A time domain experiment withSwift: monitoring of seven nearby galaxies

Abstract

Context. Focused on the study of transient sources, time domain astronomy today is one of the most active and growing areas of research in astronomy. Most of the present and planned surveys aimed at carrying out time domain studies work in the optical band and founded their searching strategies on fixed cadences. Although nothing similar currently exists in the X-ray and ultraviolet (UV) bands, the Swift satellite is certainly the most appropriate available instrument to carry out such surveys. Aims. We aimed to detect a supernova (SN) shock breakout (SBO) in nearby galaxies. The SBO marks the first escape of radiation from the blast wave that breaks through the photosphere of the star and launches the SN ejecta. The detection of an SBO is a diagnostic for the radius of the progenitor star and the ratio of explosion energy to ejecta mass. It also allows us to determine the onset of the explosion with an accuracy of a few hours to a few seconds. Methods. Using the XRT and UVOT instruments onboard the Swift satellite, we carried out a weekly cadenced, six-month monitoring of seven nearby galaxies: NGC 1084, NGC 2207/IC 2163, NGC 2770, NGC 4303/M 61, NGC 3147, NGC 3690, and NGC 6754. We searched for variable or transient sources in the collected data. These galaxies were selected because they are close (distance ≤50 Mpc), small enough to fit in the Swift/UVOT field of view, and are hosts of at least three SNe in the past 20 yr. Results. We found no evidence for an SN SBO event. Five objects located within the light of the sample galaxies were found to be variable in the X-ray and/or in the UV. These include mainly background active galactic nucleus and unresolved ULX in NGC 3690. In addition to these objects, we found two variable Galactic sources: the known nova CP Draconis (which experienced an outburst during our monitoring) and an uncatalogued eclipsing binary. Conclusions. Despite the lack of SBO detections, the results of our explorative study encourage the use of Swift in further time domain studies. Moreover, since our sample galaxies are within the Universe volume that will be reached by the forthcoming advanced gravitational wave (GW) detectors (a-LIGO and a-Virgo), this work provides an example on how to carry out Swift surveys from which the GW signal from SNe can be detected, and to detect counterparts to GW triggers.

THESEUS: A key space mission concept for Multi-Messenger Astrophysics

“…We expect up to few shock breakout events per year that can be detected with THESEUS/SXI simultaneously with their GW counterpart during the 3G GW detector era. Shock Breakout (SBO) components are temporally closer to the possibly associated GW events than the optical CCSNe counterpart, thus their detection can mark with more precision the start time of the gravitational radiation emission and can be used in the challenging signal search processes (Andreoni et al, 2016).…”

Survey-scale discovery-based research processes: Evaluating a bespoke visualisation environment for astronomical survey data

“…As an illustrative example of the evolution in the use of display environments, we look to the real-time, multi-wavelength Deeper Wider Faster (DWF) fast transient detection program (Andreoni & Cooke 2019), where the Swinburne Discovery Wall-used as a TDW without encube-has also played an important role.…”

Time domain astronomy with the THESEUS satellite

“…SBOs are temporally closer to the possible GW events than the optical CC SNe counterparts, thus their detection can mark with more precision the start time of the GW signals. This would prove extremely helpful, if not crucial, for the challenging signal search process [388] and THESEUS in synergies with the 3G network will perfectly respond to this need.…”