Time-Dependent Searches for Neutrino Point Sources with IceCube Mike Baker University of Wisconsin-Madison Erice, Sicily June 14, 2010

I have made several different analyses looking for timing structure for neutrino signals, using the dataset from the IC40 point source analysis. * Search for periodic neutrino emission from binary systems * Search for neutrinos in coincidence with GeV-TeV photon flares * Search for generic clustering in time and space of neutrinos

The event selection takes neutrinos from the northern sky. These are mainly atmospheric neutrinos with ~TeV energies. We also use energy cuts to get a sample of ~PeV muons from the southern sky, which are predominantly muons from cosmic ray air showers.

These analyses and the time-integrated search use an unbinned likelihood method, using the track angular uncertainty of individual events and energy information to find a best-fit spectral index.

Binary system search

Binary systems in the galaxy where one member is a compact object haven been posited as a source of cosmic rays. We search for clustering as a function of orbital period is a very similar analysis to searching for event clustering in MJD. We search for a best-fit Gaussian describing the events in phase.

The most significant source is Cygnus X3 – the three highest-weight events come in 1/20 of the period, which corresponds to a 15-minute window of the 4.8 hour orbit. Above is the event weights as a function of the period. After trials, the p-value is 1.8%. I think the result is interesting, but it is still compatable with background. The time of the events is still blinded, and an analysis looking for correlation with photon flares is in development.

MWL Triggered Flare Search

Blazars are candidate sources for UHECRs, and hence neutrinos, and exhibit varibility in HE photon wavebands on the order of days. We use this MWL information on variability to motivate a cut in time for a point-source search.

Two kinds of alerts, one from sources providing lightcurves with sporadic data. 1ES has a strong flare seen with VERITAS → Markarian 501 also has a short flare ← seen with VERITAS

The other kind of alert we have is from satellite sources with comprehensive coverage in a waveband Start out with a Maximum Likelihood Blocks reconstruction of the Fermi LAT lightcurve.

Instead of making a guess of what the best cut on the flux is, we maximixe with respect to the threshold, to find the best answer to the question: ”At what flux of the lightcurve does neutrino emission turn on?” threshold Resulting Pdf

Here is the discovery potential for the lightcurve of PKS I compare several methods, all using the lightcurve: In blue is the hypothetical case where we know the best cut on threshold and any lag. In red is the case used in the analysis, where we fit the threshold and allow a short lag as a method of interpolating the lightcurve.

The best source found was one high-energy event during a GeV flare of PKS , but it finds only one event. After trials, the p-value of the analysis is 29%.

Untriggered All-Sky Flare Search

Here background events are in blue, with 5 injected signal events in red. The height of the line corresponds to S/B ratio of the event in the time-integrated analysis. We know of transient astrophysical phenomena with timescales of milliseconds- seconds (GRB) to minutes-days (AGN flares, SN afterglow). Observations in photons give us candidates to test for correlations in triggered searches, but these observations are not always continuous depending on the energy range tested. We have an interest in performing a general search which covers many orders of magnitude of flare duration to find occurrences undetected or undetectable with photon emission. We fit for the best mean and sigma of a Gaussian in time to find the strongest flare from a given source location.

We find that by looking for a clustering of events in time we can dramatically reduce the number of events needed to see a discovery compared to a time- integrated search, and can make a detection which is below the upper limit in the general search.

GRBs ~Time-Integrated AGN The method's performance is similar to that of the time-integrated analysis even for long flares, opening up the possibility of looking from GRB timescales to steady sources. For flat emission, only 10% more signal is needed for discovery than a PS search even when we add two degrees of freedom to the likelihood.

????????? Another possible outcome is that we see something completely unexpected, some sort of burst of neutrinos with no counterpart in photons.

I also had a look at what the Discovery potential and upper limit looks like in terms of fluence. The fluence required is within a factor of a few of the naked-eye GRB.

Here is the skymap in RA and dec of the p-value at each location for the all-sky untriggered search.

Hottest Spot: -log10(estp): 4.68 at RA and dec. The mean is at: MJD and the flare width is 15 seconds. The spectral index fit is: 2.15 and the fit nsrc is: 2

Fifteen seconds doesn't stand out on year-long timescales, so we zoom in on the flare time to see both events.

Comparing to scrambled skymaps, the hottest spot is in the bulk of the distribution of the pretrial p-value at the hottest spot. The final p-value is ~58%.

The hottest flare corresponds to two events which are 22 seconds apart. There is a spatial separation of 2.01 degrees between the events. Paraboloid sigma = 0.60 deg Nch 65 Mue En = 3.33e4 Paraboloid sigma = 1.96 deg Nch 17 Mue En = 2.43e3

IceCube has a program with ROTSE to take optical images of close doublets of events, and this met the trigger criteria. A. Frankowiak, A. Homeier

Optical data was first taken 39 hours after the events, with 14 days of observations after that. There is no indication of variability from the optical data.

In summary, IceCube is doing a number of searches for time- variability in our neutrino data. --We have a 1.8% p-value testing periodicity in neutrino emission from the microquasar Cygnus X-3 with IC40. We will also test for flaring and periodicity with the IC59 dataset. --We tested for correlation between GeV/TeV emission from sources and neutrino emission, with results compatible with fluctuations. We also want to do a stacking analysis with BL Lac and FSRQ seen to be variable by Fermi. --We searched for any clustering in space and time during IC40, the spot which stood out most was a short flare on February 12, The p-value is 58%. An optical follow-up of the pair of events also did not show any evidence of an astrophysical source of the events.

I ran the analysis over the 7 sources, and these are the best-fit parameters and pretrial p-values: Source | (Ra, Dec) Period |pretrialP| NSrc Gamma mean sigma_w Cygnus X3 | ( ,40.958) | | SS433 | ( ,4.983) | | Cygnus X1 | ( ,35.202) | | LS I | (40.132,61.229) | | GRS | ( ,10.946) 30.8 | | XTE J | ( ,48.037) | | GRO J | (65.428,32.907) | | Minimum P-value: Best Source: Cygnus X3

Right are the periodic flux information from Fermi (top) and ASM (bottom). Fermi sees periodicity only when the source is in a high GeV state, we haven't looked at the raw times of our events yet.

One interesting thing about Cygnus X3 during the IC-40 period (April 2008 – May 2009) is that there was a series radio flares, with accompanying high states in GeV gamma rays. There is another analysis geared toward lower energies looking into neutrino coincidence also.