Evidence for Circumburst Extinction of Gamma-Ray Bursts with Dark Optical Afterglows and Evidence for a Molecular Cloud Origin of Gamma-Ray Bursts

First, we show that the gamma-ray bursts with dark optical afterglows (DOAs) cannot be explained by a failure to image deeply enough quickly enough, and argue that circumburst extinction is the most likely solution. If so, many DOAs will be ``revived'' with rapid follow up and NIR searches in the HETE-2 and Swift eras. Next, we consider the effects of dust sublimation and fragmentation, and show that DOAs occur in clouds of size R > 10L_{49}^{1/2} pc and mass M > 3x10^5L_{49} M_{sun}, where L is the luminosity of the optical flash. Stability considerations show that such clouds cannot be diffuse, but must be molecular. Consequently, we compute the expected column density distribution of bursts that occur in Galactic-like molecular clouds, and show that the column density measurements from X-ray spectra of afterglows, DOAs and otherwise, satisfy this expectation in the source frame.Comment: Invited Review. To appear in Procs. of Gamma-Ray Burst and Afterglow Astronomy 2001: A Workshop Celebrating the First Year of the HETE Mission, 8 pages, 8 figures, LaTe

To Teach or not to Teach? Panel Data Evidence on the Quitting Decision

The question we address in this paper is which factors influence the quitting decision of public sector teachers in England and Wales, using a nationally representative panel data set over 1997-2003. We document the outcomes of former teachers, fit single and competing-risks duration models and examine the influence of relative pay on retention. Surprisingly, we find that teachers who move to outside employment earn 22% less pay, work longer hours, in largely nonprofessional occupations and mainly stay within the public sector. We estimate that a 10% increase in teachers’ relative pay would reduce annual quitting rates by less than 1%.Teachers, Panel Data, Wages, Quitting

Testing for Employee Discrimination in Britain using Matched Employer-Employee Data.

We use recent matched employer-employee data to directly test if white workers have a taste for racial discrimination in Britain. We formally introduce individual and firm heterogeneity into the discrimination model used by Becker (1957, 1971) which we extend to generate predictions consistent with an employee taste for discrimination. We argue firstly that white employees with a taste for discrimination should report lower levels of job satisfaction the larger the proportion of ethnic minorities at their workplace. Secondly, white employees would have to be compensated by higher wages if required to work alongside ethnic minority co-workers. Both hypotheses are clearly supported for white males in our data, after comprehensively controlling for individual, job, and workplace characteristics. The white male wage premium for working amongst only ethnic minority co-workers, as compared to working only with whites, is about 12%. Importantly, it appears that neither of these effects operates via realised racial prejudice at the workplace or white employees' feelings concerning their job security.Matched employer-employee data, discrimination, job satisfaction, compensating wage differentials

TESTING FOR EMPLOYEE DISCRIMINATION USING MATCHED EMPLOYER-EMPLOYEE DATA: THEORY AND EVIDENCE

We use recent matched employer-employee data to directly investigate if white workers have a taste for racial discrimination in Britain. Based on a new structural model with individual and firm heterogeneity, we develop and test two predictions. Firstly, white employees with a taste for discrimination should report lower levels of job satisfaction the larger the proportion of ethnic minorities at their workplace. Secondly, white employees would have to be compensated by higher wages if required to work alongside ethnic minority co-workers. Both hypotheses are clearly supported for white males in our data, after comprehensively controlling for individual, job, and workplace characteristics. However, the evidence is weaker for females. The white male wage premium for working amongst only ethnic minority co-workers, as compared to working only with whites, is about 12%. Importantly, it appears that neither of these effects operates via realised racial prejudice at the workplace or white employees’ feelings concerning their job security.Employee Discrimination, Compensating Differentials, StructuralEstimation, Wages, Job Satisfaction

d1005+68: A New Faint Dwarf Galaxy in the M81 Group

We present the discovery of d1005+68, a new faint dwarf galaxy in the M81 Group, using observations taken with the Subaru Hyper Suprime-Cam. d1005+68's color-magnitude diagram is consistent with a distance of $3.98_{-0.43}^{+0.39}$ Mpc, establishing group membership. We derive an absolute $V$-band magnitude, from stellar isochrone fitting, of $M_{V} = -7.94_{-0.50}^{+0.38}$, with a half-light radius of $r_{h} = 188_{-41}^{+39}$ pc. These place d1005+68 within the radius-luminosity locus of Local Group and M81 satellites and among the faintest confirmed satellites outside the Local Group. Assuming an age of 12 Gyr, d1005+68's red giant branch is best fit by an isochrone of [Fe/H] $= -1.90 \pm 0.24$. It has a projected separation from nearby M81 satellite BK5N of only 5 kpc. As this is well within BK5N's virial radius, we speculate that d1005+68 may be a satellite of BK5N. If confirmed, this would make d1005+68 one of the first detected satellites-of-a-satellite.Comment: 7 pages, 4 figures, 1 table, additional affiliations include

Evidence for a Molecular Cloud Origin for Gamma-Ray Bursts: Implications for the Nature of Star Formation in the Universe

It appears that the majority of rapidly-, well-localized gamma-ray bursts with undetected, or dark, optical afterglows, or `dark bursts' for short, occur in clouds of size R > 10L_{49}^{1/2} pc and mass M > 3x10^5L_{49} M_{sun}, where L is the isotropic-equivalent peak luminosity of the optical flash. We show that clouds of this size and mass cannot be modeled as a gas that is bound by pressure equilibrium with a warm or hot phase of the interstellar medium (i.e., a diffuse cloud): Such a cloud would be unstable to gravitational collapse, resulting in the collapse and fragmentation of the cloud until a burst of star formation re-establishes pressure equilibrium within the fragments, and the fragments are bound by self-gravity (i.e., a molecular cloud). Consequently, dark bursts probably occur in molecular clouds, in which case dark bursts are probably a byproduct of this burst of star formation if the molecular cloud formed recently, and/or the result of lingering or latter generation star formation if the molecular cloud formed some time ago. We then show that if bursts occur in Galactic-like molecular clouds, the column densities of which might be universal, the number of dark bursts can be comparable to the number of bursts with detected optical afterglows: This is what is observed, which suggests that the bursts with detected optical afterglows might also occur in molecular clouds. We confirm this by modeling and constraining the distribution of column densities, measured from absorption of the X-ray afterglow, of the bursts with detected optical afterglows: We find that this distribution is consistent with the expectation for bursts that occur in molecular clouds, and is not consistent with the expectation for bursts that occur in diffuse clouds. More...Comment: Accepted to The Astrophysical Journal, 22 pages, 6 figures, LaTe

The Ursinus Weekly, December 3, 1909

Football number • Credit due coach • The scrubs • Football rules discussed • A review of the football season • Comment • Choral concert • Seminary notes • Personals • Latin-Maths and Math-Phys meet • Slonaker hurt • Football managers electedhttps://digitalcommons.ursinus.edu/weekly/2817/thumbnail.jp