Physical Sciences and Mathematics Commons^™

Veritas And Fermi-Lat Observations Of Tev Gamma-Ray Sources Discovered By Hawc In The 2hwc Catalog, P. T. Reynolds, Et Al

Physical Sciences Publications

The High Altitude Water Cherenkov (HAWC) collaboration recently published their 2HWC catalog, listing 39 very high energy (VHE; >100 GeV) gamma-ray sources based on 507 days of observation. Among these, 19 sources are not associated with previously known teraelectronvolt (TeV) gamma-ray sources. We have studied 14 of these sources without known counterparts with VERITAS and Fermi-LAT. VERITAS detected weak gamma-ray emission in the 1 TeV–30 TeV band in the region of DA 495, a pulsar wind nebula coinciding with 2HWC J1953+294, confirming the discovery of the source by HAWC. We did not find any counterpart for the selected 14 …

A Strong Limit On The Very-High-Energy Emission From Grb 150323a, P. T. Reynolds, Et Al

Physical Sciences Publications

On 2015 March 23, the Very Energetic Radiation Imaging Telescope Array System (VERITAS) responded to a Swift-Burst Alert Telescope (BAT) detection of a gamma-ray burst, with observations beginning 270 s after the onset of BAT emission, and only 135 s after the main BAT emission peak. No statistically significant signal is detected above 140 GeV. The VERITAS upper limit on the fluence in a 40-minute integration corresponds to about 1% of the prompt fluence. Our limit is particularly significant because the very-high-energy (VHE) observation started only ~2 minutes after the prompt emission peaked, and Fermi-Large Area Telescope observations …

A Search For Spectral Hysteresis And Energy-Dependent Time Lags From X-Ray And Tev Gamma-Ray Observations Of Mrk 421, A. U. Abeysekara, S. Archambault, A. Archer, W. Benbow, R. Bird, M. Buchovecky, J. H. Buckley, B. Bugaev, J. V. Cardenzana, P. T. Reynolds, Et Al

Physical Sciences Publications

Abstract

Blazars are variable emitters across all wavelengths over a wide range of timescales, from months down to minutes. It is therefore essential to observe blazars simultaneously at different wavelengths, especially in the X-ray and gamma-ray bands, where the broadband spectral energy distributions usually peak. In this work, we report on three "target-of-opportunity" observations of Mrk 421, one of the brightest TeV blazars, triggered by a strong flaring event at TeV energies in 2014. These observations feature long, continuous, and simultaneous exposures with XMM-Newton (covering the X-ray and optical/ultraviolet bands) and VERITAS (covering the TeV gamma-ray band), along with contemporaneous …

A Search For Very High-Energy Gamma Rays From The Missing Link Binary Pulsar J1023+0038 With Veritas, P. T. Reynolds, Et Al

Physical Sciences Publications

The binary millisecond radio pulsar PSR J1023+0038 exhibits many characteristics similar to the gamma-ray binary system PSR B1259–63/LS 2883, making it an ideal candidate for the study of high-energy nonthermal emission. It has been the subject of multiwavelength campaigns following the disappearance of the pulsed radio emission in 2013 June, which revealed the appearance of an accretion disk around the neutron star. We present the results of very high energy (VHE) gamma-ray observations carried out by the Very Energetic Radiation Imaging Telescope Array System before and after this change of state. Searches for steady and pulsed emission of both data …

Very High Energy Observations Of The Binaries V 404 Cyg And 4u 0115+634 During Giant X-Ray Outbursts, P. T. Reynolds, Et Al

Physical Sciences Publications

Transient X-ray binaries produce major outbursts in which the X-ray flux can increase over the quiescent level by factors as large as 107. The low-mass X-ray binary V 404 Cyg and the high-mass system 4U 0115+634 underwent such major outbursts in 2015 June and October, respectively. We present here observations at energies above hundreds of GeV with the VERITAS observatory taken during some of the brightest X-ray activity ever observed from these systems. No gamma-ray emission has been detected by VERITAS in 2.5 hr of observations of the microquasar V 404 Cyg from 2015, June 20–21. The upper flux limits …

Tev Gamma-Ray Observations Of The Galactic Center Ridge By Veritas, P. T. Reynolds, Et Al

Physical Sciences Publications

The Galactic Center ridge has been observed extensively in the past by both GeV and TeV gamma-ray instruments revealing a wealth of structure, including a diffuse component and the point sources G0.9+0.1 (a composite supernova remnant) and Sgr A* (believed to be associated with the supermassive black hole located at the center of our Galaxy). Previous very high energy (VHE) gamma-ray observations with the H.E.S.S. experiment have also detected an extended TeV gamma-ray component along the Galactic plane in the >300 GeV gamma-ray regime. Here we report on observations of the Galactic Center ridge from 2010 to 2014 by the …

Gamma-Rays From The Quasar Pks 1441+25: Story Of An Escape, P. T. Reynolds, Et Al

Physical Sciences Publications

Outbursts from gamma-ray quasars provide insights on the relativistic jets of active galactic nuclei and constraints on the diffuse radiation fields that fill the universe. The detection of significant emission above 100 GeV from a distant quasar would show that some of the radiated gamma-rays escape pair-production interactions with low-energy photons, be it the extragalactic background light (EBL), or the radiation near the supermassive black hole lying at the jet's base. VERITAS detected gamma-ray emission up to ~200 GeV from PKS 1441+25 (z = 0.939) during 2015 April, a period of high activity across all wavelengths. This observation of …

Test Of Models Of The Cosmic Infrared Background With Multiwavelength Observations Of The Blazar 1es 1218+30.4 In 2009, P. T. Reynolds

Physical Sciences Publications

We present the results of a multi-wavelength campaign targeting the blazar 1ES 1218+30.4 with observations with the 1.3 m McGraw-Hill optical telescope, the Rossi X-ray Timing Explorer (RXTE), the Fermi Gamma-Ray Space Telescope, and the Very Energetic Radiation Imaging Telescope Array System (VERITAS). The RXTE and VERITAS observations were spread over a 13 day period and revealed clear evidence for flux variability, and a strong X-ray and γ-ray flare on 2009 February 26 (MJD 54888). The campaign delivered a well-sampled broadband energy spectrum with simultaneous RXTE and VERITAS very high energy (VHE, >100 GeV) observations, as well as …

Deep Broadband Observations Of The Distant Gamma-Ray Blazar Pks 1424+240, P. T. Reynolds, Et Al

Physical Sciences Publications

We present deep VERITAS observations of the blazar PKS 1424+240, along with contemporaneous Fermi Large Area Telescope, Swift X-ray Telescope, and Swift UV Optical Telescope data between 2009 February 19 and 2013 June 8. This blazar resides at a redshift of z ≥ 0.6035, displaying a significantly attenuated gamma-ray flux above 100 GeV due to photon absorption via pair-production with the extragalactic background light. We present more than 100 hr of VERITAS observations over three years, a multiwavelength light curve, and the contemporaneous spectral energy distributions. The source shows a higher flux of (2.1 ± 0.3) × 10–7 photons m–2 …

A Search For Enhanced Very High Energy Gamma-Ray Emission From The 2013 March Crab Nebula Flare, P. T. Reynolds, Et Al

Physical Sciences Publications

In 2013 March, a flaring episode from the Crab Nebula lasting ~2 weeks was detected by Fermi-LAT (Large Area Telescope on board the Fermi Gamma-ray Space Telescope). The Very Energetic Radiation Imaging Telescope Array System (VERITAS) provides simultaneous observations throughout this period. During the flare, Fermi-LAT detected a 20 fold increase in flux above the average synchrotron flux >100 MeV seen from the Crab Nebula. Simultaneous measurements with VERITAS are consistent with the non-variable long-term average Crab Nebula flux at TeV energies. Assuming a linear correlation between the very high energy flux change >1 TeV and the flux …

Veritas Observations Of The Microquasar Cygnus X-3, P. T. Reynolds, Et Al

Physical Sciences Publications

We report results from TeV gamma-ray observations of the microquasar Cygnus X-3. The observations were made with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) over a time period from 2007 June 11 to 2011 November 28. VERITAS is most sensitive to gamma rays at energies between 85 GeV and 30 TeV. The effective exposure time amounts to a total of about 44 hr, with the observations covering six distinct radio/X-ray states of the object. No significant TeV gamma-ray emission was detected in any of the states, nor with all observations combined. The lack of a positive signal, especially …

Search For A Correlation Between Very-High-Energy Gamma Rays And Giant Radio Pulses In The Crab Pulsar, E. Aliu, S. Archambault, T. Arlen, T. Aune, M. Beilicke, W. Benbow, A. Bouvier, J. H. Buckley, V. Bugaev, P. T. Reynolds, Et Al

Physical Sciences Publications

We present the results of a joint observational campaign between the Green Bank radio telescope and the VERITAS gamma-ray telescope, which searched for a correlation between the emission of very-high-energy (VHE) gamma rays (E γ > 150 GeV) and giant radio pulses (GRPs) from the Crab pulsar at 8.9 GHz. A total of 15,366 GRPs were recorded during 11.6 hr of simultaneous observations, which were made across four nights in 2008 December and in 2009 November and December. We searched for an enhancement of the pulsed gamma-ray emission within time windows placed around the arrival time of the GRP events. …

Veritas Observations Of Six Bright, Hard-Spectrum Fermi-Lat Blazars, P. T. Reynolds, Et Al

Physical Sciences Publications

We report on VERITAS very high energy (VHE; E ≥ 100 GeV) observations of six blazars selected from the Fermi Large Area Telescope First Source Catalog (1FGL). The gamma-ray emission from 1FGL sources was extrapolated up to the VHE band, taking gamma-ray absorption by the extragalactic background light into account. This allowed the selection of six bright, hard-spectrum blazars that were good candidate TeV emitters. Spectroscopic redshift measurements were attempted with the Keck Telescope for the targets without Sloan Digital Sky Survey spectroscopic data. No VHE emission is detected during the observations of the six sources described here. Corresponding TeV …

Veritas Observations Of The Unusual Extragalactic Transient Swift J164449.3+573451, P. T. Reynolds, Et Al

Physical Sciences Publications

We report on very high energy (>100 GeV) gamma-ray observations of Swift J164449.3+573451, an unusual transient object first detected by the Swift Observatory and later detected by multiple radio, optical, and X-ray observatories. A total exposure of 28 hr was obtained on Swift J164449.3+573451 with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) during 2011 March 28-April 15. We do not detect the source and place a differential upper limit on the emission at 500 GeV during these observations of 1.4 × 10–12 erg cm–2 s–1 (99% confidence level). We also present time-resolved upper limits and use a …

Discovery Of Tev Gamma Ray Emission From Tycho's Supernova Remnant, P. T. Reynolds, Et Al

Physical Sciences Publications

We report the discovery of TeV gamma-ray emission from the Type Ia supernova remnant (SNR) G120.1+1.4, known as Tycho's SNR. Observations performed in the period 2008-2010 with the VERITAS ground-based gamma-ray observatory reveal weak emission coming from the direction of the remnant, compatible with a point source located at 00h25m270, + 64°10'50'' (J2000). The TeV photon spectrum measured by VERITAS can be described with a power law dN/dE = C(E/3.42 TeV)–Γ with Γ = 1.95 ± 0.51stat ± 0.30sys and C = (1.55 ± 0.43stat ± 0.47sys) × 10–14 cm–2 s–1 TeV–1. The integral …

Discovery Of Very High Energy Gamma-Ray Emission From The Snr G54.1+0.3, P. T. Reynolds, Et Al

Physical Sciences Publications

We report the discovery of very high energy (VHE) gamma-ray emission from the direction of the SNR G54.1+0.3 using the VERITAS ground-based gamma-ray observatory. The TeV signal has an overall significance of 6.8σ and appears pointlike given the resolution of the instrument. The integral flux above 1 TeV is 2.5% of the Crab Nebula flux and significant emission is measured between 250 GeV and 4 TeV, well described by a power-law energy spectrum dN/dE ~ E –Γ with a photon index Γ = 2.39 ± 0.23stat ± 0.30sys. We find no evidence of time variability among observations …

The Discovery Of Gamma-Ray Emission From The Blazar Rgb J0710+591, P. T. Reynolds, Et Al

Physical Sciences Publications

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) × 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 …

Discovery Of Variability In The Very High Energy Gamma-Ray Emission Of 1es 1218+304 With Veritas, P. T. Reynolds, Et Al

Physical Sciences Publications

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 …

Veritas Observations Of A Very High Energy Gamma-Ray Flare From The Blazar 3c 66a, P. T. Reynolds, Et Al

Physical Sciences Publications

The intermediate-frequency peaked BL Lacertae (IBL) object 3C 66A is detected during 2007-2008 in VHE (very high energy; E > 100 GeV) γ rays with the VERITAS stereoscopic array of imaging atmospheric Cherenkov telescopes. An excess of 1791 events is detected, corresponding to a significance of 21.2 standard deviations (σ), in these observations (32.8 hr live time). The observed integral flux above 200 GeV is 6% of the Crab Nebula's flux and shows evidence for variability on the timescale of days. The measured energy spectrum is characterized by a soft power law with photon index Γ = 4.1 ± 0.4stat ± …

The June 2008 Flare Of Markarian 421 From Optical To Tev Energies, P. T. Reynolds, Et Al

Physical Sciences Publications

We present optical, X-ray, high-energy (30 GeV) and very high energy (100 GeV; VHE) observations of the high-frequency peaked blazar Mrk 421 taken between 2008 May 24 and June 23. A high-energy γ-ray signal was detected by AGILE with between June 9 and 15, with F(E>100 MeV) = 42+14 –12 × 10–8 photons cm–2 s–1. This flaring state is brighter than the average flux observed by EGRET by a factor of ~3, but still consistent with the highest EGRET flux. In hard X-rays (20-60 keV) SuperAGILE resolved a five-day flare (June 9-15) peaking at ~55 mCrab. SuperAGILE, …

Discovery Of Very High-Energy Gamma-Ray Radiation From The Bl Lac 1es 0806+524, P. T. Reynolds, Et Al

Physical Sciences Publications

The high-frequency-peaked BL Lacertae object 1ES 0806+524, at redshift z = 0.138, was observed in the very high energy (VHE) gamma-ray regime by VERITAS between 2006 November and 2008 April. These data encompass the two- and three-telescope commissioning phases, as well as observations with the full four-telescope array. 1ES 0806+524 is detected with a statistical significance of 6.3 standard deviations from 245 excess events. Little or no measurable variability on monthly timescales is found. The photon spectrum for the period 2007 November to 2008 April can be characterized by a power law with photon index 3.6 ± 1.0stat ± 0.3sys …

Veritas Discovery Of > 200 Gev Gamma-Ray Emission From The Intermediate-Frequency-Peaked Bl Lacertae Object W Comae, P. T. Reynolds, Et Al

Physical Sciences Publications

We report the detection of very high energy γ-ray emission from the intermediate-frequency-peaked BL Lacertae object W Comae (z = 0.102) by VERITAS. The source was observed between 2008 January and April. A strong outburst of γ-ray emission was measured in the middle of March, lasting for only 4 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 Γ = 3.81 ± 0.35stat± 0.34syst. The integral photon flux above 200 GeV during those two nights corresponds to …