As a follow-up to the optical spectroscopic campaign aimed at achieving completeness in the Third Catalog of Hard Fermi-LAT Sources (3FHL), we present here the results of a sample of 28 blazars of an uncertain type observed using the 4m telescope at Cerro Tololo Inter-American Observatory in Chile. Out of these 28 sources, we find that 25 are BL Lacertae objects (BL Lacs) and 3 are flat-spectrum radio quasars (FSRQs). We measure redshifts or lower limits for 16 of these blazars, and it is observed that the 12 remaining blazars have featureless optical spectra. These results are part of a more extended optical spectroscopy follow-up campaign for 3FHL blazars, where, until now, 51 blazars of an uncertain type have been classified into BL Lac and FSRQ categories. Furthermore, this campaign has resulted in redshift measurements and lower limits for 15 of these sources. Our results contribute toward attaining a complete sample of blazars above 10 GeV, which then will be crucial in extending our knowledge on blazar emission mechanisms and the extragalactic background light.
Optical and infrared monitoring of the afterglow site of gamma-ray burst GRB 031203 has revealed a brightening source embedded in the host galaxy, which we attribute to the presence of a supernova (SN) related to the GRB ("SN 2003lw"). We present details of the discovery and evolution of SN 2003lw from 0.2 to 92 days after the GRB, derived from SMARTS consortium photometry in I and J bands. GRB 031203 was an intrinsically faint GRB, and the optical light curve is dominated by the SN after the first few days. A template Type Ic light curve, constructed from SN 1998bw photometry, is consistent with the peak brightness of SN 2003lw, although the light curves are not identical. Differential astrometry reveals that the SN, and hence the GRB, occurred less than 300h_71_^-1^pc (3sigma) from the apparent galaxy center.
Gamma-ray bursts (GRBs) have been proposed as a tool to study star formation in the Universe, so it is crucial to investigate whether their host galaxies and immediate environments are in any way special compared with other star-forming galaxies. Here we present spatially resolved maps of dust emission of the host galaxy of the closest known GRB 980425 at z=0.0085 using our new high-resolution observations from Herschel, APEX, ALMA and ATCA. We modeled the spectral energy distributions of the host and of the star-forming region displaying the Wolf-Rayet signatures in the spectrum (WR region), located 800pc away from the GRB position. The host is characterised by low dust content and high fraction of UV-visible star-formation, similar to other dwarf galaxies. Such galaxies are abundant in the local universe, so it is not surprising to find a GRB in one of them, assuming the correspondence between the GRB rate and star-formation. The WR region contributes substantially to the host emission at the far-infrared, millimeter and radio wavelengths and we propose this to be a consequence of its high gas density. If dense environments are also found close to the positions of other GRBs, then the ISM density should also be considered as an important factor influencing whether a given stellar population can produce a GRB, in a similar way as metallicity.
We present results of an all-sky hard X-ray survey based on almost four years of observations with the IBIS telescope onboard the INTEGRAL observatory. The dead time-corrected exposure of the survey is about 33Ms. Approximately 12% and 80% of the sky has been covered to limiting fluxes lower than 1 and 5mCrab, respectively. Our catalog of detected sources includes 403 objects, 316 of which exceed a 5{sigma} detection threshold on the time-averaged map of the sky, and the rest were detected in various subsamples of exposures.
This paper is the second in a series devoted to the hard X-ray (17-60keV) whole sky survey performed by the INTEGRAL observatory over seven years. Here we present a catalog of detected sources that includes 521 objects, 449 of which exceed a 5{sigma} detection threshold on the time-averaged map of the sky, and 53 were detected in various subsamples of exposures. Among the identified sources with known and suspected nature, 262 are Galactic (101 low-mass X-ray binaries, 94 high-mass X-ray binaries, 37 cataclysmic variables, and 30 of other types) and 221 are extragalactic, including 217 active galactic nuclei (AGNs) and 4 galaxy clusters. The extragalactic (|b|>5deg) and Galactic (|b|<5deg) persistently detected source samples have high identification completeness (respectively ~96% and ~93%) and are valuable for population studies.
We present for the first time a study of the 3-200keV broad band spectra of the bursting atoll source 4U 1728-34 (GX 354-0) along its hardness intensity diagram. The analysis was done using the INTEGRAL public and Galactic Center deep exposure data ranging from February 2003 to October 2004.
In this work we present the most comprehensive INTEGRAL active galactic nucleus (AGN) sample. It lists 272 AGN for which we have secure optical identifications, precise optical spectroscopy and measured redshift values plus X-ray spectral information, i.e. 2-10 and 20-100keV fluxes plus column density. Here we mainly use this sample to study the absorption properties of active galaxies, to probe new AGN classes and to test the AGN unification scheme.
We report on the first census of INTEGRAL IBIS detections (>~4{sigma} significance) above 100keV based on the Core Program and public open-time observations up to 2005 April. There are 49 sources detected in the 100-150keV band, of which 14 are also seen in the 150-300keV range. The low-energy sample is dominated by X-ray binary systems of both low and high mass but also includes 10 active galaxies.
We present sky images, sensitivity maps, and catalogs of detected sources in the three energy bands 17-60, 17-35, and 35-80keV in the Galactic plane at |b|<17.5 degrees. The total number of sources in the reference 17-60keV band includes 402 objects exceeding a 4.7{sigma} detection threshold on the nine-year time-averaged map. Among the identified sources with known and tentatively identified natures, 253 are Galactic objects (108 low-mass X-ray binaries, 82 high-mass X-ray binaries, 36 cataclysmic variables, and 27 are of other types), and 115 are extragalactic objects, including 112 active galactic nuclei (AGNs) and 3 galaxy clusters. The sample of Galactic sources with S/N>4.7 sigma has an identification completeness of ~92%, which is valuable for population studies. Since the survey is based on the nine-year sky maps, it is optimized for persistent sources and may be biased against finding transients.
We present prompt {gamma}-ray, early NIR/optical, late optical and X-ray observations of the peculiar GRB 070311 discovered by INTEGRAL, in order to gain clues on the mechanisms responsible for the prompt {gamma}-ray pulse as well as for the early and late multi-band afterglow of GRB 070311. We fitted with empirical functions the gamma-ray and optical light curves and scaled the result to the late time X-rays.
