Had I special: The Astronomical Contributions of the Herschel Family




НазваниеHad I special: The Astronomical Contributions of the Herschel Family
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Kepler Measurements of M Star Variability

Geoffrey Bryden1, J. Stauffer2, D. R. Ciardi3, NStED Science Team
1JPL, 2Caltech, 3NExScI.

Exhibit Hall

Late-type stars may be ideal candidates for detection of Earth-mass planets - lower stellar mass corresponds to larger radial-velocity amplitude and deeper transit depth for a given planet mass/size. Low-mass stars are only good targets, however, if they can be observed at noise levels similar to those for solar-type stars. As an exploration of the inherent variability of low-mass stars, we have identified a sample of 63 nearby M dwarfs within the Kepler field of view. The Kepler lightcurves for these stars generally vary by ~1% over the 33-day observational window. After subtraction of gradual long-term trends, only a handful of the stars exhibit variability above the photon-noise limit (typically 0.1-1.0 mmag). We conclude that >90% of M dwarfs are quiet within the several hour timeframe appropriate for detection of planetary transits.

140.21

Confirming sub-Neptunian Transiting Exoplanets with Kepler

Natalie M. Batalha1, Kepler Science Team
1San Jose State University.

Exhibit Hall

NASA's Kepler Mission, launched in March 2009, uses transit photometry to detect and characterize exoplanets with the objective of determining the frequency of earth-size planets in the habitable zone. The instrument is a wide field-of-view (115 square degrees) photometer comprised of a 0.95-meter effective aperture Schmidt telescope feeding an array of 42 CCDs that continuously and simultaneously monitors the brightness of up to 170,000 stars. In January, 2010, the team announced its first 5 planet discoveries identified in the first 43 days of data and confirmed by radial velocity follow-up. The "first five" are all short-period giant planets, the smallest being comparable in size to Neptune. Collectively, they are similar to the sample of transiting exoplanets that have been identified to date, the roster of which currently hovers around 100. In August 2010, an additional two planets, each orbiting the star Kepler-9, were confirmed by a combination of radial velocity and transit timing measurements. A third, smaller planet in the same system was validated stastistically by probing the parameter space for potential false-positives. Throughout 2010, a concerted effort was made to push radial velocity confirmation down toward the smaller planets. Recent progress on our efforts to confirm such candidates is discussed.

141

Gamma Ray Bursts

Poster Session

Exhibit Hall

141.01

High Metallicity LGRB Hosts

John Graham1, A. Fruchter2, E. Levesque3, L. Kewley3, J. Brinchmann4, S. Charlot5, A. Levan6, N. Tanvir7, S. Patel8, K. Misra2, K. Huang9, D. Reichart10, M. Nysewander2
1STScI & JHU, 2STScI, 3IFA, 4Leiden, Netherlands, 5Bordeaux, France, 6Warwick, United Kingdom, 7Leicester, United Kingdom, 8National Space Science & Technology Center, 9JHU, 10UNC.

Exhibit Hall

One of the most powerful means to study the formation and evolution of gamma-ray bursts is by observing there environments. While short bursts have been detected in nearby galaxies of all types, long burst hosts are dominated by blue irregulars leading to speculation of metal poor host galaxies, a result which has now been confirmed via emission line metallicity diagnostics. However beginning with LGRB 051022 at log(O/H)+12 = 8.77 (using the R23 method with Kobulnicky & Kewley 2004 scale) three exceptions to this trend have been found. This extends the metallicity range of LGRB hosts to that found throughout the Milky Way, challenges conventional wisdom that LGRBs require low metallicity progenitor environments and has significant implications in understanding LGRB formation. Here I present the results of our observations of two of these super-solar metallicity host galaxies, analysis of the high Z host population with respect to various comparison samples, and ongoing efforts to more directly probe the metallicities of the burst progenitors.

141.02

The Stellar Ages and Masses of Short GRB Host Galaxies: Investigating the Progenitor Delay Time Distribution and the Role of Mass and Star Formation in the Short GRB Rate

Camille N. Leibler1, E. Berger1
1Harvard University.

Exhibit Hall

We present multi-band optical and near-infrared observations of 19 short γ-ray burst (GRB) host galaxies, aimed at measuring their stellar masses and population ages. The goals of this study are to evaluate whether short GRBs track the stellar mass distribution of galaxies, to investigate the progenitor delay time distribution, and to explore any connection between long and short GRB progenitors. Comparing the distribution of stellar masses found using a single-stellar population model to the general galaxy mass function, we find that short GRBs track the cosmic stellar mass distribution only if the late-type hosts generally have maximal masses. However, there is an apparent dearth of early-type short GRB hosts compared to the equal contribution of early- and late-type galaxies to the cosmic stellar mass budget. These results suggest that stellar mass may not be the sole parameter controlling the short GRB rate, and raise the possibility of a two-component model with both mass and star formation playing a role (reminiscent of the case for Type Ia supernovae). If short GRBs in late-type galaxies indeed track star formation activity, the resulting typical delay time is ∼ 0.2 Gyr, while those in early-type hosts have a typical delay of ∼ 3 Gyr. Using the same stellar population models to fit 22 long GRB host galaxies in a similar redshift range we find that they have significantly lower masses and younger population ages. Most importantly, the two GRB host populations remain distinct even if we consider only the star-forming hosts of short GRBs, supporting our previous findings (based on star formation rates and metallicities) that the progenitors of long GRBs and short GRBs in late-type galaxies are distinct.
This work was partially supported by Swift AO5 grant #5080010 and AO6 grant #6090612. Additional support was provided by the Harvard College Research Program.

141.03

A Beaming-Independent Estimate of the Distribution of Gamma Ray Burst Energies

Isaac S. Shivvers1, E. Berger1
1Harvard University.

Exhibit Hall

AAS 217 Winter Meeting Abstract Submission
Isaac Shivvers
and
Dr. Edo Berger
Harvard University
A Beaming-Independent Estimate of the Distribution of Gamma Ray Burst Energies
The single most important parameter of any cosmological explosion is the energy release. Energy measurements provide insight into the progenitor object and the explosion mechanism. The measurement of gamma-ray burst (GRB) energies has, traditionally, been a complicated problem due to highly non-spherical energy distributions and relativistic beaming effects. However, on timescales of >100 days GRBs become roughly non-relativistic and spherical. Using radio observations from the Very Large Array at times >100 days after the burst, we are able to calculate the energies of 20 bursts free from the large corrections needed when using early-time observations. We find a median energy in good agreement with results calculated through detailed analysis of multi-wavelength light curves. The similarity between methods provides further evidence that the bulk of the energy budget of GRBs is in the relativistic outflow and not in slower, lagging material. Our results were achieved economically, with only a few radio-wavelength flux measurements per GRB. We suggest that similar future observations with the Expanded VLA will provide unique insight into GRB energetics.

141.04

Quantifying GRB Pulse Shape Evolution to Study the Pulse Scale Conjecture

Daniel Miller1, R. J. Nemiroff1, J. Holmes1, A. Shahmoradi1
1Michigan Technology University.

Exhibit Hall

The asymmetry of isolated gamma ray burst pulses is quantified by a simple ratio of rising to decaying fluence. This ratio can be defined in a background independent way by using only the peak of the pulse. This ratio is used to explore the prevalence of the Pulse Scale Conjecture (PSC; Nemiroff 2000) for a series of the brightest isolated BATSE GRB pulses known. The PSC posits that the shape of a GRB pulse is invariant across energy channels, scaling only in time and brightness. Within statistical uncertainties, it is found that some GRB pulses hold well to the PSC, whereas others do not. Moreover, for some GRB pulses, the PSC appears to hold only between specific energy channels. Examples will be shown and discussed.

141.05

Evidence for a Correlation Between Gamma-Ray Burst Variability and the Optical Afterglow Onset

Sarah Yost1
1St John's Univ..

Exhibit Hall

The intrinsic variability (V) of prompt gamma-ray emission from gamma-ray burst (GRB) events is compared to the properties of the subsequent afterglow onset, yielding evidence of a correlation between V and the the optical onset's peak. We used Liang et al.'s (2009) fitted properties of the optical onset bump in 16 events with an observed optical rise and known redshift, and calculated V from the lightcurves in the Swift gamma-ray data archive. The optical onset properties are known to be mutually correlated; comparing these optical bump properties to V shows positive correlations at the 3-sigma level with (de-redshifted) width, peak time, rise, and decay times and negative correlations with peak flux and the ratio of rise to decay times. When the bump peak time or width are expressed as a ratio of the GRB duration (T90), the correlation evidence with V is weaker.

141.06

Pulse Scaling Properties of Gamma-Ray Bursts

Justin Holmes1, R. J. Nemiroff1, D. Miller1
1Michigan Technological University.

Exhibit Hall

Gamma-ray bursts (GRBs) hold potential as standard candles for the high redshift universe. To help identify relationships which may arise in GRBs that could lead to a standard candle, isolated pulses from a number of very bright GRBs were inspected regarding their pulse scaling nature. A direct test of the pulse scale conjecture was conducted using energy channel data from the Burst and Transient Source Experiment (BATSE).  The test consisted of taking a light curve for a bright GRB pulse from a specific BATSE energy channel, scaling it in brightness and time, and finding the best statistical fit for the same GRB pulse in a different BATSE energy channel. Many of the GRB pulses tested showed a statistically acceptable scaling between at least two BATSE energy channels.

141.07

Search for Late Jet Breaks in X-ray Afterglows of Gamma-Ray Bursts

David N. Burrows1, J. Racusin2
1Penn State Univ., 2NASA/GSFC.

Exhibit Hall

Gamma-ray bursts are the most energetic events known since the Big Bang. Because both the prompt emission and the afterglow of GRBs is highly beamed, determination of their actual explosion energies depends on measurement of the beaming angle, which can be estimated on the basis of the detection of an achromatic jet break in the light curve. Jet break measurements for Swift GRBs have been rare; as a result, we have undertaken a program of studying X-ray GRB afterglows using the Chandra observatory to obtain very late-time flux measurements. When compared with earlier Swift XRT flux measurements, these allow the measurements of late jet breaks in some bursts, and allow strict limits to be placed on jet break times in other cases. We will present a progress report on this work and its implication for GRB energetics.

142

AGN, QSO, Blazars

Poster Session

Exhibit Hall

142.01

15 GHz Radio Variability of Gamma-Ray Blazars

Joseph Richards1, W. Max-Moerbeck1, V. Pavlidou1, T. J. Pearson1, A. C. S. Readhead1, M. A. Stevenson1, O. G. King1, R. Reeves1, E. Angelakis2, L. Fuhrmann2, J. A. Zensus2, S. E. Healey3, R. W. Romani3, M. S. Shaw3, K. Grainge4, G. B. Taylor5, G. Cotter6
1California Institute of Technology, 2Max-Planck-Institut-für-Radioastronomie, Germany, 3Stanford University, 4University of Cambridge, United Kingdom, 5University of New Mexico, 6University of Oxford, United Kingdom.

Exhibit Hall

Since 2007, the Owens Valley Radio Observatory (OVRO) 40 meter telescope has been engaged in an intensive fast-cadence gamma-ray blazar monitoring program, observing about 1500 objects twice per week. Using our intrinsic modulation index method and careful likelihood analyses, we find that gamma-ray loud objects associated with Fermi 1LAC sources in our sample demonstrate radio variability amplitudes significantly larger than do gamma-ray quiet objects. We also find significant differences in variability amplitude between flat spectrum radio quasars and BL Lacertae objects within our sample as well as possible evidence for cosmological evolution of variability amplitude.

142.02

Physical Significance Of The Time Lags In Radio/gamma-ray Cross-correlations For Fermi-gst Blazars On The Ovro 40m Blazar Monitoring Program

Walter Max-Moerbeck1, J. L. Richards1, V. Pavlidou1, T. J. Pearson1, A. C. S. Readhead1, M. A. Stevenson1, O. King1, R. Reeves1, E. Angelakis2, L. Fuhrmann2, J. A. Zensus2, S. E. Healey3, R. W. Romani3, M. S. Shaw3, K. Gainge4, G. B. Taylor5, G. Cotter6
1California Institute of Technology, 2Max-Planck-Institut für Radioastronomie, Germany, 3Stanford University, 4University of Cambridge, United Kingdom, 5University of New Mexico, 6University of Oxford, United Kingdom.

Exhibit Hall

The OVRO 40 m telescope has been monitoring ~1500 blazars since 2007. The sources are observed twice per week at 15 GHz. The sample contains all CGRaBS sources and the gamma-ray blazars detected by Fermi which are visible from OVRO. The availability of a large sample of sources with good cadence at radio and gamma-ray offers the opportunity to test the suggestion of correlated variability between these two bands. A Monte Carlo method to assess the physical significance of the cross-correlations taking into account the properties of the light curves and the uneven sampling is presented. Application to an early data set shows that in most cases the cross-correlations are not significant and that longer time duration light curves are required.

142.03
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