Interpretations of gamma-ray burst spectroscopy. I. Analytical and numerical study of spectral lags

We describe the strong spectral evolution that occurs during a gamma-ray burst pulse and the means by which it can be analyzed. Based on observed empirical correlations, an analytical model is constructed which is used to describe the pulse shape and quantize the spectral lags and their dependences on the spectral evolution parameters. We find that the spectral lag depends mainly on the pulse-decay time-scale and that hard spectra (with large spectral power-law indices alpha) give the largest lags. Similarly, large initial peak-energies, Eo, lead to large lags, except in the case of very soft spectra. The hardness ratio is found to depend only weakly on alpha and the HIC index, eta. In particular, for low Eo, it is practically independent, and is determined mainly by Eo. The relation between the hardness ratio and the lags, for a certain Eo are described by power-laws, as alpha varies. We also discuss the expected signatures of a sample of hard spectral pulses (e.g. thermal or small pitch-angle synchrotron emission) versus soft spectral pulses (e.g. optically-thin synchrotron emission). Also the expected differences between a sample of low energetic bursts (such as X-ray flashes) and of high energetic bursts (classical bursts) are discussed.Comment: Accepted by A&

CNO abundances in the Galactic bulge

The carbon, nitrogen, and oxygen abundances and trends in the bulge are discussed in the context of our recent analysis of these elements in an on-going project based on near-IR spectra (Ryde et al. 2009). We obtained these using the CRIRES spectrometer on the VLT. The formation and evolution of the Milky Way bulge can be constrained by studying elemental abundances of bulge stars. Due to the large and variable visual extinction in the line-of-sight towards the bulge, an analysis in the near-IR is preferred.Comment: Contributed talk at Chemical Abundances in the Universe, Connecting First Stars to Planets, Proceedings of the International Astronomical Union, IAU Symposium, Volume 265, K. Cunha, M. Spite and B. Barbuy, eds, Cambridge University Press, in pres

On the Hardness-Intensity Correlation in Gamma-Ray Burst Pulses

We study the hardness-intensity correlation (HIC) in gamma-ray bursts (GRBs). In particular, we analyze the decay phase of pulse structures in their light curves. The study comprises a sample of 82 long pulses selected from 66 long bursts observed by BATSE on the Compton Gamma-Ray Observatory. We find that at least 57% of these pulses have HICs that can be well described by a power law. The distribution of the power law indices, obtained by modeling the HIC of pulses from different bursts, is broad with a mean of 1.9 and a standard deviation of 0.7. We also compare indices among pulses from the same bursts and find that their distribution is significantly narrower. The probability of a random coincidence is shown to be very small. In most cases, the indices are equal to within the uncertainties. This is particularly relevant when comparing the external versus the internal shock models. In our analysis, we also use a new method for studying the HIC, in which the intensity is represented by the peak value of the E F_E spectrum. This new method gives stronger correlations and is useful in the study of various aspects of the HIC. In particular, it produces a better agreement between indices of different pulses within the same burst. Also, we find that some pulses exhibit a "track jump" in their HICs, in which the correlation jumps between two power laws with the same index. We discuss the possibility that the "track jump" is caused by strongly overlapping pulses. Based on our findings, the constancy of the index is proposed to be used as a tool for pulse identification in overlapping pulses.Comment: 20 pages with 9 eps figures (emulateapj), ApJ accepte

Racial Representation and Miss Saigon: A Zero Sum Game?

People have been protesting and supporting the musical Miss Saigon since its premiere in 1989. The musical tale of a white American GI falling in love with a Vietnamese bargirl during the Vietnam War is praised for its diverse cast and showing the Vietnamese side of the war. Miss Saigon is also criticized for its stereotypical depiction of Asian women as prostitutes and Asian men as cold and treacherous. Both sides are passionate, and there is no clear consensus or majority opinion. What, then, is the value of Miss Saigon? Should it be banned or still performed? I analyze the different positions of the protesters, and compare their opinions to Miss Saigon supporters. The debate reaches beyond Miss Saigon to comment on what quality representation in media means and whether quality representation for one group is outweighed by controversial representation of another. Ultimately, I decide that the show is still worth performing if the actors and production team are willing to contend with the issues of race and representation raised by the protesters

Prospects of Stellar Abundance Studies from Near-IR Spectra Observed with the E-ELT

In 2006 ESO Council authorized a Phase B study of a European AO-telescope with a 42 m segmented primary with a 5-mirror design, the E-ELT. Several reports and working groups have already presented science cases for an E-ELT, specifically exploiting the new capabilities of such a large telescope. One of the aims of the design has been to find a balance in the performances between an E-ELT and the James Webb Space Telescope, JWST. Apart from the larger photon-collecting area, the strengths of the former is the higher attainable spatial and spectral resolutions. The E-ELT AO system will have an optimal performance in the near-IR, which makes it specially advantageous. High-resolution spectroscopy in the near-infrared has, however, not been discussed much. This paper aims at filling that gap, by specifically discussing spectroscopy of stellar (mainly red giant), photospheric abundances. Based on studies in the literature of stellar abundances, at the needed medium to high spectral resolutions in the near-infrared (0.8-2.4 microns), I will try to extrapolate published results to the performance of the E-ELT and explore what could be done at the E-ELT in this field. A discussion on what instrument characteristics that would be needed for stellar abundance analyses in the near-IR will be given.Comment: Accepted for publication in Astronomische Nachrichten, A

Chemical Abundances of M giants in the Galactic Center: a Single Metal-Rich Population with Low [alpha/Fe]

Context. The formation and evolution of the Milky Way bulge is still largely an unanswered question. One of the most essential observables needed in its modelling are the metallicity distribution and the trends of the alpha elements as measured in stars. While Bulge regions beyond R > 50 pc of the centre has been targeted in several surveys, the central part has escaped detailed study due to the extreme extinction and crowding. The abundance gradients from the center are, however, of large diagnostic value. Aims. We aim at investigating the Galactic Centre environment by probing M giants in the field, avoiding supergiants and cluster members. Methods. For 9 field M-giants in the Galactic Centre region, we have obtained high- and low-resolution spectra observed simultaneously with CRIRES and ISAAC on UT1 and UT3 of the VLT. The low-resolution spectra provide a means of determining the effective temperatures, and the high-resolution spectra provide detailed abundances of Fe, Mg, Si, and Ca. Results. We find a metal-rich population at [Fe/H]=+0.11+-0.15 and a lack of the metal-poor population, found further out in the Bulge, corroborating earlier studies. Our [alpha/Fe] element trends, however, show low values, following the outer Bulge trends. A possible exception of the [Ca/Fe] trend is found and needs further investigation. Conclusions. The results of the analysed field M-giants in the Galactic Centre region, excludes a scenario with rapid formation, in which SNIIe played a dominated role in the chemical enrichment of the gas. The metal-rich metallicities together with low alpha-enhancement seems to indicate a bar-like population perhaps related to the nuclear bar.Comment: Accepted for publication in A&