Search

The DArk Matter Particle Explorer (DAMPE) is dedicated to exploring critical scientific domains including the indirect detection of dark matter, cosmic ray physics, and gamma ray astronomy. This study introduces a novel method for calibrating the Point Spread Function (PSF) of DAMPE, specifically designed to enhance the accuracy of gamma-ray observations. By leveraging data from regions near pulsars and bright Active Galactic Nuclei (AGNs), we have refined the PSF calibration process, resulting in an improved angular resolution that closely matches our observational data. This advancement significantly boosts the precision of gamma-ray detection by DAMPE, thereby contributing to its mission objectives in dark matter detection and gamma ray astronomy., Comment: 7 pages, 12 figures and 1 table. Accepted for publication in Astroparticle Physics

The DArk Matter Particle Explorer (DAMPE) is a cosmic-ray detector as well as a pair-converting $\gamma$-ray telescope. The effective area, reflecting the geometrical cross-section area, the $\gamma$-ray conversion probability and the photon selection efficiency, is important in the $\gamma$-ray analyses. In the work, we find a significant time variation in the effective area, as large as $\sim -4\%/{\rm yr}$ at 2 GeV for the high-energy trigger. We derive the data-based correction factors to the effective areas and apply corrections to both the effective areas and the exposure maps. The calibrated exposure can be $\sim 12\%$ smaller than the Monte Carlo one on average at 2 GeV. The calibration is further verified using the observation of the Vela pulsar, showing the spectral parameters with the correction are more consistent with those in the Fermi-LAT catalog than the ones without correction. All the corrections are now implemented in the latest version of the DAMPE $\gamma$-ray analysis toolkit DmpST., Comment: 10 pages, 9 figures and 1 table. Accepted for publication in ApJ

As the largest gravitationally bound objects in the Universe, galaxy clusters have provided the first piece of evidence for the presence of dark matter and may be suitable targets for indirect dark matter searches. Among various signals, the GeV-TeV $\gamma$-ray line has been taken as the smoking-gun signal of the dark matter annihilation/decay since no known astrophysical/physical process(es) could generate such a peculiar spectrum. With 15.5 years of Fermi-LAT P8R3 publicly available data, we search for the $\gamma$-ray line emission in the directions of a group of 13 nearby massive galaxy clusters with an unbinned likelihood analysis. A $\gamma$-ray line signal at $\sim 43.2$ GeV has a net TS value of $\approx 30$ if we only take into account the data in the directions of Virgo, Fornax and Ophiuchus clusters, three massive clusters with the highest J-factors expected to generate the dark matter annihilation signal. The signal still presents when the data of other 10 nearby massive clusters have also been included, though the TS value decreases to $\approx 21$ likely because of their lower signal-to-noise ratios. The absence of this signal in the inner Galaxy disfavors both the instrumental effect and the canonical dark matter annihilation interpretation, and a more sophisticated dark matter model or very peculiar astrophysical scenario might be needed. This $\gamma$-ray line signal, if intrinsic, could be unambiguously verified by the Very Large Area $\gamma$-ray Space Telescope in its first two years of performance., Comment: 9 pages, 7 figures, 1 table. Comments are welcome!

This study reanalyzes the detection prospects of dark matter (DM) annihilation signals in the Galactic Center, focusing on velocity-dependent dynamics within a spike density near the supermassive black hole (Sgr~A$^{\star}$). We investigate three annihilation processes -- $p$-wave, resonance, and forbidden annihilation -- under semi-relativistic velocities, leveraging gamma-ray data from Fermi and DAMPE telescopes. Our analysis integrates a fermionic DM model with an electroweak axion-like particle (ALP) portal, exploring annihilation into two or four photons. Employing a comprehensive six-dimensional integration, we precisely calculate DM-induced gamma-ray fluxes near Sgr~A$^{\star}$, incorporating velocity and positional dependencies in the annihilation cross-section and photon yield spectra. Our findings highlight scenarios of resonance and forbidden annihilation, where the larger ALP-DM-DM coupling constant $C_{a\chi\chi}$ can affect spike density, potentially yielding detectable gamma-ray line spectra within Fermi and DAMPE energy resolution. We set upper limits for $C_{a\chi\chi}$ across these scenarios, offering insights into the detectability and spectral characteristics of DM annihilation signals from the Galactic Center., Comment: 24 pages, 13 figures

Recently, the NANOGrav, PPTA, EPTA and CPTA collaborations reported compelling evidence of the existence of the Stochastic Gravitational-Wave Background (SGWB). The amplitude and spectrum of this inferred gravitational-wave background align closely with the astrophysical predictions for a signal originating from the population of supermassive black-hole binaries. In light of these findings, we explore the possibility to detect dark matter spikes surrounding massive black holes, which could potentially impact the gravitational-wave waveform and modulate the SGWB. We demonstrate that the SMBH binary evolution induced by the combined effects of GW radiation and the dynamical friction of the dark matter spike exhibits detectable manifestations within the nHz frequency range of the SGWB., Comment: 5 pages, 1 figure. arXiv admin note: text overlap with arXiv:1408.3534 by other authors

Studies have proposed that there is evidence for cosmological coupling of black holes (BHs) with an index of $k\approx 3$; hence, BHs serve as the astrophysical source of dark energy. However, the data sample is limited for the redshifts of $\leq 2.5$. In recent years, the James Webb Space Telescope (JWST) has detected many high-redshift active galactic nuclei (AGNs) and quasars. Among the JWST NIRSpec-/NIRCam-resolved AGNs, three are determined to be in early-type host galaxies with a redshift of $z\sim 4.5--7$. However, their $M_{\star}$ and $M_{\rm BH}$ are in tension with the predicted cosmological coupling of black holes with $k = 3$ at a confidence level of $\sim 2\sigma$, which challenges the hypothesis that BHs serve as the origin of dark energy. Future work on high-redshift AGNs using the JWST will further assess such a hypothesis by identifying more early-type host galaxies in the higher mass range., Comment: 9 pages, 3 figures, 2 tables; Comments are welcome!

A group of massive galaxies at redshifts of $z\gtrsim 7$ have been recently detected by the James Webb Space Telescope (JWST), which were unexpected to form so early within the framework of standard Big Bang cosmology. In this work, we propose that this puzzle can be explained by the presence of some primordial black holes (PBHs) with a mass of $\sim 1000 M_\odot$. These PBHs, clothed in dark matter halo and undergoing super-Eddington accretion, serve as seeds for the early galaxy formation with masses of $\sim 10^{8}-10^{10}~M_\odot$ at high redshift, thus accounting for the JWST observations. Using a hierarchical Bayesian inference framework to constrain the PBH mass distribution models, we find that the Lognormal model with $M_{\rm c}\sim 750M_\odot$ is preferred over other hypotheses. These rapidly growing BHs are expected to emit strong radiation and may appear as high-redshift compact objects, similar to those recently discovered by JWST. Although we focuse on PBHs in this work, the bound on the initial mass of the seed black holes remains robust even if they were formed through astrophysical channels., Comment: Accepted by Science China Physics, Mechanics & Astronomy

Precise measurements of the stellar orbits around Sagittarius A* have established the existence of a supermassive black hole (SMBH) at the Galactic centre (GC). Due to the interplay between the SMBH and dark matter (DM), the DM density profile in the innermost region of the Galaxy, which is crucial for the DM indirect detection, is still an open question. Among the most popular models in the literature, the theoretical spike profile proposed by Gondolo and Silk (1999; GS hereafter) is well adopted. In this work, we investigate the DM spike profile using updated data from the Keck and VLT telescopes considering that the presence of such an extended mass component may affect the orbits of the S-stars in the Galactic center. We examine the radius and slope of the generalized NFW spike profile, analyze the Einasto spike, and discuss the influence of DM annihilation on the results. Our findings indicate that an initial slope of $\gamma \gtrsim 0.92$ for the generalized NFW spike profile is ruled out at a 95% confidence level. Additionally, the spike radius $R_{\rm sp}$ larger than 21.5 pc is rejected at 95% probability for the Einasto spike with $\alpha=0.17$, which also contradicts the GS spike model. The constraints with the VLT/GRAVITY upper limits are also projected. Although the GS NFW spike is well constrained by the Keck and VLT observation of S2, an NFW spike with a weak annihilation cusp may still be viable, as long as the DM annihilation cross section satisfies $\left< \sigma v \right> \gtrsim 7.7\times 10^{-27}~{\rm cm^3\,s^{-1}} (m_{\rm DM}/100~{\rm GeV})$ at 95% level., Comment: 12 pages, 10 figures and 1 table. Accepted for publication in MNRAS

Ultralight bosonic dark matter is expected to be able to form a cloud surrounding the supermassive black hole (SMBH) in the Galactic center. With increasing precision of the observations of the stellar kinematics around the SMBH, tiny effects from such a dark matter cloud, including its gravitational perturbation and the direct coupling with the ordinary matter may be detectable. In this work, we search for possible evidence of the scalar cloud using accurate orbital measurements of the S2 star around Sgr~A*. We solve the first order Post-Newtonian equation, considering simultaneously the extended mass distribution of the scalar cloud and the frequency shift induced by the additional coupling via Higgs portal or photon portal interaction. Furthermore, we also investigate the impact of an astrophysical power-law component from the gas and stellar remnants. We find that the astrometric and spectroscopic data of the S2 star are well consistent with the scenario of a point-like mass of Sgr~A*. We thus derive upper limits of the coupling of the new interaction and the extended mass, with and without the contribution from the astrophysical component. The limits of the Higgs/photon coupling and the extended mass of the scalar cloud are the most stringent ones for the scalar mass window between $3.2\times 10^{-19}$~eV and $1.6\times 10^{-18}$~eV., Comment: 12 pages, 6 figures, published at PRD

The DArk Matter Particle Explorer (DAMPE) is well suitable for searching for monochromatic and sharp $\gamma$-ray structures in the GeV$-$TeV range thanks to its unprecedented high energy resolution. In this work, we search for $\gamma$-ray line structures using five years of DAMPE data. To improve the sensitivity, we develop two types of dedicated data sets (including the BgoOnly data which is the first time to be used in the data analysis for the calorimeter-based gamma-ray observatories) and adopt the signal-to-noise ratio optimized regions of interest (ROIs) for different DM density profiles. No line signals or candidates are found between 10 and 300 GeV in the Galaxy. The constraints on the velocity-averaged cross section for $\chi\chi \to \gamma\gamma$ and the decay lifetime for $\chi \to \gamma\nu$, both at 95% confidence level, have been calculated and the systematic uncertainties have been taken into account. Comparing to the previous Fermi-LAT results, though DAMPE has an acceptance smaller by a factor of $\sim 10$, similar constraints on the DM parameters are achieved and below 100 GeV the lower limits on the decay lifetime are even stronger by a factor of a few. Our results demonstrate the potential of high-energy-resolution observations on dark matter detection., Comment: 14 pages, 8 figures. Update the content to keep up with the published version

Several groups have reported a possible excess of primary electrons at high energies with the joint fit of the positron fraction and total electron/positron spectra. With the latest release of high-precision electron/positron spectra measured by AMS-02, we further confirm this excess by fitting $\Delta\Phi$ $\rm(i.e., \Phi_{e^-}-\Phi_{e^+})$ data in this work. Then we investigate the contribution of a single nearby supernova remnant to the primary electron excess and find that Monogem can reasonably account for this excess. Moreover, we predict that the electron spectrum may harden again at a few TeVs due to Vela's contribution. DAMPE, which can accurately measure electrons at TeV scale, is expected to provide the robust test of this new spectral feature in the near future. Finally, we fit the proton spectrum data of DAMPE with Monogem or Loop I. We find that both the primary electron excess and the proton spectral bump could be mainly generated by Monogem., Comment: 15 pages, 4 figures

Recently, the evidence for gamma-ray emission has been found in the $Fermi$-LAT observation for the outer halo of Andromeda galaxy (M31). The dark matter (DM) annihilation offers a possible explanation on the gamma-ray radiation. In this work, we focus on the dark matter annihilation within minispikes around intermediate-mass black holes (IMBHs) with masses ranging from $100~\mathrm{M_\odot}$ to $10^6~\mathrm{M_\odot}$. When the thermal annihilation relic cross section $\left\langle \sigma v \right\rangle = 3 \times 10^{-26}~\mathrm {cm} ^{3}\;\mathrm {s} ^{-1}$ is adopted, we conduct an investigation on the population of IMBHs in the spherical halo area of M31. We find that there could be more than 65 IMBHs with masses of $ 100~ \mathrm{M_\odot}$ surrounded by the DM minispikes as the remnants of Population III stars in the M31 spherical halo, and it is almost impossible for the existence of minspikes around IMBHs with masses above $10^4~ \mathrm{M_\odot}$ which could be formed by the collapse of primordial cold gas, for both dark matter annihilation channels $b\bar{b}$ and $\tau^{+}\tau^{-}$. The properties of dark matter have been further explored with the simulation of these two scenarios for IMBHs formation., Comment: Prepared for submission to JCAP

Sharp spectral structures in the $\gamma$-ray band are an important dark matter (DM) signature. Previously, a tentative line feature at $\sim 43~{\rm GeV}$ is reported in 16 nearby galaxy clusters (GCls) with 7.1 years of Fermi-LAT data, whose TS value is $\sim 16.7$. In this work, we search for line signals and box-shaped structures using the stacked data from those 16 GCls with 11.4-yr P8R3 data. There is still a hint at $\sim {42~\rm GeV}$, dominated by the radiation of Virgo and Ophiuchus clusters. Though the TS value was high up to 21.2 in October 2016, currently it has dropped to 13.1. Moreover, the TS value at $\sim {42~\rm GeV}$ decreases to 2.4 when the EDISP2 data are excluded from the analysis. Consequently, we do not find any statistically significant line-like signal and then set up the 95% confidence level upper limits on the thermally averaged cross section of DM annihilating into double photons. The same line search has been carried out for an alternative GCl sample from the Two Micron All-Sky Survey but no any evidence has been found. We also search for box-shaped features in those 16 baseline GCls. No signal is found as well and the corresponding upper limits on the annihilation cross section are given., Comment: 10 pages, 7 figures and 1 table. Accepted for publication in ApJ

The DArk Matter Particle Explorer (DAMPE) is a space high-energy cosmic-ray detector covering a wide energy band with a high energy resolution. One of the key scientific goals of DAMPE is to carry out indirect detection of dark matter by searching for high-energy gamma-ray line structure. To promote the sensitivity of gamma-ray line search with DAMPE, it is crucial to improve the acceptance and energy resolution of gamma-ray photons. In this paper, we quantitatively prove that the photon sample with the largest ratio of acceptance to energy resolution is optimal for line search. We therefore develop a line-search sample specifically optimized for the line search. Meanwhile, in order to increase the statistics, we also selected the so called BGO-only photons that convert into $e^+e^-$ pairs only in the BGO calorimeter. The standard, the line-search, and the BGO-only photon samples are then tested for line search individually and collectively. The results show that a significantly improved limit could be obtained from an appropriate combination of the date sets, and the increase is about 20\% for the highest case compared with using the standard sample only.

The fast developments of radio astronomy open a new window to explore the properties of Dark Matter (DM). The recent direct imaging of the supermassive black hole (SMBH) at the center of M87 radio galaxy by the Event Horizon Telescope (EHT) collaboration is expected to be very useful to search for possible new physics. In this work, we illustrate that such results can be used to detect the possible synchrotron radiation signature produced by DM annihilation from the innermost region of the SMBH. Assuming the existence of a spike DM density profile, we obtain the flux density due to DM annihilation induced electrons and positrons, and derive new limits on the DM annihilation cross section via the comparison with the EHT integral flux density at 230 GHz. Our results show that the parameter space can be probed by the EHT observations is largely complementary to other experiments. For DM with typical mass regions of being weakly interacting massive particles, the annihilation cross section several orders of magnitude below the thermal production level can be excluded by the EHT observations under the density spike assumption. Future EHT observations may further improve the sensitivity on the DM searches, and may also provide a unique opportunity to test the interplay between DM and the SMBH., Comment: 15 pages, 4 figures, one appendix. Match the JHEP version

The DArk Matter Particle Explorer (DAMPE) can measure $\gamma$-rays in the energy range from a few GeV to about 10 TeV. The direction of each $\gamma$-ray is reconstructed with respect to the reference system of the DAMPE payload. In this paper, we adopt a maximum likelihood method and use the $\gamma$-ray data centered around several bright point-like sources to measure and correct the angular deviation from the real celestial coordinate system, the so called ``boresight alignment'' of the DAMPE payload. As a check, we also estimate the boresight alignment for some sets of simulation data with artificial orientation and obtain consistent results. The time-dependent boresight alignment analysis does not show evidence for significant variation of the parameters.

GeV gamma ray is an important observation target of DArk Matter Particle Explorer (DAMPE) for indirect dark matter searching and high energy astrophysics. We present in this work a set of accurate instrument response functions of DAMPE (DmpIRFs) including the effective area, point-spread function and energy dispersion that are crucial for the gamma-ray data analysis based on the high statistics simulation data. A dedicated software named DmpST is developed to facilitate the scientific analyses of DAMPE gamma-ray data. Considering the limited number of photons and the angular resolution of DAMPE, the maximum likelihood method is adopted in the DmpST to better disentangle different source components. The basic mathematics and the framework regarding this software are also introduced in this paper., Comment: 12 pages, 9 figures, Accepted by RAA

The $\gamma$-ray observation of interstellar gas provides a unique way to probe the cosmic rays (CRs) outside the solar system. In this work, we use an updated version of Fermi-LAT data and recent multi-wavelength tracers of interstellar gas to re-analyze a mid-latitude region in the third Galactic quadrant and estimate the local CR proton spectrum. Two $\gamma$-ray production cross section models for $pp$ interaction, the commonly used one from Kamae et al. (2006) and the up-to-date one from Kafexhiu et al. (2014), are adopted separately in the analysis. Both of them can well fit the emissivity and the derived proton spectra roughly resemble the direct measurements from AMS-02 and Voyager 1, but rather different spectral parameters are indicated. A break at $4\pm1~{\rm GeV}\;c^{-1}$ is shown if the cross section model by Kamae et al. (2006) is adopted. The resulting spectrum is $\lesssim 20\%$ larger than the AMS-02 observation above $15~\rm GeV$ and consistent with the de-modulated spectrum within $2\%$. The proton spectrum based on the cross section model of Kafexhiu et al. (2014) is about $1.4-1.8$ times that of AMS-02 at $2-100~\rm GeV$, however the difference decreases to $20\%$ below $10~\rm GeV$ with respect to the de-modulated spectrum. A spectral break at $20\pm11~{\rm GeV}\;c^{-1}$ is required in this model. An extrapolation down to $300~\rm MeV$ is performed to compare with the observation of Voyager 1, and we find a deviation of $\lesssim 2.5\sigma$ for both the models. In general, an approximately consistent CR spectrum can be obtained using $\gamma$-ray observation nowadays, but we still need a better $\gamma$-ray production cross section model to derive the parameters accurately., Comment: 10 pages, 6 figures. Accepted for publication in PRD

In order to search for the line-like signals in the Fermi-LAT data, we have analyzed totally 49152 regions of interest (ROIs) that cover the whole sky. No ROI displays a line signal with test statistic (TS) value above 25, while for 50 ROIs weak line-like excesses with ${\rm TS}>16$ are presented. The intrinsic significances of these potential signals are further reduced by the large trial factor introduced in such kind of analysis. For the largest TS value of 24.3 derived in our analysis, the corresponding global significance is only $0.54\sigma$. We thus do not find any significant line-like signal and set up constraints on the cross section of dark matter annihilating to gamma-ray lines, $\left<\sigma{v}\right>_{\gamma\gamma}$., Comment: 10 pages, 6 figures, accepted by PRD

In this work, we search for $\gamma$-ray emission from the directions of some nearby Milky Way dwarf spheroidal galaxies (dSphs) and candidates with the publicly-available Pass 8 data of Fermi-LAT. Our sample includes 12 sources with the distances $<50$ kpc. Very weak $\gamma$-ray excesses ($\sim 2\sigma$) are found in some dSphs/candidates, consistent with that reported in the previous literature. Intriguingly, the peak test statistic (TS) value of the weak emission from the direction of Reticulum II rises continually. If interpreted as dark matter (DM) annihilation, the peak TS value is 13.5 for the annihilation channel of $\chi\chi \rightarrow \tau^{+}\tau^{-}$ and the DM mass of $m_\chi \sim 16$ GeV. The combination of all these nearby sources yields a more significant (with local significance $> 4\sigma$) $\gamma$-ray signal., Comment: 7 pages, 4 figures, accepted for publication in PRD

The $\gamma$-ray emission from molecular clouds is widely believed to have a hadronic origin, while unequivocal evidence is still lacking. In this work, we analyze the Fermi-LAT Pass 8 publicly available data accumulated from 2008 August 4 to 2017 June 29 and report the significant detection of a characteristic $\pi^0$-decay feature in the $\gamma$-ray spectra of the molecular clouds Orion A and Orion B. This detection provides a direct evidence for the hadronic origin of their $\gamma$-ray emission., Comment: 11 pages, 5 figures and 1 table

Recently, gamma-ray emission in the direction of Coma, with a TS value of $\sim 40$, has been reported. In this work we will discuss the possibility of such a residual emission coming from dark matter annihilation. Our results show that the gamma-ray emission within the Coma region is also spatially correlated to the mass distribution derived from weak gravitational lensing measurements very well. However the dark matter models are not supported by the spectral analysis results and constraints by observations of other targets. Thus we derive the upper limits of the dark matter annihilation cross section according to the observation of the Coma region., Comment: 8 pages, 4 figures, comments are welcome

The DArk Matter Particle Explorer (DAMPE), a high energy cosmic ray and $\gamma$-ray detector in space, has recently reported the new measurement of the total electron plus positron flux between 25 GeV and 4.6 TeV. A spectral softening at $\sim0.9$ TeV and a tentative peak at $\sim1.4$ TeV have been reported. We study the physical implications of the DAMPE data in this work. The presence of the spectral break significantly tightens the constraints on the model parameters to explain the electron/positron excesses. The spectral softening can either be explained by the maximum acceleration limits of electrons by astrophysical sources, or a breakdown of the common assumption of continuous distribution of electron sources at TeV energies in space and time. The tentive peak at $\sim1.4$ TeV implies local sources of electrons/positrons with quasi-monochromatic injection spectrum. We find that the cold, ultra-relativistic $e^+e^-$ winds from pulsars may give rise to such a structure. The pulsar is requird to be middle-aged, relatively slowly-rotated, mildly magnetized, and isolated in a density cavity. The annihilation of DM particles ($m_{\chi}\sim1.5$ TeV) into $e^+e^-$ pairs in a nearby clump or an over-density region may also explain the data. In the DM scenario, the inferred clump mass (or density enhancement) is about $10^7-10^8$ M$_\odot$ (or $17-35$ times of the canonical local density) assuming a thermal production cross section, which is relatively extreme compared with the expectation from numerical simulations. A moderate enhancement of the annihilation cross section via, e.g., the Sommerfeld mechanism or non-thermal production, is thus needed., Comment: 16 pages, 11 figures, and 3 tables

On 17 August 2017, a gravitational wave event (GW170817) and an associated short gamma-ray burst (GRB 170817A) from a binary neutron star merger had been detected. The followup optical/infrared observations also identified the macronova/kilonova emission (AT2017gfo). In this work we discuss some implications of the remarkable GW170817/GRB 170817A/AT2017gfo association. We show that the $\sim 1.7$s time delay between the gravitational wave (GW) and GRB signals imposes very tight constraint on the superluminal movement of gravitational waves (i.e., the relative departure of GW velocity from the speed of light is $\leq 4.3\times 10^{-16}$) or the possible violation of weak equivalence principle (i.e., the difference of the gamma-ray and GW trajectories in the gravitational field of the galaxy and the local universe should be within a factor of $\sim 3.4\times 10^{-9}$). The so-called Dark Matter Emulators and a class of contender models for cosmic acceleration ("Covariant Galileon") are ruled out, too. The successful identification of Lanthanide elements in the macronova/kilonova spectrum also excludes the possibility that the progenitors of GRB 170817A are a binary strange star system. The high neutron star merger rate (inferred from both the local sGRB data and the gravitational wave data) together with the significant ejected mass strongly suggest that such mergers are the prime sites of heavy r-process nucleosynthesis., Comment: 8 pages, 3 figures, Accepted for Publication in ApJL

In this work, we simulate a set of realizations of local volume dark matter subhalo population based on the distributions and relations derived from Via Lactea II N-body simulation. We calculate the J-factors of these subhalos, and find that the low mass subhalos contribute a lot to the total J-factors. Combining with 91 months of the Fermi LAT observation, we constrain on the cross section of dark matter annihilating directly to two gamma rays. This is the first work combining numerical simulation results and Fermi LAT observations to constrain dark matter cross section to gamma-ray line with subhalo population. Though the constraints derived from subhalo population are weaker than those from Fermi LAT observation of the Galactic center, they are supports of and complementary to these other results., Comment: 8 pages, 5 figures, accepted for publication in Phys. Rev. D

The modeling of Li-Paczy\'{n}ski macronova/kilonova signals gives reasonable estimate on the neutron-rich material ejected during the neutron star mergers. Usually the accretion disk is more massive than the macronova ejecta, with which the efficiencies of converting the disk mass into prompt emission of three merger-driven GRBs can hence be directly constrained. Supposing the macronovae/kilonovae associated with GRB 050709, GRB 060614 and GRB 130603B arose from radioactive decay of the r-process material, the upper limit on energy conversion efficiencies are found to be as low as $\sim 10^{-6}-10^{-4}$. Moreover, for all three events, neutrino annihilation is likely powerful enough to account for the brief gamma-ray flashes. Neutrino annihilation can also explain the "extended" emission lasting $\sim 100$ s in GRB 050709, but does not work for the one in GRB 060614. These progresses demonstrate that the macronova can serve as a novel probe of the central engine activity., Comment: 5 pages, 2 figures. Accepted for publication in ApJL

Milky Way-like galaxies are predicted to host a very large number of dark matter subhalos. Some massive and nearby subhalos could generate detectable gamma-rays, appearing as unidentified, spatially-extended and stable gamma-ray sources. We search for such sources in the third Fermi Large Area Telescope source List (3FGL) and report the identification of a new candidate, 3FGL J1924.8-1034. With the Fermi-LAT Pass 8 data, we find that 3FGL J1924.8-1034 is spatially-extended at a high confidence level of $5.4\sigma$, with a best-fit extension radius of $\sim0.15^{\circ}$. No significant variability has been found and its gamma-ray spectrum is well fitted by the dark matter annihilation into $b\bar{b}$ with a mass of $\sim 43$ GeV. All these facts make 3FGL J1924.8-1034 a possible dark matter subhalo candidate. However, due to the limited angular resolution, the possibility of that the spatial extension of 3FGL J1924.8-1034 is caused by the contamination from the other un-resolved point source can not be ruled out., Comment: 10 pages including 5 figures and 1 table, accepted for publication in Phys. Rev. D

N-body simulations predict that galaxies at the Milky Way scale host a large number of dark matter (DM) subhalos. Some of these subhalos, if they are massive enough or close enough to the Earth, might be detectable in $\gamma$ rays due to the DM annihilation. 3FGL J2212.5+0703, an unidentified gamma-ray source, has been suggested to be the counterpart candidate of a DM subhalo by Bertoni et al. (2015, 2016). In this work we analyze the Fermi-LAT Pass 8 data of 3FGL J2212.5+0703 to independently test the DM subhalo hypothesis of this source. In order to suppress the possible contamination from two nearby very-bright blazars, we just take into account the front-converting gamma-rays which have better angular resolutions than that of the back-converting photons. In addition to the spatial distribution analysis, we have extended the spectrum analysis down to the energies of $\sim 100$ MeV, and thoroughly examined the variability of the emission during the past 8 years. We confirm that 3FGL J2212.5+0703 is a steady and spatially-extended gamma-ray emitter at a high confidence level. The spectrum is well consistent with that expected from DM annihilation into $b\bar{b}$. The introduction of a phenomenological LogParabola spectrum just improves the fit slightly. All these results suggest that 3FGL J2212.5+0703 could be indicative of a DM subhalo., Comment: 8 pages, 4 figures. Accepted for publication in PRD

With 91 months of the publicly available Fermi-LAT Pass 8 data, we analyze the gamma-ray emission from the Milky Way satellites to search for potential line signals due to the annihilation of dark matter particles into double photons. The searched targets include a sample of dwarf spheroidal galaxies, the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). No significant line emission has been found neither in the stacked dwarf galaxy sample nor in the direction of LMC/SMC. The corresponding upper limits on the cross section of DM annihilation into two photons are derived. Compared with results of previous gamma-ray line searches with the Pass 7 data, the current constraints on the line emission from dwarf spheroidal galaxies has been significantly improved in a wide energy range. With the rapid increase of the sample of dwarf spheroidal galaxies (candidates), we expect that the sensitivity of gamma ray line searches will be significantly improved in the near future., Comment: 9 pages, 3 figures

Galaxy clusters are the largest gravitationally bound objects in the universe and may be suitable targets for indirect dark matter searches. With 85 months of Fermi-LAT Pass 8 publicly available data, we analyze the gamma-ray emission in the directions of 16 nearby Galaxy Clusters with an unbinned likelihood analysis. No globally statistically-significant $\gamma-$ray line feature is identified and a tentative line signal may be present at $\sim 43$ GeV. The 95\% confidence level upper limits on the velocity-averaged cross section of dark matter particles annihilating into double $\gamma-$rays (i.e., $\langle \sigma v \rangle_{\chi\chi\rightarrow \gamma\gamma}$) are derived. Unless very optimistic boost factors of dark matter annihilation in these Galaxy Clusters have been assumed, such constraints are much weaker than the bounds set by the Galactic $\gamma-$ray data., Comment: The version published in Phys. Rev. D, minor revision (10 pages including 4 eps figures)

Very recently the Dark Energy Survey (DES) Collaboration has released their second group of Dwarf spheroidal (dSph) galaxy candidates. With the publicly-available Pass 8 data of Fermi-LAT we search for $\gamma-$ray emissions from the directions of these eight newly discovered dSph galaxy candidates. No statistically significant $\gamma-$ray signal has been found in the combined analysis of these sources. With the empirically estimated J-factors of these sources, the constraint on the annihilation channel of $\chi\chi \rightarrow \tau^{+}\tau^{-}$ is comparable to the bound set by the joint analysis of fifteen previously known dSphs with kinematically constrained J-factors for the dark matter mass $m_\chi>250$ GeV. In the direction of Tucana III (DES J2356-5935), one of the nearest dSph galaxy candidates that is $\sim 25$ kpc away, there is a weak $\gamma-$ray signal and its peak test statistic (TS) value for the dark matter annihilation channel $\chi\chi\rightarrow \tau^{+}\tau^{-1}$ is $\approx 6.7$ at $m_\chi \sim 15$ GeV. The significance of the possible signal likely increases with time. More data is highly needed to pin down the physical origin of such a GeV excess., Comment: To appear in Phys. Rev. D, Fig.4 has been updated and main conclusions are unchanged

With the accurate cosmic ray (CR) electron and positron spectra (denoted as $\Phi_{\rm e^{-}}$ and $\Phi_{\rm e^{+}}$, respectively) measured by AMS-02 collaboration, the difference between the electron and positron fluxes (i.e., $\Delta \Phi=\Phi_{\rm e^{-}}-\Phi_{\rm e^{+}}$), dominated by the propagated primary electrons, can be reliably inferred. In the standard model, the spectrum of propagated primary CR electrons at energies $\geq 30$ GeV softens with the increase of energy. The absence of any evidence for such a continuous spectral softening in $\Delta \Phi$ strongly suggests a significant `excess' of primary CR electrons and at energies of $100-400$ GeV the identified excess component has a flux comparable to that of the observed positron excess. Middle-age but `nearby' supernova remnants (e.g., Monogem and Geminga) are favored sources for such an excess., Comment: 13 pages, 2 figures, Phys. Lett. B, in press