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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

8475 results found.

  1. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
  2. LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
  3. GRB 250225B: VLT optical and near-infrared candidate counterpart
  4. GRB 250225B: VLT/FORS2 candidate optical afterglow
  5. EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  6. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  7. EP250223a: Kinder optical follow-up observations
  8. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  9. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  10. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  11. GRB 250219A: EP-FXT afterglow detection
  12. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  13. EP250223a: 1.6m Mephisto and 50cm array observations
  14. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO trigger with ID 762004910: Identification of a GW compact binary merger candidate possibly associated with a sub-threshold Swift/BAT-GUANO trigger
  15. EP250223a: LCO detection of the afterglow
  16. EP250223a: NOT optical afterglow candidate
  17. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  18. GRB 250221A: 1.6m Mephisto optical detection
  19. LIGO/Virgo/KAGRA S250221gb: Retraction of GW compact binary merger candidate
  20. GRB 250221A: AKO Optical Upper Limit
  21. GRB 250221A: Swift/UVOT Detection
  22. LIGO/Virgo/KAGRA S250221eb: Retraction of GW compact binary merger candidate
  23. EP250220a: Liverpool Telescope optical upper limits
  24. EP250220a: Optical upper limit with Kinder observations
  25. GRB 250221A: Swift detection of a burst with an optical counterpart
  26. GRB 250219A: NOT optical observations
  27. GRB 250219A: 1.6m Mephisto optical upper limits
  28. GRB 250219A: Swift ToO observations
  29. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  30. GRB 250217C: Tiled Swift observations
  31. GRB 250215A / EP250215A: Encouraging Follow-up Observations of a BdHN I with a Rest-Frame Duration 2.3 s at z=4.61
  32. SVOM/sb25021804: SVOM detection of a long X-ray transient
  33. IceCube-Cascade 250215A: Upper limits from a search for additional neutrino events in IceCube
  34. GRANDMA/OPD observations of GRB250215A
  35. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  36. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  37. GRB 250215A / EP250215a: SVOM/VT optical candidate comfirmation
  38. GRB 250213A:SVOM/VT optical candidate
  39. GRB 250213A: Swift ToO observations
  40. LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
  41. EP250207B: Chandra localization of the X-ray counterpart
  42. LIGO/Virgo/KAGRA S250206dm: FTW observations of counterpart candidates AT2025bbo and AT2025bcx, and of NED galaxies
  43. EP250212a: Liverpool Telescope optical upper limits
  44. EP250207B: GTC z-band Observations
  45. LIGO/Virgo/KAGRA S250206dm: NEWFIRM NIR Follow-up of AT2025ber
  46. EP250207b: NOT optical counterpart candidate
  47. GRB 250211A: Swift ToO observations
  48. LIGO/Virgo/KAGRA S250211be: Updated Sky localization
  49. GRB 250205A / EP250205A: radio detection with the VLA
  50. IceCube-250207A: One candidate from the Zwicky Transient Facility
  51. LIGO/Virgo/KAGRA S250206dm: continued in SOAR galaxy targeted observations and identification of one possible transient
  52. Gemini-South spectroscopic redshift of EP250207b host galaxy candidate (z=0.082)
  53. LIGO/Virgo/KAGRA S250211be: Identification of a GW compact binary merger candidate
  54. LIGO/Virgo/KAGRA S250211aa: Updated Sky localization and EM Bright Classification
  55. LIGO/Virgo/KAGRA S250211aa: Identification of a GW compact binary merger candidate
  56. EP250207A: Upper limits from Fermi-GBM Observations
  57. LIGO/Virgo/KAGRA S250206dm: Upper limits from GECAM Observations
  58. IceCube-250207A: Upper limits from a search for additional neutrino events in IceCube
  59. LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of AT2025bbo and Galaxies in the Localization Volume
  60. LIGO/Virgo/KAGRA S250206dm: Observations from WINTER
  61. LIGO/Virgo/KAGRA S250206dm & FRB 20250206A: MASTER observations and possible mother galaxy
  62. LIGO/Virgo/KAGRA S250206dm: Optical observations of candidate AT 2025bbo with Kinder
  63. LIGO/Virgo/KAGRA S250206dm: further Pan-STARRS observations and one candidate AT2025bbo
  64. LIGO/Virgo/KAGRA S250207bg: Updated NED Galaxies in the Localization Volume
  65. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  66. GRB 250206A: Tiled Swift observations
  67. LIGO/Virgo/KAGRA S250118az: Updated Sky localization
  68. LIGO/Virgo/KAGRA S250208ad: Updated Sky localization
  69. LIGO/Virgo/KAGRA S250206dm: (Update-7) NED Galaxies in the Localization Volume
  70. LIGO/Virgo/KAGRA S250206dm: NEWFIRM NIR Observations
  71. LIGO/Virgo/KAGRA S250206dm: Updated Sky localization and EM Bright Classification
  72. IceCube-250203A: No transient candidates from the Zwicky Transient Facility
  73. LIGO/Virgo/KAGRA S250206dm: ePESSTO+ classification of AT2025bar
  74. LIGO/Virgo/KAGRA S250208ad: Identification of a GW compact binary merger candidate
  75. CHIME/FRB source FRB 20250206A detected less than 1 minute after LIGO-Virgo-Kagra (LVK) S250206dm, however the probability of spatial coincidence is order 0.1%
  76. LIGO/Virgo/KAGRA S250206dm: GOTO counterpart search update - AT2025bar
  77. LIGO/Virgo/KAGRA S250206dm: Pan-STARRS survey of the skymap for optical transients
  78. LIGO/Virgo/KAGRA S250206dm: DDOTI Upper Limits
  79. GRB 250207B: Tiled Swift observations
  80. LIGO/Virgo/KAGRA S250207bg: NED Galaxies in the Localization Volume
  81. IGO/Virgo/KAGRA S250206dm: Virtual Telescope Project upper limit for the Neutrino IceCube Candidate
  82. IceCube-250207A - IceCube observation of a high-energy neutrino candidate track-like event
  83. LIGO/Virgo/KAGRA S250207bg: Identification of a GW compact binary merger candidate
  84. LIGO/Virgo/KAGRA S250206dm: DDOTI Upper Limit for the Neutrino IceCube Candidate
  85. LIGO/Virgo/KAGRA S250206dm: Pan-STARRS observations of AT2025azm and AT2025azn
  86. LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of the AT 2025azn Optical Candidate
  87. LIGO/Virgo/KAGRA S250206dm: SAGUARO Detection of Two Potential Optical Counterparts
  88. LIGO/Virgo/KAGRA S250206dm: Updated-6 NED Galaxies in the Localization Volume
  89. LIGO/Virgo/KAGRA S250206dm: Updated Sky localization and EM Bright Classification
  90. LIGO/Virgo/KAGRA S250206dm: Upper limits from Fermi-GBM Observations
  91. GRB 250207A: Swift detection of a burst with optical counterpart
  92. LIGO/Virgo/KAGRA S250206dm: Coverage and upper limits from MAXI/GSC observations
  93. LIGO/Virgo/KAGRA S250206dm: Updated Sky localization and EM Bright Classification
  94. LIGO/Virgo/KAGRA S250206dm: Updated NED Galaxies in the Localization Volume
  95. LIGO/Virgo/KAGRA S250206dm: Two counterpart neutrino candidates from IceCube neutrino searches
  96. LIGO/Virgo/KAGRA S250206dm: Identification of a GW compact binary merger candidate
  97. LIGO/Virgo/KAGRA S250206dm: NED Galaxies in the Localization Volume
  98. GRB 250205A: REM NIR upper limit
  99. LIGO/Virgo/KAGRA S250205ee: Updated Sky localization and Source Classification
  100. GRB 250205A: OHP/T193 optical counterpart candidate

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