Leptoquark patterns unifying neutrino masses, flavor anomalies, and the diphoton excess

Vector leptoquarks provide an elegant solution to a series of anomalies and at the same time generate naturally light neutrino masses through their mixing with the standard model Higgs boson. We present a simple Froggatt-Nielsen model to accommodate the B physics anomalies $R_K$ and $R_D$, neutrino masses, and the $750$ GeV diphoton excess in one cohesive framework adding only two vector leptoquarks and two singlet scalar fields to the standard model field content.Comment: 12 pages, 10 figures; final version published in PR

Broad-band Modeling of GRB Afterglows

Observations of GRB afterglows ranging from radio to X-ray frequencies generate large data sets. Careful analysis of these broad-band data can give us insight into the nature of the GRB progenitor population by yielding such information like the total energy of the burst, the geometry of the fireball and the type of environment into which the GRB explodes. We illustrate, by example, how global, self-consistent fits are a robust approach for characterizing the afterglow emission. This approach allows a relatively simple comparison of different models and a way to determine the strengths and weaknesses of these models, since all are treated self-consistently. Here we quantify the main differences between the broad-band, self-consistent approach and the traditional approach, using GRB000301C and GRB970508 as test cases.Comment: Appears in "Gamma-Ray Bursts in the Afterglow Era" proceedings of the Roma 2000 GRB Workshop; 3 pages; 2 figure

The Angular Size and Proper Motion of the Afterglow of GRB 030329

The bright, nearby (z=0.1685) gamma-ray burst of 29 March 2003 has presented us with the first opportunity to directly image the expansion of a GRB. This burst reached flux density levels at centimeter wavelengths more than 50 times brighter than any previously studied event. Here we present the results of a VLBI campaign using the VLBA, VLA, Green Bank, Effelsberg, Arecibo, and Westerbork telescopes that resolves the radio afterglow of GRB 030329 and constrains its rate of expansion. The size of the afterglow is found to be \~0.07 mas (0.2 pc) 25 days after the burst, and 0.17 mas (0.5 pc) 83 days after the burst, indicating an average velocity of 3-5 c. This expansion is consistent with expectations of the standard fireball model. We measure the projected proper motion of GRB 030329 in the sky to <0.3 mas in the 80 days following the burst. In observations taken 52 days after the burst we detect an additional compact component at a distance from the main component of 0.28 +/- 0.05 mas (0.80 pc). The presence of this component is not expected from the standard model.Comment: 12 pages including 2 figures, LaTeX. Accepted to ApJ Letters on May 14, 200

A Radio Flare from GRB 020405: Evidence for a Uniform Medium Around a Massive Stellar Progenitor

We present radio observations of GRB 020405 starting 1.2 days after the burst, which reveal a rapidly-fading ``radio flare''. Based on its temporal and spectral properties, we interpret the radio flare as emission from the reverse shock. This scenario rules out a circumburst medium with a radial density profile \rho ~ r^{-2} expected around a mass-losing massive star, since in that case the reverse shock emission decays on the timescale of the burst duration t~100 s. Using published optical and X-ray data, along with the radio data presented here, we further show that a self-consistent model requires collimated ejecta with an opening angle of 6 degrees (t_j~0.95 days). As a consequence of the early jet break, the late-time (t>10 days) emission measured with the Hubble Space Telescope significantly deviates from an extrapolation of the early, ground-based data. This, along with an unusually red spectrum, F_\nu \~ \nu^{-3.9}, strengthens the case for a supernova that exploded at about the same time as GRB 020405, thus pointing to a massive stellar progenitor for this burst. This is the first clear association of a massive progenitor with a uniform medium, indicating that a \rho ~ r^{-2} profile is not a required signature, and in fact may not be present on the lengthscales probed by the afterglow in the majority of bursts.Comment: Submitted to ApJ; 14 pages, 2 tables, 3 figure

Expected characteristics of the subclass of Supernova Gamma-ray Bursts (S-GRBs)

The spatial and temporal coincidence between the gamma-ray burst (GRB) 980425 and supernova (SN) 1998bw has prompted speculation that there exists a class of GRBs produced by SNe (``S-GRBs''). Robust arguments for the existence of a relativistic shock have been presented on the basis of radio observations. A physical model based on the radio observations lead us to propose the following characteristics of supernovae GRBs (S-GRBs): 1) prompt radio emission and implied brightness temperature near or below the inverse Compton limit, 2) high expansion velocity of the optical photosphere as derived from lines widths and energy release larger than usual, 3) no long-lived X-ray afterglow, and 4) a single pulse (SP) GRB profile. Radio studies of previous SNe show that only type Ib and Ic potentially satisfy the first condition. Accordingly we have investigated proposed associations of GRBs and SNe finding no convincing evidence (mainly to paucity of data) to confirm any single connection of a SN with a GRB. If there is a more constraining physical basis for the burst time-history of S-GRBs beyond that of the SP requirement, we suggest the 1% of light curves in the BATSE catalogue similar to that of GRB 980425 may constitute the subclass. Future optical follow-up of bursts with similar profiles should confirm if such GRBs originate from some fraction of SN type Ib/Ic.Comment: 11 pages of LaTeX with 1 figure. Submitted to the Astrophysical Journal Letter

Probing the Intergalactic Medium with Fast Radio Bursts

The recently discovered fast radio bursts (FRBs), presumably of extra-galactic origin, have the potential to become a powerful probe of the intergalactic medium (IGM). We point out a few such potential applications. We provide expressions for the dispersion measure and rotation measure as a function of redshift, and we discuss the sensitivity of these measures to the HeII reionization and the IGM magnetic field. Finally we calculate the microlensing effect from an isolate, extragalctic stellar-mass compact object on the FRB spectrum. The time delays between the two lensing images will induce constructive and destructive interference, leaving a specific imprint on the spectra of FRBs. With a high all-sky rate, a large statistical sample of FRBs is expected to make these applications feasible.Comment: 4 pages, 1 figure; Typos for the variable x in Eq.6 corrected; Published in ApJ; Originally the Appendix E of arXiv:1402.4766; Separated from the main paper upon the referee's reques

The Host Galaxy of GRB980703 at Radio Wavelengths - a Nuclear Starburst in a ULIRG

We present radio observations of GRB980703 at 1.43, 4.86, and 8.46 GHz for the period of 350 to 1000 days after the burst. These radio data clearly indicate that there is a persistent source at the position of GRB980703 with a flux density of approximately 70 $\mu$Jy at 1.43 GHz, and a spectral index, $\beta\approx 0.32$, where $F_\nu\propto \nu^{-\beta}$. We show that emission from the afterglow of GRB980703 is expected to be one to two orders of magnitude fainter, and therefore cannot account for these observations. We interpret this persistent emission as coming from the host galaxy --- the first example of a gamma-ray burst (GRB) host detection at radio wavelengths. We show that emission from an AGN is unlikely, and find that it can be explained as a result of a star-formation rate (SFR) of massive stars (M>5M$_\odot$) of 90 M$_\odot$/yr, which gives a total SFR of $\approx 500$ M$_\odot$/yr. Using the correlation between the radio and far-IR (FIR) luminosities of star-forming galaxies, we find that the host of GRB980703 is at the faint end of the class of Ultra Luminous Infrared Galaxies (ULIRGs), with L_{FIR}\sim few\times 10^{12} L$_\odot$. From the radio measurements of the offset between the burst and the host, and the size of the host, we conclude that GRB980703 occurred near the center of the galaxy in a region of maximum star formation. A comparison of the properties of this galaxy with radio and optical surveys at a similar redshift ($z\approx 1$) reveals that the host of GRB980703 is an average star-forming galaxy. This result has significant implications for the potential use of a GRB-selected galaxy sample for the study of galaxies and the IGM at high redshifts.Comment: Submitted to Ap