scholarly journals The study of variability of 8 blazar candidates among the Fermi-LAT unidentified gamma-ray sources

2019 ◽  
Vol 15 (S356) ◽  
pp. 132-136
Author(s):  
Pheneas Nkundabakura ◽  
Jean D’amour Kamanzi ◽  
Jean D. Mbarubucyeye ◽  
Tom Mutabazi
Keyword(s):  
Time Series ◽  
Radio Source ◽  
Spectral Index ◽  
Gamma Ray ◽  
Galactic Plane ◽  
Object Location ◽  
X Ray ◽  
Flux Variability ◽  
Bl Lac ◽  
Variability Index

AbstractWe discuss the time-series behavior of 8 extragalactic 3FGL sources away from the Galactic plane (i.e., |b|⩾10°) whose uncertainty ellipse contains a single X-ray and one radio source. The analysis was done using the standard Fermi ScienceTools, package of version v10r0p5. The results show that sources in the study sample display a slight indication of flux variability in γ-ray on monthly timescale. Furthermore, based on the object location on the variability index versus spectral index diagram, the positions of 4 objects in the sample were found to fall in the region of the already known BL Lac positions.

scholarly journals Aperiodic Flux Variability in A 0535+262

1996 ◽  
Vol 165 ◽  
pp. 313-319
Author(s):  
Mark H. Finger ◽  
Robert B. Wilson ◽  
B. Alan Harmon ◽  
William S. Paciesas
Keyword(s):  
Neutron Star ◽  
Gamma Ray ◽  
Beat Frequency ◽  
Power Spectra ◽  
Center Frequency ◽  
X Ray ◽  
Binary Pulsar ◽  
Transient Source ◽  
Flux Variability ◽  
Burst And Transient Source

A “giant” outburst of A 0535+262, a transient X-ray binary pulsar, was observed in 1994 February and March with the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma-Ray Observatory. During the outburst power spectra of the hard X-ray flux contained a QPO-like component with a FWHM of approximately 50% of its center frequency. Over the course of the outburst the center frequency rose smoothly from 35 mHz to 70 mHz and then fell to below 40 mHz. We compare this QPO frequency with the neutron star spin-up rate, and discuss the observed correlation in terms of the beat frequency and Keplerian frequency QPO models in conjunction with the Ghosh-Lamb accretion torque model.

scholarly journals Gamma-Ray Pulsar Emission Models

1996 ◽  
Vol 160 ◽  
pp. 315-322 ◽  
Author(s):  
Alice K. Harding
Keyword(s):  
Spectral Index ◽  
Gamma Ray ◽  
High Energy ◽  
Pulsar Emission ◽  
High Energy Radiation ◽  
X Ray ◽  
Gamma Ray Detectors ◽  
Emerging Patterns ◽  
Increased Sensitivity ◽  
Emission Models

AbstractWith the increased sensitivity of gamma-ray detectors on the Compton Gamma-Ray Observatory (CGRO) the number of presently known gamma-ray pulsars has grown. The new detections are beginning to provide clues to the origin of the high-energy radiation in the form of emerging patterns and correlations among observed quantities such as gamma-ray efficiency and spectral index vs. age. But there are still many questions about the location of the emission and its relation to the radio, optical and X-ray pulses. This paper will review models for gamma-ray emission from pulsars and will examine how well the detailed predictions of these models account for the existing observations.

scholarly journals Symmetric and triangle-shaped variability of blazars

2014 ◽  
Vol 10 (S313) ◽  
pp. 97-98
Author(s):  
Kenji Yoshida
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Low Energy ◽  
Light Curves ◽  
X Ray ◽  
High Energy Electrons ◽  
Flux Variability ◽  
Low Energy Electrons ◽  
Flux Increase ◽  
Rise Phase

AbstractSymmetric and triangle-shaped flux variability in X-ray and gamma-ray light curves is observed from many blazars. We derived the X-ray spectrum changing in time by using a kinetic equation of high energy electrons. Giving linearly changing the injection of low energy electrons into accelerating and emitting region, we obtained the preliminary results that represent the characteristic X-ray variability of the linear flux increase with hardening in the rise phase and the linear decrease with softening in the decay phase.

scholarly journals The γ-ray sky seen at X-ray energies

2020 ◽  
Vol 638 ◽  
pp. A128 ◽  
Author(s):  
E. J. Marchesini ◽  
A. Paggi ◽  
F. Massaro ◽  
N. Masetti ◽  
R. D’Abrusco ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Large Fraction ◽  
Large Area ◽  
Bl Lac Objects ◽  
X Ray ◽  
Positional Uncertainty ◽  
Bl Lac ◽  
Frequency Behavior ◽  
Bl Lacs ◽  
Selection Of

Context. Nearly 50% of all sources detected by the Fermi Large Area Telescope are classified as blazars or blazar candidates, one of the most elusive classes of active galaxies. Additional blazars can also be hidden within the sample of unidentified or unassociated γ-ray sources (UGSs) that constitute about one-third of all gamma-ray sources detected to date. We recently confirmed that the large majority of Fermi blazars of the BL Lac subclass have an X-ray counterpart. Aims. Using the X-ray properties of a BL Lac training set and combining these with archival multifrequency information, we aim to search for UGSs that could have a BL Lac source within their γ-ray positional uncertainty regions. Methods. We reduced and analyzed the Swift X-ray observations of a selected sample of 327 UGSs. We then compared the X-ray fluxes and hardness ratios of all sources detected in the pointed fields with those of known Fermi BL Lacs. Results. We find at least one X-ray source, lying within the γ-ray positional uncertainty at 95% confidence level, for 223 UGSs and a total of 464 X-ray sources in all fields analyzed. The X-ray properties of a large fraction of them, eventually combined with radio, infrared, and optical information, exhibit BL Lac multi-frequency behavior, thus allowing us to select high-confidence BL Lac candidates; some of them were recently observed during our optical spectroscopic campaign which confirmed their nature. Conclusions. We find that out of 50 X-ray sources that were confirmed as BL Lacs through optical spectroscopy, 12 do not show canonical mid-infrared or radio BL Lac properties. This indicates that the selection of X-ray BL Lac candidates is a strong method to find new counterparts within Fermi UGSs. Finally, we pinpoint a sample of 32 Swift/XRT candidate counterparts to Fermi UGSs that are most likely BL Lac objects.

scholarly journals Observational Aspects of Supernova Remnants

1974 ◽  
Vol 60 ◽  
pp. 311-327 ◽  
Author(s):  
B. Y. Mills
Keyword(s):  
Radio Source ◽  
Supernova Remnants ◽  
Galactic Plane ◽  
Great Majority ◽  
Magellanic Clouds ◽  
X Ray ◽  
Yield Information ◽  
Show Evidence ◽  
Good Determination

A supernova event may lead to four observable features: a pulsar, an expanding nebulosity, a radio source and an X-ray source. The great majority of supernovae do not produce observable pulsars, and discussion is restricted largely to the other features. An increasing number of X-ray sources is now being detected and the structure and spectrum of the stronger sources investigated; these observations yield information about the physical state of the remnant. Recently, 11 new optical and radio remnants have been found in the Magellanic Clouds. These have led to a good determination of the Σ – D relation, thus providing a more reliable distance scale for galactic SNR, but have also shown that a one-to-one correspondence between a radio source and a supernova event is questionable. When these remnants are combined with corrected earlier catalogues and a new southern catalogue containing a high proportion of distant old remnants the number of known SNR is about 150. The evolution of galactic SNR may be investigated empirically, and although the derived rate of occurrence is very uncertain a rate of about 2 supernovae per century is consistent with most determinations. The galactic SNR are distributed rather like the radio disc emission, but more closely confined to the galactic plane, and selected SNR show evidence of a spiral pattern.

scholarly journals PKS 2005-489: A very bright BL Lac object in a nearby galaxy

1986 ◽  
Vol 119 ◽  
pp. 59-60
Author(s):  
J V Wall ◽  
I J Danziger ◽  
M Pettini ◽  
R S Warwick ◽  
W Wamsteker
Keyword(s):  
Radio Source ◽  
Power Law ◽  
Nearby Galaxy ◽  
Bl Lac Objects ◽  
X Ray ◽  
Spectrum Radio ◽  
Bl Lac ◽  
The Galaxy

The galaxy identified with the flat-spectrum radio source PKS 2005-489 has a bright stellar nucleus with V ⋍ 13 mag. Optical, UV and X-ray observations indicate variability and power-law continua in each of these wavebands, leading to the conclusion that PKS 2005-489 is one of the brightest BL Lac objects known.

scholarly journals Systematic Search for VHE Gamma‐Ray Emission from X‐Ray–bright High‐Frequency BL Lac Objects

2008 ◽  
Vol 681 (2) ◽  
pp. 944-953 ◽  
Author(s):  
J. Albert ◽  
E. Aliu ◽  
H. Anderhub ◽  
P. Antoranz ◽  
C. Baixeras ◽  
...  
Keyword(s):  
High Frequency ◽  
Gamma Ray ◽  
Systematic Search ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac ◽  
Gamma Ray Emission

scholarly journals A 3-year HAWC/Swift monitoring of gamma-ray/X-ray flux and correlations in the BL Lac Mrk 421

2019 ◽  
Author(s):  
Jose Andres Garcia-Gonzalez ◽  
M. Magdalena González ◽  
Nissim Fraija ◽  
Keyword(s):  
Gamma Ray ◽  
X Ray ◽  
Bl Lac

scholarly journals A search for variability of hard X-ray emission from the Vela pulsar wind nebula

2021 ◽  
Vol 2103 (1) ◽  
pp. 012006
Author(s):  
A M Krassilchtchikov ◽  
M S Pshirkov ◽  
A M Bykov
Keyword(s):  
Magnetic Field ◽  
Gamma Ray ◽  
Next Generation ◽  
Short Term ◽  
X Ray ◽  
Term Evolution ◽  
Flux Variability ◽  
Vela Pulsar ◽  
Pulsar Wind ◽  
Significant Flux

Abstract Observations of hard X-ray emission from the Vela pulsar wind nebula (PWN) with the ISGRI camera aboard INTEGRAL gamma-ray observatory have been analysed with the aim to search for possible flux variability on scales from weeks to years, which could be caused by short-term evolution of pulsar wind structures similar to those governing sharp flares and flux depressions observed in the sub-GeV emission of the Crab PWN. No statistically significant flux depressions or flares have been found in none of the considered energy ranges: 20-50 keV, 50-100 keV, and 100-200 keV, however some hints of flux instability can be seen in the former two bands. If the variability of the pulsar wind termination surface or instabilities of turbulent magnetic field in the nebula predicted by a number of PWN models indeed influence the synchrotron spectrum of such objects, the variability of the 1-30 MeV emission from the Vela PWN could be checked with the next generation of gamma-ray facilities, like eASTROGAM or HERMES.

scholarly journals Soft Gamma Repeaters Revisited with BATSE

1996 ◽  
Vol 165 ◽  
pp. 477-488
Author(s):  
C. Kouveliotou
Keyword(s):  
Radio Source ◽  
Gamma Ray ◽  
Short Review ◽  
X Ray ◽  
Soft Gamma Repeaters ◽  
Compact Radio Source ◽  
Transient Source ◽  
Soft Gamma Repeater ◽  
Burst And Transient Source

After the first 4 years of its operation, the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma Ray Observatory (CGRO), detected recurrent emission from two of the three known Soft Gamma Repeater (SGR) sources, SGR 1900+14 and SGR 1806-20. The reactivation of the latter prompted a quick international campaign resulting in the identification of the X-ray counterpart of the source, which also coincides with a compact radio source. The absence of detection of new sources in the 4 years of BATSE operation and the reactivation of two of the three already known SGRs, indicates that these objects are rare. We give here a short review of the previously detected SGR emissions and present the recent results obtained with BATSE.

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