# Presentation: 111063

## A Search For Untriggered GRB Afterglows with ROTSE-III_x0010_

**Eli Rykoff**
**ROTSE Collaboration**
**University of Michigan**

- Santorini GRB Meeting
- September 2nd, 2005
- astro-ph/0506442 (ApJ, October)

## Outline

- Robotic Optical Transient Search Experiment (ROTSE-III) Telescope Systems
- Orphan & Untriggered GRB Afterglows
- The ROTSE-III Search
- Results
- Conclusions

## ROTSE-III Specifications

- 0.45 m telescopes
- 1.85° x 1.85° field (f/1.9)
- Unfiltered 2k x 2k CCD
- 3 arcseconds/pixel
- Fast (6 s) readout
- ~ 40 deg/s max. slew speed
- Median GRB alert response time is 7 seconds
- All automated, no human intervention

## ROTSE-III Worldwide

- 3a, SSO, Australia

- 3d, TUG, Turkey

- 3c, H.E.S.S., Namibia

- 3b, McDonald, Texas

- February, 2003

- May, 2004

- March, 2003

- July, 2003

## Untriggered GRB Afterglows

- Untriggered GRBs
- Even if a satellite doesn’t detect it, there are ~ 2 GRBs/day visible to the earth
- Advantage: We know what these optical afterglows look like
- Disadvantage: Rare
- Orphan GRB Afterglows
- After the jet break, afterglows should be visible off axis
- Advantage: Rate might be > 200/day
- Disadvantage: We don’t know what they look like

## Untriggered GRBs

- Search designed to look for untriggered GRBs
- We know what we’re looking for
- How much coverage is required?
- 2 GRBs/day visible to earth (from BATSE)
- ~ 50% with visible afterglows
- 1/day/40000 deg2 
- ~ 110 deg2  yr effective coverage required
- Search strategy to have as much coverage as possible

## Search Strategy (I)

- Limiting magnitude of ~18.5 determines how long we can see a typical afterglow
- Rapid identification for follow-up
- Search equatorial stripe covered by SDSS for deep, 5 band background images

**Notes:**
If I have time, split this in two and give an image of the coverage...

## Search Strategy (II)

- Take pairs of images, each pair separated by 30 minutes
- Pair reduces chance of hot pixel “transients”, cosmic ray coincidences, etc.
- Effective coverage time is 30 minutes, assuming a typical afterglow is brighter than our limiting magnitude for ~ 1 hour
- A transient candidate must be a new object not detected in four images
- Not sensitive to objects with bright counterparts, eg flares from bright stars

**Notes:**
Actually, effective time is 30 minutes, but an afterglow is above limit for 1 hour
Also, not sensitive to supernovae from detected galaxies.

## Results

- Through March 2005, covered 1.74 deg2  yr with limiting magnitudes better than 17.5
- Four telescopes operational from May 2004
- Search is ongoing
- Found
- Four new cataclysmic variables
- Rykoff, et al (2004), IBVS 5559; Rykoff (2005), ATel 403; Rykoff (2005), ATel 423
- One flare star
- Two supernovae from dwarf galaxies
- 2005cg, 2005ch
- No unidentified transients
- And many, many rocks
- We avoid low ecliptic latitudes to reduce the number of asteroids

**Notes:**
Not as much coverage as required!  Factor of 50...
****  We have not been swamped with junk
**** all our rocks are in mpchecker database

## Results

- Sensitive to ~ 50% of typical afterglows

**Notes:**
030329 is way up there...

## Are GRBs “Spherical Fireballs”?

- Assume GRBs are “spherical fireballs” -- the optical emission is not beamed, but the -ray emission is
- From BATSE rate, if we have a double jet, the number of observable bursts is                              ~ 1500/max2 events/yr
- Our untriggered afterglow rate is                            < 78000 events/yr (95% confidence)
- max > 3.6o
- Similar to opening angles determined via standard methods
- Optical emission must be beamed

**Notes:**
Whenever a question is asked in the title, the answer is always “no”

## Conclusions

- Achieving the necessary coverage to detect untriggered GRB afterglows is difficult
- Orphans are not as bright as on-axis optical afterglows
- There are not a lot of unknown transients that get brighter than 18th magnitude
- Many low-redshift supernovae from dwarf galaxies are missed by targeted searches

## This space intentionally left blank

## Supernovae from Dwarf Galaxies

- June 2005 found two supernovae
- Dwarf galaxy hosts
- Selection bias
- 2005cg, 2005ch, each Type Ia, z ~ 0.2
- Multiple spectra from HET for 2005cg
- Blind search has implications for high-z supernovae

- Quimby et al, 2005