High energy neutrino early afterglows from gamma-ray bursts revisited

The high energy neutrino emission from gamma-ray bursts (GRBs) has been expected in various scenarios. In this paper, we study the neutrino emission from early afterglows of GRBs, especially under the reverse-forward shock model and late prompt emission model. In the former model, the early afterglow emission occurs due to dissipation made by an external shock with the circumburst medium (CBM). In the latter model, internal dissipation such as internal shocks produces the shallow decay emission in early afterglows. We also discuss implications of recent Swift observations for neutrino signals in detail. Future neutrino detectors such as IceCube may detect neutrino signals from early afterglows, especially under the late prompt emission model, while the detection would be difficult under the reverse-forward shock model. Contribution to the neutrino background from the early afterglow emission may be at most comparable to that from the prompt emission unless the outflow making the early afterglow emission loads more nonthermal protons, and it may be important in the very high energies. Neutrino-detections are inviting because they could provide us with not only information on baryon acceleration but also one of the clues to the model of early afterglows. Finally, we compare various predictions for the neutrino background from GRBs, which are testable by future neutrino-observations.Comment: 18 pages, 12 figures, accepted for publication in PR

On the Origin of the Highest Energy Cosmic Rays

We present the results of a new estimation of the photodisintegration and propagation of ultrahigh energy cosmic ray (UHCR) nuclei in intergalactic space. The critical interactions for photodisintegration and energy loss of UHCR nuclei occur with photons of the infrared background radiation (IBR). We have reexamined this problem making use of a new determination of the IBR based on empirical data, primarily from IRAS galaxies, and also collateral information from TeV gamma-ray observations of two nearby BL Lac objects. Our results indicate that a 200 EeV Fe nucleus can propagate apx. 100 Mpc through the IBR. We argue that it is possible that the highest energy cosmic rays observed may be heavy nuclei.Comment: 2 pages revtex with one figure, submitted to Physical Review Letter

Multiwavelength Observations of a Flare from Markarian 501

We present multiwavelength observations of the BL Lacertae object Markarian 501 (Mrk 501) in 1997 between April 8 and April 19. Evidence of correlated variability is seen in very high energy (VHE, E > 350 GeV) gamma-ray observations taken with the Whipple Observatory gamma-ray telescope, data from the Oriented Scintillation Spectrometer Experiment of the Compton Gamma-Ray Observatory, and quicklook results from the All-Sky Monitor of the Rossi X-ray Timing Explorer while the Energetic Gamma-Ray Experiment Telescope did not detect Mrk 501. Short term optical correlations are not conclusive but the U-band flux observed with the 1.2m telescope of the Whipple Observatory was 10% higher than in March. The average energy output of Mrk 501 appears to peak in the 2 keV to 100 keV range suggesting an extension of the synchrotron emission to at least 100 keV, the highest observed in a blazar and ~100 times higher than that seen in the other TeV-emitting BL Lac object, Mrk 421. The VHE gamma-ray flux observed during this period is the highest ever detected from this object. The VHE gamma-ray energy output is somewhat lower than the 2-100 keV range but the variability amplitude is larger. The correlations seen here do not require relativistic beaming of the emission unless the VHE spectrum extends to >5 TeV.Comment: 10 pages, 2 figures, accepted for publication in ApJ Letter

Milagro Constraints on Very High Energy Emission from Short Duration Gamma-Ray Bursts

Recent rapid localizations of short, hard gamma-ray bursts (GRBs) by the Swift and HETE satellites have led to the observation of the first afterglows and the measurement of the first redshifts from this type of burst. Detection of >100 GeV counterparts would place powerful constraints on GRB mechanisms. Seventeen short duration (< 5 s) GRBs detected by satellites occurred within the field of view of the Milagro gamma-ray observatory between 2000 January and 2006 December. We have searched the Milagro data for >100 GeV counterparts to these GRBs and find no significant emission correlated with these bursts. Due to the absorption of high-energy gamma rays by the extragalactic background light (EBL), detections are only expected for redshifts less than ~0.5. While most long duration GRBs occur at redshifts higher than 0.5, the opposite is thought to be true of short GRBs. Lack of a detected VHE signal thus allows setting meaningful fluence limits. One GRB in the sample (050509b) has a likely association with a galaxy at a redshift of 0.225, while another (051103) has been tentatively linked to the nearby galaxy M81. Fluence limits are corrected for EBL absorption, either using the known measured redshift, or computing the corresponding absorption for a redshift of 0.1 and 0.5, as well as for the case of z=0.Comment: Accepted for publication in the Astrophysical Journa

Observation of TeV Gamma Rays from the Crab Nebula with Milagro Using a New Background Rejection Technique

The recent advances in TeV gamma-ray astronomy are largely the result of the ability to differentiate between extensive air showers generated by gamma rays and hadronic cosmic rays. Air Cherenkov telescopes have developed and perfected the "imaging" technique over the past several decades. However until now no background rejection method has been successfully used in an air shower array to detect a source of TeV gamma rays. We report on a method to differentiate hadronic air showers from electromagnetic air showers in the Milagro gamma ray observatory, based on the ability to detect the energetic particles in an extensive air shower. The technique is used to detect TeV emission from the Crab nebula. The flux from the Crab is estimated to be 2.68(+-0.42stat +- 1.4sys) x10^{-7} (E/1TeV)^{-2.59} m^{-2} s^{-1} TeV^{-1}, where the spectral index is assumed to be as given by the HEGRA collaboration.Comment: 22 pages, 11 figures, submitted to Astrophysical Journa

TeV Gamma-Ray Sources from a Survey of the Galactic Plane with Milagro

A survey of Galactic gamma-ray sources at a median energy of ~20 TeV has been performed using the Milagro Gamma Ray Observatory. Eight candidate sources of TeV emission are detected with pre-trials significance $>4.5\sigma$ in the region of Galactic longitude $l\in[30^\circ,220^\circ]$ and latitude $b\in[-10^\circ,10^\circ]$. Four of these sources, including the Crab nebula and the recently published MGRO J2019+37, are observed with significances $>4\sigma$ after accounting for the trials involved in searching the 3800 square degree region. All four of these sources are also coincident with EGRET sources. Two of the lower significance sources are coincident with EGRET sources and one of these sources is Geminga. The other two candidates are in the Cygnus region of the Galaxy. Several of the sources appear to be spatially extended. The fluxes of the sources at 20 TeV range from ~25% of the Crab flux to nearly as bright as the Crab.Comment: Submitted to Ap