The Large Area Telescope (LAT) on Fermi has detected ~150 gamma-ray pulsars, about a third of which were discovered in blind searches of the \(\gamma\)-ray data. Because the angular resolution of the ...LAT is relatively poor and blind searches for pulsars (especially millisecond pulsars, MSPs) are very sensitive to an error in the position, one must typically scan large numbers of locations. Identifying plausible X-ray counterparts of a putative pulsar drastically reduces the number of trials, thus improving the sensitivity of pulsar blind searches with the LAT. I discuss our ongoing program of Swift, XMM-Newton, and Chandra observations of LAT unassociated sources in the context of our blind searches for gamma-ray pulsars.
During the month of December, 2009 the blazar 3C 454.3 became the brightest gamma-ray source in the sky, reaching a peak flux F ~2000E-8 ph/cm2/s for E > 100 MeV. Starting in November, 2009 intensive ...multifrequency campaigns monitored the 3C 454 gamma-ray outburst. Here we report the results of a 2-month campaign involving AGILE, INTEGRAL, Swift/XRT, Swift/BAT, RossiXTE for the high-energy observations, and Swift/UVOT, KANATA, GRT, REM for the near-IR/optical/UV data. The GASP/WEBT provided radio and additional optical data. We detected a long-term active emission phase lasting ~1 month at all wavelengths: in the gamma-ray band, peak emission was reached on December 2-3, 2009. Remarkably, this gamma-ray super-flare was not accompanied by correspondingly intense emission in the optical/UV band that reached a level substantially lower than the previous observations in 2007-2008. The lack of strong simultaneous optical brightening during the super-flare and the determination of the broad-band spectral evolution severely constrain the theoretical modelling. We find that the pre- and post-flare broad-band behavior can be explained by a one-zone model involving SSC plus external Compton emission from an accretion disk and a broad-line region. However, the spectra of the Dec. 2-3, 2009 super-flare and of the secondary peak emission on Dec. 9, 2009 cannot be satisfactorily modelled by a simple one-zone model. An additional particle component is most likely active during these states.
The science of AGILE: part II Pittori, C.; Tavani, M.; Barbiellini, G. ...
Nuclear physics. Section B, Proceedings supplement,
12/2002, Letnik:
113, Številka:
1
Journal Article
In this paper (Part II) we discuss the expected scientific performance of the AGILE mission, focusing on the large FOV, the spatial resolution and PSF of the γ-ray imager, and the crucial capability ...of simultaneous hard-X and γ-ray imaging with ∼ 1 – 3 arcmin resolution.
The space gamma-ray observatory AGILE Morselli, A.; Barbiellini, G.; Budini, G. ...
Nuclear physics. Section B, Proceedings supplement,
05/2000, Letnik:
85, Številka:
1
Journal Article
Odprti dostop
Gamma-rays of cosmic origin are a manifestation of the most energetic phenomena in our Universe. Many astrophysical sources emit gamma-rays including relativistic compact stars, massive black holes ...in active galactic nuclei, gamma-ray burst sources, and our Sun during intense flares. The mission AGILE (
Astro-rivelatore Gamma a Immagini LEggero) is an innovative, cost effective gamma ray mission selected by the Italian Space Agency (ASI) as first payload of the Program for Small Scientific Missions. It is designed to detect and image gamma-ray sources in the energy range 30 MeV-50 GeV and operate as an Observatory open to the international community. Primary scientific goals include the study of AGN's, gamma ray bursts, Galactic sources, unidentified gamma ray sources, solar flares and diffuse gamma ray emission. AGILE is planned to be operational during the years 2002–2005. It will an ideal ‘bridge’ between EGRET and GLAST, and support space observations and ground based multiwavelength studies of high energy sources.
The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is detected between 40 and 250 GeV with a significance of 25.5 {\sigma} using the MAGIC telescopes. Together with the ...gravitationally lensed blazar QSO B0218+357 (z = 0.944), PKS 1441+25 is the most distant very high energy (VHE) blazar detected to date. The observations were triggered by an outburst in 2015 April seen at GeV energies with the Large Area Telescope on board Fermi. Multi-wavelength observations suggest a subdivision of the high state into two distinct flux states. In the band covered by MAGIC, the variability time scale is estimated to be 6.4 +/- 1.9 days. Modeling the broadband spectral energy distribution with an external Compton model, the location of the emitting region is understood as originating in the jet outside the broad line region (BLR) during the period of high activity, while being partially within the BLR during the period of low (typical) activity. The observed VHE spectrum during the highest activity is used to probe the extragalactic background light at an unprecedented distance scale for ground-based gamma-ray astronomy.
We report the results of a deep XMM-Newton observation of the radio-faint \(\gamma\)-ray pulsar J1741-2054 and its nebula together with the analysis of 5 years of Fermi LAT data. The X-ray spectrum ...of the pulsar is consistent with an absorbed power law plus a blackbody, originating at least partly from the neutron star cooling. The nebular emission is consistent with that of a synchrotron pulsar wind nebula, with hints of spatial spectral variation. We extended the available Fermi LAT ephemeris and folded the \(\gamma\)-ray and X-ray data. We detected X-ray pulsations from the neutron star: both the thermal and non-thermal components are about 35-40% pulsed, with phase-aligned maxima. A sinusoid fits the thermal folded profile well. A 10-bin phase-resolved analysis shows softening of the non-thermal spectrum during the on-pulse phases. The radio, X-ray and \(\gamma\)-ray light curves are single-peaked, not phase-aligned, with the X-ray peak trailing the \(\gamma\)-ray peak by over half a rotation. Spectral considerations suggest that the most probable pulsar distance is in the 0.3-1.0 kpc range.
Astrophysical Journal, 795, 168 (2014) We have analyzed the new deep {\it XMM-Newton} and {\it Chandra} observations
of the energetic radio-quiet pulsar J1813$-$1246. The X-ray spectrum is
...non-thermal, very hard and absorbed. Based on spectral considerations, we
propose that J1813 is located at a distance further than 2.5 kpc. J1813 is
highly pulsed in the X-ray domain, with a light curve characterized by two
sharp, asymmetrical peaks, separated by 0.5 in phase. We detected no
significant X-ray spectral changes during the pulsar phase. We extended the
available {\it Fermi} ephemeris to five years. We found two glitches. The
$\gamma$-ray lightcurve is characterized by two peaks, separated by 0.5 in
phase, with a bridge in between and no off-pulse emission. The spectrum shows
clear evolution in phase, being softer at the peaks and hardenning towards the
bridge. The X-ray peaks lag the $\gamma$-ray ones by 0.25 in phase. We found a
hint of detection in the 30-500 keV band with {\it INTEGRAL} IBIS/ISGRI, that
is consistent with the extrapolation of both the soft X-ray and $\gamma$-ray
emission of J1813. The peculiar X and $\gamma$-ray phasing suggests a singular
emission geometry. We discuss some possibilities within the current pulsar
emission models. Finally, we develop an alternative geometrical model where the
X-ray emission comes from polar cap pair cascades.
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