We present the spectral analysis of an 87~ks emph{XMM-Newton} observation of Draco, a nearby dwarf spheroidal galaxy. Of the approximately 35 robust X-ray source detections, we focus our attention on the brightest of these sources, for which we repor
t X-ray and multiwavelength parameters. While most of the sources exhibit properties consistent with AGN, few of them possess characteristics of LMXBs and CVs. Our analysis puts constraints on population of X-ray sources with $L_X>3times10^{33}$~erg~s$^{-1}$ in Draco suggesting that there are no actively accreting BH and NS binaries. However, we find 4 sources that could be LMXBs/CVs in quiescent state associated with Draco. We also place constraints on the central black hole luminosity and on a dark matter decay signal around 3.5~keV.
For a sample of Swift and Fermi GRBs, we show that the minimum variability timescale and the spectral lag of the prompt emission is related to the bulk Lorentz factor in a complex manner: For small $Gamma$s, the variability timescale exhibits a shall
ow (plateau) region. For large $Gamma$s, the variability timescale declines steeply as a function of $Gamma$ ($delta TproptoGamma^{-4.05pm0.64}$). Evidence is also presented for an intriguing correlation between the peak times, t$_p$, of the afterglow emission and the prompt emission variability timescale.
We use a wavelet technique to investigate the time variations in the light curves from a sample of GRBs detected by Fermi and Swift. We focus primarily on the behavior of the flaring region of Swift-XRT light curves in order to explore connections be
tween variability time scales and pulse parameters (such as rise and decay times, widths, strengths, and separation distributions) and spectral lags. Tight correlations between some of these temporal features suggest a common origin for the production of X-ray flares and the prompt emission.
Curvature effects in Gamma-ray bursts (GRBs) have long been a source of considerable interest. In a collimated relativistic GRB jet, photons that are off-axis relative to the observer arrive at later times than on-axis photons and are also expected t
o be spectrally softer. In this work, we invoke a relatively simple kinematic two-shell collision model for a uniform jet profile and compare its predictions to GRB prompt-emission data for observations that have been attributed to curvature effects such as the peak-flux--peak-frequency relation, i.e., the relation between the $ u$F$_ u$ flux and the spectral peak, E$_{pk}$ in the decay phase of a GRB pulse, and spectral lags. In addition, we explore the behavior of pulse widths with energy. We present the case of the single-pulse Fermi GRB 110920, as a test for the predictions of the model against observations.
From a sample of GRBs detected by the $Fermi$ and $Swift$ missions, we have extracted the minimum variability time scales for temporal structures in the light curves associated with the prompt emission and X-ray flares. A comparison of this variabili
ty time scale with pulse parameters such as rise times,determined via pulse-fitting procedures, and spectral lags, extracted via the cross-correlation function (CCF), indicate a tight correlation between these temporal features for both the X-ray flares and the prompt emission. These correlations suggests a common origin for the production of X-ray flares and the prompt emission in GRBs.
