665 research outputs found
A critical analysis of three near-infrared photometric methods of estimating distances to cataclysmic variables
A critical analysis of three methods of estimating distances to cataclysmic
variables (CVs) is performed. These methods, by Ak et al., Beuermann, and
Knigge, all use near-infrared (JHK or Ks) magnitudes and the Barnes-Evans
relation. We compare all three methods to distances measured by trigonometric
parallax by Thorstensen, with Hubble Space Telescope, and with the HIPPARCOS
spacecraft.
We find that the method of Ak et al. works best overall for all CVs,
predicting distances on the average 4% less than those measured by
trigonometric parallaxes. The method of Beuermann overestimates distances by
52%. The method of Knigge underestimates distances by 26%, although this was
only ever meant as a lower limit, since it assumes all light comes from the
secondary star.Comment: 17 pages, 7 figures, 2 tables; accepted for publication in New
Astronom
The Orbital Period and Negative Superhumps of the Nova-Like Cataclysmic Variable V378 Pegasi
A radial velocity study is presented of the cataclysmic variable V378 Pegasi
(PG 2337+300). It is found to have an orbital period of 0.13858 +/- 0.00004 d
(3.32592 +/- 0.00096 hours). Its spectrum and long-term light curve suggest
that V378 Peg is a nova-like variable, with no outbursts. We use the
approximate distance and position in the Galaxy of V378 Peg to estimate E(B-V)
= 0.095, and use near-infrared magnitudes to calculate a distance of 680 +/- 90
pc and M_V = 4.68 +/- 0.70, consistent with V378 Peg being a nova-like.
Time-resolved photometry taken between 2001 and 2009 reveals a period of 0.1346
+/- 0.0004 d (3.23 +/- 0.01 hours). We identify this photometric variability to
be negative superhumps, from a precessing, tilted accretion disk. Our repeated
measurements of the photometric period of V378 Peg are consistent with this
period having been stable between 2001 and 2009, with its negative superhumps
showing coherence over as many as hundreds or even thousands of cycles.Comment: 24 pages, 19 figures, accepted for publication in New Astronom
Broadband X-Ray Spectral and Timing Analyses of the Black Hole Binary Candidate Swift J1658.2-4242:Rapid Flux Variation and the Turn-on of a Transient QPO
Discovery of a red supergiant counterpart to RX J004722.4-252051, a ULX in NGC 253
We present two epochs of near-infrared spectroscopy of the candidate red supergiant counterpart to RX J004722.4â252051, a ULX in NGC 253. We measure radial velocities of the object and its approximate spectral type by cross-correlating our spectra with those of known red supergiants. Our VLT/X-shooter spectrum is best matched by that of early M-type supergiants, confirming the red supergiant nature of the candidate counterpart. The radial velocity of the spectrum, taken on 2014 August 23, is 417 ± 4 kmâsâ1. This is consistent with the radial velocity measured in our spectrum taken with Magellan/MMIRS on 2013 June 28, of 410 ± 70 kmâsâ1, although the large error on the latter implies that a radial velocity shift expected for a black hole of tens of Mâ can easily be hidden. Using nebular emission lines we find that the radial velocity due to the rotation of NGC 253 is 351 ± 4 kmâsâ1 at the position of the ULX. Thus the radial velocity of the counterpart confirms that the source is located in NGC 253, but also shows an offset with respect to the local bulk motion of the galaxy of 66 ± 6 kmâsâ1. We argue that the most likely origin for this displacement lies either in a SN kick, requiring a system containing a âł 50 Mâ black hole, and/or in orbital radial velocity variations in the ULX binary system, requiring a âł 100 Mâ black hole. We therefore conclude that RX J004722.4â252051 is a strong candidate for a ULX containing a massive stellar black hole
Characterization of a large-format, fine-pitch CdZnTe pixel detector for the HEFT balloon-Borne experiment
Evidence for the Gompertz Curve in the Income Distribution of Brazil 1978-2005
This work presents an empirical study of the evolution of the personal income
distribution in Brazil. Yearly samples available from 1978 to 2005 were studied
and evidence was found that the complementary cumulative distribution of
personal income for 99% of the economically less favorable population is well
represented by a Gompertz curve of the form , where
is the normalized individual income. The complementary cumulative
distribution of the remaining 1% richest part of the population is well
represented by a Pareto power law distribution . This
result means that similarly to other countries, Brazil's income distribution is
characterized by a well defined two class system. The parameters , ,
, were determined by a mixture of boundary conditions,
normalization and fitting methods for every year in the time span of this
study. Since the Gompertz curve is characteristic of growth models, its
presence here suggests that these patterns in income distribution could be a
consequence of the growth dynamics of the underlying economic system. In
addition, we found out that the percentage share of both the Gompertzian and
Paretian components relative to the total income shows an approximate cycling
pattern with periods of about 4 years and whose maximum and minimum peaks in
each component alternate at about every 2 years. This finding suggests that the
growth dynamics of Brazil's economic system might possibly follow a
Goodwin-type class model dynamics based on the application of the
Lotka-Volterra equation to economic growth and cycle.Comment: 22 pages, 15 figures, 4 tables. LaTeX. Accepted for publication in
"The European Physical Journal B
The upstream magnetic field of collisionless GRB shocks: constraint by Fermi-LAT observations
Long-lived >100 MeV emission has been a common feature of most Fermi-LAT
detected gamma-ray bursts (GRBs), e.g., detected up to ~10^3s in long GRBs
080916C and 090902B and ~10^2s in short GRB 090510. This emission is consistent
with being produced by synchrotron emission of electrons accelerated to high
energy by the relativistic collisionless shock propagating into the weakly
magnetized medium. Here we show that this high-energy afterglow emission
constrains the preshock magnetic field to satisfy 1(n/1cc)^{9/8}
mG<B<10^2(n/1cc)^{3/8}mG, where n is the preshock density, more stringent than
the previous constraint by X-ray afterglow observations on day scale. This
suggests that the preshock magnetic field is strongly amplified, most likely by
the streaming of high energy shock accelerated particles.Comment: 9 pages, JCAP accepte
A 78 Day X-Ray Period Detected from NGC 5907 ULX1 by Swift
We report the detection of a 78.1 ± 0.5 day period in the X-ray light curve of the extreme ultraluminous X-ray source NGC 5907 ULX1 ( erg sâ1), discovered during an extensive monitoring program with Swift. These periodic variations are strong, with the observed flux changing by a factor of ~3â4 between the peaks and the troughs of the cycle; our simulations suggest that the observed periodicity is detected comfortably in excess of 3Ï significance. We discuss possible origins for this X-ray period, but conclude that at the current time we cannot robustly distinguish between orbital and super-orbital variations
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 13120â5453) 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 05189â2524 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 2â10 keV to bolometric luminosity, and unabsorbed 2â10 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
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