ترغب بنشر مسار تعليمي؟ اضغط هنا

A search for pair halos around active galactic nuclei through a temporal analysis of Fermi-LAT data

231   0   0.0 ( 0 )
 نشر من قبل Dmitry Prokhorov
 تاريخ النشر 2015
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We develop a method to search for pair halos around active galactic nuclei (AGN) through a temporal analysis of gamma-ray data. The basis of our method is an analysis of the spatial distributions of photons coming from AGN flares and from AGN quiescent states and a further comparison of these two spatial distributions. This method can also be used for a reconstruction of a point spread function (PSF). We found no evidence for a pair halo component through this method by applying it to the Fermi-LAT data in the energy bands of 4.5-6, 6-10, and >10 GeV and set upper limits on the fraction of photons attributable to a pair halo component. An illustration of how to reconstruct the PSF of Fermi-LAT is given. We demonstrate that the PSF reconstructed by using this method is in good agreement with that which was obtained by using the gamma-ray data taken by LAT in the direction of the Crab pulsar and nebula.



قيم البحث

اقرأ أيضاً

The X-ray source CXO J133815.6+043255 has counterparts in the UV, optical, and radio bands. Based on the multi-band investigations, it has been recently proposed by Kim et al. (2015) as a rarely-seen off-nucleus ultraluminous X-ray (ULX) source with a black hole mass of >= 10^4 solar mass in the nearby Seyfert galaxy NGC 5252. To explore its radio properties at very high angular resolution, we performed very long-baseline interferometry (VLBI) observations with the European VLBI Network (EVN) at 1.7 GHz. We find that the radio counterpart is remarkably compact among the known ULXs. It does not show a resolved structure with a resolution of a few milliarcsecond (mas), and the total recovered flux density is comparable to that measured in earlier sub-arcsecond-resolution images. The compact radio structure, the relatively flat spectrum, and the high radio luminosity are consistent with a weakly accreting supermassive black hole in a low-luminosity active galactic nucleus. The nucleus of NGC 5252 itself has similar radio properties. We argue that the system represents a relatively rare pair of active galactic nuclei, where both components emit in the radio.
Numerous extended sources around Galactic pulsars have shown significant $gamma$-ray emission from GeV to TeV energies, revealing hundreds of TeV energy electrons scattering off of the underlying photon fields through inverse Compton scattering (ICS) . HAWC TeV gamma-ray observations of few-degree extended emission around the pulsars Geminga and Monogem, and LAT GeV emission around Geminga, suggest that systems older than 10-100 kyr have multi-TeV $e^pm$ propagating beyond the SNR-PWN system into the interstellar medium. Following the discovery of few $gamma$-ray sources by HAWC at energies E$>100$ TeV, we investigate the presence of an extended $gamma$-ray emission in Fermi-LAT data around the three brightest sources detected by HAWC up to 100 TeV. We find an extended emission of $theta_{68} = 1.00^{+0.05}_{-0.07}$ deg around eHWC J1825-134 and $theta_{68} = 0.71pm0.10$ deg eHWC J1907+063. The analysis with ICS templates on Fermi-LAT data point to diffusion coefficient values which are significantly lower than the average Galactic one. When studied along with HAWC data, the $gamma$-ray Fermi-LAT data provide invaluable insight into the very high-energy electron and positron parent populations.
121 - Shinichiro Ando 2010
Intergalactic magnetic fields (IGMF) can cause the appearance of halos around the gamma-ray images of distant objects because an electromagnetic cascade initiated by a high-energy gamma-ray interaction with the photon background is broadened by magne tic deflections. We report evidence of such gamma-ray halos in the stacked images of the 170 brightest active galactic nuclei (AGN) in the 11-month source catalog of the Fermi Gamma-Ray Space Telescope. Excess over point spread function in the surface brightness profile is statistically significant at 3.5sigma (99.95% confidence level), for the nearby, hard population of AGN. The halo size and brightness are consistent with IGMF, B_{IGMF} ~ 10^{-15} G. The knowledge of IGMF will facilitate the future gamma-ray and charged-particle astronomy. Furthermore, since IGMF are likely to originate from the primordial seed fields created shortly after the Big Bang, this potentially opens a new window on the origin of cosmological magnetic fields, inflation, and the phase transitions in the early Universe.
The high sensitivity of the Fermi-LAT (Large Area Telescope) offers the first opportunity to study faint and extended GeV sources such as pulsar wind nebulae (PWNe). After one year of observation the LAT detected and identified three pulsar wind nebu lae: the Crab Nebula, Vela-X and the PWN inside MSH 15-52. In the meantime, the list of LAT detected pulsars increased steadily. These pulsars are characterized by high energy loss rates from ~3 times 10^{33} erg s$^{-1}$ to 5 times 10$^{38}$ erg s$^{-1}$ and are therefore likely to power a PWN. This paper summarizes the search for PWNe in the off-pulse windows of 54 LAT-detected pulsars using 16 months of survey observations. Ten sources show significant emission, seven of these likely being of magnetospheric origin. The detection of significant emission in the off-pulse interval offers new constraints on the gamma-ray emitting regions in pulsar magnetospheres. The three other sources with significant emission are the Crab Nebula, Vela-X and a new pulsar wind nebula candidate associated with the LAT pulsar PSR J1023-5746, coincident with the TeV source HESS J1023-575. We further explore the association between the H.E.S.S. and the Fermi source by modeling its spectral energy distribution. Flux upper limits derived for the 44 remaining sources are used to provide new constraints on famous PWNe that have been detected at keV and/or TeV energies.
We present a systematic search for gamma-ray emission from supernovae (SNe) in the Fermi Large Area Telescope (LAT) Pass 8 data. The sample of targets consists of 55,880 candidates from the Open Supernova Catalog. We searched for gamma rays from SNe by means of a variable-size sliding-time-window analysis. Our results confirm the presence of transient gamma-ray emission from the sources of non-AGN classes, including transitional pulsars, solar flares, gamma-ray bursts, novae, and the Crab Nebula, which are projected near some of these SNs positions, and also strengthen support to the variable signal in the direction of SN iPTF14hls. The analysis is successful in finding both short (e.g. solar flares) and long (e.g. transitional pulsars) high flux states. Our search reveals two new gamma-ray transient signals occurred in 2019 in the directions of optical transients that are SN candidates, AT2019bvr and AT2018iwp, with their flux increases within 6 months after the dates of SNs discoveries. These signals are bright and their variability is at a higher statistical level than that of iPTF14hls. An exploration of archival multi-wavelength observations towards their positions is necessary to establish their association with SNe or other classes of sources. Our analysis, in addition, shows a bright transient gamma-ray signal at low Galactic latitudes in the direction of PSR J0205+6449. In addition, we report the results of an all-sky search for gamma-ray transient sources. This provided two additional candidates to gamma-ray transient sources.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا