| Group Publications in Referred Journals: 2005 |
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The Near Infrared Background: Interplanetary Dust Or Primordial Stars?
E. Dwek, G. Arendt and F. Krennrich, Astrophysical Journal, in press, (astro-ph/0508262), 2005
The intensity of the diffuse ~ 1 - 4 micron sky emission from which solar system and Galactic
foregrounds have been subtracted is in excess of that expected from energy released by galaxies
and stars that formed during the z < 5 redshift interval (Arendt & Dwek 2003, Matsumoto et al. 2005).
The spectral signature of this excess near-infrared background light (NIRBL) component is almost
identical to that of reflected sunlight from the interplanetary dust cloud, and could therefore be
the result of the incomplete subtraction of this foreground emission component from the diffuse sky
maps. Alternatively, this emission component could be extragalactic. Its spectral signature is
consistent with that of redshifted continuum and recombination line emission from HII regions formed
by the first generation of very massive stars. In this paper we analyze the implications of this
spectral component for the formation rate of these Population III stars, the redshift interval during
which they formed, the reionization of the universe and evolution of collapsed halo masses. We find that
to reproduce the intensity and spectral shape of the NIRBL requires a peak star formation rate that is
higher by about a factor of 4 to 10 compared to those derived from hierarchical models. Furthermore, an
extragalactic origin for the NIRBL leads to physically unrealistic absorption-corrected spectra of distant
TeV blazars. All these results suggest that Pop III stars contribute only a fraction of the NIRBL intensity
with zodiacal light, star forming galaxies, and/or non-nuclear sources giving rise to the remaining fraction.
Eli Dwek, Richard G. Arendt, Frank Krennrich
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Is There an Imprint of Primordial Stars in the Tev Gamma-Ray Spectrum of Blazars?
Dwek, F. Krennrich and G. Arendt, Astrophysical Journal, in press, (see astro-ph0508133), 2005
The 1 - 5 micron diffuse sky emission from which local foreground emission from the solar system and
the Galaxy have been subtracted exceeds the brightness that can be attributed to normal star forming
galaxies. The nature of this excess near-infrared background light (NIRBL) is still controversial. On
one hand, it has been interpreted as a distinct spectral feature created by the redshifted emission from
primordial (Population III) stars that have formed at redshifts > 8. On the other hand, the NIRBL spectrum
is almost identical to that of the zodiacal cloud, raising the possibility that it is of local origin. Blazars
can, in principle, offer a simple test for the nature and origin of the NIRBL. Very high energy gamma-ray
photons emitted by these objects are attenuated on route to earth by photon-photon interactions with
the extragalactic background light (EBL). This paper examines whether the extragalactic nature of
the NIRBL can be determined from the analysis of the TeV spectra of blazars.
Eli Dwek, Frank Krennrich, Richard G. Arendt
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A Multiwavelength View of the TeV Blazar Markarian 421: Correlated Variability, Flaring and Spectral Evolution
M. Blazejowski et al. (with F. Krennrich, D.A. Lewis, T. Nagai)
We report results from a multi-wavelength monitoring campaign on Mrk 421 over the period of 2003-2004.
The source was observed simultaneously at TeV and X-ray energies, with supporting observations
frequently carried out at optical and radio wavelengths. The large amount of simultaneous data has
allowed us to examine the variability of Mrk 421 in detail. The variabilities are generally correlated
between the X-ray and gamma-ray bands, although the correlation appears to be fairly loose. The light
curves show the presence of flares with varying amplitudes on a wide range of timescales both at X-ray
and TeV energies. Of particular interest is the presence of TeV flares that have no coincident
counterparts at longer wavelengths, because the phenomenon seems difficult to understand in the context
of the proposed emission models for TeV blazars. We have also found that the TeV flux reached its peak
days before the X-ray flux during a giant flare in 2004. Such a difference in the development of the
flare presents a further challenge to the emission models. Mrk 421 varied much less at optical and
radio wavelengths. Surprisingly, the normalized variability amplitude in optical seems to be comparable
to that in radio, perhaps suggesting the presence of different populations of emitting electrons in
the jet. The spectral energy distribution (SED) of Mrk 421 is seen to vary with flux, with the two
characteristic peaks moving toward higher energies at higher fluxes. We have failed to fit the
measured SEDs with a one-zone SSC model; introducing additional zones greatly improves the fits.
We have derived constraints on the physical properties of the X-ray/gamma-ray flaring regions from
the observed variability (and SED) of the source. The implications of the results are discussed.
M. Blazejowski, I. C. De La Calle Perez, I. H. Bond, P. J. Boyle, S. M. Bradbury,
J. H. Buckley, D. A. Carter-Lewis, W. Cui, , M. Daniel , C. Dowdall, C. Duke, I. de la Calle Perez,
A. Falcone, D. J. Fegan, S. J. Fegan, J. P. Finley, L. Fortson, J. A. Gaidos, K. Gibbs, S. Gammell,
J. Hall, T. A. Hall, A. M. Hillas, J. Holder, D. Horan, M. Jordan, M. Kertzman, D. Kieda, J. Kildea,
J. Knapp, H. Krawczynski, F. Krennrich, S. LeBohec, E. T. Linton, J. Lloyd-Evans, P. Moriarty, D. Müller,
T. N. Nagai, R. Ong, M. Page, R. Pallassini, D. Petry, B. Power-Mooney, J. Quinn, P. Rebillot,
P. T. Reynolds, H. J. Rose, G. H. Sembroski, S. P. Swordy, V. V. Vassiliev, S. P. Wakely, G. Walker,
and T. C. Weekes
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The Energy Spectrum of the Blazar 1ES2344+514
M. Schroedter et al. Astrophysical Journal, in press, 2005
The BL Lacertae (BL Lac) object 1ES 2344+514 (1ES 2344), at a redshift of 0.044, was discovered as
a source of very high energy (VHE) gamma rays by the Whipple Collaboration in 1995 \citep{2344Catanese98}.
This detection was recently confirmed by the HEGRA Collaboration \citep{2344Hegra03}. As is typical for
high-frequency peaked blazars, the VHE gamma-ray emission is highly variable. On the night of 20 December,
1995, a gamma-ray flare of 5.3-sigma significance was detected, the brightest outburst from this
object to-date. The emission region is compatible with a point source. The spectrum between 0.8 TeV and
12.6 TeV can be described by a power law
$\frac{\ud^3 N}{\ud E \ud A \ud t}=(5.1\pm1.0_{st}\pm1.2_{sy})\times10^{-7} (E/ \mathrm{TeV})^{-2.54 \pm0.17_{st}\pm0.07_{sy}} \mathrm{\frac{1}{TeV m^2 s}}$.
Comparing the spectral index with that of the other five confirmed TeV blazars, the spectrum of 1ES 2344
is similar to 1ES 1959+650, located at almost the same distance. The spectrum of 1ES 2344 is steeper than
the brightest flare spectra of Markarian 421 (Mrk~421) and Markarian 501 (Mrk~501), both located at a
distance about 2/3 that of 1ES 2344, and harder than the spectra of PKS 2155-304 and H~1426+428, which
are located almost three times as far. This trend is consistent with attenuation caused by the infrared
extragalactic background radiation.
M. Schroedter, H. M. Badran, J. H. Buckley, J. Bussons Gordo, D. A. Carter-Lewis, C. Duke, D. J. Fegan,
S. F. Fegan, J. P. Finley, G. H. Gillanders, J. Grube, D. Horan, G. E. Kenny, M. Kertzman, K. Kosack,
F. Krennrich, D. B. Kieda, J. Kildea, M. J. Lang, Kuen Lee, P. Moriarty, J. Quinn, M. Quinn,
B. Power-Mooney, G. H. Sembroski, S. P. Wakely, V. V. Vassiliev, T. C. Weekes, and J. Zweerink
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Spectrum of Very High Energy Gamma Rays from the Blazar 1ES1959+650 During Flaring Activity in 2002
M. Daniel et al. (with F. Krennrich, D. A. Lewis, T. Nagai, M. Schroedter, A. Imran, M. Pohl) Astrophysical
Journal, 621, 181, 2005
The blazar 1ES 1959+650 was observed in a flaring state with the Whipple 10 m Imaging Atmospheric
Cherenkov Telescope during May of 2002. A spectral analysis has been carried out on the data from that
time period and the resulting very high energy gamma-ray spectrum ($E \geq 316$ GeV) can be well fit by a
power-law of differential spectral index \alpha = 2.78 +/- 0.12_{stat.} +/- 0.21_{sys.}. On June 4th
2002, the source flared dramatically in the gamma-ray range without any coincident increase in the X-ray
emission, providing the first unambiguous example of an `orphan' gamma-ray flare from a blazar. The
gamma-ray spectrum for these data can also be described by a simple power-law fit with \alpha = 2.82 +/-
0.15_{stat.} +/- 0.30_{sys.}. There is no compelling evidence for spectral variability, or for any
cut-off to the spectrum.
J. Holder, R.W. Atkins, H.M. Badran, G. Blaylock, S.M. Bradbury, J.H. Buckley, K.L. Byrum, D.A. Carter-Lewis,
O. Celik, Y.C.K. Chow, P. Cogan, W. Cui, M.K. Daniel, I. de la Calle Perez, C. Dowdall, P. Dowkontt, C. Duke,
A.D. Falcone, S.J. Fegan, J.P. Finley, P. Fortin, L.F. Fortson, K. Gibbs, G. Gillanders, O.J. Glidewell, J. Grube,
K.J. Gutierrez, G. Gyuk, J. Hall, D. Hanna, E. Hays, D. Horan, S.B. Hughes, T.B. Humensky, A. Imran, I. Jung, P. Kaaret,
G.E. Kenny, D. Kieda, J. Kildea, J. Knapp, H. Krawczynski, F. Krennrich, M.J. Lang, S. LeBohec, E. Linton, E.K. Little,
G. Maier, H. Manseri, A. Milovanovic, P. Moriarty, R. Mukherjee, P.A. Ogden, R.A. Ong, J.S. Perkins, F. Pizlo, M. Pohl,
J. Quinn, K. Ragan, P.T. Reynolds, E.T. Roache, H.J. Rose, M. Schroedter, G.H. Sembroski, G. Sleege, D. Steele
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SGARFACE: A Novel Detectors For Gamma Ray Bursts
S. LeBohec, F. Krennrich & G. Sleege, Astroparticle Physics, 23, 238-248, 2005
The Short GAmma Ray Front Air Cherenkov Experiment (SGARFACE) is operated at the Whipple Observatory
utilizing the Whipple 10m gamma-ray telescope. SGARFACE is sensitive to gamma-ray bursts of more than
100MeV with durations from 100ns to 35us and provides a fluence sensitivity as low as 0.8 gamma-rays per
m^2 above 200MeV (0.05 gamma-rays per m^2 above 2GeV) and allows to record the burst time structure.
S. LeBohec, F. Krennrich & G. Sleege
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Simultaneous Constraints on the Spectrum of the Extragalactic Background Light
and the Intrinsic Tev Spectra of Mrk 421, Mrk 501, and H1426+428
E. Dwek and F. Krennrich, Astrophysical Journal, 618, 657, 2005.
Very high energy (~ TeV) $\gamma$-rays from blazars are attenuated by photons from the extragalactic
background light (EBL). Observations of blazars can therefore provide an ideal opportunity for
determining the EBL intensity if their intrinsic spectrum is known. Conversely, knowledge of the EBL
intensity can be used to determine the intrinsic blazar spectrum. Unfortunately, neither the EBL
intensity nor the intrinsic blazar spectrum is known with high enough precision to accurately derive one
quantity from the other. In this paper we use the most recent data on the EBL to construct twelve
different realizations representing all possible permutations between EBL limits and the detections in
the different wavelength regions. We use these realizations to explore the effects of the EBL on the
inferred spectra of blazars. In particular, we show that the frequently cited "IR background-TeV
gamma-ray crisis" does not exist, and derive the intrinsic spectra and peak energies of the blazars Mrk
421, 501 and H1426+428 for EBL realizations that give rise to physically viable intrinsic blazar spectra.
We also show that the intrinsic spectrum of Mrk~421 during a period of intense flaring activity has a
peak energy that seems to shift to higher energies at higher flux states. Finally, we also explore the
effect of the uncertainties in the absolute calibration of the gamma-ray energies on derived TeV
opacities and the intrinsic blazar spectra.
E. Dwek and F. Krennrich
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A Survey of Unidentified EGRET Sources at Very High Energies
S. J. Fegan et al. (with F. Krennrich, D. A. Carter-Lewis,T. Nagai,
M. Schroedter) Astrophysical Journal, 624, 638, 2005
Observations of unidentified EGRET sources were made with the Whipple 10m imaging atmospheric Cherenkov
telescope between Fall 1999 and Spring 2001. During this period, a high resolution 490 pixel camera with
4 degree field of view was present on the telescope. Characterization of the off-axis response of this
instrument was done using observations of the Crab Nebula. No significant emission was detected from the
eight unidentified EGRET sources observed and upper limits are presented as a function of position.
S. J. Fegan, The VERITAS collaboration
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