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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"

19089 results found.

  1. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  2. EP250321A: COLIBRÍ Continuing Optical Observations
  3. GRB 250321B: Swift ToO observations
  4. EP250321a: WFST optical observations
  5. EP250321a: Xinglong 216 decaying optical observations
  6. GRB 250321A: Swift-XRT refined Analysis
  7. GRB 250321B: SVOM detection of a sub-threshold transient event
  8. EP 250321A: Optical counterpart detection by LCO.
  9. EP250321a: Kinder optical follow-up observations
  10. GRB 250321A: Swift/UVOT Upper Limits
  11. GRB 250320B: SVOM/GRM observation of a long burst
  12. EP250321a: LCO optical counterpart detection
  13. EP250321A: COLIBRÍ Optical Observations
  14. EP250321a: REM optical/NIR afterglow detection
  15. EP250321a: TRT optical counterpart detection
  16. EP250321a: Einstein Probe detection of an X-ray transient
  17. GRB 250321A: GOTO optical upper limits
  18. GRB 250314A: Keck/NIRC2 J-band upper limit
  19. EP250226a/GRB 250226A: KAIT optical observations
  20. GRB 250321A: Swift detection of a burst
  21. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  22. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  23. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  24. GRB 250317C: SVOM/GRM observation of a long burst
  25. GRB 250317B: Leavitt Observatory optical upper limit
  26. GRB 250317B: Mondy AZT-33IK Optical Observations
  27. GRB 250317B: NOT optical observations suggest an optical plateau phase
  28. GRB 250317B: OHP/T193 optical observations
  29. GRB250312A: Swift/UVOT Upper Limits
  30. GRB 250317B: REM optical/NIR observations
  31. GRB 250316A: Swift/UVOT Upper Limits
  32. GRB 250314A: REM optical/NIR upper limits
  33. GRB 250316A: AbAO AS-32 Optical Upper Limit
  34. EP 250317B: Fading optical counterpart detection by LCO
  35. GRB 250316A: Swift-XRT afterglow detection
  36. GRB 250317B: LCO detection of the fading optical afterglow
  37. GRB 250317B: SVOM/VT detection of an optical candidate from VHF data
  38. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  39. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  40. GRB 250317B: SVOM detection of a burst
  41. GRB 250316A: Swift ToO observations
  42. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  43. GRB 250314A: Swift/UVOT Upper Limits
  44. GRB 250314A: Swift XRT Detection
  45. EP250315a: optical counterpart candidate detected by Gemini North
  46. EP250315a: Einstein Probe detection of an X-ray transient
  47. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  48. SVOM/MXT upper limit on GRB 250314A
  49. GRB 250314A: SVOM/VT upper limit
  50. GRB 250314A: NOT near-infrared candidate counterpart
  51. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  52. GRB 250314A: SVOM detection of a burst
  53. GRB 250313A: Swift ToO observations
  54. EP250304a: Pan-STARRS r and i-band imaging and photometry
  55. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  56. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  57. GRB 250312A: Enhanced Swift-XRT position
  58. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  59. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  60. GRB 250312A: Swift detection of a burst
  61. GRB 241213A: VIRT Optical Upper Limit
  62. GRB 241228A: VIRT Optical Upper Limit
  63. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  64. GRB 250309B: 1.3m DFOT Optical observations
  65. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  66. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  67. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  68. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
  69. GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
  70. GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
  71. GRB 250309B: PRIME near-infrared detection
  72. EP250304a: Chandra detection
  73. GRB 250225B: Swift-BAT refined analysis
  74. GRB 250311A/EP250311a: TRT optical upper limit
  75. GRB 250311A: Tiled Swift observations
  76. EP250311a/GRB 250311A: EP-WXT detection
  77. GRB 250308A: CALET Gamma-Ray Burst Monitor detection
  78. GRB 250311B: SVOM detection of a burst
  79. GRB 250309B / AT2025dws: further SAO RAS optical observations
  80. EP250308a: 1.6m Mephisto optical upper limits
  81. Konus-Wind detection of GRB 250309B
  82. IPN triangulation of GRB 250308A (short)
  83. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  84. GRB 250309B / AT2025dws: SAO RAS optical observations
  85. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  86. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  87. IceCube-250309A: No candidates from the Zwicky Transient Facility
  88. Fermi-LAT gamma-ray observations of IceCube-250309A
  89. GRB 230509B: Tiled Swift observations
  90. EP250308a: Einstein Probe detection of an X-ray transient
  91. EP250308a: NOT optical upper limit
  92. EP250304a: MeerKAT detection of a possible radio counterpart
  93. GRB 250305A: AstroSat CZTI detection
  94. EP250302a:Xinglong optical observations
  95. GRB 250306A: AstroSat CZTI detection
  96. GRB250101A: Radio upper limits from VLA observations
  97. GRB 250305A: SVOM/GRM observation of a burst
  98. Fermi-LAT Gamma-ray Observations of IceCube-250302A
  99. EP250302a: Optical Observations at CrAO and SAO RAS
  100. GRB 250219A: SVOM/C-GFT optical upper limit at early phase

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