NICER detects 245 Hz pulsations from IGR J17511-3057
ATel #17032; M. Ng (McGill Univ.), T. Boztepe (Istanbul Univ.), A. Sanna (University of Cagliari), G. Illiano, A. Papitto (INAF-OAR), G. K. Jaisawal (DTU Space), K. C. Gendreau, Z. Arzoumanian (NASA GSFC), D. Chakrabarty (MIT), E. C. Ferrara (Univ. of Maryland, CRESST II, NASA GSFC) on behalf of the NICER team
on 11 Feb 2025; 21:16 UT
Credential Certification: Mason Ng (masonng@mit.edu)
Subjects: X-ray, Neutron Star, Transient, Pulsar
Referred to by ATel #: 17061
Observations by INTEGRAL indicated the outburst onset of the known accreting millisecond X-ray pulsar, IGR J17511-3057, after a ten-year-long quiescence phase (ATel #17029). NICER observations were quickly scheduled to follow up on the source. NICER collected 1490 s of exposure over two good time intervals (GTIs) starting on 2025-02-11 at 16:52 UTC. The 0.35-10 keV count rate (normalized to 52 detectors) remained constant at around 52.43 ± 0.19 c/s across the two intervals separated by approximately 90 minutes.
We conducted a coherent pulsation search over the 0.3-10.0 keV energy range with an acceleration search and detected very significant (over 20σ, single-trial) pulsations at a frequency of around 245 Hz in both GTIs. We also searched for pulsations by folding the data using the available timing solution from the 2015 outburst within 1σ parameter uncertainties (Papitto et al., 2016) and recovered the expected ~245 Hz pulsation, with a sinusoidal fractional amplitude of around 20%.
The 0.5-10.0 keV spectrum can be well fit in XSPEC with an absorbed disk blackbody and thermal blackbody component, with nH = (1.34 ± 0.02) × 1022 cm-2 (assuming ISM abundances and using the tbabs model), inner disk temperature Tin = 1.19 ± 0.08 keV, inner disk normalization of 5.8 (-1.1, +1.4), blackbody temperature of kT = 2.46 (-0.19, +0.24) keV, and blackbody normalization of 0.8 (-0.2, +0.3). The total absorbed flux and unabsorbed flux in the 0.5-10 keV range are (3.3 ± 0.3) × 10-10 erg/s/cm2 and 4.27 (-0.03, +0.04) × 10-10 erg/s/cm2, respectively. While the outburst is still in progress, we note that the current flux level is roughly half the peak flux of the 2015 outburst in the same energy range (Papitto et al., 2016). All uncertainties are given to 68% confidence.
NICER will continue to observe IGR J17511-3057. We encourage further observations of this source with other facilities.
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.
