The Rapidly Flaring Afterglow of the Very Bright and Energetic GRB 070125

We report on multiwavelength observations, ranging from X-ray to radio wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic observations reveal the presence of absorption lines due to O i,Si ii,and C iv, implying a likely redshift of z ¼1:547. The well-sampled light curves, in particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days, corresponding to a jet opening angle of $7.0, and implying an intrinsic GRB energy in the 1Y10,000 keV band of around E ¼(6:3Y6:9) ; 1051 ergs (based on the fluences measured by the gamma-ray de-tectorsof the IPN).GRB070125 is among the brightest afterglows observed to date.The SEDimplies ahostextinction of AV \u3c 0:9 mag. Two rebrightening episodes are observed, one with excellent time coverage, showing an increase in fluxof 56$8000 s.The evolution of the afterglow light curve is achromatic at all times.Late-time observationsof the afterglow do not show evidence for emission from an underlying host galaxy or supernova. Any host galaxy would be subluminous, consistent with current GRB host galaxy samples. Evidence for strong Mg ii absorption features is not found, which is perhaps surprising in view of the relatively high redshift of this burst and the high likelihood for such features along GRB-selected lines of sight

Thermophysical Characterization of Potential Spacecraft Target (101955) 1999 RQ36

We report on thermal emission measurements of 1999 RQ36 from Spitzer. The derived size is in agreement with radar measurements, and we find a moderately high thermal inertia and homogeneous surface properties

Mass and radius determinations for five transiting M-dwarf stars

We have derived masses and radii for both components in five short-period single-lined eclipsing binary stars discovered by the TrES wide-angle photometric survey for transiting planets. All these systems consist of a visible F-star primary and an unseen M-star secondary (M_A > 0.8 M_sun, M_B < 0.45 M_sun). The spectroscopic orbital solution combined with a high precision transit light curve for each system gives sufficient information to calculate the density of the primary star and the surface gravity of the secondary. The masses of the primary stars were obtained using stellar evolution models. The solutions were compared with results obtained by calculating the radius of the primary stars under the assumption of rotational synchronization with the orbital period and alignment between their spin axis and the axis of the orbit. Four systems show an acceptable match between the two sets of results, but one system shows a clear mismatch between the two solutions, which may indicate the absence of synchronization or a misalignment between the rotational and orbital axis. When compared to low-mass stellar evolution models, the derived masses and radii of the unseen M dwarfs are inconsistent (three only marginally) with the predicted values, with all of the radii being larger than expected for their masses. These results confirm the discrepancy shown in previous work between the predicted and observed radii on low-mass binary stars. This work also shows that reliance on the assumption of synchronization to derive the mass and radius of stars in eclipsing single--lined F+M binaries is a useful tool, but may not always be warranted and should be carefully tested against stellar evolution models.Comment: 36 pages: 20 pages of text, 13 tables, 7 figures. Accepted for publication in Ap

Serendipitous Geodesy from Bennu's Short-Lived Moonlets

The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx; or OREx) spacecraft arrived at its target, near-Earth asteroid (101955) Bennu, on December 3, 2018. The OSIRIS-REx spacecraft has since collected a wealth of scientific information in order to select a suitable site for sampling. Shortly after insertion into orbit on December 31, 2018, particles were identified in starfield images taken by the navigation camera (NavCam 1). Several groups within the OSlRlS-REx team analyzed the particle data in an effort to better understand this newfound activity of Bennu and to investigate the potential sensitivity of the particles to Bennu's geophysical parameters. A number of particles were identified through automatic and manual methods in multiple images, which could be turned into short sequences of optical tracking observations. Here, we discuss the precision orbit determination (OD) effort focused on these particles at NASA GSFC, which involved members of the Independent Navigation Team (INT) in particular. The particle data are combined with other OSIRIS-REx tracking data (radiometric from OSN and optical landmark data) using the NASA GSFC GEODYN orbit determination and geodetic parameter estimation software. We present the results of our study, particularly those pertaining to the gravity field of Bennu. We describe the force modeling improvements made to GEODYN specifically for this work, e.g., with a raytracing-based modeling of solar radiation pressure. The short-lived, low-flying moonlets enable us to determine a gravity field model up to a relatively high degree and order: at least degree 6 without constraints, and up to degree 10 when applying Kaula-like regularization. We can backward- and forward-integrate the trajectory of these particles to the ejection and landing sites on Bennu. We assess the recovered field by its impact on the OSIRIS-REx trajectory reconstruction and prediction quality in the various mission phases (e.g., Orbital A, Detailed Survey, and Orbital B)

The Transit Light Curve (TLC) Project. I. Four Consecutive Transits of the Exoplanet XO-1b

We present RIz photometry of four consecutive transits of the newly discovered exoplanet XO-1b. We improve upon the estimates of the transit parameters, finding the planetary radius to be R_P = 1.184 +0.028/-0.018 R_Jupiter and the stellar radius to be R_S = 0.928 +0.018/-0.013 R_Sun, assuming a stellar mass of M_S = 1.00 +/- 0.03 M_Sun. The uncertainties in the planetary and stellar radii are dominated by the uncertainty in the stellar mass. These uncertainties increase by a factor of 2-3 if a more conservative uncertainty of 0.10 M_Sun is assumed for the stellar mass. Our estimate of the planetary radius is smaller than that reported by McCullough et al. (2006) and yields a mean density that is comparable to that of TrES-1 and HD 189733b. The timings of the transits have an accuracy ranging from 0.2 to 2.5 minutes, and are marginally consistent with a uniform period.Comment: 22 pages, 5 figures, 2 tables. Accepted for publication in Ap

The operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations

During its approach to asteroid (101955) Bennu, NASA's Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed Bennu's immediate environment, photometric properties, and rotation state. Discovery of a dusty environment, a natural satellite, or unexpected asteroid characteristics would have had consequences for the mission's safety and observation strategy. Here we show that spacecraft observations during this period were highly sensitive to satellites (sub-meter scale) but reveal none, although later navigational images indicate that further investigation is needed. We constrain average dust production in September 2018 from Bennu's surface to an upper limit of 150 g s(-1) averaged over 34 min. Bennu's disk-integrated photometric phase function validates measurements from the pre-encounter astronomical campaign. We demonstrate that Bennu's rotation rate is accelerating continuously at 3.63 +/- 0.52 x 10(-6) degrees day(-2), likely due to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, with evolutionary implications.This material is based upon work supported by NASA under Contract NNM10AA11C issued through the New Frontiers Program. This work made use of sbpy (http://sbpy. org), a community-driven Python package for small-body planetary astronomy supported by NASA PDART Grant No. 80NSSC18K0987. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. M.A.B. and S.F. acknowledge financial support from CNES

Dynamical Evolution of Simulated Particles Ejected from Asteroid Bennu

In early 2019, the OSIRIS‐REx spacecraft discovered small particles being ejected from the surface of the near‐Earth asteroid Bennu. Although they were seen to be ejected at slow speeds, on the order of tens of cm/s, a number of particles were surprisingly seen to orbit for multiple revolutions and days, which requires a dynamical mechanism to quickly and substantially modify the orbit to prevent re‐impact upon their first periapse passage. This paper demonstrates that, based on simulations constrained by the conditions of the observed events, the combined effects of gravity, solar radiation pressure, and thermal radiation pressure from Bennu can produce many sustained orbits for ejected particles. Furthermore, the simulated populations exhibit two interesting phenomena that could play an important role in the geophysical evolution of bodies such as Bennu. First, small particles (<1 cm radius) are preferentially removed from the system, which could lead to a deficit of such particles on the surface. Second, re‐impacting particles preferentially land near or on the equatorial bulge of Bennu. Over time, this can lead to crater in‐filling and growth of the equatorial radius without requiring landslides

Nuclear spectra of comet 28P Neujmin

We present visible and near-infrared spectra of the nucleus of comet 28P/Neujmin 1, obtained in 2001, 2002, and 2003, while it had no detectable coma. The spectra show no strong features in this wavelength range, which prevented the identification of specific compounds on the surface of comet 28P. We found evidence for spectral variability, as our 2002 near-infrared spectrum has a significantly steeper slope than those obtained in 2001 and 2003. We compare the spectra of 28P with published spectra of other comet nuclei, with primitive asteroids and with meteorites. At near-infrared wavelengths, all the comet nuclei show spectra with red\u27\u27 slopes and the 2002 spectrum of comet 28P is among the reddest even when compared with Trojan asteroids. Three of the four properly observed Jupiter-family comets have significantly redder spectral slopes in the near-infrared than the one Halley-type comet in this sample. We found reasonably good matches among Trojan asteroids to the albedo and spectral shape of comet 28P. Such similarities are consistent with an analogous formation and evolutionary environment for Trojan asteroids and Jupiter-family comets, as proposed by Morbidelli and coworkers. One CI meteorite showed a partial fit to our 2003 near-infrared spectrum of comet 28P; however, no close spectral matches to our target were found among chondritic meteorites