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ULTRASPEC observations of Swift J1818.0-1607

ATel #13603; Kaustubh Rajwade(University of Manchester), Puji Irawati (NARIT), Siraprapa Sanpa-arsa (NARIT), Vikram Dhillon (University of Sheffield), Fabian Jankowski (University of Manchester), Michael Keith (University of Manchester), Chryssa Kouveliotou (George Washington University), Michael Kramer (Max Planck Institute for Radio Astronomy), Andrew Lyne (University of Manchester), Thomas Marsh (University of Warwick), Mitchell Mickaliger (University of Manchester), Brendan O'Connor (George Washington University), Lina Levin Preston (University of Manchester), Benjamin Stappers (University of Manchester), Alexander van den Horst (George Washington University), Patrick Weltevrede (University of Manchester)
on 1 Apr 2020; 17:25 UT
Credential Certification: Kaustubh Rajwade (rkaustubh10@gmail.com)

Subjects: Optical, Neutron Star, Soft Gamma-ray Repeater, Magnetar

Following the X-ray and radio detection of a new magnetar, Swift J1818.0-1607 (ATel# 13551, ATel# 13553, ATel# 13554), we performed optical follow-up observations of the source using the ULTRASPEC instrument mounted on the 2.4m Thai National Telescope. The observations were performed on 17th of March starting at UT 21:40:51.81 in the SDSS i'-band and at UT 21:45:15.65 in SDSS r'-band with a total exposure time of 243 seconds for each filter. More observations were performed with the same instrument on 22nd of March with SDSS z'-band filter and i+z-band filter starting at UT 20:43:23.7 for a total of 363 seconds per filter. The data for all filters were processed and searched for any new sources by comparing the image with the reference Pan-STARRS (Chambers et al. 2016) image at the best known source position. We confirm that no new optical sources were detected within 1.5' of the best known source position of the magnetar (RA: 18:18:03.7, DEC: 16:07:31.8). We compute the upper limit on the optical emission from the magnetar in the three optical band as follows: SDSS r'-band(mag): 21.4, SDSS i'-band(mag): 21.0 and SDSS z'-band(mag): 20.5. Our i'-band limit is consistent with the upper limit reported in ATel# 13574. We thank the staff of the Thai National Telescope for promptly scheduling observations with ULTRASPEC.