3,597 research outputs found
More data on (possible) gamma ray (point) sources
The 2CG catalog of gamma ray sources was compiled before detailed knowledge was available on the fine-scale structure of the diffuse Galactic gamma-ray emission. Two independent analyses to discriminate sources which are either compact objects of due to very local and strong enhancements in the Galactic cosmic-ray distribution from those which are artifacts due to the clumpy gas distribution are about to be completed: a maximum likelihood analysis and a cross correlation analysis. Arguments are given why differences, and therefore confusion, and in resulting source lists can be expected. Detailed analysis of all COS-B gamma-ray data on Geminga (2CG195+04), reveals the existence of a drastic spectral break below 200 MeV. A power-law spectrum with index -1.88 fits the data above about 100 MeV to 3.2 GeV, however, there are also indications for a spectral break above these energies. For energies above about 100 MeV no evidence for a long-term time variability was found. The error region of Geminga was searched for a radio counterpart at wavelengths of 90, 49, 21, 6, and 2 cm using the Westerbork Synthesis Radio Telescope and the Very Large Array. So far, 16 sources were detected in this error region. In the direction of 1E0630+178, the Einstein x ray source proposed to be a Vela-like pulsar and the counterpart of Geminga, no radio source was found at 21, 49, and 90 cm with 3 sigma upper limits on the flux densities ranging from 0.5 mJy at 21 cm to 4.5 mJy at 90 cm. Detailed structures in local molecular cloud complexes are so far only resolved in gamma rays for the closet and most massive complexes, namely those in the Orion-Monoceros and the Ophiuchus regions. For both region, there is circumstantial evidence for gamma ray emission from molecular gas that was photodissociated after the passage of a SN shell
The Fermi LAT detection of magnetar-like pulsar PSR J1846-0258 at high-energy gamma-rays
We report the detection of the pulsed signal of the radio-quiet magnetar-like
pulsar PSR J1846-0258 in the high-energy \gr-ray data of the Fermi Large Area
Telescope (Fermi LAT). We produced phase-coherent timing models exploiting RXTE
PCA and Swift XRT monitoring data for the post- (magnetar-like) outburst period
from 2007 August 28 to 2016 September 4, with independent verification using
INTEGRAL ISGRI and Fermi GBM data. Phase-folding barycentric arrival times of
selected Fermi LAT events from PSR J1846-0258, resulted in a 4.2 sigma
detection (30--100 MeV) of a broad pulse consistent in shape and aligned in
phase with the profiles that we measured with Swift XRT (2.5--10 keV), INTEGRAL
ISGRI (20--150 keV) and Fermi GBM (20--300 keV). The pulsed flux (30--100 MeV)
is (3.91 +/- 0.97)E-9 photons/(cm^2 s MeV). Declining significances of the
INTEGRAL ISGRI 20--150 keV pulse profiles suggest fading of the pulsed hard
X-ray emission during the post-outburst epochs. We revisited with greatly
improved statistics the timing and spectral characteristics of PSR B1509-58 as
measured with the Fermi LAT. The broad-band pulsed emission spectra (from 2 keV
up to GeV energies) of PSR J1846-0258 and PSR B1509-58 can be accurately
described with similarly curved shapes, with maximum luminosities at 3.5 +/-
1.1 MeV (PSR J1846-0258) and 2.23 +/- 0.11 MeV (PSR B1509-58). We discuss
possible explanations for observational differences between Fermi LAT detected
pulsars that reach maximum luminosities at GeV energies, like the second
magnetar-like pulsar PSR J1119-6127, and pulsars with maximum luminosities at
MeV energies, which might be due to geometric differences rather than exotic
physics in high-B fields.Comment: 13 pages, 8 figures, accepted by MNRAS on 2017 November 3
Spectral constraints on unidentified EGRET gamma-ray sources from COMPTEL MeV observations
We investigated the MeV properties of 173 unidentified or only tentatively
identified EGRET sources listed in the third EGRET catalogue, by analyzing the
simultaneously collected COMPTEL MeV data for each individual source. The
sources can generally be divided into 4 groups. In this paper we focus on one
of these, a group of 22 EGRET sources for which we can provide additional
constraining information: their spectral extrapolations from the energy range
above 100 MeV towards lower energies overshoot the fluxes or upper limits
derived simultaneously at MeV energies. This means that for these sources a
spectral turnover/break between 1 MeV and 100 MeV is required. At least two of
these sources, but most likely the majority of this sample, have the maxima of
their gamma-ray luminosities in this energy band. The sources have rather soft
EGRET spectra (average photon index: 2.72), and seem to spatially cluster in
the inner Galaxy. Variability analyses revealed 11 out of the 22 sources to be
significantly variable. Object classes proposed as possible counterparts for
the unidentified EGRET sources are discussed in the light of these additional
constraints.Comment: 9 pages including 4 figures; A&A accepte
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