Severe Limits on Variations of the Speed of Light with Frequency

Explosive astrophysical events at high red shift can be used to place severe limits on the fractional variation in the speed of light ($\Delta c/c$), the photon mass ($m_{\gamma}$), and the energy scale of quantum gravity ($E_{QG}$). I find $\Delta c/c < 6.3 \times 10^{-21}$ based on the simultaneous arrival of a flare in GRB 930229 with a rise time of $220 \pm 30 \mu s$ for photons of 30 keV and 200 keV. The limit on $m_{\gamma}$ is $4.2 \times 10^{-44} g$ for GRB 980703 from radio to gamma ray observations. The limit on $E_{QG}$ is $8.3 \times 10^{16}$ GeV for GRB 930131 from 30 keV to 80 MeV photons.Comment: 7 pages, Submitted to PR

Explaining the Gamma-Ray Burst E_peak Distribution

The characteristic photon energy for Gamma Ray Bursts, E_peak, has a remarkably narrow distribution for bursts of similar peak flux, with values between 150 and 600 keV for most faint bursts. This result is surprising within the framework of internal shock models, since spectral shifts associated with the jet's blue shift (by a Lorentz factor of Gamma) and the cosmological red shift (by a factor of 1+z) should cause substantial smearing in the distribution of the spectral peak in the jet's co-moving frame, E_rest. For the general case where the luminosity (L) varies as Gamma^N and E_rest varies as Gamma^M, then the observed E_peak will vary as L^{(M+1)/N}(1+z)^{-1}. For two independent set of 20 and 84 bursts, E_peak(1+z) varies as a power law of the luminosity with an index of (M+1)/N=0.36+-0.03. With this measured value, the above functional dependence of E_peak on L and z results in E_peak being roughly constant for bursts of similar peak flux, P_256. Thus, the kinematic smearing will be small, hence allowing the E_peak distribution to be narrow. This model also predicts that bright bursts will have high E_peak values because they all have some combination of high luminosity (and hence a large blue shift Gamma) and a nearby distance (and hence a small cosmological red shift). Quantitatively, E_peak should vary roughly as P_256^0.36, and this model prediction is strikingly confirmed with BATSE data by Mallozzi et al. A prediction of this model is that GRBs at very high red shift z~10 should all appear with E_peak at ~200 keV. A further prediction of this model is that normal bursts with P_256 below the BATSE trigger threshold will appear as x-ray flashes with E_peak~70 keV; just as is reported by Kippen et al. and Heise et al.Comment: ApJ Letters in press, 16 pages, 3 figure

Hadronic Wave Functions in the Instanton Model

We study hadronic wave functions using an instanton model for the QCD vacuum. The wave functions are defined in terms of gauge invariant Bethe Salpeter amplitudes which we have determined numerically using a Monte Carlo simulation of the instanton ensemble. We find that the pion and the proton, as well as the rho meson and the delta have very similar wave functions but observe a sizeable splitting between mesons or baryons with different spin. We compare our results with data obtained in lattice gauge simulations.Comment: 20 pages, uuencoded postscript file appended, SUNY-NTG-94-

Newly Determined Explosion Center of Tycho's Supernova and the Implications for Proposed Ex-Companion Stars of the Progenitor

`Star G', near the center of the supernova remnant of Tycho's SN1572, has been claimed to be the ex-companion star of the exploding white dwarf, thus pointing to the progenitor being like a recurrent nova. This claim has been controversial, but there have been no confident proofs or disproofs. Previously, no has seriously addressed the question as to the exact explosion site in 1572. We now provide accurate measures of the supernova position by two radically different methods. Our first method is to use the 42 measured angular distances between the supernova in 1572 and bright nearby stars, with individual measures being as good as 84 arc-seconds, and all resulting in a position with a 1-$\sigma$ error radius of 39 arc-seconds (including systematic uncertainties). Our second method is to use a detailed and realistic expansion model for 19 positions around the edge of the remnant, where the swept-up material has measured densities, and we determine the center of expansion with a chi-square fit to the 19 measured radii and velocities. This method has a 1-$\sigma$ error radius of 7.5 arc-seconds. Both measures are substantially offset from the geometric center, and both agree closely, proving that neither has any significant systematic errors. Our final combined position for the site of the 1572 explosion is J2000 $\alpha$=0h 25m 15.36s, $\delta=64^{\circ} 8' 40.2"$, with a 7.3 arc-second 1-sigma uncertainty. Star G is rejected at the 8.2-$\sigma$ confidence level. Our new position lies mostly outside the region previously searched for ex-companion stars.Comment: to be published in Ap

Investigation of the Progenitors of the Type Ia Supernovae Associated With the LMC Supernova Remnants 0505-67.9 and 0509-68.7

Although Type Ia supernovae have been heavily scrutinized due to their use in making cosmological distance estimates, we are still unable to definitively identify the progenitors for the entire population. While answers have been presented for certain specific systems, a complete solution remains elusive. We present observations of two supernova remnants (SNRs) in the Large Magellanic Cloud, SNR 0505-67.9 and SNR 0509-68.7, for which we have identified the center of the remnant and the 99.73% containment central region in which any companion star left over after the supernova must be located. Both remnants have a number of potential ex-companion stars near their centers; all possible single and double degenerate progenitor models remain viable for these two supernovae. Future observations may be able to identify the true ex-companions for both remnants.Comment: 8 pages, 4 figures, 4 tables, ApJ In Press; Table 2 truncated, full version available in published paper or directly from author

Identifying and Quantifying Recurrent Novae Masquerading as Classical Novae

Recurrent novae (RNe) are cataclysmic variables with two or more nova eruptions within a century. Classical novae (CNe) are similar systems with only one such eruption. Many of the so-called 'CNe' are actually RNe for which only one eruption has been discovered. Since RNe are candidate Type Ia supernova progenitors, it is important to know whether there are enough in our galaxy to provide the supernova rate, and therefore to know how many RNe are masquerading as CNe. To quantify this, we collected all available information on the light curves and spectra of a Galactic, time-limited sample of 237 CNe and the 10 known RNe, as well as exhaustive discovery efficiency records. We recognize RNe as having (a) outburst amplitude smaller than 14.5 - 4.5 * log(t_3), (b) orbital period >0.6 days, (c) infrared colors of J-H > 0.7 mag and H-K > 0.1 mag, (d) FWHM of H-alpha > 2000 km/s, (e) high excitation lines, such as Fe X or He II near peak, (f) eruption light curves with a plateau, and (g) white dwarf mass greater than 1.2 M_solar. Using these criteria, we identify V1721 Aql, DE Cir, CP Cru, KT Eri, V838 Her, V2672 Oph, V4160 Sgr, V4643 Sgr, V4739 Sgr, and V477 Sct as strong RN candidates. We evaluate the RN fraction amongst the known CNe using three methods to get 24% +/- 4%, 12% +/- 3%, and 35% +/- 3%. With roughly a quarter of the 394 known Galactic novae actually being RNe, there should be approximately a hundred such systems masquerading as CNe.Comment: 3 figures, 7 tables, accepted for publication in Ap