VERITAS Collaboration, V. A. Acciari, E. Aliu, T. Arlen, M. Beilicke, W. Benbow, S. M. Bradbury, J. H. Buckley, V. Bugaev, Y. Butt, K. L. Byrum, O. Celik, A. Ce… 展开作者
VERITAS Collaboration, V. A. Acciari, E. Aliu, T. Arlen, M. Beilicke, W. Benbow, S. M. Bradbury, J. H. Buckley, V. Bugaev, Y. Butt, K. L. Byrum, O. Celik, A. Cesarini, L. Ciupik, Y. C. K. Chow, P. Cogan, P. Colin, W. Cui, M. K. Daniel, T. Ergin, A. D. Falcone, S. J. Fegan, J. P. Finley, P. Fortin, L. F. Fortson, A. Furniss, G. H. Gillanders, J. Grube, R. Guenette, G. Gyuk, D. Hanna, E. Hays, J. Holder, D. Horan, C. M. Hui, T. B. Humensky, A. Imran, P. Kaaret, N. Karlsson, M. Kertzman, D. B. Kieda, J. Kildea, A. Konopelko, H. Krawczynski, F. Krennrich, M. J. Lang, S. LeBohec, G. Maier, A. McCann, M. McCutcheon, P. Moriarty, R. Mukherjee, T. Nagai, J. Niemiec, R. A. Ong, D. Pandel, J. S. Perkins, M. Pohl, J. Quinn, K. Ragan, L. C. Reyes, P. T. Reynolds, H. J. Rose, M. Schroedter, G. H. Sembroski, A. W. Smith, D. Steele, S. P. Swordy, J. A. Toner, L. Valcarcel, V. V. Vassiliev, R. Wagner, S. P. Wakely, J. E. Ward, T. C. Weekes, A. Weinstein, R. J. White, D. A. Williams, S. A. Wissel, M. Wood, B. Zitzer
备注：
Accepted for publication in The Astrophysical Journal
VERITAS合作报告了从位于z=0.182的红移处的高频峰值BL Lac对象1 ES 1218+304检测到甚高能量（VHE）伽马射线发射。在2007年前三个月的观测中，探测到了一个伽马射线信号，其统计显著性为10.4标准差（10.4西格玛），证实了MAGIC合作发现了这个物体。在~160 GeV和~1.8 TeV之间的光子谱可以用指数为Gamma = 3.08 +/- 0.34_stat +/- 0.2_sys的幂律很好地描述。积分通量为Phi（E > 200 GeV）=（12.2 +/- 2.6）X 10^-12 cm^-2 s^-1，相当于蟹状星云的约6%。光变曲线没有显示VHE通量变化的任何证据。利用银河系外背景光在近中红外波段的密度下限，我们能够限制1 ES 1218+304的内禀能谱范围。我们表明，固有光子谱具有比Gamma = 2.32 +/- 0.37_stat更硬的指数。当包括来自1 ES 1101-232和1 ES 0229+200的谱的约束时，1 ES 1218+304的谱可能比Gamma = 1.86 +/- 0.37_stat更难。
英文摘要：
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 a statistical significance of 10.4 standard deviations (10.4 sigma) for the observations taken during the first three months of 2007, confirming the discovery of this object made by the MAGIC collaboration. 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 is Phi(E > 200 GeV) = (12.2 +/- 2.6) X 10^-12 cm^-2 s^-1, which 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 in the near to mid-infrared we are able to limit the range of intrinsic energy spectra for 1ES 1218+304. We show that the intrinsic photon spectrum has an index that is harder than Gamma = 2.32 +/- 0.37_stat. 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_stat.
Here we present highlights from VERITAS observations of high-frequency-peaked BL Lac objects (HBLs). We discuss the key science motivations for observing these sources -- including performing multiwavelength campaigns critical to understanding the emission mechanisms at work in HBLs, constraining the intensity and spectra shape of the extragalactic background light, and placing limits on the strength of the intergalactic magnetic field.
VERITAS, an array of imaging atmospheric-Cherenkov telescopes, studies blazars in the energy range between ~100 GeV and ~30 TeV. With its excellent sensitivity at these energies, and ever-deepening source exposures, VERITAS is in a position to probe distant blazars for clear absorption signatures in their very-high-energy gamma-ray spectra due to interactions with the extragalactic background light (EBL). We discuss results from recent VERITAS observations of PG 1553+113 (z > 0.4) which have resulted in the most significant very-high-energy detection ever obtained for this source. The most rec…
High-frequency-peaked BL Lacs (HBLs) dominate the extragalactic TeV sky, with more than 50 objects detected by the current generation of TeV observatories. Still, the properties of TeV-emitting HBLs as a population are poorly understood due to biases introduced by the observing strategies of Cherenkov Telescopes, limiting our ability to estimate the potential contribution of TeV blazars to the diffuse neutrino, gamma-ray, and cosmic-ray background as well as their role in the late-stage evolution of active galactic nuclei. The VERITAS telescope array has designed a program to quantify and mini…
The discovery of the high-frequency-peaked BL Lac object 1ES 0806+524 (z=0.138) as a source of very-high-energy (VHE, E>100 GeV) gamma-ray photons was announced in 2008 by the VERITAS Collaboration, at a level of 1.8% of the Crab Nebula flux above 300 GeV. Since then, VERITAS has continued observing the source over multiple seasons, significantly improving the significance of the detection. We report the results of the analysis of the 2006-2014 VERITAS data, corresponding to a total exposure of about 70 hours. We present the new, average VHE spectrum of the source, together with the multi-year…
The VERITAS array of 12-m atmospheric-Cherenkov telescopes in southern Arizona is one of the world's most-sensitive detectors of very-high-energy (VHE, E>100 GeV) gamma rays. More than 50 extragalactic sources are known to emit VHE photons; these include blazars, radio galaxies, and starburst galaxies. Blazar observations are one of the VERITAS Collaboration's Key Science Projects. More than 400 hours per year are devoted to this program and ~100 blazars have already been observed with the array, in most cases with the deepest ever VHE exposure. These observations have resulted in 21 detection…
VERITAS is an array of four imaging atmospheric Cherenkov telescopes that observes gamma-ray sources in the very high energy range (VHE, E>100 GeV). A large fraction of the known gamma-ray sources are of extragalactic origin and belong to the blazar class: active galactic nuclei with relativistic jets pointing along the line of sight. Gamma-ray emission from blazars is typically variable. Part of the VERITAS observation program is devoted to follow-up triggers on flaring blazars, initiated by observations at other wavelengths. We will present those target of opportunity observations based on o…
The improved sensitivity of current-generation atmospheric-Cherenkov telescope (ACT) arrays enables us to probe for the first time low-frequency-peaked and intermediate-frequency-peaked BL Lac (LBL and IBL, respectively) objects as very high energy (VHE) $γ$-ray emitters. VERITAS is currently one of the most sensitive VHE gamma-ray observatories in the world and is particularly suited to study these objects. In this paper we will present recent results from VERITAS observations of a selected set of LBLs and IBLs.
VERITAS is the high-sensitivity instrument of latest generation. It is often used for the short AGN monitoring exposures evenly distributed over entire observational season of a source of interest. Each of these exposures is long enough to detect the source at the flux level of about 1 Crab. During the 2009 observing season a number of exposures of Mkn 501 with VERITAS revealed variable TeV gamma-ray emission at the flux level eventually exceeding 2 Crab. The spectral and flux variability measurements in TeV gamma rays for the 2009 data sample of Mkn 501 are summarized in this paper.
The BL Lac object 1ES 0229+200 is a firmly established very-high-energy (VHE; E >100 GeV) source. Located at a redshift of 0.1396, its published VHE spectrum is particularly hard (Gamma ~2.5) and is widely used to perform studies on the extragalactic background light (EBL) and the intergalactic magnetic field (IGMF). We present here the results of a long-term observing campaign on 1ES 0229+200 with VERITAS, lasting from 2009 to 2012, supported by multi-wavelength observations. We discuss the VERITAS results with a particular emphasis on the implications for the synchrotron-self-Compton modelin…
BL Lacertae is the prototype of the blazar subclass known as BL Lac type objects. BL Lacertae object itself is a low-frequency-peaked BL Lac(LBL). Very high energy (VHE) gamma ray emission from this source was discovered in 2005 by MAGIC observatory while the source was at a flaring state. Since then, VHE gamma rays from this source has been detected several times. However, all of those times the source was in a high activity state. Former studies suggest several non-thermal zones emitting in gamma-rays, then gamma-ray flare should be composed of a convolution. Observing the BL Lacertae object…
Most of the ~50 blazars detected to date at TeV energies (E>0.1 TeV) are high-frequency-peaked BL Lacs (HBLs). Only a handful episodic TeV detections of low- and intermediate-frequency-peaked BL Lacs (LBL/IBLs, with synchrotron peak frequencies in the infrared and optical regime) have been reported, typically during high-flux states. The VERITAS array, a ground-based TeV observatory located in southern Arizona has observed five known TeV LBL/IBLs since 2009: 3C 66A, W Comae, PKS 1424+240, S5 0716+714 and BL Lacertae, with at least 5-10 hours/year, which so far resulted in the detection of a br…
We report on the discovery of two gamma-ray sources at E > 200 GeV with VERITAS: RX J0648.7+1516 and VER J0521+211. Both sources are located at low galactic latitudes (|b| < 10 deg), and were previously classified as active galactic nuclei of unknown type. The discovery and characterization of gamma-ray emission together with follow-up optical spectroscopy permitted the identification of RX J0648.7+1516 and VER J0521+211 as BL Lac-type blazars. In the case of RX J0648.7+1516, a spectroscopic redshift of z = 0.179 was derived.
The giant radio galaxy M 87 is located at a distance of 16.7 Mpc and harbors a super-massive black hole (6 billion solar masses) in its center. M 87 is one of just three radio galaxies known to emit TeV gamma-rays. The structure of its relativistic plasma jet, which is not pointing towards our line of sight, is spatially resolved in X-ray (Chandra), optical and radio (VLA/VLBA) observations. The mechanism and location of the TeV emitting region is one of the least understood aspects of AGN. In spring 2008 and 2010, the three TeV observatories VERITAS, MAGIC and H.E.S.S. detected two major TeV …
The Crab pulsar has been widely studied across the electromagnetic spectrum from radio to gamma-ray energies. The exact nature of the emission processes taking place in the pulsar is a matter of broad debate. Above a few GeV the energy spectrum turns over suddenly. The shape of this cutoff can provide unique insight in to the particle acceleration processes taking place in the pulsar magnetosphere. Here we discuss the detection of pulsed gamma-rays from the Crab Pulsar above 100 GeV with the VERITAS telescopes in the context of measurements made with the Fermi space telescope below 10 GeV. Lim…
1ES 1218+304 is a moderate-redshift (z = 0.182) high-frequency-peaked BL Lac object (HBL). Detected by both the MAGIC and VERITAS gamma-ray observatories, 1ES 1218+304 is frequently monitored by VERITAS as part of its long-term blazar monitoring program. On the 3rd of January 2019, during a regularly scheduled blazar snapshot, VERITAS observed 1ES 1218+304 to have an elevated VHE flux state which continued through January 5 (ATEL #12360). In addition to VERITAS observations, MAGIC also detected elevated VHE emission (ATEL #12354) and Swift-BAT/XRT and Tuorla observations, in X-ray and optical …
Radio galaxies are the only non-blazar AGN detected in the VHE (E > 100 GeV) band. These objects enable the investigation of the main substructures of the AGN, in particular the core, the jet and its interaction with the intergalactic environment. VERITAS observations have included exposures on a number of radio galaxies. Recently, the discovery by Fermi of GeV emission from the radio galaxy NGC 1275 triggered VERITAS observations of this source. Results from the VERITAS observations of radio galaxies and future plans are presented.
Our goal is to understand the nature of blazars and the mechanisms for the generation of high-energy $γ$-rays, through the investigation of the blazar 3C 66A. We model the high energy spectrum of 3C 66A, which has been observed recently with the Fermi-LAT and VERITAS telescope. The spectrum has a hard change from the energy range of 0.2-100 GeV to 200-500 GeV in recent almost contemporaneous observations of two telescopes. The de-absorbed VERITAS spectrum greatly depends on the redshift, which is highly uncertain. If z=0.444 is adopted, we are able to use the SSC model to produce the Fermi-LAT…
VERITAS is one of the world's most sensitive detectors of astrophysical very high energy (VHE; E > 100 GeV) gamma rays. This observatory has operated for ~14 years, and nearly 7,000 hours of its observations have been targeted on active galactic nuclei (AGN). Approximately 300 AGN were observed with VERITAS, and 40 are detected. These studies are generally accompanied by contemporaneous, broadband observations, which enable detailed probes of the underlying jet-powered processes. Recent scientific results from VERITAS AGN observations are presented.
Intermediate-frequency-peaked BL Lacertae objects (IBLs) are a class of blazars characterized by a spectral energy distribution (SED) with a lower-energy synchrotron peak than the majority of extragalactic sources detected by ground-based imaging atmospheric Cherenkov telescopes (IACTs). Consequently, the peak gamma-ray flux falls outside the very-high-energy regime (VHE, >100 GeV) covered by IACTs such as VERITAS, making IBLs difficult to detect except during infrequent episodes of elevated flux. However, the study of these sources in a low-flux state is essential for developing a complete un…
VERITAS is one of the world's most sensitive detectors of astrophysical VHE (E $>$ 100 GeV) gamma rays. This array of four 12-m imaging atmospheric-Cherenkov telescopes has operated for 12 years, and $>$6,000 hours of observations have been targeted on active galactic nuclei (AGN). Approximately 300 AGN have been observed with VERITAS, and 39 are detected. Most of these detections are accompanied by contemporaneous, broadband observations, which enable detailed studies of the underlying jet-powered processes. Recent highlights from the VERITAS AGN observation program and scientific results are…
The VERITAS array of four 12-m imaging atmospheric-Cherenkov telescopes began full-scale operations in 2007, and is one of the world's most sensitive detectors of astrophysical VHE (E>100 GeV) $γ$-rays. Observations of active galactic nuclei (AGN) are a major focus of the VERITAS Collaboration, and more than 60 AGN, primarily blazars, are known to emit VHE photons. Approximately 3400 hours have been devoted to the VERITAS AGN observation program and roughly 160 AGN are already observed with the array, in most cases with the deepest VHE exposure to date. These observations have resulted in 34 d…
The VERITAS array of four 12-m imaging atmospheric-Cherenkov telescopes began full-scale operations in 2007, and is one of the world's most sensitive detectors of astrophysical very high energy (VHE; E>100 GeV) gamma rays. Observations of active galactic nuclei (AGN) are a major focus of the VERITAS Collaboration, and more than 60 AGN, primarily blazars, are known to emit VHE photons. Approximately 4000 hours have been devoted to the VERITAS AGN observation program, resulting in 34 detections. Most of these detections are accompanied by contemporaneous, broadband observations, enabling a more …
During May 2013, a gamma-ray flare from the BL Lac object 1ES 1727+502 (z=0.055) has been detected with the VERITAS Cherenkov telescopes. This detection represents the first evidence of very-high-energy (E>100 GeV) variability from this blazar and has been achieved using a reduced-high-voltage configuration which allows observations under bright moonlight. The integral flux is about five times higher than the archival VHE flux measured by MAGIC. The detection triggered additional VERITAS observations during standard dark-time and multiwavelength observations from infrared to X-rays with the FL…
The VERITAS array of 12-m atmospheric-Cherenkov telescopes in southern Arizona is currently the world's most-sensitive detector of astrophysical very high energy (VHE; E>100 GeV) gamma rays. Approximately 25 blazars are known to emit VHE photons, and observations of blazars are one of the VERITAS collaboration's key science projects (KSP). More than 50 of these objects have been observed with the array, in most cases with the deepest-ever VHE exposure. This contribution summarizes the VERITAS blazar KSP, with a focus on the upper limits measured in the blazar discovery program. VERITAS blazar …
Since the commissioning of the array in Spring 2007, the VERITAS array (sensitive in the 0.1-50 TeV energy range) has acquired over 300 hours of observations investigating the TeV emission from X-ray binary star systems, in particular focusing on the known TeV binary targets LS I +61 303 and HESS J0632+057. Both TeV binaries have been monitored by VERITAS for several years and the resulting dataset is continuing to yield important results in the characterization of these poorly understood systems. We present these results, as well as the contemporaneous observations of these sources taken with…
The VERITAS array of 12-m atmospheric-Cherenkov telescopes in southern Arizona began full-scale operations in 2007, and it is one of the world's most sensitive detectors of astrophysical VHE (E > 100 GeV) gamma rays. Forty-one blazars are known to emit VHE photons, and observations of blazars are one of the VERITAS Collaboration's Key Science Projects (KSPs). More than 400 hours per year are devoted to this program, and ~100 blazars have already been observed with the array, in most cases with the deepest-ever VHE exposure. These observations have resulted in 20 detections, including 10 new VH…
The intermediate-frequency-peaked BL Lac object 3C 66A was detected in a flaring state by the Fermi-LAT and VERITAS observatories in October 2008. These data and follow-up observations at other wavelengths create a rich sample of light curves and a constraining spectral energy distribution (SED). This is the first time that simultaneous observations at GeV and TeV energies were obtained for a flaring blazar. Results from these joint Fermi-LAT and VERITAS observations are presented in this conference proceeding.
VERITAS is an array of four 12-m atmospheric Cherenkov telescopes, designed to observe the very-high-energy (VHE; E $\geq$100 GeV) sky. Since 2007, it has detected more than 20 extra-galactic sources, the majority of which are active-galactic-nuclei of the blazar class. In this paper we present a selection of the most recent results from the VERITAS blazar observing program, in particular in the context of broad-band multi-wavelength campaigns. Four results are highlighted: the detection of the flat-spectrum-radio-quasar PKS 1222+216 (4C +21.35) during March 2014; the $γ$-ray flare from the BL…
The VERITAS collaboration has approved long-term observations on several distant, hard-spectrum blazars. We present first results from VERITAS long-term observations of 1ES1218+304, 1ES0229+200, and 1ES0414+009. Gamma-ray observations of distant, hard-spectrum blazars has emerged as an effective, indirect probe of the universe's diffuse extragalactic background light (EBL), due to the extinction of gamma-rays via the pair production interaction $γ_{TeV}γ_{EBL}\rightarrow e^{+}e^{-}$, which is expected to produce absorption features in distant gamma-ray sources. The sources presented here emit …
The gamma-ray binary HESS J0632+057 has been observed at very-high energies for almost ten years by all major systems of imaging atmospheric Cherenkov telescopes. We present new observations taken by the VERITAS observatory and an updated analysis of the previously published observations. HESS J0632+057 has been detected by VERITAS with a total significance $>20σ$ at energies above 350 GeV in about 200 hours of observations. The exposure covers now almost the entire orbital period of 315 days including the flux enhancements at phases $\approx$0.35 and, for the first time, detected with VERITAS…
The VERITAS array of four 12-m diameter imaging atmospheric-Cherenkov telescopes in southern Arizona is used to study very high energy (VHE; E>100 GeV) gamma-ray emission from astrophysical objects. VERITAS is currently the most sensitive VHE gamma-ray observatory in the world and one of the VERITAS collaboration's Key Science Projects (KSP) is the study of blazars. These active galactic nuclei (AGN) are the most numerous class of identified VHE sources, with ~30 known to emit VHE photons. More than 70 AGN, almost all of which are blazars, have been observed with the VERITAS array since 2007, …
VERITAS is one of the world's most sensitive detectors of astrophysical VHE (Very High Energy; E > 100 GeV) gamma rays. This array of four 12-m imaging atmospheric-Cherenkov telescopes has operated for ~10 years, and nearly 5000 hours of observations have been targeted on active galactic nuclei (AGN). These studies of blazars and radio galaxies have resulted in 36 detections. Most of these detections are accompanied by contemporaneous, broadband observations, which enable detailed studies of the underlying jet-powered processes. Recent highlights from the VERITAS AGN observation program and sc…
HESS J1943+213 is a very-high-energy (VHE; >100 GeV) gamma-ray point source detected during the H.E.S.S. Galactic Plane Survey. Radio, infrared, X-ray, and GeV gamma-ray counterparts have been identified for HESS J1943+213; however, the classification of the source is still uncertain. Recent publications have argued primarily in favor of an extreme BL Lac object behind the Galactic plane, though the scenario that HESS J1943+213 is a young pulsar wind nebula is viable as well. We present deep VERITAS observations of HESS J1943+213, which provide the most significant VHE detection of the source …
The VERITAS array of Cherenkov telescopes was used to observe ~130 blazars from 2007 to 2012. Of these, 25 were detected as very-high-energy (VHE; E > 100 GeV) sources. We present here the results of the analysis of 65 VERITAS non-detected blazars, including upper limits on their VHE flux. Results from a stacked analysis of the entire data set and of smaller sub-sets (defined as a function of the redshift and the blazar class) are presented and discussed.
In any given 24-hour period, the Fermi-LAT detects photons with energies of order 100 GeV not associated with any known VHE emitter. The RA/Dec of these photons frequently falls into the field of view of VERITAS the following evening. A single photon in the LAT can potentially mean many detectable photons on the ground due to the superior collection area of the IACT (Imaging Atmospheric Cherenkov Technique) method. During the 2011-2012 observing season, VERITAS implemented a new target-of-opportunity (ToO) program to trigger VERITAS observations on a small sample of the highest energy LAT phot…
Located in southern Arizona, VERITAS is amongst the most sensitive detectors for astrophysical very high energy (VHE; E>100 GeV) gamma rays and has been operational since April 2007. We highlight some recent results from VERITAS observations. These include the long-term observations of the gamma-ray binaries HESS J0632+057 and LS I +61° 303, the observations of the Galactic Center region, and of the supernova remnant Cas~A. We discuss the results from a decade of multi-wavelength observations of the blazar 1ES 1215+303, the EHT 2017 campaign on the M87 galaxy, the discovery of 3C 264 in VHE, a…
The study of $γ$-ray emission from galactic sources such as supernova remnants (SNR) may provide key insights into their potential role as accelerators of cosmic rays up to the knee ($\sim 10^{15}$ eV). The VERITAS Observatory is sensitive to galactic and extragalactic $γ$-ray sources in the 100 GeV to 30 TeV energy range. We report here on VERITAS observations of the vicinity of the cocoon of freshly accelerated cosmic rays reported by Fermi, which lies between potential accelerators in the Cygnus OB2 association and the $γ$-Cygni SNR. A particular focus is placed on the source VER J2019 +407…
HESS J0632+057 is an unidentified gamma-ray source located in the Monoceros region, probably associated with the massive Be star MWC 148. H.E.S.S. and VERITAS observations in the very high energy (VHE) range combined with Swift X-ray data indicate that this object is a new member of the elusive gamma-ray binary class. We present here results of VHE gamma-ray observations from VERITAS and HESS at energies above 100 GeV taken over more than six years. The observations confirm HESS J0632+057 as a point-like VHE source with a significance of more than 12 standard deviations. The VHE gamma-ray resu…
The gamma-ray binary HESSJ0632+057 (VERJ0633+057) has been observed at very-high energies for a decade by all major systems of imaging atmospheric Cherenkov telescopes. We present here new observations taken by the VERITAS observatory during the season 2015-2016. The observations cover now all phases of the binary orbit (with its period of about 315 days), showing clearly enhancements around phases 0.35 and 0.75. The results are discussed along with simultaneous observations with Swift's X-Ray Telescope.
During its first cycle of observations, VERITAS observed several GRBs in response to broadcast alerts from the Gamma-ray bursts Coordinates Network (GCN). The GRBs were followed up and observed thereafter with typical delays of 2 to 4 minutes from the beginning of the burst and of 92 s in the best case, searching for a very high energy (VHE) component above 100 GeV. The aim of the search for VHE emission from GRBs is to understand the behavior, composition and dynamics of the most accelerated particles in the bursts, as well as to get a better overall understanding of the model of GRBs. We rep…
The canonical observation mode for IACT gamma-ray observations employs four discrete pointings in the cardinal directions (the "wobble" mode). For the VERITAS Observatory, the target source is offset by 0.5-0.7 degrees from the camera center, and the observation lasts 20 minutes. During January/February of 2011, the VERITAS Observatory tested a new "orbit" observation mode, where the target source is continuously rotated around the camera center at a fixed radial offset and constant angular velocity. This mode of observation may help better estimate the cosmic ray background across the field o…
Gamma-ray binaries are variable sources of GeV-to-TeV photons with the peak in their spectral energy distributions above 100 MeV. There are only five Galactic gamma-ray binaries known and the processes which govern particle acceleration, non-thermal emission and the variability patterns are not well understood. We present here for the first time results of the VERITAS binary discovery program at VHE energies and a summary of eleven years of observations of the gamma-ray binary HESS J0632+057. VERITAS has acquired more than 220 hours of observations on HESS J0632+057. The results are discussed …
A few Galactic objects are known to be variable sources of photons with energies above 100 GeV. These systems are mostly binaries, where variability can often be connected to the orbital period. Particle acceleration and gamma-ray production processes in binaries are generally not well understood. We present here an overview of VERITAS observations of binary systems at very-high energies (VHE) with emphasis on LS I +61 303 and 1A0535+262. The results are discussed in the context of recent observations of RXTE, Swift and Fermi LAT at X- and Gamma-ray energies.
VERITAS is an array of four 12-m diameter imaging atmospheric-Cherenkov telescopes located in southern Arizona. Its aim is to study the very high energy (VHE: E > 100 GeV) gamma-ray emission from astrophysical objects. The study of Active Galactic Nuclei (AGN) is intensively pursued through the VERITAS blazar key science project, but also through the large MWL observational campaigns on radio galaxies. The successful VERITAS AGN research program has provided insights to the jet inner structures and started a more detailed classification of blazars. Moreover, the synergy between Fermi and VERIT…
Supernova remnants (SNRs) are widely considered the most likely source of cosmic rays below the knee ($10^{15}$ eV). Studies of GeV and TeV gamma-ray emission in the vicinity of SNRs, in combination with multi-wavelength observations, can trace and constrain the nature of the charged particle population believed to be accelerated within SNR shocks. They may also speak to the diffusion and propagation of these energetic particles and to the nature of the acceleration mechanisms involved. We report here on recent observations of SNRs with VERITAS, including the discoveries of VHE gamma-ray emiss…
The VERITAS array of 12-m atmospheric-Cherenkov telescopes in southern Arizona began full-scale operations in 2007, and is one of the world's most-sensitive detectors of astrophysical VHE (E>100 GeV) gamma rays. Approximately 50 blazars are known to emit VHE photons, and observations of blazars are a major focus of the VERITAS Collaboration. Nearly 2000 hours have been devoted to this program and ~130 blazars have already been observed with the array, in most cases with the deepest-ever VHE exposure. These observations have resulted in 21 detections, including 10 VHE discoveries. Recent highli…
Due to its extraordinarily high concentration of known relativistic particle accelerators such as pulsar wind nebula, supernova remnants, dense molecular cloud regions, and the supermassive black hole (Sgr A*); the center of the Milky Way galaxy has long been an ideal target for high energy (HE, 0.1-100 GeV) and very high energy ( VHE, 50 GeV-50 TeV) gamma-ray emission. Indeed, detections of Sgr A* and other nearby regions of gamma-ray emission have been reported by EGRET and Fermi-LAT in the HE band, as well as CANGAROO, Whipple, HESS, VERITAS, and MAGIC in the VHE band. Here we report on the…
CTA 1 (G119.5+10.2) is a composite supernova remnant (SNR) with a shell-type structure, visible in the radio band, surrounding a smaller pulsar wind nebula. Fermi detected a radio-quiet pulsar PSR J0007+7303 within the radio shell. 26.5 hours of VERITAS observation revealed extended TeV emission from CTA 1. The centroid of the TeV emission is located near the Fermi pulsar. The integral flux of the emission was ~4% of the Crab Nebula flux (>1TeV). We present an update on the source analysis with additional exposure and possible interpretations.
Magnetars are rotating neutron stars with extremely strong magnetic fields (~ 10^14-10^15 G). X-ray and soft gamma-ray observations have revealed the existence of non-thermal particle populations which may suggest emission of very high energy photons. VERITAS, an array of four 12m imaging atmospheric Cherenkov telescopes, is designed to observe gamma-ray emission between 100 GeV and 30 TeV. Here we present the results of VERITAS observations of two magnetars, 4U 0142+61 and 1E 2259+586.
The VERITAS array of 12-m atmospheric-Cherenkov telescopes is used in an intensive observation program focused on the discovery of VHE (E > 100 GeV) gamma-ray-emitting blazars. Since VERITAS began full-scale operation in 2007, more than 1000 hours of observation, on ~90 targets, have been devoted to the VHE blazar discovery effort and to timely follow-up in multi-wavelength (MWL) observation campaigns. These data have resulted in the discovery of VHE emission from 10 blazars (6 HBLs and 4 IBLs). A summary of these VHE discoveries is presented.
Fast radio burst (FRBs) are an exciting class of bright, extragalactic, millisecond radio transients. The recent development of large field-of-view (FOV) radio telescopes has caused a rapid rise in the number of identified single burst and repeating FRBs. This has allowed for the extensive multi-wavelength follow-up to search for the potential counterparts predicted by theoretical models. New observations of similar radio transients in Galactic magnetars like SGR 1935+2154 have continued to motivate the search for rapid optical and very-high-energy (VHE, >100 GeV) counterparts. Since 2016 VERI…
The giant radio galaxy M 87 is located at a distance of ~16 Mpc and harbors a supermassive black hole in its center. The structure of its relativistic plasma jet is resolved at radio, optical and X-ray wavelengths. M 87 belongs to the class of active galactic nuclei (AGN) and is one of the few extragalactic TeV gamma-ray source not belonging to the class of blazars. M 87 is also detected by Fermi in the GeV energy range. This makes it a unique laboratory for the study of the jet substructures and the morphology of the non-thermal emission processes. In spring 2010 a major flare was observed at…
We present long-term observations of several VHE (E > 100 GeV) blazars with VERITAS, together with contemporaneous Swift and RXTE X-ray data. The observed targets include Mrk 421, Mrk 501, 1ES 2344+514. Strong flux and spectral variability is seen in Mrk 421 on nightly time-scales between January and June 2008, revealing a highly correlated X-ray to GeV/TeV connection. Modest X-ray variability is evident in Mrk 501. Observations of 1ES 2344+514 in December 2007 show VHE gamma-ray and X-ray flux doubling on nightly time-scales.
The study of shell-type supernova remnants is a key science focus for the VERITAS TeV telescope array. Supernova remnants (SNRs) are widely considered to be the strongest candidate for the source of cosmic rays below the knee around 10^15 eV. This presentation will highlight new VERITAS results including new measurements of the spectra of Cas A and IC 443 and observations of the "Forbidden Velocity Wing" FVW 190.2+1.1. These results and their implications for the nature of the cosmic rays - hadronic or electronic - accelerated in the remnants will be discussed.
The Fermi space telescope has detected over 100 pulsars. These discoveries have ushered in a new era of pulsar astrophysics at gamma-ray energies. Gamma-ray pulsars, regardless of whether they are young, old, radio-quiet etc, all exhibit a seemingly unifying characteristic: a spectral energy distribution which takes the form of a power law with an exponential cut-off occurring between ~1 and ~10 GeV. The single known exception to this is the Crab pulsar, which was recently discovered to emit pulsed gamma rays at energies exceeding a few hundred GeV. Here we present an update on observations of…
The study of supernova remnants and pulsar wind nebulae was one of the Key Science Projects for the first two years of VERITAS observations. VERITAS is an array of four imaging Cherenkov telescopes located at the Whipple Observatory in southern Arizona. Supernova remnants are widely considered to be the strongest candidate for the source of cosmic rays below the knee at around 10^15 eV. Pulsar wind nebulae are synchrotron nebulae powered by the spin-down of energetic young pulsars, and comprise one of the most populous very-high-energy gamma-ray source classes. This poster will summarize the r…
We present a catalog of results of gamma-ray observations made by VERITAS, published from 2008 to 2020. VERITAS is a ground based imaging atmospheric Cherenkov telescope observatory located at the Fred Lawrence Whipple Observatory (FLWO) in southern Arizona, sensitive to gamma-ray photons with energies in the range of ~100 GeV - 30 TeV. Its observation targets include galactic sources such as binary star systems, pulsar wind nebulae, and supernova remnants, extragalactic sources like active galactic nuclei, star forming galaxies, and gamma-ray bursts, and some unidentified objects. The catalog…
CTA 1 (G119.5+10.2) is a composite supernova remnant (SNR) with a shell-type structure in the radio band and a center filled morphology at X-ray energies. Fermi has detected a radio-quiet pulsar PSR J0007+7303 within the radio shell of CTA 1 in a blind search within its first months of operation. Located within an X-ray synchrotron pulsar wind nebula (PWN), the Fermi source is spatially coincident with the EGRET source 3EG J0010+7309. We present the the detection of the system in very-high-energy (VHE) gamma rays by VERITAS, with a preliminary comparison to other TeV-detected PWNe.
Fast radio bursts (FRBs) are bright, unresolved, millisecond-duration flashes of radio emission originating from outside of the Milky Way. The source of these mysterious outbursts is unknown, but their high luminosity, high dispersion measure and short duration requires an extreme, high-energy, astrophysical process. The majority of FRBs have been discovered as single events which would require a chance coincidence for contemporaneous multiwavelength observations. However, two have been observed to repeat: FRB 121102 and the recently detected FRB 180814.J0422+73. These repeating FRBs have allo…
