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The detection of pulsed gamma rays with energy above 50 MeV from the soft X-ray source 1E0630 + 178 is reported, confirming the identification of Geminga with this X-ray source. The period derivative (11.4 +/- 1.7) x 10 exp -15 s/s suggests that Geminga is a nearby isolated rotating neutron star with a magnetic field of 1.6 x 10 exp 12 gauss, a characteristic age of 300,000 yr, and a spin-down energy loss rate of 3.5 x 10 exp 34 erg/s.

A classical nova results from runaway thermonuclear explosions on the surface of a white dwarf that accretes matter from a low-mass main-sequence stellar companion. In 2012 and 2013, three novae were detected in γ rays and stood in contrast to the first γ-ray–detected nova V407 Cygni 2010, which belongs to a rare class of symbiotic binary systems. Despite likely differences in the compositions and masses of their white dwarf progenitors, the three classical novae are similarly characterized as soft-spectrum transient γ-ray sources detected over 2- to 3-week durations. The γ-ray detections point to unexpected high-energy particle acceleration processes linked to the mass ejection from thermonuclear explosions in an unanticipated class of Galactic γ-ray sources.

Issue Title: The Multi-Messenger Approach to High-Energy Gamma-Ray Sources: Third Workshop on the Nature of Unidentified High-Energy Sources Gamma-ray astrophysics depends in many ways on multiwavelength studies. The Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch of the observatory. Some of the high-priority multiwavelength needs include: (1) availability of contemporaneous radio and X-ray timing of pulsars; (2) expansion of blazar catalogs, including redshift measurements; (3) improved observations of molecular clouds, especially at high galactic latitudes; (4) simultaneous broad-band blazar monitoring; (5) characterization of gamma-ray transients, including gamma ray bursts; (6) radio, optical, X-ray and TeV counterpart searches for reliable and effective sources identification and characterization. Several of these activities are needed to be in place before launch. [PUBLICATION ABSTRACT]

We performed deep observations to search for radio pulsations in the directions of 375 unassociated Fermi Large Area Telescope (LAT) gamma-ray sources using the Giant Metrewave Radio Telescope (GMRT) at 322 and 607 MHz. In this paper we report the discovery of three millisecond pulsars (MSPs), PSR J0248+4230, PSR J1207\\(-\\)5050 and PSR J1536\\(-\\)4948. We conducted follow up timing observations for around 5 years with the GMRT and derived phase coherent timing models for these MSPs. PSR J0248\\(+\\)4230 and J1207\\(-\\)5050 are isolated MSPs having periodicities of 2.60 ms and 4.84 ms. PSR J1536-4948 is a 3.07 ms pulsar in a binary system with orbital period of around 62 days about a companion of minimum mass 0.32 solar mass. We also present multi-frequency pulse profiles of these MSPs from the GMRT observations. PSR J1536-4948 is an MSP with an extremely wide pulse profile having multiple components. Using the radio timing ephemeris we subsequently detected gamma-ray pulsations from these three MSPs, confirming them as the sources powering the gamma-ray emission. For PSR J1536-4948 we performed combined radio-gamma-ray timing using around 11.6 years of gamma-ray pulse times of arrivals (TOAs) along with the radio TOAs. PSR J1536-4948 also shows evidence for pulsed gamma-ray emission out to above 25 GeV, confirming earlier associations of this MSP with a >10 GeV point source. The multi-wavelength pulse profiles of all three MSPs offer challenges to models of radio and gamma-ray emission in pulsar magnetospheres.

We present the first Fermi - Large Area Telescope (LAT) solar flare catalog covering the 24 th solar cycle. This catalog contains 45 Fermi -LAT solar flares (FLSFs) with emission in the gamma-ray energy band (30 MeV - 10 GeV) detected with a significance greater than 5 sigma over the years 2010-2018. A subsample containing 37 of these flares exhibit delayed emission beyond the prompt-impulsive hard X-ray phase with 21 flares showing delayed emission lasting more than two hours. No prompt-impulsive emission is detected in four of these flares. We also present in this catalog the observations of GeV emission from 3 flares originating from Active Regions located behind the limb (BTL) of the visible solar disk. We report the light curves, spectra, best proton index and localization (when possible) for all the FLSFs. The gamma-ray spectra is consistent with the decay of pions produced by >300 MeV protons. This work contains the largest sample of high-energy gamma-ray flares ever reported and provides the unique opportunity to perform population studies on the different phases of the flare and thus allowing to open a new window in solar physics.

We report the discovery of PSR J0952\\(-\\)0607, a 707-Hz binary millisecond pulsar which is now the fastest-spinning neutron star known in the Galactic field (i.e., outside of a globular cluster). PSR J0952\\(-\\)0607 was found using LOFAR at a central observing frequency of 135 MHz, well below the 300 MHz to 3 GHz frequencies typically used in pulsar searches. The discovery is part of an ongoing LOFAR survey targeting unassociated Fermi Large Area Telescope \\(\\gamma\\)-ray sources. PSR J0952\\(-\\)0607 is in a 6.42-hr orbit around a very low-mass companion (\\(M_\\mathrm{c}\\gtrsim0.02\\) M\\(_\\odot\\)) and we identify a strongly variable optical source, modulated at the orbital period of the pulsar, as the binary companion. The light curve of the companion varies by 1.6 mag from \\(r^\\prime=22.2\\) at maximum to \\(r^\\prime>23.8\\), indicating that it is irradiated by the pulsar wind. Swift observations place a 3-\\(\\sigma\\) upper limit on the \\(0.3-10\\) keV X-ray luminosity of \\(L_X < 1.1 \\times 10^{31}\\) erg s\\(^{-1}\\) (using the 0.97 kpc distance inferred from the dispersion measure). Though no eclipses of the radio pulsar are observed, the properties of the system classify it as a black widow binary. The radio pulsed spectrum of PSR J0952\\(-\\)0607, as determined through flux density measurements at 150 and 350 MHz, is extremely steep with \\(\\alpha\\sim-3\\) (where \\(S \\propto \\nu^{\\alpha}\\)). We discuss the growing evidence that the fastest-spinning radio pulsars have exceptionally steep radio spectra, as well as the prospects for finding more sources like PSR J0952\\(-\\)0607.

Gamma radiation above 100 MeV in energy has been detected from the radio pulsar PSR1706-44. The gamma emission forms a single broad peak within the pulsar period of 102 ms, in contrast to the two narrow peaks seen in the other three known high-energy gamma-ray pulsars. The emission mechanism in all cases is probably the same, the differences arising from the geometry of the magnetic and rotation axes and the line of sight. Gamma-ray emission accounts for as much as 1 percent of the total neutron star spindown energy in these pulsars, much more than emerges at optical or radio frequencies. Thus, study of this emission is important in understanding pulsar emission and evolution.

We have discovered six radio millisecond pulsars (MSPs) in a search with the Arecibo telescope of 34 unidentified gamma-ray sources from the Fermi Large Area Telescope (LAT) 4-year point source catalog. Among the 34 sources, we also detected two MSPs previously discovered elsewhere. Each source was observed at a center frequency of 327 MHz, typically at three epochs with individual integration times of 15 minutes. The new MSP spin periods range from 1.99 to 4.66 ms. Five of the six pulsars are in interacting compact binaries (period < 8.1 hr), while the sixth is a more typical neutron star-white dwarf binary with an 83-day orbital period. This is a higher proportion of interacting binaries than for equivalent Fermi-LAT searches elsewhere. The reason is that Arecibo's large gain afforded us the opportunity to limit integration times to 15 minutes, which significantly increased our sensitivity to these highly accelerated systems. Seventeen of the remaining 26 gamma-ray sources are still categorized as strong MSP candidates, and will be re-searched.

In a search with the Parkes radio telescope of 56 unidentified Fermi-LAT gamma-ray sources, we have detected 11 millisecond pulsars (MSPs), 10 of them discoveries, of which five were reported in Kerr et al. (2012). We did not detect radio pulsations from another six pulsars now known in these sources. We describe the completed survey, which included multiple observations of many targets done to minimize the impact of interstellar scintillation, acceleration effects in binary systems, and eclipses. We consider that 23 of the 39 remaining sources may still be viable pulsar candidates. We present timing solutions and polarimetry for five of the MSPs, and gamma-ray pulsations for PSR J1903-7051 (pulsations for five others were reported in the second Fermi-LAT catalog of gamma-ray pulsars). Two of the new MSPs are isolated and five are in >1 d circular orbits with 0.2-0.3 Msun presumed white dwarf companions. PSR J0955-6150, in a 24 d orbit with a ~0.25 Msun companion but eccentricity of 0.11, belongs to a recently identified class of eccentric MSPs. PSR J1036-8317 is in an 8 hr binary with a >0.14 Msun companion that is probably a white dwarf. PSR J1946-5403 is in a 3 hr orbit with a >0.02 Msun companion with no evidence of radio eclipses.

Fermi has provided the largest sample of gamma-ray selected blazars to date. In this work we use a uniformly selected set of 211 BL Lacertae (BL Lac) objects detected by it Fermi during its first year of operation. We have obtained redshift constraints for 206 out of the 211 BL Lacs in our sample making it the largest and most complete sample of BL Lacs available in the literature. We use this sample to determine the luminosity function of BL Lacs and its evolution with cosmic time. We find that for most BL Lac classes, the evolution is positive with a space density peaking at modest redshift (z~1.2). The low-luminosity, high-synchrotron peaked (HSP) BL Lacs are an exception, showing strong negative evolution, with number density increasing for z\\(\\lesssim\\)0.5. Since this rise corresponds to a drop-off in the density of flat-spectrum radio quasars (FSRQs), a possible interpretation is that these HSPs represent an accretion-starved end-state of an earlier merger-driven gas-rich phase. We additionally find that the known BL Lac correlation between luminosity and photon spectral index persists after correction for the substantial observational selection effects with implications for the so called `blazar sequence'. Finally, estimating the beaming corrections to the luminosity function, we find that BL Lacs have an average Lorentz factor of \\(\\gamma=6.1^{+1.1}_{-0.8}\\), and that most are seen within 10\\(^{\\circ}\\) of the jet axis.