Abstract
ABSTRACT We present a systematic search for γ-ray emission from supernovae (SNe) in the Fermi Large Area Telescope (LAT) Pass 8 data. The sample of targets consists of 55,880 candidates from the Open Supernova Catalogue. We searched for γ rays from SNe by means of a variable-size sliding-time-window analysis. Our results confirm the presence of transient γ-ray emission from the sources of non-AGN classes, including transitional pulsars, solar flares, γ-ray bursts, novae, and the Crab Nebula, which are projected near some of these SN’s positions, and also strengthen support to the variable signal in the direction of SN iPTF14hls. The analysis is successful in finding both short (e.g. solar flares) and long (e.g. transitional pulsars) high flux states. Our search reveals two new γ-ray transient signals occurred in 2019 in the directions of optical transients that are SN candidates, AT2019bvr and AT2018iwp, with their flux increases within 6 months after the dates of SN’s discoveries. These signals are bright and their variability is at a higher statistical level than that of iPTF14hls. An exploration of archival multiwavelength observations towards their positions is necessary to establish their association with SNe or other classes of sources. Our analysis, in addition, shows a bright transient γ-ray signal at low Galactic latitudes in the direction of PSR J0205+6449. In addition, we report the results of an all-sky search for γ-ray transient sources. This provided two additional candidates to gamma-ray transient sources.
Highlights
Supernovae (SNe) are luminous explosions of stars occuring during their last evolutionary stages
We detected two new sources belonging to the set, X, which can potentially be associated with SNe given that the variability of sources from this set is at a high statistical level and that these γ-ray signals started within a 300-day time interval after the date of a SN discovery
We found that the γ-ray source at the position of AT2018iwp is at an 11.3σ statistical level and that the γ-ray source at the position of AT2019bvr is at a 10.3σ statistical level. (We clarify that these significances correspond to the detection of a γ-ray source at the given position during the high flux time interval, while the significances shown in Table 1 are for the existence of a high flux time interval.) It demonstrates that these signals are at a high statistical level and a potential for revealing new γ-ray-emitting sources using a variable-size sliding-time-window, see the signals, N09 and N12, in Sects. 3.2 and 3.3
Summary
Supernovae (SNe) are luminous explosions of stars occuring during their last evolutionary stages (for a review, see Bethe 1990; Hillebrandt & Niemeyer 2000). The reduced χ2 of the fit of the light curve with the constant flux is another technique which is adopted in the Fermi -LAT catalog (Abdollahi et al 2020) for testing about 5,000 γ-ray sources Both of these statistics allow tests of a large number of positions or sources and are not computationally expensive for a single analysis. The detection of transient γ-ray emission in the direction of iPTF14hls gives rise to a question whether γray emission comes only from unusual SNe (for a review of the models for iPTF14hls, see Woosley 2018) These γ-ray observational properties require a search for similar sources accounting for both a start and duration of emission which serve as two variables. By using a variable-size slidingtime-window analysis, we found two new candidates with flux increases within 300 days after the SN candidate discoveries, one new variable unidentified source at a low Galactic latitude in the direction of PSR J0205+6449, and confirmed a number of known γ-ray transient sources, including γ-ray bursts, solar flares, novae, and especially transitional pulsars, revealing high flux time intervals
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