NICER spin-period detection and spectral analysis of the newly-discovered candidate magnetar SGR 1830-0645

ATel #14086; G. Younes (George Washington Univ.), Tolga Guver (Istanbul Univ.), Zorawar Wadiasingh, Keith Gendreau, Zaven Arzoumanian (NASA/GSFC), Paul S. Ray (U. S. Naval Research Laboratory), Wynn C. G. Ho (Haverford), Walid A. Majid (JPL, Caltech), Teruaki Enoto (RIKEN), on behalf of the NICER magnetar team
on 11 Oct 2020; 00:00 UT
Credential Certification: George Younes (gyounes@email.gwu.edu)

Tweet

NICER spin-period detection and spectral analysis of the newly-discovered candidate magnetar SGR 1830-0645 G. Younes (George Washington Univ.), Tolga Guver (Istanbul Univ.), Zorawar Wadiasingh, Keith Gendreau, Zaven Arzoumanian (NASA/GSFC), Paul S. Ray (U.S. Naval Research Laboratory), Wynn C.G. Ho (Haverford), Walid A. Majid (JPL, Caltech), Teruaki Enoto (RIKEN)…, on behalf of the NICER magnetar team On 2020 October 10 at 14:49:24 UT, Swift BAT detected a short, soft transient with location consistent within the Galactic plane, possibly indicating the discovery of a new magnetar (Page et al. GCN #28594). Follow-up analysis of the XRT data detected coherent pulsations at the spin period of 10.4 seconds (Gogus et al. ATel #14085).

Here we report NICER observations (with an exposure of about 2.5 ks) of the source starting at 19:05:21 UT, five hours after the BAT trigger. The source is clearly detected with a count rate of about 9 counts/s. We confirm detection of coherent pulsations (ATel #14085) and find a best-fit spin frequency of 0.0960086(7) Hz (P=10.41573 s; 1 sigma uncertainty in parentheses) in the energy range 0.7-8 keV. The pulse profile in the same energy band is complex, displaying a multiple-peaked morphology, and the rms pulse fraction is 65(1)%, implying a highly pulsed signal. We do not find a strong dependence of pulse shape on energy; however, the pulsed flux approaches 100% at low energies between 0.7-2 keV. With the current NICER data, which covers a total of 3.27 hours, we can only derive an upper limit on the spin-down rate <5E-8 s/s. The epoch for the quoted spin period is 59132.775262 MJD (TDB).

We also performed phase-averaged spectral analysis. We used a background as estimated following the "space weather" method (Gendreau et al., in prep.) and version 1.02 of the response and ancillary files. We grouped the spectrum to have at least 50 counts per channel. We fitted the data with a model consisting of two absorbed blackbody components. For determination of the neutral hydrogen column density NH, we assumed interstellar abundances (Wilms et al. 2000) and used the "tbabs" model. We found a best-fit NH = (1.3 +/- 0.1) x10^22 cm^-2. The best fit parameters for the two thermal components are kT = 0.39 +/- 0.04 keV, R = 7.5 +/- 5.7 km and kT = 1.04+/- 0.04 keV, R = 1.77 +/- 0.76 km, respectively. For the apparent emitting radius, we assumed a distance of 10 kpc. The resulting reduced chi2 of the fit is 1.0789 for 138 degrees of freedom. The total unabsorbed flux of the source is found to be (5.39 +/- 0.08) x10^-11 erg/s/cm^2 in the 0.5-10 keV energy range, which corresponds to a luminosity of about 6x10^35 erg/s at 10 kpc.

More NICER observations are planned to track the evolution of this newly detected magnetar. We highly encourage multi-wavelength follow-up.

NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA.