An extreme particle accelerator powered by PSR J1849-0001

Abstract

Pulsar wind nebulae (PWNe) are bubbles of relativistic particles, powered by the rotational energy loss of the central pulsars. The Crab Nebula, powered by the Milky Way's most energetic pulsar, was discovered by the Large High Altitude Air Shower Observatory (LHAASO) as a PeV gamma-ray emitter, thereby establishing it as an extreme particle accelerator along with multiwavelength observations. Here we report LHAASO's detection of a point-like ultrahigh-energy (UHE, photon energy $E>100\,$TeV) gamma-ray source associated with the PWN powered by PSR~J1849-0001, a pulsar of spindown power 50 times lower than the Crab pulsar. The measured gamma-ray spectrum extends to PeV energies following a power-law distribution, with the PeV luminosity a few times higher than that of the Crab Nebula. Combined X-ray observations constrain the average magnetic field within the PWN to about $3μ\,$G, and reveal an extreme particle acceleration efficiency approaching or even exceeding unity. The result challenges the particle acceleration theory in PWN and implies non-ideal magnetohydrodynamics (MHD) conditions within the accelerator, potentially involving magnetic reconnection upstream of the termination shock.

Figures (22)

• Figure 1: Significance maps of LHAASO J1849-0002. Panel (a): WCDA map with energy in $2-40~\rm{TeV}$. The blue plus sign indicates the best fit position. Panel (b): KM2A map with energy $25-100~\rm{TeV}$. Panel (c): KM2A map with energy $> 100~\rm{TeV}$. The red plus signs in the panels (b) and (c) indicate the best-fit positions in these two energy bands. The black circle marks the positions of PSR J1849-0001. The white circle in the bottom-right corner of the figures represent the instrument's PSF, indicating the $68\%$ containment radius.
• Figure 1: Test of the high-energy cutoff energy of the spectrum. Left panel: Fitting to the spectrum of LHAASO J1849-0002 above 63 TeV. The black dots represent the data and its 1 $\sigma$ uncertainties. The magenta and grey lines represent the best-fit results with a PL and a PL exponential cutoff models, respectively. Shaded region marks the $1\sigma$ uncertain bands of the fit. Right panel: Values of $\Delta$TS as a function of $E_{\rm cut}$ under cutoff PL model with respect to PL model. The red dots represent the $E_{\rm cut}$ tested, and the blue solid line is the interpolation based on these points. The vertical grey dashed line indicates the $E_{\rm cut}$ corresponding to the maximum $\Delta$TS value. The horizontal black dot-dashed line indicates the TS baseline when fitting the spectrum with a power-law function. The blue dashed line represent the $1 \sigma$ C.L.
• Figure 1: The pointing error of LHAASO based on the position offset of Crab Nebula's emission measured by LHAASO to the nebula's reference position. The left and middle panels show the offsets in RA and Decl. relative to the Crab Nebula's position measured in different energy bins. Blue circles and orange squares represent the measurements from WCDA and KM2A in different energy bins. The blue dotted line and orange dotted line indicate the mean offsets for WCDA and KM2A, respectively. The blue star and orange star mark the best-fit position offsets derived from the full energy band data of WCDA and KM2A, respectively. Right panel: Total angular offsets across different energy bins. Numbers mark the median energy of each bin. The blue and orange crosses represent the mean values of these offsets for WCDA and KM2A, respectively. The red and cyan stars mark the best-fit positions offset obtained from the full energy band data of WCDA and KM2A.
• Figure 2: Gamma-ray spectrum of LHAASO J1849-0002 measured by LHAASO. Blue and red circles are flux measured by LHAASO-WCDA and LHAASO-KM2A respectively, where error bars represent $1\sigma$ uncertainties of the fluxes and arrows indicate $95\%$ upper limits. Blue and red lines represent the corresponding power-law function fitting results, and shaded region show the $1\sigma$ uncertainties of the fitting. The cyan error band represents the overall spectrum described by the broken power-law function. The last red data point combines three energy bins from 630 TeV to 2.5 PeV, while the purple data points represent the individual data points for each of the three energy bins. For comparison, the solid gray curves shows the best-fit spectrum of Crab Nebula measured by LHAASOLHAASO2021_Crab.
• Figure 2: Chandra radial profile in the $2-7\,$keV band, combining observations 23596, 24494, and 24495. Error bars of data points represent $1\sigma$ uncertainties. The dashed red, dotted deepskyblue, dashdot cyan, dashed blue and dashed grey represent the emission from the pulsar, inner PWN, extended PWN, PWN, and background, respectively, while the solid black curve shows the total emission from all models. The pulsar's emission was modeled using a MARX PSF simulation in CIAO.