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Start Over Subject gamma-ray astronomy
1. Abundance ratio in gamma-ray burst
ID:
ivo://CDS.VizieR/J/MNRAS/469/3125
Title:
Abundance ratio in gamma-ray burst
Short Name:
J/MNRAS/469/3125
Date:
21 Oct 2021
Publisher:
CDS
Description:
The distribution of the N/O element abundance ratios calculated by the detailed modelling of different galaxy spectra at z<4 is investigated. Supernova (SN) and long gamma-ray-burst (LGRB) host galaxies cover different redshift domains. N/O ratios in SN hosts increase due to secondary N production towards low z (0.01) accompanying the growing trend of active galaxies [active galactic nucleus (AGN), low-ionization nuclear emission-line region (LINER)]. N/O ratios in LGRB hosts decrease rapidly between z>1 and z~0.1 following the N/H trend and reach the characteristic N/O ratios calculated for the H II regions in local and nearby galaxies. The few short-period gamma-ray-burst (SGRB) hosts included in the galaxy sample show N/H<=0.04 solar and O/H solar. They seem to continue the low bound N/H trend of SN hosts at z<0.3. The distribution of N/O as a function of metallicity for SN and LGRB hosts is compared with star chemical evolution models. The results show that several LGRB hosts can be explained by star multibursting models when 12+log(O/H)<8.5, while some objects follow the trend of continuous star formation models. N/O in SN hosts at log(O/H)+12<8.5 are not well explained by stellar chemical evolution models calculated for starburst galaxies. At 12+log(O/H)>8.5 many different objects are nested close to O/H solar with N/O ranging between the maximum corresponding to starburst galaxies and AGN and the minimum corresponding to HII regions and SGRB.
2. A comprehensive statistical study of gamma-ray bursts
ID:
ivo://CDS.VizieR/J/ApJ/893/77
Title:
A comprehensive statistical study of gamma-ray bursts
Short Name:
J/ApJ/893/77
Date:
07 Mar 2022 07:29:40
Publisher:
CDS
Description:
In order to obtain an overview of gamma-ray bursts (GRBs), we need a full sample. In this paper, we collected 6289 GRBs (from GRB 910421 to GRB 160509A) from the literature, including their prompt emission, afterglow, and host galaxy properties. We hope to use this large sample to reveal the intrinsic properties of GRBs. We have listed all of the data in machine-readable tables, including the properties of the GRBs, correlation coefficients and linear regression results of two arbitrary parameters, and linear regression results of any three parameters. These machine-readable tables could be used as a data reservoir for further studies on the classifications or correlations. One may find some intrinsic properties from these statistical results. With these comprehensive tables, it is possible to find relations between different parameters and to classify the GRBs into different subgroups. Upon completion, they may reveal the nature of GRBs and may be used as tools like pseudo-redshift indicators, standard candles, etc.
3. Afterglow light curve of GRB 090926A
ID:
ivo://CDS.VizieR/J/ApJ/720/862
Title:
Afterglow light curve of GRB 090926A
Short Name:
J/ApJ/720/862
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present VLT/FORS2 spectroscopy and Gamma-ray Optical/Near-Infrared Detector optical/near-IR photometry of the afterglow of the bright Fermi/LAT GRB 090926A. The spectrum shows prominent Lyman-{alpha} absorption with N_HI_=10^21.73+/-0.07^cm^-2^ and a multitude of metal lines at a common redshift of z=2.1062+/-0.0004, which we associate with the redshift of the gamma-ray burst (GRB). The metallicity derived from SII is log(Z/Z_{sun}_)~-1.9, one of the lowest values ever found in a GRB Damped Lyman-{alpha} (DLA) system. This confirms that the spread of metallicity in GRB-DLAs at z~2 is at least two orders of magnitude. We argue that this spread in metallicity does not require a similar range in abundances of the GRB progenitors, since the neutral interstellar medium probed by the DLA is expected to be at a significant distance from the explosion site. The hydrogen column density derived from the Swift/XRT afterglow spectrum (assuming log(Z/Z_{sun}_)~-1.9) is ~100 times higher than the N_HI_ obtained from the Lyman-{alpha} absorptions. This suggests either a large column density of ionized gas or a higher metallicity of the circum-burst medium compared to the gas traced by the DLA. We also discuss the afterglow light curve evolution and energetics. The absence of a clear jet-break like steeping until at least 21 days post-burst suggests a beaming-corrected energy release of E_{gamma}_>3.5x10^52^erg, indicating that GRB 090926A may have been one of the most energetic bursts ever detected.
4. Afterglows of short and long-duration GRBs
ID:
ivo://CDS.VizieR/J/ApJ/701/824
Title:
Afterglows of short and long-duration GRBs
Short Name:
J/ApJ/701/824
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a comparative study of the observed properties of the optical and X-ray afterglows of short- and long-duration {gamma}-ray bursts (GRBs). Using a large sample of 37 short and 421 long GRBs, we find a strong correlation between the afterglow brightness measured after 11hr and the observed fluence of the prompt emission. Both the optical (R band) and X-ray flux densities (F_R_ and F_X_) scale with the {gamma}-ray fluence, F_{gamma}_. For bursts with a known redshift, a tight correlation exists between the afterglow flux densities at 11hr (rest frame) and the total isotropic {gamma}-ray energy, E_{gamma},ISO_: F_R,X_{prop.to}E_{gamma},ISO_^{alpha}^, with {alpha}~1.
5. A gamma-ray emission zone in 3C 279
ID:
ivo://CDS.VizieR/J/A+A/630/A56
Title:
A gamma-ray emission zone in 3C 279
Short Name:
J/A+A/630/A56
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the relationship between the variable gamma-ray emission and jet properties in the blazar 3C 279, by combining the Fermi/LAT data spanning a period of eight years with concurrent radio measurements made at multiple epochs with VLBA at 15 and 43 GHz within the MOJAVE and VLBA-BU monitoring programs. The aim of this paper is to compare the flux variability of the different components found in the VLBA observations, to the variability in the gamma-rays. This analysis helps to investigate whether any of the jet components can be associated with the gamma-ray variability. Through Spearman rank correlation we found that the gamma-ray variability is correlated with a particular region (feature B, in the MOJAVE images) downstream from the observed base (core) of the jet. This jet component is therefore a likely location at which an important fraction of the variable gamma-ray emission is produced. We also calculated the average proper motion of the component with respect to the VLBA core and found that it moves at an apparent superluminal velocity of (3.70+/-0.35)c, implying that one of the gamma-ray emission zones is not stationary. This jet component is also found between 6.86mas and 8.68mas, which translates to a distance from the radio core of at least 42pc.
6. AGILE bright gamma-ray sources updated list
ID:
ivo://CDS.VizieR/J/A+A/558/A137
Title:
AGILE bright gamma-ray sources updated list
Short Name:
J/A+A/558/A137
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a variability study of a sample of bright {gamma}-ray (30MeV-50GeV ) sources. This sample is an extension of the first AGILE catalogue of -ray sources (1AGL), obtained using the complete set of AGILE observations in pointing mode performed during a 2.3 year period from July 9, 2007 until October 30, 2009. The dataset of AGILE pointed observations covers a long time interval and its {gamma}-ray data archive is useful for monitoring studies of medium-to-high brightness {gamma}-ray sources. In the analysis reported here, we used data obtained with an improved event filter that covers a wider field of view, on a much larger (about 27.5 months) dataset, integrating data on observation block time scales, which mostly range from a few days to thirty days. The data processing resulted in a better characterized source list than 1AGL was, and includes 54 sources, 7 of which are new high galactic latitude (|BII|>=5) sources, 8 are new sources on the galactic plane, and 20 sources from the previous catalogue with revised positions. Eight 1AGL sources (2 high-latitude and 6 on the galactic plane) were not detected in the final processing either because of low Observing Block (OB) exposure and/or due to their position in complex galactic regions. We report the results in a catalogue of all the detections obtained in each single OB, including the variability results for each of these sources. In particular, we found that 12 sources out of 42 or 11 out of 53 are variable, depending on the variability index used, where 42 and 53 are the number of sources for which these indices could be calculated. Seven of the 11 variable sources are blazars, the others are Crab pulsar+nebula, LS I +61 303, Cyg X-3, and 1AGLR J2021+4030.
7. AGILE Mini-Calorimeter {gamma}-ray burst catalog
ID:
ivo://CDS.VizieR/J/A+A/553/A33
Title:
AGILE Mini-Calorimeter {gamma}-ray burst catalog
Short Name:
J/A+A/553/A33
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Mini-Calorimeter of the AGILE satellite can observe the high-energy part of gamma-ray bursts with good timing capability. We present the data of the 85 hard gamma-ray bursts observed by the Mini-Calorimeter since the launch (April 2007) until October 2009. We report the timing data for 84 and spectral data for 21 bursts.
8. 231 AGN candidates from the 2FGL catalog
ID:
ivo://CDS.VizieR/J/ApJ/782/41
Title:
231 AGN candidates from the 2FGL catalog
Short Name:
J/ApJ/782/41
Date:
21 Oct 2021
Publisher:
CDS
Description:
The second Fermi-LAT source catalog (2FGL) is the deepest all-sky survey available in the gamma-ray band. It contains 1873 sources, of which 576 remain unassociated. Machine-learning algorithms can be trained on the gamma-ray properties of known active galactic nuclei (AGNs) to find objects with AGN-like properties in the unassociated sample. This analysis finds 231 high-confidence AGN candidates, with increased robustness provided by intersecting two complementary algorithms. A method to estimate the performance of the classification algorithm is also presented, that takes into account the differences between associated and unassociated gamma-ray sources. Follow-up observations targeting AGN candidates, or studies of multiwavelength archival data, will reduce the number of unassociated gamma-ray sources and contribute to a more complete characterization of the population of gamma-ray emitting AGNs.
9. AGN Fermi/LAT {gamma}-ray and 37GHz fluxes
ID:
ivo://CDS.VizieR/J/A+A/535/A69
Title:
AGN Fermi/LAT {gamma}-ray and 37GHz fluxes
Short Name:
J/A+A/535/A69
Date:
21 Oct 2021
Publisher:
CDS
Description:
Although the Fermi mission has increased our knowledge of {gamma}-ray AGN, many questions remain, such as the site of {gamma}-ray production, the emission mechanism, and the factors that govern the strength of the emission. Using data from a high radio band, 37GHz, uncontaminated by other radiation components besides the jet emission, we study these questions with averaged flux densities over the the first year of Fermi operations. We look for possible correlations between the 100MeV-100GeV band used by the Fermi satellite and 37GHz radio band observed at the Aalto University Metsahovi Radio Telescope, as well as for differences between the {gamma}-ray emission of different AGN subsamples. We use data averaged over the 1FGL period. Our sample includes 249 northern AGN, including a complete sample of 68 northern AGN with a measured average flux density exceeding 1Jy.
10. AGN/pulsar distinction for 2FGL sources
ID:
ivo://CDS.VizieR/J/MNRAS/424/L64
Title:
AGN/pulsar distinction for 2FGL sources
Short Name:
J/MNRAS/424/L64
Date:
21 Oct 2021
Publisher:
CDS
Description:
Dark matter annihilation signals coming from Galactic subhaloes may account for a small fraction of unassociated point sources detected in the second Fermi-LAT Catalogue (2FGL). To investigate this possibility, we present SIBYL, a Random Forest classifier that offers predictions on class memberships for unassociated Fermi-LAT sources at high Galactic latitudes using gamma-ray features extracted from the 2FGL. SIBYL generates a large ensemble of classification trees that are trained to vote on whether a particular object is an active galactic nucleus (AGN) or a pulsar. After training on a list of 908 identified/associated 2FGL sources, SIBYL reaches individual accuracy rates of up to 97.7 per cent for AGNs and 96.5 per cent for pulsars. Predictions for the 269 unassociated 2FGL sources at |b|>=10{deg} suggest that 216 are potential AGNs and 16 are potential pulsars (with majority votes greater than 70 per cent). The remaining 37 objects are inconclusive, but none is an extreme outlier. These results could guide future quests for dark matter Galactic subhaloes.