescopes. The observations, taken between 2008 December and 2009 March and totaling 22.1 hr, yield the discovery of VHE gamma rays from the source. RGB J0710+591 is detected at a statistical significance of 5.5 standard deviations (5.5σ) above the background, corresponding to an integral flux of (3.9 +/- 0.8) x 10-12 cm-2 s-1 (3% of the Crab Nebula's flux) above 300 GeV. The observed spectrum can be fit by a power law from 0.31 to 4.6 TeV with a photon spectral index of 2.69 +/- 0.26stat +/- 0.20sys. These data are complemented by contemporaneous multiwavelength data from the Fermi Large Area Telescope, the Swift X-ray Telescope, the Swift Ultra-Violet and Optical Telescope, and the Michigan-Dartmouth-MIT observatory. Modeling the broadband spectral energy distribution (SED) with an equilibrium synchrotron self-Compton model yields a good statistical fit to the data. The addition of an external-Compton component to the model does not improve the fit nor brings the system closer to equipartition. The combined Fermi and VERITAS data constrain the properties of the high-energy emission component of the source over 4 orders of magnitude and give measurements of the rising and falling sections of the SED.

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arXiv2010

Observations of the shell-type SNR Cassiopeia A at TeV energies with VERITAS

We report on observations of very high-energy gamma rays from the shell-type supernova remnant Cassiopeia A with the VERITAS stereoscopic array of four imaging atmospheric Cherenkov telescopes in Arizona. The total exposure time for these observations is 22 hours, accumulated between September and November of 2007. The gamma-ray source associated with the SNR Cassiopeia A was detected above 200 GeV with a statistical significance of 8.3 s.d. The estimated integral flux for this gamma-ray source is about 3% of the Crab-Nebula flux. The photon spectrum is compatible with a power law dN/dE ~ E^(-Gamma) with an index Gamma = 2.61 +/- 0.24(stat) +/- 0.2(sys). The data are consistent with a point-like source. We provide a detailed description of the analysis results, and discuss physical mechanisms that may be responsible for the observed gamma-ray emission.

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arXiv2010

Discovery of Variability in the Very High Energy Gamma-Ray Emission of 1ES 1218+304 with VERITAS

We present results from an intensive VERITAS monitoring campaign of the high-frequency peaked BL Lac object 1ES 1218+304 in 2008/2009. Although 1ES 1218+304 was detected previously by MAGIC and VERITAS at a persistent level of ~6% of the Crab Nebula flux, the new VERITAS data reveal a prominent flare reaching ~20% of the Crab. While very high energy (VHE) flares are quite common in many nearby blazars, the case of 1ES 1218+304 (redshift z = 0.182) is particularly interesting since it belongs to a group of blazars that exhibit unusually hard VHE spectra considering their redshifts. When correcting the measured spectra for absorption by the extragalactic background light, 1ES 1218+304 and a number of other blazars are found to have differential photon indices less than 1.5. The difficulty in modeling these hard spectral energy distributions in blazar jets has led to a range of theoretical gamma-ray emission scenarios, one of which is strongly constrained by these new VERITAS observations. We consider the implications of the observed light curve of 1ES 1218+304, which shows day scale flux variations, for shock acceleration scenarios in relativistic jets, and in particular for the viability of kiloparsec-scale jet emission scenarios.

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arXiv2009

Highlight Talk: Recent Results from VERITAS

VERITAS is a state-of-the-art ground-based gamma-ray observatory that operates in the very high-energy (VHE) region of 100 GeV to 50 TeV. The observatory consists of an array of four 12m-diameter imaging atmospheric Cherenkov telescopes located in southern Arizona, USA. The four-telescope array has been fully operational since September 2007, and over the last two years, VERITAS has been operating with high efficiency and with excellent performance. This talk summarizes the recent results from VERITAS, including the discovery of eight new VHE gamma-ray sources.

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arXiv2009

Detection of Extended VHE Gamma Ray Emission from G106.3+2.7 with VERITAS

We report the detection of very-high-energy (VHE) gamma-ray emission from supernova remnant (SNR) G106.3+2.7. Observations performed in 2008 with the VERITAS atmospheric Cherenkov gamma-ray telescope resolve extended emission overlapping the elongated radio SNR. The 7.3 sigma (pre-trials) detection has a full angular extent of roughly 0.6deg by 0.4deg. Most notably, the centroid of the VHE emission is centered near the peak of the coincident 12CO (J = 1-0) emission, 0.4deg away from the pulsar PSR J2229+6114, situated at the northern end of the SNR. Evidently the current-epoch particles from the pulsar wind nebula are not participating in the gamma-ray production. The VHE energy spectrum measured with VERITAS is well characterized by a power law dN/dE = N_0(E/3 TeV)^{-G} with a differential index of G = 2.29 +/- 0.33stat +/- 0.30sys and a flux of N_0 = (1.15 +/- 0.27stat +/- 0.35sys)x 10^{-13} cm^{-2} s^{-1} TeV^{-1}. The integral flux above 1 TeV corresponds to ~5 percent of the steady Crab Nebula emission above the same energy. We describe the observations and analysis of the object and briefly discuss the implications of the detection in a multiwavelength context.

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arXiv2009

A connection between star formation activity and cosmic rays in the starburst galaxy M 82

Although Galactic cosmic rays (protons and nuclei) are widely believed to be dominantly accelerated by the winds and supernovae of massive stars, definitive evidence of this origin remains elusive nearly a century after their discovery [1]. The active regions of starburst galaxies have exceptionally high rates of star formation, and their large size, more than 50 times the diameter of similar Galactic regions, uniquely enables reliable calorimetric measurements of their potentially high cosmic-ray density [2]. The cosmic rays produced in the formation, life, and death of their massive stars are expected to eventually produce diffuse gamma-ray emission via their interactions with interstellar gas and radiation. M 82, the prototype small starburst galaxy, is predicted to be the brightest starburst galaxy in gamma rays [3, 4]. Here we report the detection of >700 GeV gamma rays from M 82. From these data we determine a cosmic-ray density of 250 eV cm-3 in the starburst core of M 82, or about 500 times the average Galactic density. This result strongly supports that cosmic-ray acceleration is tied to star formation activity, and that supernovae and massive-star winds are the dominant accelerators.

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arXiv2009

VERITAS Upper Limit on the VHE Emission from the Radio Galaxy NGC 1275

The recent detection by the Fermi gamma-ray space telescope of high-energy gamma-rays from the radio galaxy NGC 1275 makes the observation of the very high energy (VHE: E > 100 GeV) part of its broadband spectrum particularly interesting, especially for the understanding of active galactic nuclei (AGN) with misaligned multi-structured jets. The radio galaxy NGC 1275 was recently observed by VERITAS at energies above 100 GeV for about 8 hours. No VHE gamma-ray emission was detected by VERITAS from NGC 1275. A 99% confidence level upper limit of 2.1% of the Crab Nebula flux level is obtained at the decorrelation energy of approximately 340 GeV, corresponding to 19% of the power-law extrapolation of the Fermi Large Area Telescope (LAT) result.

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arXiv2009

Multiwavelength observations of a TeV-Flare from W Comae

We report results from an intensive multiwavelength campaign on the intermediate-frequency-peaked BL Lacertae object W Com (z=0.102) during a strong outburst of very high energy gamma-ray emission in June 2008. The very high energy gamma-ray signal was detected by VERITAS on 2008 June 7-8 with a flux F(>200 GeV) = (5.7+-0.6)x10^-11 cm-2s-1, about three times brighter than during the discovery of gamma-ray emission from W Com by VERITAS in 2008 March. The initial detection of this flare by VERITAS at energies above 200 GeV was followed by observations in high energy gamma-rays (AGILE, E>100 MeV), and X-rays (Swift and XMM-Newton), and at UV, and ground-based optical and radio monitoring through the GASP-WEBT consortium and other observatories. Here we describe the multiwavelength data and derive the spectral energy distribution (SED) of the source from contemporaneous data taken throughout the flare.

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arXiv2009

Observation of Extended VHE Emission from the Supernova Remnant IC 443 with VERITAS

We present evidence that the very-high-energy (VHE, E > 100 GeV) gamma-ray emission coincident with the supernova remnant IC 443 is extended. IC 443 contains one of the best-studied sites of supernova remnant/molecular cloud interaction and the pulsar wind nebula CXOU J061705.3+222127, both of which are important targets for VHE observations. VERITAS observed IC 443 for 37.9 hours during 2007 and detected emission above 300 GeV with an excess of 247 events, resulting in a significance of 8.3 standard deviations (sigma) before trials and 7.5 sigma after trials in a point-source search. The emission is centered at 06 16 51 +22 30 11 (J2000) +- 0.03_stat +- 0.08_sys degrees, with an intrinsic extension of 0.16 +- 0.03_stat +- 0.04_sys degrees. The VHE spectrum is well fit by a power law (dN/dE = N_0 * (E/TeV)^-Gamma) with a photon index of 2.99 +- 0.38_stat +- 0.3_sys and an integral flux above 300 GeV of (4.63 +- 0.90_stat +- 0.93_sys) * 10^-12 cm^-2 s^-1. These results are discussed in the context of existing models for gamma-ray production in IC 443.

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arXiv2009

Evidence for long-term Gamma-ray and X-ray variability from the unidentified TeV source 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. The variability in the gamma-ray and X-ray fluxes supports interpretation of the ob ject as a gamma-ray emitting binary.

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arXiv2009

Multiwavelength Observations of LS I +61 303 with VERITAS, Swift and RXTE

We present results from a long-term monitoring campaign on the TeV binary LSI +61 303 with VERITAS at energies above 500 GeV, and in the 2-10 keV hard X-ray bands with RXTE and Swift, sampling nine 26.5 day orbital cycles between September 2006 and February 2008. The binary was observed by VERITAS to be variable, with all integrated observations resulting in a detection at the 8.8 sigma (2006/2007) and 7.3 sigma (2007/2008) significance level for emission above 500 GeV. The source was detected during active periods with flux values ranging from 5 to 20% of the Crab Nebula, varying over the course of a single orbital cycle. Additionally, the observations conducted in the 2007-2008 observing season show marginal evidence (at the 3.6 sigma significance level) for TeV emission outside of the apastron passage of the compact object around the Be star. Contemporaneous hard X-ray observations with RXTE and Swift show large variability with flux values typically varying between 0.5 and 3.0*10^-11 ergs cm^-2 s^-1 over a single orbital cycle. The contemporaneous X-ray and TeV data are examined and it is shown that the TeV sampling is not dense enough to detect a correlation between the two bands.

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arXiv2009

Multiwavelength Observations of Markarian 421 in 2005 - 2006

Since September 2005, the Whipple 10m Gamma-ray Telescope has been operated primarily as a blazar monitor. The five Northern Hemisphere blazars that have already been detected at the Whipple Observatory, Markarian 421, H1426+428, Markarian 501, 1ES 1959+650 and 1ES 2344+514, are monitored routinely each night that they are visible. We report on the Markarian 421 observations taken from November 2005 to June 2006 in the gamma-ray, X-ray, optical and radio bands. During this time, Markarian 421 was found to be variable at all wavelengths probed. Both the variability and the correlations among different energy regimes are studied in detail here. A tentative correlation, with large spread, was measured between the X-ray and gamma-ray bands, while no clear correlation was evident among the other energy bands. In addition to this, the well-sampled spectral energy distribution of Markarian 421 (1101+384) is presented for three different activity levels. The observations of the other blazar targets will be reported separately.

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arXiv2008

Status of the VERITAS Observatory

VERITAS, an Imaging Atmospheric Cherenkov Telescope (IACT) system for gammma-ray astronomy in the GeV-TeV range, has recently completed its first season of observations with a full array of four telescopes. A number of astrophysical gamma-ray sources have been detected, both galactic and extragalactic, including sources previously unknown at TeV energies. We describe the status of the array and some highlight results, and assess the technical performance, sensitivity and shower reconstruction capabilities.

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arXiv2008

VERITAS Observations of the BL Lac Object 1ES 1218+304

The VERITAS collaboration reports the detection of very-high-energy (VHE) gamma-ray emission from the high-frequency-peaked BL Lac object 1ES 1218+304 located at a redshift of z=0.182. A gamma-ray signal was detected with high statistical significance for the observations taken during several months in the 2006-2007 observing season. The photon spectrum between ~160 GeV and ~1.8 TeV is well described by a power law with an index of Gamma = 3.08 +/- 0.34(stat) +/- 0.2(sys). The integral flux above 200 GeV corresponds to ~6% of that of the Crab Nebula. The light curve does not show any evidence for VHE flux variability. Using lower limits on the density of the extragalactic background light (EBL) in the near-IR to mid-IR we are able to limit the range of intrinsic energy spectra for 1ES 1218+304. We show that the intrinsic photon spectrum is harder than a power law with an index of Gamma = 2.32 +/- 0.37. When including constraints from the spectra of 1ES 1101-232 and 1ES 0229+200, the spectrum of 1ES 1218+304 is likely to be harder than Gamma = 1.86 +/- 0.37.

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arXiv2008

VERITAS Discovery of >200GeV Gamma-ray Emission from the Intermediate-frequency-peaked BL Lac Object W Comae

We report the detection of very high-energy gamma-ray emission from the intermediate-frequency-peaked BL Lacertae object W Comae (z=0.102) by VERITAS. The source was observed between January and April 2008. A strong outburst of gamma-ray emission was measured in the middle of March, lasting for only four days. The energy spectrum measured during the two highest flare nights is fit by a power-law and is found to be very steep, with a differential photon spectral index of Gamma = 3.81 +- 0.35_stat +- 0.34_syst. The integral photon flux above 200GeV during those two nights corresponds to roughly 9% of the flux from the Crab Nebula. Quasi-simultaneous Swift observations at X-ray energies were triggered by the VERITAS observations. The spectral energy distribution of the flare data can be described by synchrotron-self-Compton (SSC) or external-Compton (EC) leptonic jet models, with the latter offering a more natural set of parameters to fit the data.

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arXiv2008

VERITAS Observations of the gamma-Ray Binary LS I +61 303

LS I +61 303 is one of only a few high-mass X-ray binaries currently detected at high significance in very high energy gamma-rays. The system was observed over several orbital cycles (between September 2006 and February 2007) with the VERITAS array of imaging air-Cherenkov telescopes. A signal of gamma-rays with energies above 300 GeV is found with a statistical significance of 8.4 standard deviations. The detected flux is measured to be strongly variable; the maximum flux is found during most orbital cycles at apastron. The energy spectrum for the period of maximum emission can be characterized by a power law with a photon index of Gamma=2.40+-0.16_stat+-0.2_sys and a flux above 300 GeV corresponding to 15-20% of the flux from the Crab Nebula.

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arXiv2008

Observation of gamma-ray emission from the galaxy M87 above 250 GeV with VERITAS

The multiwavelength observation of the nearby radio galaxy M87 provides a unique opportunity to study in detail processes occurring in Active Galactic Nuclei from radio waves to TeV gamma-rays. Here we report the detection of gamma-ray emission above 250 GeV from M87 in spring 2007 with the VERITAS atmospheric Cherenkov telescope array and discuss its correlation with the X-ray emission. The gamma-ray emission is measured to be point-like with an intrinsic source radius less than 4.5 arcmin. The differential energy spectrum is fitted well by a power-law function: dPhi/dE=(7.4+-1.3_{stat}+-1.5_{sys})(E/TeV)^{-2.31+-0.17_{stat}+-0.2_{sys}} 10^{-9}m^{-2}s^{-1}TeV^{-1}. We show strong evidence for a year-scale correlation between the gamma-ray flux reported by TeV experiments and the X-ray emission measured by the ASM/RXTE observatory, and discuss the possible short-time-scale variability. These results imply that the gamma-ray emission from M87 is more likely associated with the core of the galaxy than with other bright X-ray features in the jet.

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arXiv2008

A Search for Dark Matter Annihilation with the Whipple 10m Telescope

We present observations of the dwarf galaxies Draco and Ursa Minor, the local group galaxies M32 and M33, and the globular cluster M15 conducted with the Whipple 10m gamma-ray telescope to search for the gamma-ray signature of self-annihilating weakly interacting massive particles (WIMPs) which may constitute astrophysical dark matter (DM). We review the motivations for selecting these sources based on their unique astrophysical environments and report the results of the data analysis which produced upper limits on excess rate of gamma rays for each source. We consider models for the DM distribution in each source based on the available observational constraints and discuss possible scenarios for the enhancement of the gamma-ray luminosity. Limits on the thermally averaged product of the total self-annihilation cross section and velocity of the WIMP, <σv>, are derived using conservative estimates for the magnitude of the astrophysical contribution to the gamma-ray flux. Although these limits do not constrain predictions from the currently favored theoretical models of supersymmetry (SUSY), future observations with VERITAS will probe a larger region of the WIMP parameter phase space, <σv> and WIMP particle mass (m_χ).

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