116 research outputs found
XMM-Newton observations of the Vela pulsar
We present spectral analysis from XMM-Newton observations of the Vela pulsar.
We analyzed thermal emission from the pulsar dominating below ~ 1 keV since
extracted spectra are heavily contaminated by nebular emission at higher
energy. Featureless high-resolution spectra of the Reflection Grating
Spectrometer aboard XMM-Newton suggest the presence of a hydrogen atmosphere,
as previously indicated by Chandra results. Both the temperature and radius are
consistent with those values deduced from Chandra. The derived Chandra and
XMM-Newton temperature of T^{\infty} ~ (6.4-7.1)*10^5 K at its age of ~10^4
years is below the standard cooling curve.Comment: 6 pages, 3 figures, accepted for publication in Adv Sp Res:
Proceedings of the 34th COSPAR Scientific Assembl
Evidence for a Binary Companion to the Central Compact Object 1E 1207.4-5209
Unique among neutron stars, 1E 1207.4-5209 is an X-ray pulsar with a spin
period of 424 ms that contains at least two strong absorption features in its
energy spectrum. This neutron star has been identified as a member of the
radio-quiet compact central objects in supernova remnants. It has been found
that 1E 1207.4-5209 is not spinning down monotonically suggesting that this
neutron star undergoes strong, frequent glitches, contains a fall-back disk, or
possess a binary companion. Here, we report on a sequence of seven XMM-Newton
observations of 1E 1207.4-5209 performed during a 40 day window in June/July
2005. Due to unanticipated variance in the phase measurements beyond the
statistical uncertainties, we could not identify a unique phase-coherent timing
solution. The three most probable timing solutions give frequency time
derivatives of +0.9, -2.6, and +1.6 X 10^(-12) Hz/s (listed in descending order
of significance). We conclude that the local frequency derivative during our
XMM-Newton observing campaign differs from the long-term spin-down rate by more
than an order of magnitude, effectively ruling out glitch models for 1E
1207.4-5209. If the long-term spin frequency variations are caused by timing
noise, the strength of the timing noise in 1E 1207.4-5209 is much stronger than
in other pulsars with similar period derivatives. Therefore, it is highly
unlikely that the spin variations are caused by the same physical process that
causes timing noise in other isolated pulsars. The most plausible scenario for
the observed spin irregularities is the presence of a binary companion to 1E
1207.4-5209. We identified a family of orbital solutions that are consistent
with our phase-connected timing solution, archival frequency measurements, and
constraints on the companions mass imposed by deep IR and optical observations.Comment: 8 pages, 4 figures. To be published in the proceedings of "Isolated
Neutron Stars: from the Interior to the Surface" (April 24-28, 2006) - eds.
D. Page, R. Turolla & S. Zan
Implications of Compressed Supersymmetry for Collider and Dark Matter Searches
Martin has proposed a scenario dubbed ``compressed supersymmetry'' (SUSY)
where the MSSM is the effective field theory between energy scales M_{\rm weak}
and M_{\rm GUT}, but with the GUT scale SU(3) gaugino mass M_3<< M_1 or M_2. As
a result, squark and gluino masses are suppressed relative to slepton, chargino
and neutralino masses, leading to a compressed sparticle mass spectrum, and
where the dark matter relic density in the early universe may be dominantly
governed by neutralino annihilation into ttbar pairs via exchange of a light
top squark. We explore the dark matter and collider signals expected from
compressed SUSY for two distinct model lines with differing assumptions about
GUT scale gaugino mass parameters. For dark matter signals, the compressed
squark spectrum leads to an enhancement in direct detection rates compared to
models with unified gaugino masses. Meanwhile, neutralino halo annihilation
rates to gamma rays and anti-matter are also enhanced relative to related
scenarios with unified gaugino masses but, depending on the halo dark matter
distribution, may yet be below the sensitivity of indirect searches underway.
In the case of collider signals, we compare the rates for the potentially
dominant decay modes of the stop_1 which may be expected to be produced in
cascade decay chains at the LHC: \tst_1\to c\tz_1 and \tst_1\to bW\tz_1. We
examine the extent to which multilepton signal rates are reduced when the
two-body decay mode dominates. For the model lines that we examine here, the
multi-lepton signals, though reduced, still remain observable at the LHC.Comment: 22 pages including 24 eps figure
Neutralino, axion and axino cold dark matter in minimal, hypercharged and gaugino AMSB
Supersymmetric models based on anomaly-mediated SUSY breaking (AMSB)
generally give rise to a neutral wino as a WIMP cold dark matter (CDM)
candidate, whose thermal abundance is well below measured values. Here, we
investigate four scenarios to reconcile AMSB dark matter with the measured
abundance: 1. non-thermal wino production due to decays of scalar fields ({\it
e.g} moduli), 2. non-thermal wino production due to decays of gravitinos, 3.
non-thermal wino production due to heavy axino decays, and 4. the case of an
axino LSP, where the bulk of CDM is made up of axions and thermally produced
axinos. In cases 1 and 2, we expect wino CDM to constitute the entire measured
DM abundance, and we investigate wino-like WIMP direct and indirect detection
rates. Wino direct detection rates can be large, and more importantly, are
bounded from below, so that ton-scale noble liquid detectors should access all
of parameter space for m_{\tz_1}\alt 500 GeV. Indirect wino detection rates via
neutrino telescopes and space-based cosmic ray detectors can also be large. In
case 3, the DM would consist of an axion plus wino admixture, whose exact
proportions are very model dependent. In this case, it is possible that both an
axion and a wino-like WIMP could be detected experimentally. In case 4., we
calculate the re-heat temperature of the universe after inflation. In this
case, no direct or indirect WIMP signals should be seen, although direct
detection of relic axions may be possible. For each DM scenario, we show
results for the minimal AMSB model, as well as for the hypercharged and gaugino
AMSB models.Comment: 29 pages including 13 figure
A NuSTAR Survey of Nearby Ultraluminous Infrared Galaxies
We present a Nuclear Spectroscopic Telescope Array (NuSTAR), Chandra, and XMM-Newton survey of nine of the nearest ultraluminous infrared galaxies (ULIRGs). The unprecedented sensitivity of NuSTAR at energies above 10 keV enables spectral modeling with far better precision than was previously possible. Six of the nine sources observed were detected sufficiently well by NuSTAR to model in detail their broadband X-ray spectra, and recover the levels of obscuration and intrinsic X-ray luminosities. Only one source (IRAS 13120–5453) has a spectrum consistent with a Compton-thick active galactic nucleus (AGN), but we cannot rule out that a second source (Arp 220) harbors an extremely highly obscured AGN as well. Variability in column density (reduction by a factor of a few compared to older observations) is seen in IRAS 05189–2524 and Mrk 273, altering the classification of these borderline sources from Compton-thick to Compton-thin. The ULIRGs in our sample have surprisingly low observed fluxes in high-energy (>10 keV) X-rays, especially compared to their bolometric luminosities. They have lower ratios of unabsorbed 2–10 keV to bolometric luminosity, and unabsorbed 2–10 keV to mid-IR [O iv] line luminosity than do Seyfert 1 galaxies. We identify IRAS 08572+3915 as another candidate intrinsically X-ray weak source, similar to Mrk 231. We speculate that the X-ray weakness of IRAS 08572+3915 is related to its powerful outflow observed at other wavelengths
Collider and Dark Matter Searches in Models with Mixed Modulus-Anomaly Mediated SUSY Breaking
We investigate the phenomenology of supersymmetric models where moduli fields
and the Weyl anomaly make comparable contributions to SUSY breaking effects in
the observable sector of fields. This mixed modulus-anomaly mediated
supersymmetry breaking (MM-AMSB) scenario is inspired by models of string
compactification with fluxes, which have been shown to yield a de Sitter vacuum
(as in the recent construction by Kachru {\it et al}). The phenomenology
depends on the so-called modular weights which, in turn, depend on the location
of various fields in the extra dimensions. We find that the model with zero
modular weights gives mass spectra characterized by very light top squarks
and/or tau sleptons, or where M_1\sim -M_2 so that the bino and wino are
approximately degenerate. The top squark mass can be in the range required by
successful electroweak baryogenesis. The measured relic density of cold dark
matter can be obtained via top squark co-annihilation at low \tan\beta, tau
slepton co-annihilation at large \tan\beta or via bino-wino coannihilation.
Then, we typically find low rates for direct and indirect detection of
neutralino dark matter. However, essentially all the WMAP-allowed parameter
space can be probed by experiments at the CERN LHC, while significant portions
may also be explored at an e^+e^- collider with \sqrt{s}=0.5--1 TeV. We also
investigate a case with non-zero modular weights. In this case,
co-annihilation, A-funnel annihilation and bulk annihilation of neutralinos are
all allowed. Results for future colliders are qualitatively similar, but
prospects for indirect dark matter searches via gamma rays and anti-particles
are somewhat better.Comment: 38 pages including 22 EPS figures; latest version posted to conform
with published versio
The Phoenix galaxy as seen by NuSTAR
Aims. We study the long-term variability of the well-known Seyfert 2 galaxy Mrk 1210 (a.k.a. UGC 4203, or the Phoenix galaxy). Methods. The source was observed by many X-ray facilities in the last 20 years. Here we present a NuSTAR observation and put the results in context of previously published observations. Results. NuSTAR observed Mrk 1210 in 2012 for 15.4 ks. The source showed Compton-thin obscuration similar to that observed by Chandra, Suzaku, BeppoSAX and XMM-Newton over the past two decades, but different from the first observation by ASCA in 1995, in which the active nucleus was caught in a low flux state - or obscured by Compton-thick matter, with a reflection-dominated spectrum. Thanks to the high-quality hard X-ray spectrum obtained with NuSTAR and exploiting the long-term spectral coverage spanning 16.9 years, we can precisely disentangle the transmission and reflection components and put constraints on both the intrinsic long-term variability and hidden nucleus scenarios. In the former case, the distance between the reflector and the source must be at least ~ 2 pc, while in the latter one the eclipsing cloud may be identified with a water maser-emitting clump.<br/
Nustar and Chandra Insight into the Nature of the 3-40 Kev Nuclear Emission in Ngc 253
We present results from three nearly simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR) and Chandra monitoring observations between 2012 September 2 and 2012 November 16 of the local star-forming galaxy NGC 253. The 3-40 kiloelectron volt intensity of the inner approximately 20 arcsec (approximately 400 parsec) nuclear region, as measured by NuSTAR, varied by a factor of approximately 2 across the three monitoring observations. The Chandra data reveal that the nuclear region contains three bright X-ray sources, including a luminous (L (sub 2-10 kiloelectron volt) approximately few 10 (exp 39) erg per s) point source located approximately 1 arcsec from the dynamical center of the galaxy (within the sigma 3 positional uncertainty of the dynamical center); this source drives the overall variability of the nuclear region at energies greater than or approximately equal to 3 kiloelectron volts. We make use of the variability to measure the spectra of this single hard X-ray source when it was in bright states. The spectra are well described by an absorbed (power-law model spectral fit value, N(sub H), approximately equal to 1.6 x 10 (exp 23) per square centimeter) broken power-law model with spectral slopes and break energies that are typical of ultraluminous X-ray sources (ULXs), but not active galactic nuclei (AGNs). A previous Chandra observation in 2003 showed a hard X-ray point source of similar luminosity to the 2012 source that was also near the dynamical center (Phi is approximately equal to 0.4 arcsec); however, this source was offset from the 2012 source position by approximately 1 arcsec. We show that the probability of the 2003 and 2012 hard X-ray sources being unrelated is much greater than 99.99% based on the Chandra spatial localizations. Interestingly, the Chandra spectrum of the 2003 source (3-8 kiloelectron volts) is shallower in slope than that of the 2012 hard X-ray source. Its proximity to the dynamical center and harder Chandra spectrum indicate that the 2003 source is a better AGN candidate than any of the sources detected in our 2012 campaign; however, we were unable to rule out a ULX nature for this source. Future NuSTAR and Chandra monitoring would be well equipped to break the degeneracy between the AGN and ULX nature of the 2003 source, if again caught in a high state
Collider and Dark Matter Phenomenology of Models with Mirage Unification
We examine supersymmetric models with mixed modulus-anomaly mediated SUSY
breaking (MM-AMSB) soft terms which get comparable contributions to SUSY
breaking from moduli-mediation and anomaly-mediation. The apparent (mirage)
unification of soft SUSY breaking terms at Q=mu_mir not associated with any
physical threshold is the hallmark of this scenario. The MM-AMSB structure of
soft terms arises in models of string compactification with fluxes, where the
addition of an anti-brane leads to an uplifting potential and a de Sitter
universe, as first constructed by Kachru {\it et al.}. The phenomenology mainly
depends on the relative strength of moduli- and anomaly-mediated SUSY breaking
contributions, and on the Higgs and matter field modular weights, which are
determined by the location of these fields in the extra dimensions. We
delineate the allowed parameter space for a low and high value of tan(beta),
for a wide range of modular weight choices. We calculate the neutralino relic
density and display the WMAP-allowed regions. We show the reach of the CERN LHC
and of the International Linear Collider. We discuss aspects of MM-AMSB models
for Tevatron, LHC and ILC searches, muon g-2 and b->s \gamma branching
fraction. We also calculate direct and indirect dark matter detection rates,
and show that almost all WMAP-allowed models should be accessible to a
ton-scale noble gas detector. Finally, we comment on the potential of colliders
to measure the mirage unification scale and modular weights in the difficult
case where mu_mir>>M_GUT.Comment: 34 pages plus 42 EPS figures; version with high resolution figures is
at http://www.hep.fsu.edu/~bae
Mixed Higgsino Dark Matter from a Large SU(2) Gaugino Mass
We observe that in SUSY models with non-universal GUT scale gaugino mass
parameters, raising the GUT scale SU(2) gaugino mass |M_2| from its unified
value results in a smaller value of -m_{H_u}^2 at the weak scale. By the
electroweak symmetry breaking conditions, this implies a reduced value of \mu^2
{\it vis \`a vis} models with gaugino mass unification. The lightest neutralino
can then be mixed Higgsino dark matter with a relic density in agreement with
the measured abundance of cold dark matter (DM). We explore the phenomenology
of this high |M_2| DM model. The spectrum is characterized by a very large wino
mass and a concomitantly large splitting between left- and right- sfermion
masses. In addition, the lighter chargino and three light neutralinos are
relatively light with substantial higgsino components. The higgsino content of
the LSP implies large rates for direct detection of neutralino dark matter, and
enhanced rates for its indirect detection relative to mSUGRA. We find that
experiments at the LHC should be able to discover SUSY over the portion of
parameter space where m_{\tg} \alt 2350-2750 ~GeV, depending on the squark
mass, while a 1 TeV electron-positron collider has a reach comparable to that
of the LHC. The dilepton mass spectrum in multi-jet + \ell^+\ell^- + \eslt
events at the LHC will likely show more than one mass edge, while its shape
should provide indirect evidence for the large higgsino content of the decaying
neutralinos.Comment: 36 pages with 26 eps figure
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