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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"

26389 results found.

  1. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  2. IPN triangulation of GRB 250322B
  3. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  4. EP250321a: Mondy AZT-33IK Continued Optical Observations
  5. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  6. GRB 250322A: third epoch of NOT optical observations
  7. GRB 250322A: Swift-BAT refined analysis
  8. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  9. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  10. GRB 250322A: further NOT optical observations
  11. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  12. GRB 250322A: Swift/UVOT Upper Limits
  13. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  14. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  15. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  16. GRB 250321B: Swift-XRT observations
  17. GRB 250322A: Swift-XRT refined Analysis
  18. EP250321a: TNOT Observation of Optical Counterpart
  19. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  20. SVOM/sb25032302: SVOM detection of a long X-ray transient
  21. GRB 250322B: AstroSat CZTI detection of a bright long burst
  22. GRB 250322A: VLT optical observations
  23. GRB 250322A: VLT near-infrared observations
  24. FRB 250316A: DDOTI Continued Optical Observations
  25. GRB 250322A: NOT optical upper limits
  26. GRB 250322A: Enhanced Swift-XRT position
  27. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  28. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  29. EP250321a: Liverpool Telescope optical follow-up
  30. EP250321a: Mondy AZT-33IK Optical Observations
  31. GRB 250322A: Swift detection of a short burst
  32. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  33. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  34. EP250321A: COLIBRÍ Continuing Optical Observations
  35. EP250321a: WFST optical observations
  36. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  37. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  38. GRB 250320B: Fermi GBM Observation
  39. EP250321a: Xinglong 216 decaying optical observations
  40. GRB 250321A: Swift-BAT refined analysis
  41. GRB 250321A: Swift-XRT refined Analysis
  42. EP 250321A: Optical counterpart detection by LCO.
  43. EP250321a: Kinder optical follow-up observations
  44. GRB 250321A: Swift/UVOT Upper Limits
  45. GRB 250320B: SVOM/GRM observation of a long burst
  46. EP250321a: LCO optical counterpart detection
  47. EP250321a: Swift-XRT detection of an X-ray source
  48. EP250321A: COLIBRÍ Optical Observations
  49. GRB 250320B: AstroSat CZTI detection
  50. EP250321a: REM optical/NIR afterglow detection
  51. EP250321a: TRT optical counterpart detection
  52. Swift GRB 250321A: Global MASTER-Net observations report
  53. EP250321a: Einstein Probe detection of an X-ray transient
  54. GRB 250321A: GOTO optical upper limits
  55. GRB 250314A: Keck/NIRC2 J-band upper limit
  56. EP250226a/GRB 250226A: KAIT optical observations
  57. GRB 250321A: Fermi GBM Observation
  58. GRB 250321A: Swift detection of a burst
  59. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  60. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  61. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  62. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  63. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  64. GRB 250317D: EIRSAT-1 GMOD Detection
  65. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  66. GRB 250314A: ATCA radio upper limits
  67. GRB 250317B: OHP/T193 continued follow-up
  68. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  69. GRB 250317C: SVOM/GRM observation of a long burst
  70. GRB 250317B: Leavitt Observatory optical upper limit
  71. GRB 250317B: Mondy AZT-33IK Optical Observations
  72. GRB 250317B: NOT optical observations suggest an optical plateau phase
  73. GRB 250317C: GECAM-B detection
  74. GRB 250317B: OHP/T193 optical observations
  75. GRB250312A: Swift/UVOT Upper Limits
  76. GRB 250317B: REM optical/NIR observations
  77. GRB 250317B: Swift-XRT observations
  78. GRB 250316A: Swift/UVOT Upper Limits
  79. GRB 250314A: REM optical/NIR upper limits
  80. GRB 250316A: AbAO AS-32 Optical Upper Limit
  81. EP 250317B: Fading optical counterpart detection by LCO
  82. GRB 250316A: Swift-XRT afterglow detection
  83. GRB 250317B: LCO detection of the fading optical afterglow
  84. GRB 250317B: SVOM/VT detection of an optical candidate from VHF data
  85. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  86. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  87. GRB 250317B: SVOM detection of a burst
  88. GRB 250316A: Fermi GBM Observation
  89. GRB 250316A: Swift-XRT observations
  90. GRB 250314A: SVOM/GRM analysis
  91. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  92. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  93. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  94. GRB 250314A: EP-FXT afterglow detection
  95. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  96. GRB 250314A: Swift/UVOT Upper Limits
  97. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  98. GRB 250314A: Swift XRT Detection
  99. EP250315a: optical counterpart candidate detected by Gemini North
  100. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3

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