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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"

45435 results found.

  1. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  2. Konus-Wind detection of GRB 250322A (short)
  3. IPN triangulation of GRB 250322B
  4. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  5. EP250321a: Mondy AZT-33IK Continued Optical Observations
  6. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  7. GRB 250322A: third epoch of NOT optical observations
  8. GRB 250322A: Swift-BAT refined analysis
  9. The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
  10. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  11. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  12. GRB 250322A: further NOT optical observations
  13. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  14. GRB 250322A: Swift/UVOT Upper Limits
  15. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  16. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  17. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  18. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  19. GRB 250321B: Swift-XRT observations
  20. GRB 250322A: Swift-XRT refined Analysis
  21. EP250321a: TNOT Observation of Optical Counterpart
  22. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  23. GRB 250322A: Gemini-North redshift of candidate host galaxy
  24. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  25. SVOM/sb25032302: SVOM detection of a long X-ray transient
  26. GRB 250322A: AstroSat CZTI detection of a short burst
  27. GRB 250322B: AstroSat CZTI detection of a bright long burst
  28. GRB250322A: STEP/T80S optical limits
  29. GRB 250322A: Gemini-South optical observations
  30. GRB 250322A: VLT optical observations
  31. GRB 250322A: VLT near-infrared observations
  32. FRB 250316A: DDOTI Continued Optical Observations
  33. GRB 250322A: NOT optical upper limits
  34. GRB 250322A: Enhanced Swift-XRT position
  35. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  36. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  37. GRB 250322A: MASTER optical observation
  38. EP250321a: Liverpool Telescope optical follow-up
  39. EP250321a: Mondy AZT-33IK Optical Observations
  40. GRB 250322A: Swift detection of a short burst
  41. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  42. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  43. EP250321a: KAIT optical observations
  44. EP250321A: COLIBRÍ Continuing Optical Observations
  45. GRB 250225B: GECAM-A detection
  46. GRB 250312A: GECAM-A detection
  47. GRB 250321B: Swift ToO observations
  48. EP250321a: WFST optical observations
  49. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  50. GRB 250321C: Fermi GBM Final Real-time Localization
  51. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  52. GRB 250320B: Fermi GBM Observation
  53. EP250321a: Xinglong 216 decaying optical observations
  54. GRB 250321A: Swift-BAT refined analysis
  55. GRB 250321A: Swift-XRT refined Analysis
  56. GRB 250320B: Fermi-LAT detection
  57. GRB 250321B: SVOM detection of a sub-threshold transient event
  58. EP250321a: SVOM/VT optical observation
  59. EP 250321A: Optical counterpart detection by LCO.
  60. EP250321a: Kinder optical follow-up observations
  61. GRB 250321A: Swift/UVOT Upper Limits
  62. GRB 250320B: SVOM/GRM observation of a long burst
  63. EP250321a: LCO optical counterpart detection
  64. EP250321a: Swift-XRT detection of an X-ray source
  65. EP250321A: COLIBRÍ Optical Observations
  66. EP250321a: VLT/X-shooter redshift z = 4.368
  67. GRB 250320B: AstroSat CZTI detection
  68. EP250321a: REM optical/NIR afterglow detection
  69. Fermi GRB 250320B: Global MASTER-Net observations report
  70. EP250321a: BOOTES-5/JGT optical afterglow detection
  71. EP250321a: TRT optical counterpart detection
  72. EP250321a: Global MASTER-Net observations report
  73. Swift GRB 250321A: Global MASTER-Net observations report
  74. Fermi GRB 250321A: Global MASTER-Net observations report
  75. EP250321a: Einstein Probe detection of an X-ray transient
  76. GRB 250321A: GOTO optical upper limits
  77. GRB 250321A: Swift-XRT localisation
  78. GRB 250314A: Keck/NIRC2 J-band upper limit
  79. EP250226a/GRB 250226A: KAIT optical observations
  80. GRB 250321A: Fermi GBM Observation
  81. GRB 250321A: Swift detection of a burst
  82. GRB 250321A: Fermi GBM Final Real-time Localization
  83. GRB 250320B: Fermi GBM Final Real-time Localization
  84. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  85. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  86. GRB 250320A: Fermi GBM Final Real-time Localization
  87. Fermi GRB 250319B: Global MASTER-Net observations report
  88. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  89. GRB 250313A: GRBAlpha detection
  90. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  91. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  92. GRB 250319B: Fermi GBM Final Localization
  93. GRB 250319A: Fermi GBM Final Localization
  94. GRB 250317D: EIRSAT-1 GMOD Detection
  95. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  96. GRB 250314A: ATCA radio upper limits
  97. EP250302a: VLA observations
  98. GRB 250317B: OHP/T193 continued follow-up
  99. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  100. GRB 250317C: SVOM/GRM observation of a long burst

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