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Start Over Subject gamma-ray astronomy
251. Mrk 421 multi-wavelength variability, 2007-2009
ID:
ivo://CDS.VizieR/J/A+A/593/A91
Title:
Mrk 421 multi-wavelength variability, 2007-2009
Short Name:
J/A+A/593/A91
Date:
21 Oct 2021
Publisher:
CDS
Description:
We perform an extensive multi-band variability and correlation study of the TeV blazar Mrk 421 on year time scales, which can bring additional insight on the processes responsible for its broadband emission. We observed Mrk 421 in the very high energy gamma-ray range with the Cherenkov telescope MAGIC-I from March 2007 to June 2009. The 2.3-year long MAGIC light curve is complemented with data from the Swift/BAT and RXTE/ASM satellites and the KVA, GASP-WEBT, OVRO, and Metsahovi telescopes from February 2007 to July 2009, allowing for an excellent characterisation of the multi-band variability and correlations over year time scales.
252. Multi-band photometry of GRB 130427A
ID:
ivo://CDS.VizieR/J/ApJ/781/37
Title:
Multi-band photometry of GRB 130427A
Short Name:
J/ApJ/781/37
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present multiwavelength observations of the afterglow of GRB130427A, the brightest (in total fluence) Gamma-Ray Burst (GRB) of the past 29yr. Optical spectroscopy from Gemini-North reveals the redshift of the GRB to be z=0.340, indicating that its unprecedented brightness is primarily the result of its relatively close proximity to Earth; the intrinsic luminosities of both the GRB and its afterglow are not extreme in comparison to other bright GRBs. We present a large suite of multiwavelength observations spanning from 300s to 130days after the burst and demonstrate that the afterglow shows relatively simple, smooth evolution at all frequencies, with no significant late-time flaring or rebrightening activity. The entire data set from 1GHz to 10GeV can be modeled as synchrotron emission from a combination of reverse and forward shocks in good agreement with the standard afterglow model, providing strong support to the applicability of the underlying theory and clarifying the nature of the GeV emission observed to last for minutes to hours following other very bright GRBs. A tenuous, wind-stratified circumburst density profile is required by the observations, suggesting a massive-star progenitor with a low mass-loss rate, perhaps due to low metallicity. GRBs similar in nature to GRB 130427A, inhabiting low-density media and exhibiting strong reverse shocks, are probably not uncommon but may have been difficult to recognize in the past owing to their relatively faint late-time radio emission; more such events should be found in abundance by the new generation of sensitive radio and millimeter instruments.
253. Multi-band photometry of GRB 110205A + 110213A
ID:
ivo://CDS.VizieR/J/ApJ/743/154
Title:
Multi-band photometry of GRB 110205A + 110213A
Short Name:
J/ApJ/743/154
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present rich, early-time, multiband data sets for two Swift events, GRB 110205A and GRB 110213A. The former shows optical emission since the early stages of the prompt phase, followed by the steep rising in flux up to ~1000s after the burst (t^-{alpha}^ with {alpha}=-6.13+/-0.75). We discuss this feature in the context of the reverse-shock scenario and interpret the following single power-law decay as being forward-shock dominated. Polarization measurements, obtained with the RINGO2 instrument mounted on the Liverpool Telescope, also provide hints on the nature of the emitting ejecta. The latter event, instead, displays a very peculiar optical to near-infrared light curve, with two achromatic peaks. In this case, while the first peak is probably due to the onset of the afterglow, we interpret the second peak to be produced by newly injected material, signifying a late-time activity of the central engine.
254. Multi-wavelength analysis of CGRaBS blazars
ID:
ivo://CDS.VizieR/J/ApJ/851/33
Title:
Multi-wavelength analysis of CGRaBS blazars
Short Name:
J/ApJ/851/33
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a multi-frequency, time-averaged analysis of blazars included in the Candidate Gamma-ray Blazar Survey catalog. Our sample consists of 324 {gamma}-ray detected ({gamma}-ray loud) and 191 {gamma}-ray undetected ({gamma}-ray quiet) blazars; we consider all the data up to 2016 April 1. We find that both the {gamma}-ray loud and {gamma}-ray quiet blazar populations occupy similar regions in the WISE color-color diagram, and {gamma}-ray loud sources are brighter in the radio and X-ray bands. A simple one-zone synchrotron inverse-Compton emission model is applied to derive the physical properties of both populations. We find that the central black hole mass and accretion disk luminosity (L_disk_) computed from the modeling of the optical-UV emission with a Shakura-Sunyaev disk reasonably matches that estimated from the optical spectroscopic emission-line information. A significantly larger Doppler boosting in the {gamma}-ray loud blazars is noted, and their jets are more radiatively efficient. On the other hand, the {gamma}-ray quiet objects are more MeV-peaked and thus could be potential targets for next-generation MeV missions. Our results confirm earlier findings about the accretion-jet connection in blazars; however, many of the {gamma}-ray quiet blazars tend to deviate from the recent claim that the jet power exceeds L_disk_ in blazars. A broadband study, considering a larger set of {gamma}-ray quiet objects and also including BL Lacs, will be needed to confirm/reject this hypothesis as well as to verify the evolution of the powerful high-redshift blazars into their low-power nearby counterparts.
255. Multiwavelength observations of Mrk 501 in 2008
ID:
ivo://CDS.VizieR/J/A+A/573/A50
Title:
Multiwavelength observations of Mrk 501 in 2008
Short Name:
J/A+A/573/A50
Date:
21 Oct 2021
Publisher:
CDS
Description:
Blazars are variable sources on various timescales over a broad energy range spanning from radio to very high energy (>100GeV, hereafter VHE). Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. However, most of the {gamma}-ray studies performed on Mrk 501 during the past years relate to flaring activity, when the source detection and characterization with the available {gamma}-ray instrumentation was easier to perform. Our goal is to characterize in detail the source {gamma}-ray emission, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE {gamma}-ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopesMAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. This provided extensive energy and temporal coverage of Mrk 501 throughout the entire campaign.
256. Multiwavelength obs. of GRB 161219B
ID:
ivo://CDS.VizieR/J/ApJ/862/94
Title:
Multiwavelength obs. of GRB 161219B
Short Name:
J/ApJ/862/94
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present detailed multiwavelength observations of GRB 161219B at z=0.1475, spanning the radio to X-ray regimes, and the first Atacama Large Millimeter/submillimeter Array (ALMA) light curve of a {gamma}-ray burst (GRB) afterglow. The centimeter- and millimeter-band observations before 8.5 days require emission in excess of that produced by the afterglow forward shock (FS). These data are consistent with radiation from a refreshed reverse shock (RS) produced by the injection of energy into the FS, signatures of which are also present in the X-ray and optical light curves. We infer a constant- density circumburst environment with an extremely low density, n_0_~3x10^-4^cm^-3^, and show that this is a characteristic of all strong RS detections to date. The Karl G. Lansky Very Large Array (VLA) observations exhibit unexpected rapid variability on roughly minute timescales, indicative of strong interstellar scintillation. The X-ray, ALMA, and VLA observations together constrain the jet break time, t_jet_~32 days, yielding a wide jet opening angle of {theta}_jet_~13{deg}, implying beaming-corrected {gamma}-ray and kinetic energies of E_{gamma}~4.9x10^48^erg and E_K_~1.3x10^50^erg, respectively. Comparing the RS and FS emission, we show that the ejecta are only weakly magnetized, with relative magnetization, R_B_~1, compared to the FS. These direct, multifrequency measurements of a refreshed RS spanning the optical to radio bands highlight the impact of radio and millimeter data in probing the production and nature of GRB jets.
257. 2014-2018 multiwavelength obs. of PKS 1502+106
ID:
ivo://CDS.VizieR/J/ApJ/881/125
Title:
2014-2018 multiwavelength obs. of PKS 1502+106
Short Name:
J/ApJ/881/125
Date:
21 Oct 2021
Publisher:
CDS
Description:
The origin of the multiband activities (outbursts/flares) of blazars is still a heavily debated topic. Shock and magnetic reconnection have long been considered as possible triggers of the multiband activities. In this paper, we present an exploration of the origin of multiband activities for a high-redshift (z=1.8385) flat-spectrum radio quasar PKS 1502+106. Utilizing multiband data from radio to {gamma}-ray and optical polarization observations, we investigate two dramatic activities in detail: a {gamma}-ray- dominated outburst in 2015 and an optical-dominated outburst in 2017. Our main results are as follows. (I) A fast {gamma}-ray flare with a flux-doubling timescale as short as 1 hr in 2015 is discovered. Based on the variability timescale, the physical parameters of the flaring region (e.g., minimum Doppler factor, emission region size, etc.) are constrained. At the peak of the flare, the {gamma}-ray spectrum hardens to {Gamma}_{gamma}_=1.82+/-0.04 and exhibits an obvious curvature/break characteristic that is caused by the typical "cooling break." Modeling of multiband spectral energy distributions reveal a very hard electronic energy spectrum with the electronic spectral index of 1.07+/-0.53. This result suggests that this fast {gamma}-ray flare may be triggered by magnetic reconnection. (II) During the outburst in 2017, the degree of optical polarization and optical fluxes showed a very tight correlation. By analyzing the Stokes parameters of polarization observations, our results show that this outburst could be triggered by a transverse shock with a compression ratio of {eta}>2.2, and the magnetic field intensity of the shock emission region is about 0.032G.
258. Multi-wavelength variability of Mrk 421
ID:
ivo://CDS.VizieR/J/A+A/647/A88
Title:
Multi-wavelength variability of Mrk 421
Short Name:
J/A+A/647/A88
Date:
21 Oct 2021
Publisher:
CDS
Description:
The origin of the gamma-ray emission of the blazar Mrk 421 is still a matter of debate. We used 5.5 years of unbiased observing campaign data, obtained using the FACT telescope and the Fermi LAT detector at TeV and GeV energies, the longest and densest so far, together with contemporaneous multi-wavelength observations, to characterise the variability of Mrk 421 and to constrain the underlying physical mechanisms. We studied and correlated light curves obtained by ten different instruments and found two significant results. The TeV and X-ray light curves are very well correlated with a lag of <0.6 days. The GeV and radio (15GHz band) light curves are widely and strongly correlated. Variations of the GeV light curve lead those in the radio. Lepto-hadronic and purely hadronic models in the frame of shock acceleration predict proton acceleration or cooling timescales that are ruled out by the short variability timescales and delays observed in Mrk 421. Instead the observations match the predictions of leptonic models.
259. Multiwavelength view of blazar PKS 2155-304
ID:
ivo://CDS.VizieR/J/A+A/539/A149
Title:
Multiwavelength view of blazar PKS 2155-304
Short Name:
J/A+A/539/A149
Date:
21 Oct 2021
Publisher:
CDS
Description:
Multiwavelength (MWL) observations of the blazar PKS 2155-304 during two weeks in July and August 2006, the period when two exceptional flares at very high energies (VHE, E>=100GeV) occurred, provide a detailed picture of the evolution of its emission. The complete data set from this campaign is presented, including observations in VHE gamma-rays (H.E.S.S.), X-rays (RXTE, CHANDRA, SWIFT XRT), optical (SWIFT UVOT, Bronberg, Watcher, ROTSE), and in the radio band (NRT, HartRAO, ATCA). Optical and radio light curves from 2004 to 2008 are compared to the available VHE data from this period, to put the 2006 campaign into the context of the long-term evolution of the source. The data set offers a close view of the evolution of the source on different time scales and yields new insights into the properties of the emission process. The predictions of synchrotron self-Compton (SSC) scenarios are compared to the MWL data, with the aim of describing the dominant features in the data down to the hour time scale. The spectral variability in the X-ray and VHE bands is explored and correlations between the integral fluxes at different wavelengths are evaluated. SSC modelling is used to interpret the general trends of the varying spectral energy distribution.
260. 2nd Fermi LAT cat. of gamma-ray pulsars (2PC)
ID:
ivo://CDS.VizieR/J/ApJS/208/17
Title:
2nd Fermi LAT cat. of gamma-ray pulsars (2PC)
Short Name:
J/ApJS/208/17
Date:
21 Oct 2021
Publisher:
CDS
Description:
This catalog summarizes 117 high-confidence >= 0.1 GeV gamma-ray pulsar detections using three years of data acquired by the Large Area Telescope (LAT) on the Fermi satellite. Half are neutron stars discovered using LAT data through periodicity searches in gamma-ray and radio data around LAT unassociated source positions. The 117 pulsars are evenly divided into three groups: millisecond pulsars, young radio-loud pulsars, and young radio-quiet pulsars. We characterize the pulse profiles and energy spectra and derive luminosities when distance information exists. Spectral analysis of the off-peak phase intervals indicates probable pulsar wind nebula emission for four pulsars, and off-peak magnetospheric emission for several young and millisecond pulsars. We compare the gamma-ray properties with those in the radio, optical, and X-ray bands. We provide flux limits for pulsars with no observed gamma-ray emission, highlighting a small number of gamma-faint, radio-loud pulsars. The large, varied gamma-ray pulsar sample constrains emission models. Fermi's selection biases complement those of radio surveys, enhancing comparisons with predicted population distributions.