A generalized event selection algorithm for AstroSat CZT imager data

Ratheesh, Ajay; Rao, A. R.; Mithun, N. P. S.; Vadawale, S.; Vibhute, A.; Bhattacharya, Dipankar; Pradeep, P. I.; Sreekumar, S.; Bhalerao, V.

doi:10.1007/s12036-021-09716-4

Cited by 4 publications

(5 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…There is an ongoing effort to improve upon the existing noise rejection algorithms for CZTI. Ratheesh et al (2021) summarize the new improvements in the background and noise rejection methods. One of the important developments, particularly for the polarization analysis, is the implementation of a "Compton noise" algorithm.…”

Section: Improvement In Noise Rejectionmentioning

confidence: 99%

See 1 more Smart Citation

Hard X-Ray Polarization Catalog for a Five-year Sample of Gamma-Ray Bursts Using AstroSat CZT Imager

Chattopadhyay

Gupta

Iyyani

et al. 2022

ApJ

Self Cite

View full text Add to dashboard Cite

The Cadmium Zinc Telluride Imager (CZTI) on board AstroSat has been regularly detecting gamma-ray bursts (GRBs) since its launch in 2015. Its sensitivity to polarization measurements at energies above 100 keV allows CZTI to attempt spectropolarimetric studies of GRBs. Here, we present the first catalog of GRB polarization measurements made by CZTI during its first five years of operation. This includes the time-integrated polarization measurements of the prompt emission of 20 GRBs in the energy range 100–600 keV. The sample includes the bright GRBs that were detected within an angle range of 0°–60° and 120°–180° where the instrument has useful polarization sensitivity and is less prone to systematics. We implement a few new modifications in the analysis to enhance the polarimetric sensitivity of the instrument. The majority of the GRBs in the sample are found to possess less/null polarization across the total bursts’ duration in contrast to a small fraction of five GRBs that exhibit high polarization. The low polarization across the bursts might be due either to the burst being intrinsically weakly polarized or to a varying polarization angle within the burst even when it is highly polarized. In comparison to POLAR measurements, CZTI has detected a larger number of cases with high polarization. This may be a consequence of the higher energy window of CZTI observations, which results in the sampling of a shorter duration of burst emissions than POLAR, thereby probing emissions with less temporal variation in polarization properties.

show abstract

Section: Improvement In Noise Rejectionmentioning

confidence: 99%

“…This is carried out separately for the edge and the corner pixels. Further details on the Compton noise analysis can be found in Ratheesh et al (2021). We generate the Compton event list for all 20 GRBs after applying the two-pixel noise correction.…”

Section: Improvement In Noise Rejectionmentioning

confidence: 99%

Hard X-Ray Polarization Catalog for a Five-year Sample of Gamma-Ray Bursts Using AstroSat CZT Imager

Chattopadhyay

Gupta

Iyyani

et al. 2022

ApJ

Self Cite

View full text Add to dashboard Cite

show abstract

“…The new method, DPHclean, effectively removes the events from the affected pixels and this algorithm can be easily included in the ground analysis software. A new event cleaning method based on these and other considerations has been developed and it is described in detail elsewhere (Ratheesh et al 2021). spatial clustering or not.…”

Section: Discussionmentioning

confidence: 99%

“…However, we have also used the 'Level 1' FITS files to repeat the exercise for some of the data sets. The details of the data structure and this ground data analysis pipeline can be found in Ratheesh et al (2021).…”

Section: Examination Of Spatial Structures In the Datamentioning

confidence: 99%

“…The DPHstructure rate is 0:25 s À1 and their duration is in tens of milliseconds, whereas the bunches are more numerous (70 s À1 ) and are of very short duration ( $ 0.1 ms), hence, there will be a large number of chance associations in millisecond timescales. Therefore, we have examined the occurrence of the start of a DPHstructure after a 'super bunch', defined as a bunch with the participating number of events more than 100 (Ratheesh et al 2021). The rate of such super bunches is about 1:5 s À1 .…”

Section: Dphcleanmentioning

confidence: 99%

See 1 more Smart Citation

Characterisation of cosmic ray induced noise events in AstroSat-CZT imager

et al. 2021

Self Cite

View full text Add to dashboard Cite

The Cadmium Zinc Telluride (CZT) Imager onboard AstroSat consists of pixelated CZT detectors, which are sensitive to hard X-rays above 20 keV. The individual pixels are triggered by ionising events occurring in them, and the detectors operate in a self-triggered mode, recording each event separately with information about its time of incidence, detector co-ordinates, and channel that scales with the amount of ionisation. The detectors are sensitive not only to photons from astrophysical sources of interest, but also prone to a number of other events like background X-rays, cosmic rays, and noise in detectors or the electronics. In this work, a detailed analysis of the effect of cosmic rays on the detectors is made and it is found that cosmic rays can trigger multiple events which are closely packed in time (called 'bunches'). Higher energy cosmic rays, however, can also generate delayed emissions, a signature previously seen in the PICsIT detector on-board INTEGRAL. An algorithm to automatically detect them based on their spatial clustering properties is presented. Residual noise events are examined using examples of Gamma Ray Bursts as target sources.

show abstract

The search for fast transients with CZTI

et al. 2021

Self Cite

View full text Add to dashboard Cite

The Cadmium Zinc Telluride Imager on AstroSat has proven to be a very effective all-sky monitor in the hard X-ray regime, detecting over three hundred GRBs and putting highly competitive upper limits on X-ray emissions from gravitational wave sources and fast radio bursts. We present the algorithms used for searching for such transient sources in CZTI data, and for calculating upper limits in case of non-detections. We introduce CIFT: the CZTI Interface for Fast Transients, a framework used to streamline these processes. We present details of 88 new GRBs detected by this framework that were previously not detected in CZTI.

show abstract

A generalized event selection algorithm for AstroSat CZT imager data

Cited by 4 publications

References 10 publications

Hard X-Ray Polarization Catalog for a Five-year Sample of Gamma-Ray Bursts Using AstroSat CZT Imager

Hard X-Ray Polarization Catalog for a Five-year Sample of Gamma-Ray Bursts Using AstroSat CZT Imager

Characterisation of cosmic ray induced noise events in AstroSat-CZT imager

The search for fast transients with CZTI

Contact Info

Product

Resources

About