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Science Highlights from VERITAS
M. Santander – University of Alabama et al.
Deposited 07/15/2019
Citation of published version:
Staszak, D., et al. (2016): Science Highlights from VERITAS. Proceedings of Science, vol. 236 DOI: https://doi.org/10.22323/1.236.0868
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PoS(ICRC2015)868 http://pos.sissa.it/ SCIENCE SCIENCE PROCEEDINGS PROCEEDINGS OF † for the VERITAS Collaboration ∗ [email protected] Speaker. veritas.sao.arizona.edu VERITAS is a ground-based array ofof four the world’s 12-meter most telescopes sensitive detectors near of Tucson, veryITAS Arizona high has and energy a (VHE: is wide >100 one GeV) scientific gamma reachwell rays. that VER- as includes the the search study of forrays. extragalactic astrophysical In and this signatures Galactic presentation, of we objects will dark as present summarize some matter the of current and the status the scientific of highlights measurement the since VERITAS of 2013. observatory and cosmic ∗ † Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. ~ ~ flY4iil flY4iil c
The 34th International Cosmic Ray Conference, 30 July- 6 August, 2015 The Hague, The Netherlands McGill University E-mail: David Staszak Science Highlights from VERITAS PoS(ICRC2015)868 ], ], 8 3 165 ∼ ]. Each 1 David Staszak 30 TeV. VERITAS has > to map out the scientific pri- at 1 TeV (68% containment), an ◦ 100 m between telescopes[ ∼ Long Term Plan 2 ]. We collect data under bright moonlight conditions using 7 1400 hours of data per season, with two months of monsoons ∼ 50%[ ] and instrumented each of the cameras with new, high efficiency ]. In the current configuration, VERITAS can detect a 1% Crab 4 6 > 25%, and a pointing accuracy of less than 50 arcsec. − 25 hours and has an angular resolution of 0.1 ∼ field of view on the sky. Since inauguration, the array has undergone two major ◦ ]. The new PMTs collect significantly more light and have impacted the VERITAS science ]. This upgrade, when combined with a newly developed mirror alignment technique[ 5 shows the array in its current configuration and summarizes the overall sensitivity of these 2 VERITAS is now a mature scientific instrument that has completed 8 years of successful data VERITAS typically collects The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is a ground-based The VERITAS array was completed in 2007 and consists of four imaging atmospheric 1 collection with minimal hardware problems.from at The least VERITAS eight sourcesource different catalog source now discovery classes. lists to 54 collecting The objects bounty. scientific deep focus Last exposures of year on VERITAS the known has collaboration evolved objects developed from that a yield the most scientific two non-standard techniques, one withfilters reduced high placed voltage over PMT settings theconditions and PMTs. was the demonstrated other by with the The detection UV of utilityunder a bright of moonlight flare conditions. state aggressively in This a represents adding the BLdata first Lac observation by such object, VERITAS. publication time 1ES using 1727+502[ bright under moonlight these orities for the nextfor five our years. core The science planwithin plan, each reserves which of 70% includes the of a main our mix VERITAS science average of programs. yearly sources The observational that remaining time offer time the is most opened up scientific at impact an an- improved the angular resolution ofCrab the Nebula source instrument down and from brought 50replaced the hours the of sensitivity L2 observation for trigger to detecting 30 system[ hours. aPMTs[ 1% The second, over 2011-2012, programs where low energy sensitivity issoft critical. spectrum In AGN particular, that we would have noture now have detected been several possible new under thethree original hardware array configuration. configurations[ Fig- Nebula source in energy resolution of 15 in July and Augustcharacterized where by observation the moon is in impossible. the sky but Of with this moon illumination total, less than low 30%, moonlight accounts observations, for array located at theworld’s Fred most Lawrence sensitive Whipple gamma-ray instruments Observatory at in energies southern of Arizona 85 and GeV is to one of the Cherenkov telescopes (IACTs) with typical baselines of VERITAS Science Highlights 1. Introduction a wide scientific reach thatsearch includes for the astrophysical study signatures of of dark extragalacticwill matter and present and some Galactic the of objects measurement the of as recent cosmic scientificresults well highlights rays. shown as from at This the VERITAS, the paper focusing 2015 in ICRC particular on in those The Hague, Netherlands. telescope comprises a 12 m reflectorcreating and a an 3.5 imaging camera thathardware is upgrades. instrumented with The 499 first, PMTs, array[ in 2009, relocated one of the telescopes to better symmetrize the hours. Additionally, VERITAS has actively pursued observationswhere into the bright moon moonlight is conditions, illuminated PoS(ICRC2015)868 ~ J ! cuts [TeV] cuts cuts . cuts 1 soft soft soft cute : : soft 65% of all (V6): 10 soft (V4) (Vs) ; (VS): energy David Staszak ∼ (V6) 2007-2009 2012-today 2009-2012 operations HV operations ration Area filter educed r UV ective Configu Configuration Configuration Eff VERITAS • - 10 -VERITAS-GIFermi program 2 3 10 10 3 ° 40% of VERITAS observational time and cuts Energy(Tev1 ∼ StdMed for hours 50 with cuts cuts cuts sensitivity Medium Medium Medium , , , V4 V5 V6 At the top the VERITAS array is shown in its present configuration. Shown in the bottom left ------.....,.._ Differential http://fermi.gsfc.nasa.gov/ssc/proposals/veritas.html Extragalactic sources account for 1 Figure 1: panel is the VERITAS differentialprior sensitivity to using T1 similar cuts move, inbottom V5 all right - three panel after hardware are T1 configurations:bright VERITAS move moonlight effective V4 but observing areas - before configurations. for PMT these upgrade, hardware V6 configurations - as after well PMT as upgrade. fornual the Shown time-allocation two in competition. the Additionally, up tois 15% accessible, with of funding, the to total external VERITAS observation scientists time through the 2. Extragalactic Science VERITAS detections. All of these detections aregalaxy BL Lac M82 objects and with the three two exceptions, radio the galaxies100 starburst M87 northern and blazars NGC and 1275. pursues an VERITAS now activeknown multi-wavelength has and monitoring exposures candidate program on to objects. over detect BL flaresto in Lacs hours are to known years, to and exhibit catching fluxwhere an variation otherwise object on its in the a quiescent scale high state of state may minutes may be be too a dim. means to Further, discover besides VHE a emission means of discovering new VERITAS Science Highlights PoS(ICRC2015)868 -LAT ], here 9 15 hours ]. Unlike ∼ 15 Fermi David Staszak 3), but VERITAS has been . 0 ] and this source was targeted , effectively creating a gamma- 0.41), PKS 1222+16 (z=0.432), < − 20 < z e z ][ + < 19 + e → in 6 hours of VERITAS exposure[ 0.60), as well as two new source detections, ]. VERITAS has an active program to monitor -LAT as a good candidate for VHE observation VHE > σ γ 18 4 10 + ∼ Fermi EBL γ ]. The redshift of this object is unknown (photometrically 17 ][ 16 [ σ ]. The redshift for this object is particularly distant, z=0.939, mak- 14 0.58), PKS 1424+240 (z < z < 39) but it was identified by . 3). VERITAS observations were triggered by an email alert from the . 0 -LAT team[ 3 > ∼ -LAT data of known and potential VHE emitters[ Fermi FHL 1 Γ The scientific focus of blazar observations at VERITAS has historically been a mix of source One of the biggest blazar science stories over the last couple of years has been the detection Multi-wavelength (MWL) data is critical to blazar science during both flaring and quiescent The last six months have been particularly active for northern gamma-ray blazars, result- Fermi 5% Crab Nebula flux above 80 GeV. VERITAS observations were triggered by a detection the discovery and deep exposures onprogram, known VERITAS now objects. focuses the majority To of maximize itsgroup observational the time of scientific on sources. deep output This exposures of of program a is the select discussed blazar in more detail elsewhere in these proceedings[ of VHE gamma-ray sources thatthis are story. more and Most more blazars distant. are VERITAS relatively has close been (with at redshifts the of center of in their hard source catalog, 1FHLthe J2244.0+2020[ other recent flare detections, this source isdate rather ( soft and was not assumed toteam. be a good VHE candi- we will focus on a few recent highlights and ongoing studies. collecting a sizable list of more distant objects: 3C 66A (0.33 ing preliminary Extragalactic Background Light (EBL)J2243+203 constraints was for observed this flare for competitive. 280 RGB cumulative minutes significance between of Dec. 5.6 21stestimated and at Dec. z 24th, 2014, resulting in a for observations after it(z=0.135) exhibited is a an LBL/IBL flux that increase was detected in at the 1-100 GeV band. Finally, S3 1227+25 PG 1553+113 (0.43 S3 0218+357 (z=0.944), and PKSing 1441+25 because (0.939). VHE gamma Distant rays blazarsbackground are light are expected (EBL) cosmologically to via interest- interact pair with creation, intervening low-energy extragalactic states, and VERITAS has many ongoingof MWL the programs spectral energy and distribution partnerships. (SED)tions Broadband provides within a modelling the means source to jets, study the andensure relativistic to all particle distinguish VERITAS popula- between blazar different detections gamma-ray haveto emission MWL be models. data. compatible We with To the date, synchrotron mostfavor self-compton other VERITAS (SSC) SEDs mechanisms. emission are models, found though a few slightly ing in several new VERITASJ2243+203, detections and S3 of 1227+25. potentially PKS interestingtected 1441+25 by objects: is VERITAS and the PKS the second 1441+25, fifth flat RGB at spectrum VHE radio energies. quasar (FSRQ) VERITAS observed de- this object for VERITAS Science Highlights sources, flares provide a way toperiod accumulate of large time. gamma-ray statistics on Thiscosmological a can quantities given be can object be in used probed. a to short push spectral measurements to higher energies where many over the course of a∼ week starting the nightprevious of April night 15th, from 2015, MAGIC, andfrom which found the were it themselves to exhibit triggered a by steady monitoring and alert emails ray "horizon". The probability of this interaction is characterized by an exponential attenuation PoS(ICRC2015)868 David Staszak 100 GeV are ∼ Fermi-LAT and ) z ' )' [H 1( V ' ~ + --9-+ i- t t ' 0' 1 'tt ~ \+ -<> ' 0' 1 -t- ), we did not extend the energy for which on-corrected ) ti -+-+ ' 52 --+- 4 Fermi-LAT data are additionally shown, where both 10' 56 -+- o S " ) ) Absorption-corrected Absorp 5 ot'I i l 10 -+- 750 GeV energy range. Measured and deabsorbed using the EBL model from Gilmore[13]. Unfortu- 54682 t 54998 56368 D vs. 8.5σ ------.--- + − J D 2 J Observa M ( M i MJD 1 ( 2 2 ( 11 11 s 1 1 m e 0 0 r 0 e t t 1 1 10 1 iOn Fe ∼ St.a Sta 3 1 h data is also presented. Insets show the deabsorbed spectral points 20 Low Hig s - · Obsetvat -t u T T i e,o m ..... r n e a. 'it r F /UVO T -»4 l'.Jo 17 ... ¥' m 0 XRT/UVO XR Fermi 1 t t te r r ended i i n t Sw Sw Co Ex □ □ 3 inσ exposure(14.4 2. is the optical depth and depends on the object’s redshift and the gamma-ray 1 2 a- 11 u '11- '!! 1 1 1 13 6[12]. The early 2009 VERITAS dataset was complemented by a deep 2013 0 0 a τ 1 ∼ , 10 10 1 I0 10 10 , 0. :;. ~ 3: 3: ¥ "- ._ > z , where Broadband PKS 1424+240 SEDs for VERITAS data collected in 2009 and 2013, corresponding τ − e VERITAS blazar measurements can also be used to indirectly probe the magnetic fields that PKS 1424+240 is a HBL discovered by VERITAS in 2009 that was recently found to be very there was a spectral measurement. Inenergies both is datasets seen a after marginal correcting hardening foridence in EBL of the an absorption. spectrum overestimation at A of higher high theinternal energy EBL photon-photon spectral density hardening absorption or can or some be more gamma-raycosmic-ray ev- exotic production line-of-sight physical interactions. from mechanism, secondary such as cascades caused by nately, the flux in 2013with was the less factor than of in 2009, so while the detection of the source is improved spectra for these datasets are shown in Fig. energy. Of particular utility in these studies is the fact that gamma rays below dataset and both were analyzed over the factor, distant, with Figure 2: to relatively high and low states, respectively.contemporaneous Swift and and the full set of for both datasets. not expected to be significantlyVERITAS energies absorbed, can be so used a to extract comparisonspectra, information respectively. of about energy the intrinsic spectra and at absorbed gamma-ray VERITAS Science Highlights PoS(ICRC2015)868 16 15 − − 10 × , where the , and 10 10) 16 David Staszak 15 − − − 5 ( 10 , 10 < 14 . − σ = 10 data) / IGMF shows this comparison for three 3 11 2 + t ion t J052 imula VER S - - 6 2015 for energies between 160 GeV and 1 TeV. ICAC 1 - − s 1 VEAITAS 0.01 − 0 ) for three of the VERITAS blazars considered in [21], Mrk 501, VER 2 TeV 2 − 1 , 0. cm .... , 200. Shown in the top panels are the data in blue and simulated point sources .. 12 0.09 on − ati l 10 0.07 0.08 Simu Mrk501 0.06 - - 2.69× 0.05 0.04 2015 ICAC 0.03 - .... The angular distribution (θ .: • 0.02 211, and 1ES 0229+ . . ; VEAITAS • The VERITAS observations of seven VHE gamma-ray blazars have allowed for a sensitive Two starburst galaxies (SBGs), galaxies that are characterized by exceptionally high star for- using a three dimensional semi-analytical cascadea code[22]. range that The VERITAS could field potentially strengths be selectedexpected sensitive represent to, angular bounded broadening by would the limit be of object, too upper small limits to are detect. placed on Foremission the (as each fraction opposed field to of strength direct the and emission). total VERITAS Based measured on emission these arising ULs, from IGMF cascade strengths of search for an angularinvestigation broadening are signature hard-spectrum, of relatively the distantat IGMF[21]. point-source VHE blazars energies. The that The best are spatialthe sources strongly extent simulated for detected of VERITAS this the point-spread data type function for of (PSF). each Figure of these seven objects is compared with fill the voids between the large-scalethe structures of intergalactic the magnetic universe. field These (IGMF), fields,leaving are known their collectively believed as magnitude to and exist origin butrays as are a of difficult to critical order measure unresolved of directly, problem.positron hundreds pair As whose of described trajectory above, GeV is gamma sensitive aremicrowave to the expected background IGMF. to These (CMB) electrons interact photons canrays. then with to up-scatter Cascade the create cosmic gamma rays EBL, a would creating secondary exhibitof temporal an the cascade and IGMF, electron- spatial of such properties as lower imprinted a byinstrument energy time-delay the PSF. and gamma strength an angular broadening of the gamma-ray signal beyond the of the seven blazarsdependent considered limits here. are presented for No assumed significant IGMF strengths evidence of of B broadening is found. Model G are excluded at 95%that are confidence strong level. enough to Note isotropizefields that the considered a electron/positron here. non-detection pair at here Model-independent thecalculated does source limits assuming not and a on rule spectral only the index applies out matching flux to fields limits the the from intrinsic of spectral 0.17− extended index, emission resulting 99% were CL also upper (MC) in red. Shown in the bottom panels are the residuals defined as (MC− Figure 3: J0521+ VERITAS Science Highlights PoS(ICRC2015)868 David Staszak ◄) oli(2012) (2013} l . l a (2013) (201 , et al. al et et no&Capr i erezhko Slane Mor1 B Zhang • , . , ,. . , , . -- -- Fermi-LAT and VERITAS data in filled red 7 ' · -LATFermi data and upper limits of the extended object with VERITAS 10 10 E ., " ., w z 32 "C > - w S' Spectral energy distribution of the Tycho SNR with 0014. Our result on Arp 220 represents the most sensitive upper limits on a ULIRG at VHE VERITAS has a rich and varied Galactic program with 20 source detections, including super- At this conference we present several new Crab Nebula and pulsar results. This includes the Figure 4: energies to date and begins toSFR constrain and theoretical VHE models. emission We with further a test deepgalaxy the exposure to correlation on between the the nearby Milky galaxy Way M andtest 31. contains this M a correlation. 31 dense, is the star-forming In closest ring31 [24], spiral at which we lower is show energies of a with particular detailed interest analysis to of the detection and morphology of M mation rates (SFRs), have beenThese detected objects provide by strong VHE evidence gamma-rayand of instruments, represent the the M correlation only 82 between known andativistic high extragalactic NGC point-sources SFRs jet. detected 253. and at Ultra-luminous VHE VHE emission, infraredcosmic-ray energies galaxies without acceleration a (ULIRGs) and rel- are emission objectstain mechanisms. predicted large to They amounts exhibit are of[23], similar objects dust, we with show which high upper absorbs limits SFRs17208− the on that VHE object’s con- gamma-ray UV emission light, from two re-radiating ULIRGs, it Arp in 220 and the IRAS FIR. In data. 3. Galactic Science nova remnants (SNR), pulsar wind nebulae (PWN), high-masssources, x-ray and binaries one (HMXB), unidentified pulsar. From itsregions position of in intense the star northern formation hemisphere, like VERITASsar, is the the able Cygnus Galactic to arm, observe Center iconic region objects (above likeGalactic 2 the objects TeV), Crab as visible Nebula well to and VERITAS as pul- are most the of most the thoroughly historical studied SNRs. objects Many acrossfirst of the the VERITAS spectrum. measurement on thefinding extension no evidence of for the25]. extension[ VHE emission Further, we region show of contemporaneous the VERITAS Crab data taken Nebula, VERITAS Science Highlights squares and circles, respectively. Acomparison. representative sample of gamma-ray emission models is presented for PoS(ICRC2015)868 . With syst 30 David Staszak 0. ± stat 51 72 hours of VERITAS 0. ∼ ± 95 1. = 2 times more VERITAS data than 0.8 Γ ∼ Fermi-LAT energies and demonstrate no
1010
dN/dE [m dN/dE E GeV sr s
] -induced muon track events (events that have the best angular uncertainties,
•1 •1 •1 •2 3 µ ν Preliminary cosmic-ray electron spectrum from 4 TeV energy range. Also shown are other satellite-based and ground-based measurements with ∼ knowledge of the time dependence of the source light curve. Based on a Monte Carlo study, ). The list of observed positions includes 3 published events and 20 unpublished events that VERITAS has recently completed its eighth successful year of operations, and the scientific The IceCube discovery of an astrophysical flux of high energy neutrinos provides evidence of ◦ 1 priori ∼ have been shared with VERITAS through a cooperationshow agreement. no Observations statistically of significant these gamma-ray positions signalsfew and percent we of calculate the upper Crab Nebula limits flux in above the 100 range GeV of for a each position[49]. 8. Conclusion and Outlook output of VERITAS since the last ICRCfactors, conference including remains the strong. dedicated This operations is work madeVERITAS of possible observing the by program local many from FLWO source staff, discovery a toobjects, shift deep in exposures as on the well scientifically focus interesting as of the the cultivation of several strong MWL partnerships. Many of the outstanding the interaction of energetic hadrons and pointsrays[48]. to the sites However, of IceCube the acceleration eventsbeen of to high discovered. energy date cosmic For appear the isotropicevents, past and focusing two on no years neutrino VERITAS point-sources has have been observing the positions of IceCube GeV to overlapping energy data points. The besttion fit and to is the shown as VERITAS data an comes overlaid from dashed a line. broken The power-law gray distribu- band represents the systematical uncertainty. we determined that this method improvesreanalyze our a sensitivity sub-sample to of GRB-like VERITAS signals GRBs. and has been used to 7. IceCube Events Figure 8: VERITAS Science Highlights PoS(ICRC2015)868 David Staszak ], and HFit, a 2D 44 Astropart. Phys, 32, 2009 Fermi ][ 51 and to continue to operate until the data is shown in many of the results -LAT to increase communication and Fermi Swi ft NuSTAR ], a template method[ 42 ][ Astropart.Phys. 25, 391-401, 2006. 14 21 ][ 6 ]. These first results represent an avenue that VERITAS will 2013 ICRC proceedings, arXiv:1307.8360. 40 ]. Additionally, simultaneous A new mirror alignment system for the VERITAS telescopes. 50 VERITAS Telescope 1 Relocation: Details and Improvements. , since they are sensitive to the same non-thermal, relativistic populations of The First VERITAS Telescope. The VERITAS Upgraded Telescope-Level Trigger Systems: Technical Details and NuSTAR and Performance Characterization. proceedings, arXiv:0912.3841. 325, 2010. In addition to upgrading hardware, VERITAS is implementing new analysis techniques to Finally, the results presented here are only a subsample of the science coming from VERITAS This research is supported by grants from the U.S. Department of Energy Office of Science, The VERITAS Collaboration is grateful to Trevor Weekes for his seminal contributions and [3] McCann, A., et al. [4] Zitzer, B., et al. [2] Perkins, J., et al. [1] Holder, J., et al. improve the sensitivity ofadvanced our analysis instrument. methods as a Inboosted replacement decision these of tree the proceedings multivariate standard analyses[ we Hillas show box cuts, several including results the using use of for the last two years.utilize VERITAS overlap plans with to new operate instruments at like least HAWC and until 2019, giving us the opportunity to the U.S. National Science Foundation andWe the acknowledge Smithsonian the Institution, excellent and work byObservatory of and NSERC the at in the technical Canada. collaborating institutions support in staff the construction at and the operation of Fred the Lawrence instrument. Whipple leadership in the field of VHE gamma-ray astrophysics, which made this study possible. References since there is typically excellent coordinationare between the particularly two well instruments. matched HAWC for andsky VERITAS collaboration at since the they same time. view The essentiallyings HAWC the have experiment been same recently set completed region up their of between full the collaboration HAWC, array, VERITAS, between and and annual the meet- experiments. gaussian image fitting technique[ continue to improve, building techniques that will become standard in VERITAS analyses. next generation of ground-based arrays come online. Acknowledgements particles producing gamma-ray emission.this One conference of represents the MWL theseveral campaigns most absolutely of simultaneous complete Mrk snapshots broadband 501 allowing campaigngamma-ray presented SED energies[ at reconstruction on from this radio object through VHE to date, with VERITAS Science Highlights issues in VHE astrophysics willpaigns only are underway be to solved contemporaneously with studythe the MWL spectrum. nature data. In of particular, AGN Several jets we long-termSwi using benefit ft MWL instruments from across cam- simultaneous observations by X-ray instruments, like PoS(ICRC2015)868 David Staszak ApJ 800, 61, These 2011 ICRC ApJS 209, 34, 2013. ApJ 799, 7, 2015. These proceedings. These proceedings. These proceedings. These proceedings. These proceedings. These proceedings. arXiv:1506.06246 15 -ray flaring activity from the BL Lac object 1ES γ MNRAS 422, 3189, 2012. Proc. 32nd ICRC, 2011. 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