1110.6172
Mapping the galactic center with gravitational wave measurements using pulsar timing
Kocsis. Ray, Zwart
Examine nHz GW foreground of stars and BHs orbiting SgrA*. Cusp of stars and BHs generates a continuous GW spectrum below 40 nHz; individual BHs within 1mpc to SgrA* stick out in the spectrum at higher GW frequencies. The GWs and gravitational near-field effects can be resolved by timing pulsars within a few pc of this region. [How does this work?] Observations with the SKA may be expecialy sensitive to intermediate mass black holes (IMBHs) in this region, if present. A 100ns-10mus timing accuracy is sufficient to detect BHs of mass 1e3 Msun with pulsars at distance 0.1-1pc in a 3 yr observation baseline. Unlike EM imaging techniques, the prospects for resolving individual objects through GW measurements improve closer to SgrA*, even if the number density of objects increases inwards steeply. Scattering by the interstellar medium will pose the biggest challenge for such observations.
* What exactly is the pulsar measuring? It should be showing modification in its pulsar signal time-of-arrival, due to the strong gravitational field.
* What exactly is the pulsar measuring? It should be showing modification in its pulsar signal time-of-arrival, due to the strong gravitational field.
1110.6173
On the origin of high energy correlations in gamma-ray bursts
Kocevski
Investigate origin of hte observed correlation between GRB's nuFnu spectral peak Kpk, and its isotropic equivalent energy Eiso through the use of population synthesis code to model the prompt gamma-ray emission from GRBs. [what model of GRB is assumed here? how are each measured?] Using prescriptions for the distribution of prompt spectral parameters as well as the population's luminosity function and co-moving rate density, generate a simulated population of GRBs and examine how bursts of varying spectral properties and redshift would appear to a detector on Earth. Find a strong observed correlation between the source frame Epk and Eiso for the detected population, despite the existence of only a weak and broad correlation in the original simulated population. The energy dependence of gamma-ray detector's flux-limited detection threshold acts to produce a correlation between the source frame Epk and Eiso for a low luminosity GRBs, producing the left boundary of the observed correlation. Conversely, very luminous GRBs are found at higher redshifts than the low luminosity ones due to the standard Malmquist bias, causing bursts in the low Epk, high Eiso regime to go undetected because their Epk values would be redshifted to energies at which most detectors become less sensitive. This previously unexamined effect produces the right boundary of the observed correlation. The origin of the observed correlation is a complex combination of the instrument's detection threshold, the intrinsic cutoff in the GRB luminosity function, and the broad range of redshifts over which GRBs are detected. These simulations serve to demonstrate how selection effects caused by a combination of instrumental sensitivity and the cosmological nature of an astrophysical population can act to produce an artificially strong correlation between observed properties.
MPIfR Lunch Colloquium
Geodetic VLBI and the 100m telescope
Axel Nothagel
Geodetic, geophysical and astrometric results from VLBI (Very Long Baseline Interferometry) observations.
On the origin of high energy correlations in gamma-ray bursts
Kocevski
Investigate origin of hte observed correlation between GRB's nuFnu spectral peak Kpk, and its isotropic equivalent energy Eiso through the use of population synthesis code to model the prompt gamma-ray emission from GRBs. [what model of GRB is assumed here? how are each measured?] Using prescriptions for the distribution of prompt spectral parameters as well as the population's luminosity function and co-moving rate density, generate a simulated population of GRBs and examine how bursts of varying spectral properties and redshift would appear to a detector on Earth. Find a strong observed correlation between the source frame Epk and Eiso for the detected population, despite the existence of only a weak and broad correlation in the original simulated population. The energy dependence of gamma-ray detector's flux-limited detection threshold acts to produce a correlation between the source frame Epk and Eiso for a low luminosity GRBs, producing the left boundary of the observed correlation. Conversely, very luminous GRBs are found at higher redshifts than the low luminosity ones due to the standard Malmquist bias, causing bursts in the low Epk, high Eiso regime to go undetected because their Epk values would be redshifted to energies at which most detectors become less sensitive. This previously unexamined effect produces the right boundary of the observed correlation. The origin of the observed correlation is a complex combination of the instrument's detection threshold, the intrinsic cutoff in the GRB luminosity function, and the broad range of redshifts over which GRBs are detected. These simulations serve to demonstrate how selection effects caused by a combination of instrumental sensitivity and the cosmological nature of an astrophysical population can act to produce an artificially strong correlation between observed properties.
MPIfR Lunch Colloquium
Geodetic VLBI and the 100m telescope
Axel Nothagel
Geodetic, geophysical and astrometric results from VLBI (Very Long Baseline Interferometry) observations.
No comments:
Post a Comment