79 research outputs found
Identification of activity peaks in time-tagged data with a scan-statistics driven clustering method and its application to gamma-ray data samples
The investigation of activity periods in time-tagged data-samples is a topic
of large interest. Among Astrophysical samples, gamma-ray sources are widely
studied, due to the huge quasi-continuum data set available today from the
FERMI-LAT and AGILE-GRID gamma-ray telescopes. To reveal flaring episodes of a
given gamma-ray source, researchers make use of binned light-curves. This
method suffers several drawbacks: the results depends on time-binning, the
identification of activity periods is difficult for bins with low signal to
noise ratio. I developed a general temporal-unbinned method to identify flaring
periods in time-tagged data and discriminate statistically-significant flares:
I propose an event clustering method in one-dimension to identify flaring
episodes, and Scan-statistics to evaluate the flare significance within the
whole data sample. This is a photometric algorithm. The comparison of the
photometric results (e.g., photometric flux, gamma-ray spatial distribution)
for the identified peaks with the standard likelihood analysis for the same
period is mandatory to establish if source-confusion is spoiling results. The
procedure can be applied to reveal flares in any time-tagged data sample. The
study of the gamma ray activity of 3C 454.3 and of the fast variability of the
Crab Nebula are shown as examples. The result of the proposed method is similar
to a photometric light curve, but peaks are resolved, they are statistically
significant within the whole period of investigation, and peak detection
capability does not suffer time-binning related issues. The method can be
applied for gamma-ray sources of known celestial position. Furthermore the
method can be used when it is necessary to assess the statistical significance
within the whole period of investigation of a flare from an unknown gamma-ray
source.Comment: 17 pages, 10 figures Accepted for publication in A&
Waiting times between gamma-ray flares of Flat Spectrum Radio Quasars, and constraints on emission processes
The physical scenario responsible for gamma-ray flaring activity and its
location for Flat Spectrum Radio Quasars is still debated. The study of the
statistical distribution of waiting-times between flares (the time intervals
between consecutive activity peaks) can give information on the distribution of
flaring times, and constrain the physical mechanism responsible for gamma-ray
emission. We adopt here a Scan-Statistic driven clustering method (iSRS) to
recognize flaring states within the FERMI-LAT data, and identify the time of
activity-peaks. Results: Flares waiting times can be described with a
poissonian process, consisting of a set of overlapping bursts of flares, with
an average burst duration of about 0.6 year, and average rate of 1.3/y . For
waiting times below 1d host-frame we found a statistically-relevant second
population, the fast-component, mainly from CTA 102 data. The period of
conspicuous detection of the fast component for CTA 102 coincides with the
crossing-time of the superluminal K1 feature with the C1 stationary feature in
radio reported in Jorstad et al. (2017); Casadio et al. (2019). Conclusions: To
reconcile the mechanism proposed in Jorstad et al. (2017); Casadio et al.
(2019) with the bursting-activity, we have to assume that plasma streams with a
typical length of about 2pc (in the stream reference-frame) reach the
recollimation-shock. Otherwise, the distribution of waiting-times can be
interpreted as originating from relativistic-plasma moving along the jet for a
deprojected length of about 30-50pc (assuming a Lorentz-factor=10), that
sporadically produces gamma-ray flares. In magnetic-reconnection scenario,
reconnection events or plasma injection to the reconnection-sites should be
intermittent. Individual plasmoids can be resolved in a few favourable cases
only (Christie et al., 2019); they could be responsible for the fast component.Comment: 15 pages, 11 figures, 3 tables, accepted for publication on Astronomy
and astrophysic
ATel 7783: Optical/UV, High Energy Gamma-ray activity from the FSRQ PKS 1502+106
We asked a Swift ToO campaign on the FSRQ PKS 1502+106 (z=1.83853), triggered by prolonged High Energy activity detected with FERMI-LAT. The HE trigger detected activity at E > 10 GeV with TS ~153, from 2015-06-17 to 2015-07-10, following the prescription of Pacciani et al
ATel 8323: Optical, X-, Gamma-ray flare of the FSRQ PKS 2320-035
We asked a Swift ToO campaign on the FSRQ PKS 2320-035 (z=1.411), triggered by prolonged High Energy activity detected with FERMI-LAT. The trigger method detected activity at E > 20GeV/(1+z) with TS ~44 and emission up to 54 GeV from 2015-09-03 to 2015-11-16, following the prescription of Pacciani et al. 2014, ApJ, 790, 45. The flux integrated on the whole period is (32.1+-1.6)E^-8 ph cm^-2 s^-1 (E > 0.1 GeV), and the gamma-ray photon index 2.20+-0.06
SAFEE TE pseudo ESA TM packets
Si descrive il formato telemetrico dei dati prodotti dal test equipment della SAFE
ATel 8483: Optical, X, Gamma-ray activity of the FSRQ PKS 1313-333
We asked a Swift ToO campaign on the FSRQ PKS 1313-333 (z=1.21), triggered by prolonged High Energy activity detected with FERMI-LAT. The trigger method detected activity at E > 20GeV/(1+z) with TS ~79 from 2015-12-10 to 2015-12-30, following the prescription of Pacciani et al. 2014, ApJ, 790, 45. FERMI-LAT detected Two Gamma-ray photons of about 50 GeV within the last week
ATel 7402: Optical, X-, Gamma-ray flare of the FSRQ PKS 1441+25
We detected a gamma-ray flare from the FSRQ PKS 1441+25 (z=0.939), triggering on FERMI-LAT data at E > 10 GeV with TS ~44, from 2015-03-21 to 2015-04-15, following the prescription of Pacciani et al
ATel 7588: Optical, X-, Gamma-ray flare of the FSRQ PKS 2032+107
We detected a gamma-ray flare from the FSRQ PKS 2032+107 (z=0.601), triggering on FERMI-LAT data at E > 10 GeV with TS ~46, from 2015-05-23 to 2015-06-02, following the prescription of Pacciani et al
ATel 9009: Optical, X, HE gamma-ray flare of the FSRQ S4 1030+61
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed unusually high activity above 10 GeV from a source positionally consistent with the flat spectrum radio quasar S4 1030+61 (z=1.40)
ATel 7526: Swift simultaneous observations of the VHE flare of S3 1227+25
We detected a gamma-ray flare from the low-synchrotron-peaked BL Lac (z=0.135) S3 1227+25, triggering on FERMI-LAT data at E > 10 GeV with TS ~35, from 2015-05-06 to 2015-05-15, following the prescription of Pacciani et al. ..
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