A Black Hole in the X-Ray Nova Velorum 1993

We have obtained 17 moderate-resolution (~2.5 A) optical spectra of the Galactic X-ray Nova Velorum 1993 in quiescence with the Keck-II telescope. The orbital period (P) is 0.285206 +/- 0.0000014 d, and the semiamplitude (K_2) is 475.4 +/- 5.9 km/s. Our derived mass function, f(M_1) = PK_2^3 /2 pi G = 3.17 +/- 0.12 M_sun, is close to the conventional absolute limiting mass for a neutron star (~ 3.0-3.2 M_sun) -- but if the orbital inclination i is less than 80 degrees (given the absences of eclipses), then M_1 is greater than 4.2-4.4 M_sun for nominal secondary-star masses of 0.5 M_sun (M0) to 0.65 M_sun (K6). The primary star is therefore almost certainly a black hole rather than a neutron star. The velocity curve of the primary from H-alpha emission has a semiamplitude (K_1) of 65.3 +/- 7.0 km/s, but with a phase offset by 237 degrees (rather than 180 degrees) from that of the secondary star. The nominal mass ratio q = M_2/M_1 = K_1/K_2 = 0.137 +/- 0.015, and hence for M_2 = 0.5-0.65 M_sun we derive M_1 = 3.64-4.74 M_sun. An adopted mass M_1 ~ 4.4 M_sun is significantly below the typical value of ~ 7 M_sun found for black holes in other low-mass X-ray binaries. Keck observations of MXB 1659-29 (V2134 Oph) in quiescence reveal a probable optical counterpart at R = 23.6 +/- 0.4 mag.Comment: 16 pages, 9 figures, added references, revised per. referee's comments Accepted for publication in August 1999 issue of PAS

IPN localizations of Konus short gamma-ray bursts

Between the launch of the \textit{GGS Wind} spacecraft in 1994 November and the end of 2010, the Konus-\textit{Wind} experiment detected 296 short-duration gamma-ray bursts (including 23 bursts which can be classified as short bursts with extended emission). During this period, the IPN consisted of up to eleven spacecraft, and using triangulation, the localizations of 271 bursts were obtained. We present the most comprehensive IPN localization data on these events. The short burst detection rate, $\sim$18 per year, exceeds that of many individual experiments.Comment: Published versio

AGILE detection of a strong gamma-ray flare from the blazar 3C 454.3

We report the first blazar detection by the AGILE satellite. AGILE detected 3C 454.3 during a period of strongly enhanced optical emission in July 2007. AGILE observed the source with a dedicated repointing during the period 2007 July 24-30 with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the hard X-ray imager Super-AGILE sensitive in the 30 MeV-50 GeV and 18-60 keV, respectively. Over the entire period, AGILE detected gamma-ray emission from 3C 454.3 at a significance level of 13.8-$\sigma$ with an average flux (E$>$100 MeV) of $(280 \pm 40) \times 10^{-8}$ photons cm$^{-2}$ s$^{-1}$. The gamma-ray flux appears to be variable towards the end of the observation. No emission was detected by Super-AGILE in the energy range 20-60 keV, with a 3-$\sigma$ upper limit of $2.3 \times 10^{-3}$ photons cm$^{-2}$ s$^{-1}$. The gamma-ray flux level of 3C 454.3 detected by AGILE is the highest ever detected for this quasar and among the most intense gamma-ray fluxes ever detected from Flat Spectrum Radio Quasars.Comment: Accepted by Astrophysical Journal Letters; 14 pages, 3 EPS Figures, 1 Tabl

AGILE observation of a gamma-ray flare from the blazar 3C 279

Context. We report the detection by the AGILE satellite of an intense gamma-ray flare from the gamma-ray source 3EG J1255-0549, associated to the Flat Spectrum Radio Quasar 3C 279, during the AGILE pointings towards the Virgo Region on 2007 July 9-13. Aims. The simultaneous optical, X-ray and gamma-ray covering allows us to study the spectral energy distribution (SED) and the theoretical models relative to the flaring episode of mid-July. Methods. AGILE observed the source during its Science Performance Verification Phase with its two co-aligned imagers: the Gamma- Ray Imaging Detector (GRID) and the hard X-ray imager (Super-AGILE) sensitive in the 30 MeV - 50 GeV and 18 - 60 keV respectively. During the AGILE observation the source was monitored simultaneously in optical band by the REM telescope and in the X-ray band by the Swift satellite through 4 ToO observations. Results. During 2007 July 9-13 July 2007, AGILE-GRID detected gamma-ray emission from 3C 279, with the source at ~2 deg from the center of the Field of View, with an average flux of (210+-38) 10^-8 ph cm^-2 s^-1 for energy above 100 MeV. No emission was detected by Super-AGILE, with a 3-sigma upper limit of 10 mCrab. During the observation lasted about 4 days no significative gamma-ray flux variation was observed. Conclusions. The Spectral Energy Distribution is modelled with a homogeneous one-zone Synchrotron Self Compton emission plus the contributions by external Compton scattering of direct disk radiation and, to a lesser extent, by external Compton scattering of photons from the Broad Line Region.Comment: Accepted for publication in Astronomy and Astrophysic

The flaring blazars of the first 1.5 years of the AGILE mission

We report the AGILE gamma-ray observations and the results of the multiwavelength campaigns on seven flaring blazars detected by the mission: During two multiwavelength campaigns, we observed gamma-ray activity from two Flat Spectrum Radio Quasars of the Virgo region, e.g. 3C 279 and 3C 273 (the latter being the first extragalactic source simultaneously observed with the gamma-ray telescope and the hard X ray imager of the mission). Due to the large FOV of the AGILE/GRID instrument, we achieved an almost continuous coverage of the FSRQ 3C 454.3. The source showed flux above 10E-6 photons/cm2/s (E > 100 MeV) and showed day by day variability during all the AGILE observing periods. In the EGRET era, the source was found in high gamma-ray activity only once. An other blazar, PKS 1510-089 was frequently found in high gamma-ray activity. S5 0716+71, an intermediate BL Lac object, exhibited a very high gamma-ray activity and fast gamma-ray variability during a period of intense optical activity. We observed high gamma-ray activity from W Comae, a BL Lac object, and Mrk 421, an high energy peaked BL Lac object. For this source, a multiwavelength campaign from optical to TeV has been performed

Direct Evidence for Hadronic Cosmic-Ray Acceleration in the Supernova Renmant IC 443

The Supernova Remnant (SNR) IC 443 is an intermediate-age remnant well known for its radio, optical, X-ray and gamma-ray energy emissions. In this Letter we study the gamma-ray emission above 100 MeV from IC 443 as obtained by the AGILE satellite. A distinct pattern of diffuse emission in the energy range 100 MeV-3 GeV is detected across the SNR with its prominent maximum (source "A") localized in the Northeastern shell with a flux F = (47 \pm 10) 10^{-8} photons cm^{-2} s^{-1} above 100 MeV. This location is the site of the strongest shock interaction between the SNR blast wave and the dense circumstellar medium. Source "A" is not coincident with the TeV source located 0.4 degree away and associated with a dense molecular cloud complex in the SNR central region. From our observations, and from the lack of detectable diffuse TeV emission from its Northeastern rim, we demonstrate that electrons cannot be the main emitters of gamma-rays in the range 0.1-10 GeV at the site of the strongest SNR shock. The intensity, spectral characteristics, and location of the most prominent gamma-ray emission together with the absence of co-spatial detectable TeV emission are consistent only with a hadronic model of cosmic-ray acceleration in the SNR. A high-density molecular cloud (cloud "E") provides a remarkable "target" for nucleonic interactions of accelerated hadrons: our results show enhanced gamma-ray production near the molecular cloud/shocked shell interaction site. IC 443 provides the first unambiguous evidence of cosmic-ray acceleration by SNRs.Comment: 5 pages, 2 figures; accepted by ApJLetters on Jan 21, 201

Calibration of AGILE-GRID with In-Flight Data and Monte Carlo Simulations

Context: AGILE is a gamma-ray astrophysics mission which has been in orbit since 23 April 2007 and continues to operate reliably. The gamma-ray detector, AGILE-GRID, has observed Galactic and extragalactic sources, many of which were collected in the first AGILE Catalog. Aims: We present the calibration of the AGILE-GRID using in-flight data and Monte Carlo simulations, producing Instrument Response Functions (IRFs) for the effective area A_eff), Energy Dispersion Probability (EDP), and Point Spread Function (PSF), each as a function of incident direction in instrument coordinates and energy. Methods: We performed Monte Carlo simulations at different gamma-ray energies and incident angles, including background rejection filters and Kalman filter-based gamma-ray reconstruction. Long integrations of in-flight observations of the Vela, Crab and Geminga sources in broad and narrow energy bands were used to validate and improve the accuracy of the instrument response functions. Results: The weighted average PSFs as a function of spectra correspond well to the data for all sources and energy bands. Conclusions: Changes in the interpolation of the PSF from Monte Carlo data and in the procedure for construction of the energy-weighted effective areas have improved the correspondence between predicted and observed fluxes and spectra of celestial calibration sources, reducing false positives and obviating the need for post-hoc energy-dependent scaling factors. The new IRFs have been publicly available from the Agile Science Data Centre since November 25, 2011, while the changes in the analysis software will be distributed in an upcoming release