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We present phase-resolved spectroscopy and photometry of a source discovered with the Chandra Galactic Bulge Survey (GBS), CXOGBSJ174444.7-260330 (aka CX93 and CX153 in the previously published GBS list). We find two possible values for the orbital period P, differing from each other by 13 seconds. The most likely solution is P =5.69014(6) hours. The optical lightcurves show ellipsoidal modulations, whose modeling provides an inclination of 32+-1 degrees for the most likely P. The spectra are dominated by a K5V companion star (the disc veiling is, Comment: 9 pages, 5 figures. Accepted for publication in MNRAS

In 1975, E. R. Robinson conducted the hallmark study of the behavior of classical nova light curves before eruption, and this work has now become part of the standard knowledge of novae. He made three points; that 5 out of 11 novae showed pre-eruption rises in the years before eruption, that one nova (V446 Her) showed drastic changes in the variability across eruptions, and that all but one of the novae (excepting BT Mon) have the same quiescent magnitudes before and after the outburst. This work has not been tested since it came out. We have now tested these results by going back to the original archival photographic plates and measuring large numbers of pre-eruption magnitudes for many novae using comparison stars on a modern magnitude scale. We find in particular that four out of five claimed pre-eruption rises are due to simple mistakes in the old literature, that V446 Her has the same amplitude of variations across its 1960 eruption, and that BT Mon has essentially unchanged brightness across its 1939 eruption. Out of 22 nova eruptions, we find two confirmed cases of significant pre-eruption rises (for V533 Her and V1500 Cyg), while T CrB has a deep pre-eruption dip. These events are a challenge to theorists. We find no significant cases of changes in variability across 27 nova eruptions beyond what is expected due to the usual fluctuations seen in novae away from eruptions. For 30 classical novae plus 19 eruptions from 6 recurrent novae, we find that the average change in magnitude from before the eruption to long after the eruption is 0.0 mag. However, we do find five novae (V723 Cas, V1500 Cyg, V1974 Cyg, V4633 Sgr, and RW UMi) that have significantly large changes, in that the post-eruption quiescent brightness level is over ten times brighter than the pre-eruption level., Comment: 91 pages (preprint), AJ accepted

Since launch in 2008, the Fermi Gamma-ray Burst Monitor (GBM) has detected many hundreds of bursts from magnetar sources. While the vast majority of these bursts have been attributed to several known magnetars, there is also a small sample of magnetar-like bursts of unknown origin. Here we present the Fermi/GBM magnetar catalog, giving the results of the temporal and spectral analyses of 440 magnetar bursts with high temporal and spectral resolution. This catalog covers the first five years of GBM magnetar observations, from July 2008 to June 2013. We provide durations, spectral parameters for various models, fluences and peak fluxes for all the bursts, as well as a detailed temporal analysis for SGR J1550-5418 bursts. Finally, we suggest that some of the bursts of unknown origin are associated with the newly discovered magnetar 3XMM J185246.6+0033.7., Comment: 65 pages, 24 figures, 13 tables; accepted for publication in ApJ Supplement

We present optical lightcurves of variable stars consistent with the positions of X-ray sources identified with the Chandra X-ray Observatory for the Chandra Galactic Bulge Survey. Using data from the Mosaic-II instrument on the Blanco 4m Telescope at CTIO, we gathered time-resolved photometric data on timescales from $\sim2$ hr to 8 days over the $\frac{3}{4}$ of the X-ray survey containing sources from the initial GBS catalog. Among the lightcurve morphologies we identify are flickering in interacting binaries, eclipsing sources, dwarf nova outbursts, ellipsoidal variations, long period variables, spotted stars, and flare stars. $87\%$ of X-ray sources have at least one potential optical counterpart. $24\%$ of these candidate counterparts are detectably variable; a much greater fraction than expected for randomly selected field stars, which suggests that most of these variables are real counterparts. We discuss individual sources of interest, provide variability information on candidate counterparts, and discuss the characteristics of the variable population., Accepted for publication in the Astrophysical Journal Supplements

The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of such unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest $\gamma$-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the non-thermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock., Comment: 30 pages, 6 figures. Accepted for publication in Science. Corresponding authors: S. Zhu (sjzhu@umd.edu); J. Chiang (jchiang@slac.stanford.edu); C. Dermer (charles.dermer@nrl.navy.mil); N. Omodei (nicola.omodei@stanford.edu); G. Vianello (giacomov@slac.stanford.edu); S. Xiong (Shaolin.Xiong@uah.edu)

We consider the distribution of many samples of Gamma-Ray Bursts (GRBs) when plotted in a diagram with their bolometric fluence (Sbolo) versus the observed photon energy of peak spectral flux (Epeak,obs). In this diagram, bursts that obey the Amati relation must lie above some limiting line, although observational scatter is expected to be substantial. We confirm that early bursts with spectroscopic redshifts are consistent with this limit. But, we find that the bursts from BATSE, Swift, Suzaku, and Konus are all greatly in violation of the limit. In the Sbolo-Epeak,obs diagram, we find that every satellite has a greatly different distribution. This requires that selection effects are dominating these distributions, which we identify. For detector selections, the trigger threshold and the threshold to measure Epeak,obs combine to make a diagonal cutoff with the position of this cutoff varying greatly detector to detector. For selection effects due to the intrinsic properties of the burst population, the distribution of Epeak,obs makes for bursts with low and high values to be rare, while the fluence distribution makes bright bursts uncommon. For a poor threshold, the combination of selection effects serves to allow only bursts within a region along the limit to be measured; these bursts will then appear to follow an Amati relation. Therefore, the Amati relation is an artifact of selection effects within the burst population and the detector. Therefore, the Amati relation should not be used for cosmological tasks. This failure is in no way prejudicial against the other luminosity relations., Comment: 39 pages, 14 figures, 1 table, ApJ Accepted

While Epeak has been extensively used in the past, for example with luminosity indicators, it has not been thoroughly examined for possible sources of scatter. In the literature, the reported error bars for Epeak are the simple Poisson statistical errors. Additional uncertainties arise due to the choices made by analysts in determining Epeak (e.g., the start and stop times of integration), imperfect knowledge of the response of the detector, different energy ranges for various detectors, and differences in models used to fit the spectra. We examine the size of these individual sources of scatter by comparing many independent pairs of published Epeak values for the same bursts. Indeed, the observed scatter in multiple reports of the same burst (often with the same data) is greatly larger than the published statistical error bars. We measure that the one-sigma uncertainty associated with the analyst's choices is 28%, i.e., 0.12 in Log10(Epeak), with the resultant errors always being present. The errors associated with the detector response are negligibly small. The variations caused by commonly-used alternative definitions of Epeak (such as present in all papers and in all compiled burst lists) is typically 23%-46%, although this varies substantially with the application. The implications of this are: (1) Even the very best measured Epeak values will have systematic uncertainties of 28%. (2) Thus, GRBs have a limitation in accuracy for a single event, with this being reducible by averaging many bursts. (3) The typical one-sigma total uncertainty for collections of bursts is 55%. (4) We also find that the width of the distribution for Epeak in the burst frame must be near zero, implying that some mechanism must exist to thermostat GRBs. (5) Our community can only improve on this situation by using collections of bursts which all have identical definitions for the Epeak calculation., Comment: 25 pages, 2 figures, ApJ accepted

We identify a new class of novae characterized by the post-eruption quiescent light curve being more than roughly a factor of ten brighter than the pre-eruption light curve. Eight novae (V723 Cas, V1500 Cyg, V1974 Cyg, GQ Mus, CP Pup, T Pyx, V4633 Sgr, and RW UMi) are separated out as being significantly distinct from other novae. This group shares a suite of uncommon properties, characterized by the post-eruption magnitude being much brighter than before eruption, short orbital periods, long-lasting supersoft emission following the eruption, a highly magnetized white dwarf, and secular declines during the post-eruption quiescence. We present a basic physical picture which shows why all five uncommon properties are causally connected. Most novae do not have adequate accretion for continuous hydrogen burning, but some can achieve this if the companion star is nearby (with short orbital period) and a magnetic field channels the matter onto a small area on the white dwarf so as to produce a locally high accretion rate. The resultant supersoft flux irradiates the companion star and drives a higher accretion rate (with a brighter post-eruption phase), which serves to keep the hydrogen burning and the supersoft flux going. The feedback loop cannot be perfectly self-sustaining, so the supersoft flux will decline over time, forcing a decline in the accretion rate and the system brightness. We name this new group after the prototype, V1500 Cyg. V1500 Cyg stars are definitely not progenitors of Type Ia supernovae. The V1500 Cyg stars have similar physical mechanisms and appearances as predicted for nova by the hibernation model, but with this group accounting for only 14% of novae., Comment: Astronomical Journal, in press, 39 pages, 10 figures

Firmani et al. (2006) proposed a new Gamma Ray Burst (GRB) luminosity relation that showed a significant improvement over the Liso−Epeak relation. (Liso is the isotropic peak luminosity and Epeak is the photon energy of the spectral peak for the burst.) The new proposed relation simply modifies the Epeak value by multiplying it by a power of T0.45, where T0.45 is a particular measure of the GRB duration. We begin by reproducing the results of Firmani for his 19 bursts. We then test the Firmani relation for the same 19 bursts except that we use independently measured values for Liso, T0.45 and Epeak, and we find that the relation deteriorates substantially. We further test the relation by using 60 GRBs with measured spectroscopic redshifts, and find a relation that has a comparable scatter as the original Liso−Epeak relation. That is, a much larger sample of bursts does not reproduce the small scatter as reported by Firmani et al. Finally, we investigate whether the Firmani relation is improved by the use of any of 32 measures of duration (e.g., T90, T50, T90/Npeak, the fluence divided by the peak flux, T0.30, and T0.60) in place of T0.45. The quality of each alternative duration measure is evaluated with the root mean square of the scatter between the observed and fitted logarithmic Liso values. Although we find some durations yield slightly better results than T0.45, the differences between the duration measures are minimal. We find that the addition of a duration does not add any significant improvement to the Liso−Epeak relation. We also present a simple and direct derivation of the Firmani relation from both the Liso−Epeak and Amati (2002) relations. In all we conclude that the Firmani relation neither has an independent existence nor does it provide any significant improvement on previously known relations that are simpler.

A directed search for previously-undiscovered nova eruptions was conducted in the astronomical plate archives at Harvard College Observatory and Sonneberg Observatory. We found that an eruption of V2487 Oph (Nova Oph 1998) occurred on 1900 June 20. V2487 Oph was previously classified as a classical nova, which we identified as a probable recurrent nova based on its large expansion velocities and the presence of high excitation lines in the outburst spectrum. The event was recorded on Harvard plate AM 505, at a B magnitude of 10.27 +/- 0.11, which is near peak. The outburst can only be seen on one plate, but the image has a characteristic dumbbell shape (caused by a double exposure) that is identical to the other star images on the plate, and thus is not a plate defect. We conclude that this is in fact a previously-undiscovered nova outburst of V2487 Oph, confirming our prediction that it is a recurrent nova. We also examine the discovery efficiency for eruptions of the system and conclude that a randomly-timed outburst has, on average, a 30% chance of being discovered in the past century. Using this, we deduce a recurrence time for V2487 Oph of approximately 18 years, which implies that the next eruption is expected around 2016., Comment: 18 pages, 2 figures, to be published in the Astronomical Journal

Firmani et al. proposed a new Gamma Ray Burst (GRB) luminosity relation that showed a significant improvement over the L_iso-E_peak relation. The new proposed relation simply modifies the E_peak value by multiplying it by a power of T_0.45, where T_0.45 is a particular measure of the GRB duration. We begin by reproducing the results of Firmani for his 19 bursts. We then test the Firmani relation for the same 19 bursts except that we use independently measured values for L_iso, T_0.45, and E_peak, and we find that the relation deteriorates substantially. We further test the relation by using 60 GRBs with measured spectroscopic redshifts, and find a relation that has a comparable scatter as the original L_iso-E_peak relation. That is, a much larger sample of bursts does not reproduce the small scatter as reported by Firmani et al. Finally, we investigate whether the Firmani relation is improved by the use of any of 32 measures of duration in place of T_0.45. The quality of each alternative duration measure is evaluated with the root mean square of the scatter between the observed and fitted logarithmic Liso values. Although we find some durations yield slightly better results than T_0.45, the differences between the duration measures are minimal. We find that the addition of a duration does not add any significant improvement to the L_iso-E_peak relation. We also present a simple and direct derivation of the Firmani relation from both the L_iso-E_peak and Amati relations. In all we conclude that the Firmani relation neither has an independent existence nor does it provide any significant improvement on previously known relations that are simpler., Comment: ApJ in press, 17 pages, 3 figures, 3 tables

Long duration Gamma-Ray Bursts (GRBs) have eight luminosity relations where observable burst properties can yield the burst luminosity and hence distance. This turns GRBs into useful tools of cosmology. Recently, two tests have been proposed (by Nakar & Piran and by Li) for which one of the eight relations is claimed to have significant problems. In this paper, we generalize these tests and apply them to all eight GRB luminosity relations. (a) All eight relations pass the Nakar & Piran test after accounting for the uncertainties on the data and the dispersions of the correlations. (b) All eight relations are good when the GRB redshifts are known, for example for calibration of the relations and for GRB Hubble diagram purposes. (c) We confirm the earlier results that the E_gamma,iso - E_peak Amati relation must produce very large error bars whenever an unknown redshift being sought is >1.4. (d) The E_gamma - E_peak relation of Ghirlanda et al. must produce very large error bars whenever an unknown redshift being sought is >3.4. (e) The other six relations have no problem at all from the ambiguity test of Li., Ap.J. Letters in press, 11 pages

We introduce the Galactic Bulge Survey (GBS) and we provide the Chandra source list for the region that has been observed to date. Among the goals of the GBS are constraining the neutron star equation of state and the black hole mass distribution via the identification of eclipsing neutron star and black hole low-mass X-ray binaries. The latter goal will, in addition, be obtained by significantly enlarging the number of black hole systems for which a black hole mass can be derived. Further goals include constraining X-ray binary formation scenarios, in particular the common envelope phase and the occurrence of kicks, via source-type number counts and an investigation of the spatial distribution of X-ray binaries, respectively. The GBS targets two strips of 6x1 degrees (12 square degrees in total), one above (1, Comment: Accepted for publication in ApJS, 12 pages, 7 figures, 4 Tables, Table 3 with the full source list is available at http://www.sron.nl/~peterj/gbs/publications.html

Science 343(6166), 51 - 54(2014). doi:10.1126/science.1242302, Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse up to 2.5 seconds is possibly the brightest well-isolated pulse observed to date. A fine time resolution spectral analysis shows power-law decays of the peak energy from the onset of the pulse, consistent with models of internal synchrotron shock pulses. However, a strongly correlated power-law behavior is observed between the luminosity and the spectral peak energy that is inconsistent with curvature effects arising in the relativistic outflow. It is difficult for any of the existing models to account for all of the observed spectral and temporal behaviors simultaneously., Published by American Association for the Advancement of Science, Washington, DC [u.a.]