Probing heavy dark matter decays with multi-messenger astrophysical data

We set conservative constraints on decaying dark matter particles with masses spanning a very wide range ($10^4-10^{16}$ GeV). For this we use multimessenger observations of cosmic-ray (CR) protons/antiprotons, electrons/positrons, neutrinos/antineutrinos and gamma rays. Focusing on decays into the $\bar{b}b$ channel, we simulate the spectra of dark matter yields by using the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi equations and the $\texttt{Pythia}$ package. We then propagate the CRs of dark matter origin till Earth by using the state-of-the-art numerical frameworks $\texttt{CRPropa}$, $\texttt{GALPROP}$ and $\texttt{HelMod}$ for the solution of the CR transport equation in the extragalactic, Galactic region and the heliosphere, respectively. Conservative limits are obtained by requiring that the predicted dark matter spectra at Earth be less than the observed CR spectra. Overall, we exclude dark matter lifetimes of $10^{28}$ s or shorter for all the masses investigated in this work. The most stringent constraints reach $10^{30}$ s for very heavy dark matter particles with masses in the range $10^{11}-10^{14}$ GeV.Comment: 22 pages, 10 figures, V2: Minor changes to match JCAP published versio

Suzaku Observation of the Anomalous X-ray Pulsar 1E 1841-045

We report the results of a Suzaku observation of the anomalous X-ray pulsar (AXP) 1E 1841-045 at a center of the supernova remnant Kes 73. We confirmed that the energy-dependent spectral models obtained by the previous separate observations were also satisfied over a wide energy range from 0.4 to ~70 keV, simultaneously. Here, the models below ~10 keV were a combination of blackbody (BB) and power-law (PL) functions or of two BBs wit h different temperatures at 0.6 - 7.0 keV (Morii et al. 2003), and that above ~20 keV was a PL function (Kuiper Hermsen Mendez 2004). The combination BB + PL + PL was found to best represent the phase-averaged spectrum. Phase-resolved spectroscopy indicated the existence of two emission regions, one with a thermal and the other with a non-thermal nature. The combination BB + BB + PL was also found to represent the phase-averaged spectrum well. However, we found that this model is physically unacceptable due to an excessively large area of the emission region of the blackbody. Nonetheless, we found that the temperatures and radii of the two blackbody components showed moderate correlations in the phase-resolved spectra. The fact that the same correlations have been observed between the phase-averaged spectra of various magnetars (Nakagawa et al. 2009) suggests that a self-similar function can approximate the intrinsic energy spectra of magnetars below ~10 keV.Comment: Accepted for publication in the PAS

The Performance Test of pnCCD with FPGA-Based Operating System for a CubeSat Mission

On 17 August 2017, the LIGO/Virgo collaboration detected a signal of gravitational waves, named GW170817, associated with the merger of two neutron stars. This event was the first detection of the electromagnetic counterpart of gravitational wave events. In general, the error image region of the gravitational wave detectors ranges from a few square degrees to several hundred square degrees. To search for the origin of the gravitational waves or the energetic explosions such as the gamma-ray burst, X-ray observation covering a wide field of view with a good sensitivity is essential to achieve the goal. One of the good candidate instruments to achieve our goal is the combination of an X-ray optics called Lobster-eye optics (LEO) and a large area Si pixel imaging sensor. Furthermore, thanks to the light weight of LEO, it is possible to install on a small platform such as a CubeSat. Here, we introduce a future 3U CubeSat mission for searching the electromagnetic counterpart of gravitational waves in the soft X-ray band (0.4 ~ 10 keV) with ~arcmin localization accuracy. The pnCCD detector fabricated by PNSensor Inc. can achieve our mission requirements as an X-ray detector. To operate the pnCCD detector, we developed an FPGA-based fast readout system which is a very compact design to install on the CubeSat mission.Also, we investigate the readout noise of CAMEX, which is the readout ASIC of pnCCD. As a result, the readout noise was ~ 7.4 e-. In this paper, we report the performance of pnCCD applying our compact FPGA-based data processing system