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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"

16173 results found.

  1. GRB 250329A: VLT/X-shooter redshift z = 2.921
  2. GRB 250329A: SVOM/VT optical counterpart confirmation
  3. GRB 250329A: SVOM detection of a burst
  4. GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
  5. GRB 250327B: J-band observations with WINTER
  6. GRB 250327B: MASTER detection of OT rebrightening
  7. GRB 250327B: LCO optical counterpart detection
  8. GRB 250328A: GWAC-F50A optical upper limit
  9. FRB 20250316A: FTW optical observations
  10. GRB 250327B: CrAO and SAO RAS Optical Observations
  11. GRB 250327B: OHP/T193 spectroscopic observations and redshift confirmation
  12. GRB 250327B: further optical observations by LCOGT
  13. EP250315a: Pan-STARRS r and i-band imaging and photometry
  14. GRB 250327b: Liverpool Telescope optical observations
  15. GRB 250322A: GRANDMA/TNOT optical upper limits
  16. GRB 250327B: Las Cumbres optical counterpart detection
  17. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  18. GRB 250327B: 1.6m Mephisto optical observations
  19. GRB 250327B: NOT spectroscopic redshift z = 3.035
  20. GRB 250327B: GOTO optical counterpart detection
  21. GRB 250327B: SVOM/VT optically bright counterpart
  22. GRB 250327B: SAO RAS optical candidate
  23. GRB 250327B: SVOM detection of a burst
  24. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  25. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  26. GRB 250327A: SVOM/VT optical candidate
  27. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  28. GRB 250327A: DDOTI Optical Observations
  29. GRB 250327A: COLIBRÍ optical upper limit
  30. EP250321a: Mondy AZT-33IK Continued Optical Observations
  31. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  32. GRB 250322A: third epoch of NOT optical observations
  33. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  34. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  35. GRB 250322A: further NOT optical observations
  36. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  37. GRB 250322A: Swift/UVOT Upper Limits
  38. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  39. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  40. EP250321a: TNOT Observation of Optical Counterpart
  41. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  42. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  43. GRB250322A: STEP/T80S optical limits
  44. GRB 250322A: Gemini-South optical observations
  45. GRB 250322A: VLT optical observations
  46. FRB 250316A: DDOTI Continued Optical Observations
  47. GRB 250322A: NOT optical upper limits
  48. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  49. GRB 250322A: MASTER optical observation
  50. EP250321a: Liverpool Telescope optical follow-up
  51. EP250321a: Mondy AZT-33IK Optical Observations
  52. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  53. EP250321a: KAIT optical observations
  54. EP250321A: COLIBRÍ Continuing Optical Observations
  55. EP250321a: WFST optical observations
  56. EP250321a: Xinglong 216 decaying optical observations
  57. EP250321a: SVOM/VT optical observation
  58. EP 250321A: Optical counterpart detection by LCO.
  59. EP250321a: Kinder optical follow-up observations
  60. GRB 250321A: Swift/UVOT Upper Limits
  61. GRB 250320B: SVOM/GRM observation of a long burst
  62. EP250321a: LCO optical counterpart detection
  63. EP250321a: Swift-XRT detection of an X-ray source
  64. EP250321A: COLIBRÍ Optical Observations
  65. EP250321a: VLT/X-shooter redshift z = 4.368
  66. EP250321a: REM optical/NIR afterglow detection
  67. EP250321a: BOOTES-5/JGT optical afterglow detection
  68. EP250321a: TRT optical counterpart detection
  69. GRB 250321A: GOTO optical upper limits
  70. EP250226a/GRB 250226A: KAIT optical observations
  71. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  72. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  73. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  74. GRB 250314A: ATCA radio upper limits
  75. EP250302a: VLA observations
  76. GRB 250317B: OHP/T193 continued follow-up
  77. GRB 250317C: SVOM/GRM observation of a long burst
  78. GRB 250317B: Leavitt Observatory optical upper limit
  79. GRB 250309B/AT2025dws: further ATCA observations
  80. GRB 250317B: Mondy AZT-33IK Optical Observations
  81. GRB 250317B: NOT optical observations suggest an optical plateau phase
  82. GRB 250317B: OHP/T193 optical observations
  83. GRB250312A: Swift/UVOT Upper Limits
  84. GRB 250317B: REM optical/NIR observations
  85. GRB 250317B: Swift-XRT observations
  86. GRB 250316A: Swift/UVOT Upper Limits
  87. GRB 250314A: REM optical/NIR upper limits
  88. GRB 250316A: AbAO AS-32 Optical Upper Limit
  89. EP 250317B: Fading optical counterpart detection by LCO
  90. GRB 250317B: LCO detection of the fading optical afterglow
  91. GRB 250317B: SVOM/VT detection of an optical candidate from VHF data
  92. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  93. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  94. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  95. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  96. GRB 250314A: Swift/UVOT Upper Limits
  97. GRB 250314A: Swift XRT Detection
  98. EP250315a: optical counterpart candidate detected by Gemini North
  99. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  100. GRB 250314A: NOT near-infrared candidate counterpart

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