List of contributions from the CTA Consortium presented at the 34th International Cosmic Ray Conf... more List of contributions from the CTA Consortium presented at the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands.
B21215+30 is a BL-Lac-type blazar that was first detected at TeV energies by the MAGIC atmospher... more B21215+30 is a BL-Lac-type blazar that was first detected at TeV energies by the MAGIC atmospheric Cherenkov telescopes and subsequently confirmed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory with data collected between 2009 and 2012. In 2014 February 08, VERITAS detected a large-amplitude flare from B21215+30 during routine monitoring observations of the blazar 1ES1218 +304, located in the same field of view. The TeV flux reached 2.4 times the Crab Nebula flux with a variability timescale of <3.6 hr. Multiwavelength observations with Fermi-LAT, Swift, and the Tuorla Observatory revealed a correlated high GeV flux state and no significant optical counterpart to the flare, with a spectral energy distribution where the gamma-ray luminosity exceeds the synchrotron luminosity. When interpreted in the framework of a onezone leptonic model, the observed emission implies a high degree of beaming, with Doppler factor d > 10, and an electron population with spectral index < p 2.3.
Peer-review status of attached le: eerEreviewed Citation for published item: erhmultD F nd erherD... more Peer-review status of attached le: eerEreviewed Citation for published item: erhmultD F nd erherD eF nd fenowD F nd firdD F nd fiteuD tF nd fuhovekyD wF nd fukleyD tF rF nd fugevD F nd fyrumD uF nd gerrutiD wF nd ghenD F nd giupikD vF nd gonnollyD wF F nd guiD F nd iishD tF hF nd irrndoD wF nd ploneD eF nd pengD F nd pinleyD tF F nd pleishhkD rF nd portinD F nd portsonD vF nd purnissD eF nd qillndersD qF rF nd qri0nD F nd qrueD tF nd qyukD qF nd r¤ uttenD wF nd r¦ knssonD xF nd rnnD hFY rolderD tF nd rumenskyD F fF nd tohnsonD gF eF nd uretD F nd urD F nd uelleyEroskinsD xF nd uertzmnD wF nd uiedD hF nd uruseD wF nd urennrihD pF nd uumrD F nd vngD wF tF nd wierD qF nd werthurD F nd wgnnD eF nd wegherD uF nd worirtyD F nd wukherjeeD F nd xguyenD F nd xietoD hF nd y9pol¡ in de fhr¡ oitheD eF nd yngD F eF nd ytteD eF xF nd rkD xF nd erkinsD tF F nd ihelD eF nd ohlD wF nd opkowD eF nd ueshelD iF nd uinnD tF nd gnD uF nd eynoldsD F F nd ihrdsD qF F nd oheD iF nd overoD eF gF nd ntnderD wF nd emroskiD qF rF nd hhinynD uF nd mithD eF F nd tszkD hF nd elezhinskyD sF nd uiD tF F nd ylerD tF nd inentD F nd kelyD F F nd einerD yF wF nd einsteinD eF nd illimsD hF eF nd itzerD fF nd the ise ollortionD nd pumglliD wF nd rohskD tF F @PHITA 9pper limits from (ve yers of lzr oservtions with the ise gherenkov telesopesF9D estronomil journlFD ISI @TAF pF IRPF
The Galactic Center Ridge has been observed extensively in the past by both GeV and TeV gammaray ... more The Galactic Center Ridge has been observed extensively in the past by both GeV and TeV gammaray instruments revealing a wealth of structure, including a diffuse component as well as 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 gammaray component along the Galactic plane in the >300 GeV gamma-ray regime. Here we report on observations of the Galactic Center Ridge from 2010-2014 by the VERITAS telescope array in the >2 TeV energy range. From these observations we 1.) provide improved measurements of the differential energy spectrum for Sgr A* in the >2 TeV gamma-ray regime, 2.) provide a detection in the >2 TeV gamma-ray emission from the composite SNR G0.9+0.1 and an improved determination of its multi-TeV gamma-ray energy spectrum, 3.) report on the detection of VER J1746-289, a localized enhancement of >2 TeV gamma-ray emission along the Galactic plane.
The F-type star KIC 8462852 has recently been identified as an exceptional target for SETI (searc... more The F-type star KIC 8462852 has recently been identified as an exceptional target for SETI (search for extraterrestrial intelligence) observations. We describe an analysis methodology for optical SETI, which we have used to analyse nine hours of serendipitous archival observations of KIC 8462852 made with the VERITAS gamma-ray observatory between 2009 and 2015. No evidence of pulsed optical beacons, above a pulse intensity at the Earth of approximately 1 photon m −2 , is found. We also discuss the potential use of imaging atmospheric Cherenkov telescope arrays in searching for extremely short duration optical transients in general.
The TeV binary system LSI+61°303 is known for its regular, non-thermal emission pattern that t... more The TeV binary system LSI+61°303 is known for its regular, non-thermal emission pattern that traces the orbital period of the compact object in its 26.5 day orbit around its B0 Ve star companion. The system typically presents elevated TeV emission around apastron passage with flux levels between 5% and 15% of the steady flux from the Crab Nebula (>300 GeV). In this article, VERITAS observations of LSI+61°303 taken in late 2014 are presented, during which bright TeV flares around apastron at flux levels peaking above 30% of the Crab Nebula flux were detected. This is the brightest such activity from this source ever seen in the TeV regime. The strong outbursts have rise and fall times of less than a day. The short timescale of the flares, in conjunction with the observation of 10 TeV photons from LSI+61°303 during the flares, provides constraints on the properties of the accelerator in the source.
We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-... more We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift UVOT, X-ray observations by the Swift X-ray Telescope (XRT), high-energy gamma-ray observations with the Fermi Large Area Telescope (LAT) and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 17 April 2012 and 1 June 2012 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that the parameters required to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected-emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not
We present the results of 71.6 hours of observations of the Geminga pulsar (PSR J0633+1746) with ... more We present the results of 71.6 hours of observations of the Geminga pulsar (PSR J0633+1746) with the VERITAS very-high-energy gamma-ray telescope array. Data taken with VERITAS between November 2007 and February 2013 were phase-folded using a Geminga pulsar timing solution derived from data recorded by the XMM-Newton and Fermi-LAT space telescopes. No significant pulsed emission above 100 GeV is observed, and we report upper limits at the 95% confidence level on the integral flux above 135 GeV (spectral analysis threshold) of 4.0×10 −13 s −1 cm −2 and 1.7×10 −13 s −1 cm −2 for the two principal peaks in the emission profile. These upper limits, placed in context with phaseresolved spectral energy distributions determined from five years of data from the Fermi-LAT, constrain possible hardening of the Geminga pulsar emission spectra above ∼50 GeV.
List of contributions from the CTA Consortium presented at the 34th International Cosmic Ray Conf... more List of contributions from the CTA Consortium presented at the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands.
B21215+30 is a BL-Lac-type blazar that was first detected at TeV energies by the MAGIC atmospher... more B21215+30 is a BL-Lac-type blazar that was first detected at TeV energies by the MAGIC atmospheric Cherenkov telescopes and subsequently confirmed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory with data collected between 2009 and 2012. In 2014 February 08, VERITAS detected a large-amplitude flare from B21215+30 during routine monitoring observations of the blazar 1ES1218 +304, located in the same field of view. The TeV flux reached 2.4 times the Crab Nebula flux with a variability timescale of <3.6 hr. Multiwavelength observations with Fermi-LAT, Swift, and the Tuorla Observatory revealed a correlated high GeV flux state and no significant optical counterpart to the flare, with a spectral energy distribution where the gamma-ray luminosity exceeds the synchrotron luminosity. When interpreted in the framework of a onezone leptonic model, the observed emission implies a high degree of beaming, with Doppler factor d > 10, and an electron population with spectral index < p 2.3.
Peer-review status of attached le: eerEreviewed Citation for published item: erhmultD F nd erherD... more Peer-review status of attached le: eerEreviewed Citation for published item: erhmultD F nd erherD eF nd fenowD F nd firdD F nd fiteuD tF nd fuhovekyD wF nd fukleyD tF rF nd fugevD F nd fyrumD uF nd gerrutiD wF nd ghenD F nd giupikD vF nd gonnollyD wF F nd guiD F nd iishD tF hF nd irrndoD wF nd ploneD eF nd pengD F nd pinleyD tF F nd pleishhkD rF nd portinD F nd portsonD vF nd purnissD eF nd qillndersD qF rF nd qri0nD F nd qrueD tF nd qyukD qF nd r¤ uttenD wF nd r¦ knssonD xF nd rnnD hFY rolderD tF nd rumenskyD F fF nd tohnsonD gF eF nd uretD F nd urD F nd uelleyEroskinsD xF nd uertzmnD wF nd uiedD hF nd uruseD wF nd urennrihD pF nd uumrD F nd vngD wF tF nd wierD qF nd werthurD F nd wgnnD eF nd wegherD uF nd worirtyD F nd wukherjeeD F nd xguyenD F nd xietoD hF nd y9pol¡ in de fhr¡ oitheD eF nd yngD F eF nd ytteD eF xF nd rkD xF nd erkinsD tF F nd ihelD eF nd ohlD wF nd opkowD eF nd ueshelD iF nd uinnD tF nd gnD uF nd eynoldsD F F nd ihrdsD qF F nd oheD iF nd overoD eF gF nd ntnderD wF nd emroskiD qF rF nd hhinynD uF nd mithD eF F nd tszkD hF nd elezhinskyD sF nd uiD tF F nd ylerD tF nd inentD F nd kelyD F F nd einerD yF wF nd einsteinD eF nd illimsD hF eF nd itzerD fF nd the ise ollortionD nd pumglliD wF nd rohskD tF F @PHITA 9pper limits from (ve yers of lzr oservtions with the ise gherenkov telesopesF9D estronomil journlFD ISI @TAF pF IRPF
The Galactic Center Ridge has been observed extensively in the past by both GeV and TeV gammaray ... more The Galactic Center Ridge has been observed extensively in the past by both GeV and TeV gammaray instruments revealing a wealth of structure, including a diffuse component as well as 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 gammaray component along the Galactic plane in the >300 GeV gamma-ray regime. Here we report on observations of the Galactic Center Ridge from 2010-2014 by the VERITAS telescope array in the >2 TeV energy range. From these observations we 1.) provide improved measurements of the differential energy spectrum for Sgr A* in the >2 TeV gamma-ray regime, 2.) provide a detection in the >2 TeV gamma-ray emission from the composite SNR G0.9+0.1 and an improved determination of its multi-TeV gamma-ray energy spectrum, 3.) report on the detection of VER J1746-289, a localized enhancement of >2 TeV gamma-ray emission along the Galactic plane.
The F-type star KIC 8462852 has recently been identified as an exceptional target for SETI (searc... more The F-type star KIC 8462852 has recently been identified as an exceptional target for SETI (search for extraterrestrial intelligence) observations. We describe an analysis methodology for optical SETI, which we have used to analyse nine hours of serendipitous archival observations of KIC 8462852 made with the VERITAS gamma-ray observatory between 2009 and 2015. No evidence of pulsed optical beacons, above a pulse intensity at the Earth of approximately 1 photon m −2 , is found. We also discuss the potential use of imaging atmospheric Cherenkov telescope arrays in searching for extremely short duration optical transients in general.
The TeV binary system LSI+61°303 is known for its regular, non-thermal emission pattern that t... more The TeV binary system LSI+61°303 is known for its regular, non-thermal emission pattern that traces the orbital period of the compact object in its 26.5 day orbit around its B0 Ve star companion. The system typically presents elevated TeV emission around apastron passage with flux levels between 5% and 15% of the steady flux from the Crab Nebula (>300 GeV). In this article, VERITAS observations of LSI+61°303 taken in late 2014 are presented, during which bright TeV flares around apastron at flux levels peaking above 30% of the Crab Nebula flux were detected. This is the brightest such activity from this source ever seen in the TeV regime. The strong outbursts have rise and fall times of less than a day. The short timescale of the flares, in conjunction with the observation of 10 TeV photons from LSI+61°303 during the flares, provides constraints on the properties of the accelerator in the source.
We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-... more We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift UVOT, X-ray observations by the Swift X-ray Telescope (XRT), high-energy gamma-ray observations with the Fermi Large Area Telescope (LAT) and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 17 April 2012 and 1 June 2012 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that the parameters required to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected-emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not
We present the results of 71.6 hours of observations of the Geminga pulsar (PSR J0633+1746) with ... more We present the results of 71.6 hours of observations of the Geminga pulsar (PSR J0633+1746) with the VERITAS very-high-energy gamma-ray telescope array. Data taken with VERITAS between November 2007 and February 2013 were phase-folded using a Geminga pulsar timing solution derived from data recorded by the XMM-Newton and Fermi-LAT space telescopes. No significant pulsed emission above 100 GeV is observed, and we report upper limits at the 95% confidence level on the integral flux above 135 GeV (spectral analysis threshold) of 4.0×10 −13 s −1 cm −2 and 1.7×10 −13 s −1 cm −2 for the two principal peaks in the emission profile. These upper limits, placed in context with phaseresolved spectral energy distributions determined from five years of data from the Fermi-LAT, constrain possible hardening of the Geminga pulsar emission spectra above ∼50 GeV.
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Papers by N. Hakansson