The Fermi-LAT detection of magnetar-like pulsar PSR J1846-0258 at high-energy gamma-rays

We report the detection of the pulsed signal of the radio-quiet magnetar-like pulsar PSR J1846−0258 in the high-energy γ-ray data of the Fermi Large Area Telescope (Fermi LAT). We produced phase-coherent timing models exploiting RXTE PCA and Swift XRT monitoring data for the post- (magnetar-like) outburst period from 2007 August 28 to 2016 September 4, with independent verification using INTEGRAL ISGRI and Fermi GBM data. Phase-folding barycentric arrival times of selected Fermi LAT events from PSR J1846−0258 resulted in a 4.2σ detection (30–100 MeV) of a broad pulse consistent in shape and aligned in phase with the profiles that we measured with Swift XRT (2.5–10 keV), INTEGRAL ISGRI (20–150 keV), and Fermi GBM (20–300 keV). The pulsed flux (30–100 MeV) is (3.91 ± 0.97) × 10−9 photons cm−2 s−1 MeV−1. Declining significances of the INTEGRAL ISGRI 20–150 keV pulse profiles suggest fading of the pulsed hard X-ray emission during the post-outburst epochs. We revisited with greatly improved statistics the timing and spectral characteristics of PSR B1509−58 as measured with the Fermi LAT. The broad-band pulsed emission spectra (from 2 keV up to GeV energies) of PSR J1846−0258 and PSR B1509−58 can be accurately described with similarly curved shapes, with maximum luminosities at 3.5 ± 1.1 MeV (PSR J1846−0258) and 2.23 ± 0.11 MeV (PSR B1509−58). We discuss possible explanations for observational differences between Fermi LAT detected pulsars that reach maximum luminosities at GeV energies, like the second magnetar-like pulsar PSR J1119−6127, and pulsars with maximum luminosities at MeV energies, which might be due to geometric differences rather than exotic physics in high-B fields.