GeV Gamma-Ray Sources

We report on the preliminary extension of our work on cataloging the GeV sky to approximately 7 years of CGRO/EGRET observations with special emphasis on a search for transient sources. The search method and significance levels are presented. Our initial results on 13 possible transients indicate that 3 may be new gamma-ray sources. Sixteen new steady GeV sources are also detected, 3 of which have never been reported as gamma-ray sources

Rapid variability in the synchrotron self Compton model for blazars

Blazars are characterized by large amplitude and fast variability, indicating that the electron distribution is rapidly changing, often on time scales shorter than the light crossing time. The emitting region is sufficiently compact to let radiative losses dominate the cooling of high energy electrons. We study the time dependent behaviour of the electron distribution after episodic electron injection phases, and calculate the observed synchrotron and self Compton radiation spectra. Since photons produced in different part of the source have different travel times, the observed spectrum is produced by the electron distribution at different stages of evolution. Even a homogeneous source then resembles an inhomogeneous one. Time delays between the light curves of fluxes at different frequencies are possible, as illustrated for the specific case of the BL Lac object Mkn 421.Comment: 11 pages, 11 figures, Submitted to MNRAS, revised version after referee's repor

Discovery of Pulsed X-ray Emission from the SMC Transient RX J0117.6-7330

We report on the detection of pulsed, broad-band, X-ray emission from the transient source RX J0117.6-7330. The pulse period of 22 seconds is detected by the ROSAT/PSPC instrument in a 1992 Sep 30 - Oct 2 observation and by the CGRO/BATSE instrument during the same epoch. Hard X-ray pulsations are detectable by BATSE for approximately 100 days surrounding the ROSAT observation (1992 Aug 28 - Dec 8). The total directly measured X-ray luminosity during the ROSAT observation is 1.0E38 (d/60 kpc)^2 ergs s-1. The pulse frequency increases rapidly during the outburst, with a peak spin-up rate of 1.2E-10 Hz s-1 and a total frequency change 1.8%. The pulsed percentage is 11.3% from 0.1-2.5 keV, increasing to at least 78% in the 20-70 keV band. These results establish RX J0117.6-7330 as a transient Be binary system.Comment: 17 pages, Latex, aasms, accepted for publication in ApJ Letter

Discovery of 16.6 and 25.5 s Pulsations from the Small Magellanic Cloud

We report the serendipitous detection of two previously unreported pulsars from the direction of the Small Magellanic Cloud, with periods of 16.6 and 25.5 seconds. The detections are based on archival PCA data from the Rossi X-ray Timing Explorer (RXTE). The observation leading to these detections occurred in September 2000 extending over 2.1 days with an exposure of 121 ks. A possible identification of the 16.6 s pulsar with an X-ray source RX J0051.8-7310 seen by both ROSAT and ASCA imaging X-ray satellites is presented.Comment: 9 pages with 3 figures. Submitted to ApJ Letter

X-ray observations of Be/X-ray binaries in the SMC

(shortened) Fifteen Be/X-ray binaries and candidates in the SMC were observed serendipitously with the EPIC instruments of XMM-Newton during two observations of SNR 0047-73.5 and SNR 0103-72.6 in October 2000. A total of twelve of those sources are detected. For eleven of them an accurate position and in part detection of X-ray pulsations support the proposed identification as Be/X-ray binaries. The detection of pulsations (172.2 s, 320.1 s and 751 s) from three hard X-ray sources with periods known from ASCA observations confirm their proposed identifications with ROSAT sources and their optical Be star counterparts. In addition, pulsations with a period of 263.6 s were found from XMMUJ004723.7-731226=RXJ0047.3-7312. For SAXJ0103.2-7209 a pulse period of 341.2$\pm$0.5 s was determined, continuing the large spin-up seen with ASCA, BeppoSAX and Chandra between 1996 and 1999 with a period derivative of $-$1.6 s yr$^{-1}$ covering now 4.5 years. The 0.3-10.0 keV EPIC spectra of all eleven Be/X-ray binaries and candidates are consistent with power-law energy distributions with derived photon indices strongly peaked at 1.00 with a standard deviation of 0.16. No pulsations are detected from RXJ0049.2-7311 and RXJ0049.5-7310 (both near the 9 s pulsar AXJ0049-732) and RXJ0105.1-7211 (near AXJ0105-722, which may pulsate with 3.3 s), leaving the identification of the ASCA sources with ROSAT and corresponding XMM-Newton objects still unclear. We present an updated list of high mass X-ray binaries (HMXBs) and candidates in the SMC incorporating improved X-ray positions obtained from Chandra and XMM-Newton observations. Including the results from this work and recent publications the SMC HMXB catalogue comprises 65 objects with at least 37 showing X-ray pulsations.Comment: 10 pages, 7 figures, accepted for publication in A&

High-Energy sources before INTEGRAL -- INTEGRAL reference catalog --

We describe the INTEGRAL reference catalog which classifies previously known bright X-ray and gamma-ray sources before the launch of INTEGRAL. These sources are, or have been at least once, brighter than ~1 mCrab above 3 keV, and are expected to be detected by INTEGRAL. This catalog is being used in the INTEGRAL Quick Look Analysis to discover new sources or significantly variable sources. We compiled several published X-ray and gamma-ray catalogs, and surveyed recent publications for new sources. Consequently, there are 1122 sources in our INTEGRAL reference catalog. In addition to the source positions, we show an approximate spectral model and expected flux for each source, based on which we derive expected INTEGRAL counting rates. Assuming the default instrument performances and at least ~10^5 sec exposure time for any part of the sky, we expect that INTEGRAL will detect at least ~700 sources below 10 keV and ~400 sources above 20 keV over the mission life.Comment: Accepted to A&A Letter INTEGRAL special issu

Temporal and Spectral Variabilities of High Energy Emission from Blazars Using Synchrotron Self-Compton Models

Multiwavelength observations of blazars such as Mrk 421 and Mrk 501 show that they exhibit strong short time variabilities in flare-like phenomena. Based on the homogeneous synchrotron self-Compton (SSC) model and assuming that time variability of the emission is initiated by changes in the injection of nonthermal electrons, we perform detailed temporal and spectral studies of a purely cooling plasma system. One important parameter is the total injected energy E and we show how the synchrotron and Compton components respond as E varies. We discuss in detail how one could infer important physical parameters using the observed spectra. In particular, we could infer the size of the emission region by looking for exponential decay in the light curves. We could also test the basic assumption of SSC by measuring the difference in the rate of peak energy changes of synchrotron and SSC peaks. We also show that the trajectory in the photon-index and flux plane evolves clockwise or counter-clockwise depending on the value of E and observed energy bands.Comment: 35 pages, 18 figures, accepted by the Astrophysical Journa

Low power BL Lacertae objects and the blazar sequence: Clues on the particle acceleration process

The spectral properties of blazars seem to follow a phenomenological sequence according to the source luminosity. By inferring the source physical parameters through (necessarily) modeling the blazar spectra, we have previously proposed that the sequence arises because the particles responsible for most of the emission suffer increasing radiative losses as the luminosity increases. Here we extend those results by considering the widest possible range of blazar spectral properties. We find a new important ingredient for shaping the spectra of the lowest power objects, namely the role of a finite timescale for the injection of relativistic particles. Only high energy particles radiatively cool in such timescale leading to a break in the particle distribution: particles with this break energy are those emitting most of the power, and this gives raise to a link between blazar spectra and total energy density inside the source, which controls the cooling timescale. The emerging picture requires two phases for the particle acceleration: a first pre-heating phase in which particles reach a characteristic energy as the result of balancing heating and radiative cooling, and a more rapid acceleration phase which further accelerate these particles to form a power law distribution. While in agreement with standard shock theory, this scenario also agrees with the idea that the luminosity of blazars is produced through internal shocks, which naturally lead to shocks lasting for a finite time.Comment: 10 pages, 5 figures, accepted for publication in A&