NICER Confirms Burst Activity from the Magnetar 1E 1841-045
ATel #16789; M. Ng (MIT), G. Younes (NASA/CRESST II/UMBC), C.-P. Hu (NCUE), T. Enoto (Kyoto Univ.), B. Begicarslan, T. Guver (Istanbul Univ.), G. K. Jaisawal (DTU Space), Z. Arzoumanian, K. C. Gendreau (NASA/GSFC), Z. Wadiasingh (UMD, NASA/GSFC), on behalf of the NICER team
on 24 Aug 2024; 18:44 UT
Credential Certification: Mason Ng (masonng@mit.edu)
Subjects: X-ray, Neutron Star, Transient, Pulsar, Magnetar
Swift/BAT reported the detection of possible burst activity from 1E 1841-045 at 19:01:18 UT on 2024 August 20 (GCN #37211). A subsequent notice reported three additional bursts detected by Swift/BAT over the next 24 hours, suggesting that the source has entered a bursting phase for the first time since Swift/BAT last detected it in 2016 (GCN #37222, ATel #16784). Follow-up Fermi/GBM observations detected 8 bursts, 3 of which were also reported by Swift/BAT (GCNs #37222, #37234, ATel #16786). Supplementing its biweekly monitoring campaign, NICER triggered observations of 1E 1841-045 starting on 2024 August 20 at 23:28 UT for a total exposure time of 4.6 ks.
NICER data show a 0.4-10.0 keV persistent count rate of 15.0 ± 0.2 c/s (52-detector normalized) in the first good time interval (GTI), which includes the magnetar and contamination from the surrounding supernova remnant Kes 73. In the GTI starting on 2024 August 21 at 10:22 UT, the source exhibited sporadic burst activity lasting for around 300 s, and peaking at around 220 c/s. We detected 8 burst candidates using the Bayesian blocks technique; their properties are listed below. The source returned to its persistent count rate of 15.34 ± 0.15 c/s, immediately after the bursting interval, consistent with the first GTI. The previous NICER observation on August 3 exhibited a slightly higher count rate of 16.18 ± 0.13 c/s.
We performed preliminary timing analysis with the most recent NICER observation on 2024 August 3, as well as on the data from the latest trigger. We find a signature of the pulse profile changing from a doubly-peaked profile in the August 3 data to singly-peaked in the latest trigger. Details of the timing analysis will be reported elsewhere.
In order to characterize the persistent emission of the source, we extracted an X-ray spectrum using the data obtained across the first ~2.8 hours of the NICER observation (resulting in a 1087 s exposure), during which no obvious bursting activity was observed. To take into account the X-ray emission of the surrounding supernova remnant (Kes 73), we used a template spectral model (containing absorbed VPSHOCK and NEI components) based on Chandra archival data. For the magnetar emission, we used a power-law model. The best-fit photon index is found to be Γ = 3.07 ± 0.11 and the 0.5-10.0 keV absorbed source flux is 5.94 ± 0.10 × 10-11 erg/s/cm2. Using the same approach, we also analyzed the August 3 data and inferred an absorbed 0.5-10.0 keV flux of 4.79 ± 0.07 × 10-11 erg/s/cm2 with a similar photon index value. The change in the source flux implies a roughly 25% increase in the persistent emission of the magnetar.
NICER will continue to observe 1E 1841-045/Kes 73 while the burst activity persists. The latest schedule is available at https://heasarc.gsfc.nasa.gov/docs/nicer/schedule/nicer_sts_current.html. We encourage multiwavelength observations 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.
Burst start (barycentric MJD) | Duration (s) | Fluence (erg/cm2)
60543.24196948 | 0.288 | 2.36 × 10-10
60543.24643731 | 0.129 | 1.54 × 10-10
60543.24786750 | 1.789 | 2.08 × 10-9
60543.31634509 | 1.079 | 5.86 × 10-10
60543.31908608 | 0.056 | 1.23 × 10-10
60543.31946517 | 0.196 | 8.74 × 10-10
60543.44606956 | 0.579 | 5.42 × 10-9
60543.44802456 | 3.362 | 1.93 × 10-9
