Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA new gamma-ray source unveiled by AGILE in the region of Orion
73
0
0.0
(
0
)
Authors
N. Marchili
Ask ChatGPT about the research
No Arabic abstract
Diffuse galactic gamma-ray emission is produced by the interaction of cosmic rays (CRs) with the interstellar environment. The study of gamma-ray emission is therefore a powerful tool to investigate the origin of CRs and the processes through which they are accelerated. We aim to gain deeper insights of the nature of gamma-ray emission in the region of Orion, which is one of the best studied sites of on-going star formation, by analysing data from the AGILE satellite. The diffuse gamma-ray emission expected from the Orion region is relatively high. Its separation from the galactic plane also ensures a very low contribution from foreground or background emission, which makes it an ideal site for studying the processes of particle acceleration in star forming environments. The AGILE data are modelled through a template that quantifies the gamma-ray diffuse emission expected from atomic and molecular hydrogen. Other sources of emission are modelled as an isotropic contribution. Gamma-ray emission exceeding the amount expected by the diffuse emission model is detected with high level of significance. The main excess is in the high-longitude part of Orion A. A thorough analysis of this feature suggests a connection between the observed gamma-ray emission and the B0.5 Ia star k Orionis. The location of the gamma-ray excess is compatible with the site where stellar wind collides with the ISM. Both scattering on dark gas and cosmic-ray acceleration at the shock between the two environments are discussed as possible explanations, with the latter hypothesis being supported by the hardness of the energy spectrum of the emission. If confirmed, this would be the first direct detection of gamma-ray emission from the interaction between ISM and a single stars stellar wind.
rate research
Read More
Using gamma-ray data collected by the Astrorivelatore Gamma ad Immagini LEggero (AGILE) satellite over a period of almost one year (from 2007 July to 2008 June), we searched for pulsed signals from 35 potentially interesting radio pulsars, ordered according to $F_{gamma}propto sqrt{dot{E}} d^{-2}$ and for which contemporary or recent radio data were available. AGILE detected three new top-ranking nearby and Vela-like pulsars with good confidence both through timing and spatial analysis. Among the newcomers we find pulsars with very high rotational energy losses, such as the remarkable PSR B1509-58 with a magnetic field in excess of 10^13 Gauss, and PSR J2229+6114 providing a reliable identification for the previously unidentified EGRET source 3EG 2227+6122. Moreover, the powerful millisecond pulsar B1821-24, in the globular cluster M28, is detected during a fraction of the observations. Four other promising gamma-ray pulsar candidates, among which is the notable J2043+2740 with an age in excess of 1 million years, show a possible detection in the timing analysis only and deserve confirmation.
Context. After the release of the gamma-ray source catalog produced by the Fermi satellite during its first two years of operation, a significant fraction of sources still remain unassociated at lower energies. In addition to well-known high-energy emitters (pulsars, blazars, supernova remnants, etc.) theoretical expectations predict new classes of gamma-ray sources. In particular, gamma-ray emission could be associated with some of the early phases of stellar evolution, but this interesting possibility is still poorly understood. Aims. The aim of this paper is to assess the possibility of the Fermi gamma-ray source 2FGL J0607.5-0618c being associated with the massive star forming region Monoceros R2. Methods. A multi-wavelength analysis of the Monoceros R2 region is carried out using archival data at radio, infrared, X-ray, and gamma-ray wavelengths. The resulting observational properties are used to estimate the physical parameters needed to test the different physical scenarios. Results. We confirm the 2FGL J0607.5-0618c detection with improved confidence over the Fermi two-year catalog. We find that a combined effect of the multiple young stellar objects in Monoceros R2 is a viable picture for the nature of the source.
Since its launch in April 2007, the AGILE satellite detected with its Gamma-Ray Imaging Detector (GRID) several blazars at high significance: 3C 279, 3C 454.3, PKS 1510-089, S5 0716+714, 3C 273, W Comae, Mrk 421 and PKS 0537-441. Moreover, AGILE was able both to rapidly respond to sudden changes in blazar activity state at other wavelengths and to alert other telescopes quickly in response to changes in the gamma-ray fluxes. Thus, we were able to obtain multiwavelength data from other observatories such as Spitzer, Swift, RXTE, Suzaku, INTEGRAL, MAGIC, VERITAS, as well as radio-to-optical coverage by means of the GASP Project of the WEBT and REM. This large multifrequency coverage gave us the opportunity to study the Spectral Energy Distribution of these sources from radio to gamma-rays energy bands and to investigate the different mechanisms responsible for their emission. We present an overview of the AGILE results on these gamma-ray blazars and the relative multifrequency data.
Identification of gamma-ray-emitting Galactic sources is a long-standing problem in astrophysics. One such source, 1AGL J2022+4032, coincident with the interior of the radio shell of the supernova remnant Gamma Cygni (SNR G78.2+2.1) in the Cygnus Region, has recently been identified by Fermi as a gamma-ray pulsar, LAT PSR J2021+4026. We present long-term observations of 1AGL J2022+4032 with the AGILE gamma-ray telescope, measuring its flux and light curve. We compare the light curve of 1AGL J2022+4032 with that of 1AGL J2021+3652 (PSR J2021+3651), showing that the flux variability of 1AGL J2022+4032 appears to be greater than the level predicted from statistical and systematic effects and producing detailed simulations to estimate the probability of the apparent observed variability. We evaluate the possibility that the gamma-ray emission may be due to the superposition of two or more point sources, some of which may be variable, considering a number of possible counterparts. We consider the possibility of a nearby X-ray quiet microquasar contributing to the flux of 1AGL J2022+4032 to be more likely than the hypotheses of a background blazar or intrinsic gamma-ray variabilty of LAT PSR J2021+4026.
The LIGO-Virgo Collaboration (LVC) detected, on 2017 August 17, an exceptional gravitational-wave (GW) event temporally consistent within $sim,1.7 , rm s$ with the GRB 1708117A observed by Fermi-GBM and INTEGRAL. The event turns out to be compatible with a neutron star-neutron star (NS-NS) coalescence that subsequently produced a radio/optical/X-ray transient detected at later times. We report the main results of the observations by the AGILE satellite of the GW170817 localization region (LR) and its electromagnetic (e.m.) counterpart. At the LVC detection time $T_0$, the GW170817 LR was occulted by the Earth. The AGILE instrument collected useful data before and after the GW-GRB event because in its spinning observation mode it can scan a given source many times per hour. The earliest exposure of the GW170817 LR by the gamma-ray imaging detector (GRID) started about 935 s after $T_0$. No significant X-ray or gamma-ray emission was detected from the LR that was repeatedly exposed over timescales of minutes, hours, and days before and after GW170817, also considering Mini-calorimeter and Super-AGILE data. Our measurements are among the earliest ones obtained by space satellites on GW170817 and provide useful constraints on the precursor and delayed emission properties of the NS-NS coalescence event. We can exclude with high confidence the existence of an X-ray/gamma-ray emitting magnetar-like object with a large magnetic field of $10^{15} , rm G$. Our data are particularly significant during the early stage of evolution of the e.m. remnant.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
