VERITAS Observations of the γ‐Ray Binary LS I +61 303

Acciari, V. A.; Beilicke, M.; Blaylock, G.; Bradbury, S. M.; Buckley, J. H.; Bugaev, V.; Butt, Y.; Byrum, K.; Çelik, Ö.; Cesarini, A.; Ciupik, L.; Chow, Y. C. K.; Cogan, P.; Colin, P.; Cui, Wei; Daniel, M. K.; Duke, C.; Ergin, T.; Falcone, A.; Fegan, S. J.; Finley, J. P.; Fortin, P.; Fortson, L.; Gall, D.; Gibbs, K.; Gillanders, G. H.; Grube, J.; Guénette, R.; Hanna, D.; Hays, E.; Holder, J.; Horan, D.; Hughes, Shaun M. G.; Hui, C. M.; Humensky, T. B.; Kaaret, P.; Kieda, D.; Kildea, J.; Konopelko, A.; Krawczynski, H.; Krennrich, F.; Lang, M. J.; LeBohec, S.; Lee, K.; Maier, G.; McCann, A.; McCutcheon, M.; Millis, J.; Moriarty, P.; Mukherjee, R.; Nagai, T.; Ong, R. A.; Pandel, D.; Perkins, J. S.; Pizlo, Filip; Pohl, M.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Rose, H. J.; Schroedter, M.; Sembroski, G. H.; Smith, A. W.; Steele, D.; Swordy, S. P.; Toner, J. A.; Valcarcel, L.; Vassiliev, V. V.; Wagner, R. G.; Wakely, S. P.; Ward, J. E.; Weekes, T. C.; Weinstein, A. J.R.; White, R.; Williams, D. A.; Wissel, S.; Wood, M.; Zitzer, B.

doi:10.1086/587736

Cited by 178 publications

(176 citation statements)

References 38 publications

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“…Orbital modulations of the high-energy (HE, >100 MeV) and VHE fluxes have indeed been observed. The modulations unambiguously identify the gamma-ray source with the binary (Aharonian et al 2006;Albert et al 2006;Acciari et al 2008).…”

Section: Introductionmentioning

confidence: 87%

Relativistic Doppler-boosted emission in gamma-ray binaries

Dubus¹,

Cerutti²,

Henri³

2010

A&A

104

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Context. Gamma-ray binaries could be compact pulsar wind nebulae formed when a young pulsar orbits a massive star. The pulsar wind is contained by the stellar wind of the O or Be companion, creating a relativistic comet-like structure accompanying the pulsar along its orbit. Aims. The X-ray and the very high energy (>100 GeV, VHE) gamma-ray emission from the binary LS 5039 are modulated on the orbital period of the system. Maximum and minimum flux occur at the conjunctions of the orbit, suggesting that the explanation is linked to the orbital geometry. The VHE modulation has been proposed to be due to the combined effect of Compton scattering and pair production on stellar photons, both of which depend on orbital phase. The X-ray modulation could be due to relativistic Doppler boosting in the comet tail where both the X-ray and VHE photons would be emitted. Methods. Relativistic aberrations change the seed stellar photon flux in the comoving frame so Doppler boosting affects synchrotron and inverse Compton emission differently. The dependence with orbital phase of relativistic Doppler-boosted (isotropic) synchrotron and (anisotropic) inverse Compton emission is calculated, assuming that the flow is oriented radially away from the star (LS 5039) or tangentially to the orbit (LS I +61 • 303, PSR B1259-63).Results. Doppler boosting of the synchrotron emission in LS 5039 produces a lightcurve whose shape corresponds to the X-ray modulation. The observations imply an outflow velocity of 0.15-0.33c consistent with the expected flow speed at the pulsar wind termination shock. In LS I +61 • 303, the calculated Doppler boosted emission peaks in phase with the observed VHE and X-ray maximum. Conclusions. Doppler boosting is not negligible in gamma-ray binaries, even for mildly relativistic speeds. The boosted modulation reproduces the X-ray modulation in LS 5039 and could also provide an explanation for the puzzling phasing of the VHE peak in LS I +61 • 303.

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Section: Introductionmentioning

confidence: 87%

Relativistic Doppler-boosted emission in gamma-ray binaries

Dubus¹,

Cerutti²,

Henri³

2010

A&A

104

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“…5.1. The position of PSR J0248+6021 is at the corner of both the MAGIC (Albert et al 2006) and the VERITAS (Acciari et al 2008) TeV significance maps for LS I+61 • 303. No evidence of TeV emission from a putative PWN is apparent.…”

Section: Evidence Of a Pulsar Wind Nebula?mentioning

confidence: 99%

PSRs J0248+6021 and J2240+5832: young pulsars in the northern Galactic plane

Theureau

Parent

Cognard

et al. 2010

A&A

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Context. Pulsars PSR J0248+6021 (with a rotation period P = 217 ms and spin-down powerĖ = 2.13 × 10 35 erg s −1 ) and PSR J2240+5832 (P = 140 ms,Ė = 2.12 × 10 35 erg s −1 ) were discovered in 1997 with the Nançay radio telescope during a northern Galactic plane survey, using the Navy-Berkeley Pulsar Processor (NBPP) filter bank. The GeV gamma-ray pulsations from both were discovered using the Fermi Large Area Telescope. Aims. We characterize the neutron star emission using radio and gamma-ray observations, and explore the rich environment of PSR J0248+6021. Methods. Twelve years of radio timing data, including glitches, with steadily improved instrumentation, such as the Berkeley-Orleans-Nançay pulsar backend, and a gamma-ray data set 2.6 times larger than previously published allow detailed investigations of these pulsars. Radio polarization data allow comparison with the geometry inferred from gamma-ray emission models. Results. The two pulsars resemble each other in both radio and gamma-ray data. Both are rare in having a single gamma-ray pulse offset far from the radio peak. The anomalously high dispersion measure for PSR J0248+6021 (DM = 370 pc cm −3 ) is most likely due to its being within the dense, giant HII region W5 in the Perseus arm at a distance of 2 kpc, as opposed to being beyond the edge of the Galaxy as obtained from models of average electron distributions. Its large transverse velocity and the low magnetic field along the line-of-sight favor this small distance. Neither gamma-ray, X-ray, nor optical data yield evidence of a pulsar wind nebula surrounding PSR J0248+6021. We report the discovery of gamma-ray pulsations from PSR J2240+5832. We argue that it could be in the outer arm, although slightly nearer than its DM-derived distance, but that it may be in the Perseus arm at half the distance. Conclusions. The energy flux and distance yield a gamma-ray luminosity for PSR J0248+6021 of L γ = (1.4 ± 0.3) × 10 34 erg s −1 . For PSR J2240+5832, we find either L γ = (7.9 ± 5.2) × 10 34 erg s −1 if the pulsar is in the outer arm, or L γ = (2.2 ± 1.7) × 10 34 erg s −1 for the Perseus arm. These luminosities are consistent with an L γ ∝ √Ė rule. Comparison of the gamma-ray pulse profiles with model predictions, including the constraints obtained from radio polarization data, implies outer magnetosphere emission. These two pulsars differ mainly in terms of their inclination angles and acceleration gap widths, which in turn explain the observed differences in the gamma-ray peak widths.

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“…Observations are performed in moonless nights in the "wobble" mode of operation, where the telescopes are pointed to positions offset by ‫5.0ע‬Њ (alternating in direction) with respect to the source position, to allow for a simultaneous background estimation. More details about VERITAS, the data calibration, and the analysis techniques can be found in Acciari et al (2008).…”

Section: Veritas Consists Of Fourmentioning

confidence: 99%

VERITAS Discovery of >200 GeV Gamma-Ray Emission from the Intermediate-Frequency-Peaked BL Lacertae Object W Comae

Acciari

Aliu

Beilicke

et al. 2008

ApJ

Self Cite

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We report the detection of very high energy g-ray emission from the intermediate-frequency-peaked BL Lacertae object W Comae ( ) by VERITAS. The source was observed between 2008 January and April. A strong z p 0.102 outburst of g-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 . The integral photon flux above during those G p 3.81 ‫ע‬ 0.35 ‫ע‬ 0.34 200 GeV stat syst two nights corresponds to roughly of the flux from the Crab Nebula. Quasi-simultaneous Swift observations 9% at X-ray energies were triggered by the VERITAS observations. The spectral energy distribution of the flare data can be described by synchrotron self-Compton (SSC) or external Compton (EC) leptonic jet models.

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VERITAS Observations of the γ‐Ray Binary LS I +61 303

Cited by 178 publications

References 38 publications

Relativistic Doppler-boosted emission in gamma-ray binaries

Relativistic Doppler-boosted emission in gamma-ray binaries

PSRs J0248+6021 and J2240+5832: young pulsars in the northern Galactic plane

VERITAS Discovery of >200 GeV Gamma-Ray Emission from the Intermediate-Frequency-Peaked BL Lacertae Object W Comae

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